By JOE B. GOLDBERG, O.D.Virginia Beach, VA Human eyes have a combined 180-degree horizontal field of simultaneous vision. This can be divided into direct vision (eyes focused on an object) and indirect vision (other objects in the Vieth-Muller horopter circle1, 2 are perceived). From this perspective, vision with aspheric multifocal lenses might be more aptly named "simultaneous perception and selective vision." The ocular surface geometry of an aspheric contact lens influences patient sensation and perception. The patterns of these perceptions vary according to the dioptric powers of the refracting surface, and they are influenced by lens position, pupil size and normal aberrations of the eye. Levy3 reported that an aspheric multifocal contact lens, with its controlled area and predetermined power, would allow light rays from objects at all distances to be directed to a common focal point. The brain selectively interprets those images relevant to the object under observation. Angle alpha may also offset the visual axis 5 to 7 degrees nasally from the optic axis. Visual Clarity with Aspheric MultifocalsWith aspheric multifocal contact lenses, a progressive power change from the lens apex to the periphery creates a merging of an infinite number of images along the visual axis. As a result, the wearer need not sacrifice visual clarity at any viewing distance. Vision is satisfactory when the diameter of the diffusion disc is no greater than one minute.4 When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

Focal lengthof mirror formula

REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np.

IRIS USA made its mark nearly 25 years ago when it became the first company to introduce clear plastic storage containers to the US market.

Lens focal length equationexample

Symbiont Service Corp. strives to provide the most cost-effective, energy efficient pool/spa heating and cooling systems available today.

Visual Clarity with Aspheric MultifocalsWith aspheric multifocal contact lenses, a progressive power change from the lens apex to the periphery creates a merging of an infinite number of images along the visual axis. As a result, the wearer need not sacrifice visual clarity at any viewing distance. Vision is satisfactory when the diameter of the diffusion disc is no greater than one minute.4 When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

Focal lengthformula for convexlens

Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

Focal lengthof convexlens

What isfocal lengthoflens

A red filter blocks green light and blue light: Only red light can get through to your eyes. The white banana and the yellow peel both reflect some red light, ...

It is also possible to draw a graph, on graph paper, of 1/v (y-axis) against 1/u. The equation of the line can be compared to the standard form of linear equation, y = mx + c. In this case it is: 1/v = -1/u + 1/f. This cuts (intercepts) the y-axis (1/v axis) when x (1/u) is zero i.e. 1/v = 0 + 1/f. Similarly the line intercepts the 1/u axis when 1/v is zero, giving us 1/u = 1/f. From your graph get the average of the two intercepts, find the reciprocal to get the value of f.

A very nice tube based amplifier with plenty of power and clarity to power even demanding headphones like the Beyerdynamic T1 gen 1. Seller is very responsive ...

The ocular surface geometry of an aspheric contact lens influences patient sensation and perception. The patterns of these perceptions vary according to the dioptric powers of the refracting surface, and they are influenced by lens position, pupil size and normal aberrations of the eye. Levy3 reported that an aspheric multifocal contact lens, with its controlled area and predetermined power, would allow light rays from objects at all distances to be directed to a common focal point. The brain selectively interprets those images relevant to the object under observation. Angle alpha may also offset the visual axis 5 to 7 degrees nasally from the optic axis. Visual Clarity with Aspheric MultifocalsWith aspheric multifocal contact lenses, a progressive power change from the lens apex to the periphery creates a merging of an infinite number of images along the visual axis. As a result, the wearer need not sacrifice visual clarity at any viewing distance. Vision is satisfactory when the diameter of the diffusion disc is no greater than one minute.4 When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

By JOE B. GOLDBERG, O.D.Virginia Beach, VA Human eyes have a combined 180-degree horizontal field of simultaneous vision. This can be divided into direct vision (eyes focused on an object) and indirect vision (other objects in the Vieth-Muller horopter circle1, 2 are perceived). From this perspective, vision with aspheric multifocal lenses might be more aptly named "simultaneous perception and selective vision." The ocular surface geometry of an aspheric contact lens influences patient sensation and perception. The patterns of these perceptions vary according to the dioptric powers of the refracting surface, and they are influenced by lens position, pupil size and normal aberrations of the eye. Levy3 reported that an aspheric multifocal contact lens, with its controlled area and predetermined power, would allow light rays from objects at all distances to be directed to a common focal point. The brain selectively interprets those images relevant to the object under observation. Angle alpha may also offset the visual axis 5 to 7 degrees nasally from the optic axis. Visual Clarity with Aspheric MultifocalsWith aspheric multifocal contact lenses, a progressive power change from the lens apex to the periphery creates a merging of an infinite number of images along the visual axis. As a result, the wearer need not sacrifice visual clarity at any viewing distance. Vision is satisfactory when the diameter of the diffusion disc is no greater than one minute.4 When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np.

Abstract. A diffractive optical element (DOE) uses thin micro‐structure patterns to alter the phase of the light that is propagated through it. Those micro‐ ...

Lens focal length equationderivation

When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

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Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

What isfocal lengthoflensClass 10

When a ray box is placed on one side of a converging (convex) lens and a screen is placed on the other side, a real image of the object (slit at front of ray box) can be formed on the screen. The ray box is moved and the image located on the screen. The object distance (u) and image distance (v) are measured. The focal length (f) can then be calculated using the formula: 1/f = 1/u + 1/v. Note 1: In this simulation a focal length (between 15 and 35 cm) is set initially and you need to calculate its value. Note 2: If the ray box is inside the focal point you do not get a real image. It is virtual and in front of the lens.

Jan 31, 2001 — Edmund Optics Inc. (EO; Barrington, NJ; www.edmundoptics.com) is selling its Edmund Scientific consumer science catalog business to Science ...

When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

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Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

Levy3 reported that an aspheric multifocal contact lens, with its controlled area and predetermined power, would allow light rays from objects at all distances to be directed to a common focal point. The brain selectively interprets those images relevant to the object under observation. Angle alpha may also offset the visual axis 5 to 7 degrees nasally from the optic axis. Visual Clarity with Aspheric MultifocalsWith aspheric multifocal contact lenses, a progressive power change from the lens apex to the periphery creates a merging of an infinite number of images along the visual axis. As a result, the wearer need not sacrifice visual clarity at any viewing distance. Vision is satisfactory when the diameter of the diffusion disc is no greater than one minute.4 When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

Sep 25, 2010 — The equation I use is 2 * object distance * tan(angle of view/2) for the appropriate angle of view (horizontal, vertical, or diagonal). If you' ...

Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03

Human eyes have a combined 180-degree horizontal field of simultaneous vision. This can be divided into direct vision (eyes focused on an object) and indirect vision (other objects in the Vieth-Muller horopter circle1, 2 are perceived). From this perspective, vision with aspheric multifocal lenses might be more aptly named "simultaneous perception and selective vision." The ocular surface geometry of an aspheric contact lens influences patient sensation and perception. The patterns of these perceptions vary according to the dioptric powers of the refracting surface, and they are influenced by lens position, pupil size and normal aberrations of the eye. Levy3 reported that an aspheric multifocal contact lens, with its controlled area and predetermined power, would allow light rays from objects at all distances to be directed to a common focal point. The brain selectively interprets those images relevant to the object under observation. Angle alpha may also offset the visual axis 5 to 7 degrees nasally from the optic axis. Visual Clarity with Aspheric MultifocalsWith aspheric multifocal contact lenses, a progressive power change from the lens apex to the periphery creates a merging of an infinite number of images along the visual axis. As a result, the wearer need not sacrifice visual clarity at any viewing distance. Vision is satisfactory when the diameter of the diffusion disc is no greater than one minute.4 When fixating at distance, peripheral rays are highly refractive and unfocused, and energy is widely distributed over the retina.5 The distance (axial) rays are focused on the fovea, and the areas surrounding the fovea are in good focus. The sharp contrast between the background and highlighted areas of vision increases the patient"s ability to discriminate. The distribution of energy raises the background level slightly, but does not interfere with the contrast or affect respective acuity. When fixating at near, the central rays are out of focus and the peripheral rays are in focus.5 In this instance energy is distributed widely, even from the center. The amount of energy per unit receptor is reduced; the peripheral rays are optically refractive and are in focus for the near distance. They are focused sharply on the receptors. The result: high contrast. Some of the light passing through the pupillary area is in focus and some is not. The focused light furnishes a high-contrast threshold. Simultaneous Binocular VisionCorrecting far and near vision simultaneously confirms that the analytical mechanism of the brain is functioning. Thus, when the two discrete impulses received by the brain lead to only one sensation, the eye has single, simultaneous binocular vision. How does this translate for the wearer of aspheric multifocal contact lenses? Among the most commonly acknowledged advantages are: Improved lens-to-cornea fitting relationship Better pressure distribution Improved comfort Reduced flare and halos Optimum choice for atypical corneas The lens-to-cornea relationship with this type of lens is perhaps the most vital advantage over spherical gas permeable lenses. Consider that with the latter, the pre-fitting refractive state, the refractive state when the lens is worn, and the refractive state just after removal may vary considerably. Gas Permeable Lenses and Corneal TopographyA gas permeable lens fit with an alignment dye pattern that corrects vision to acceptable levels and therefore precludes changing the power implies that refractive stability is achieved. This may not be the case, however, since the posterior surface of the tear layer changes with corneal curve and may neutralize induced refractive changes.6 Doing a refraction immediately after removing spherical lenses may result in myopic increases, hyperopic decreases or a reduction in astigmatism. The induced refractive changes may occur independently of corneal topographical changes, because more than one variable may be changing.6 The sequence of changes in different components includes corneal edema, corneal index of refraction, corneal thickness, possibly the anterior and posterior corneal curvatures and anterior chamber depth. A 10 percent increase in the cornea"s index of refraction induces a change of -1.87D; a 10 percent change in reduced depth of the anterior chamber creates a change of +1.25D. Actual recovery time for refractive stability after removing lenses may indicate how much induced corneal compression or edema has occurred. A gas permeable corneal lens fit with a spherical base curve and apical clearance may induce corneal swelling and physiological changes that prevent the wearer from easily interchanging contact lenses and eyeglasses. The swelling may be provoked by changes in tear osmolarity, reduced corneal oxygen levels, mechanical trauma and partial obstruction of the eflux of carbon dioxide from the cornea, which may also affect corneal thickness.7 Refractive changes from corneal swelling are also related to the degree of transient stromal swelling during initial wearing periods. It"s important to keep a record of induced post-refraction changes resulting from gas permeable contact lens wear. Modify the lens design variables when the post-refraction changes exceed +0.50D or -0.50D to help control the degree of corneal physiological and structural responses to lens wear. This also prevents the post-wear refractive state from becoming irreversible, which could create permanent disturbance or deformed cornea. Dr. Goldberg (JGoldb8255@aol.com) is an Emeritus Fellow of the AAO and practices in Virginia Beach, Va. REFERENCES 1. Davson H. Visual perception. In The Physiology of the Eye. New York: Little, Brown and Co. (1963):316-76.2. Zoethout WD. Binocular vision. In Physiological Optics. Chicago: Professional Press (1939):264-82.3. Levy B. Clinical evaluation of the PS45 lens in presbyopia. Opt Prism 1990 (Sept-Oct);23-4.4. Cowan A. Aperture of the system, diffusion images. In Aberrations of the Eye in Refraction of the Eye. Philadelphia: Lea & Febiger (1945):133.5. Volk D, Goldberg JB. Physiological optics and effects of aspheric corneal lenses. CLS 1988 (Jan):65-7.6. Rengstorff RH. Corneal refraction, relative effects of each corneal component. AOA 1985;56(3):218.7. Larke J. Corneal swelling and its clinical sequelae. In The Eye in Contact Lens Wear. London: Butterworth & Co., Ltd. (1985):np. Vol. No: 140:03Issue: 3/15/03