Fiber Connector Types: The Ultimate Guide - fiber connectorization

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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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What is beamdivergence

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

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

Divergence angleformula

Zhang, G., Wu, J., Li, Y., Wang, X., Yu, X., Gao, S., & Ma, L. (2023). A Review of Variable-Beam Divergence Angle FSO Communication Systems. Photonics, 10(7), 756. https://doi.org/10.3390/photonics10070756

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

Lowdivergencelaser

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

Zhang, Guoqiang, Jiabin Wu, Yatian Li, Ximing Wang, Xichang Yu, Shijie Gao, and Lie Ma. 2023. "A Review of Variable-Beam Divergence Angle FSO Communication Systems" Photonics 10, no. 7: 756. https://doi.org/10.3390/photonics10070756

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

Divergence anglecalculator

by TC Bond · 2006 · Cited by 2835 — Depending on the parameters chosen, π electrons affect predicted absorption most; the number of free conduction electrons is much lower and they have little ...

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.

Gaussian beamdivergencecalculator

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

Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.

USB 3.1 Type C to USB 3.0 Micro B - This cable easily connects a computer with a USB Type C port to an external hard drive, Smartphone or tablet with a USB 3.0 ...

Zhang G, Wu J, Li Y, Wang X, Yu X, Gao S, Ma L. A Review of Variable-Beam Divergence Angle FSO Communication Systems. Photonics. 2023; 10(7):756. https://doi.org/10.3390/photonics10070756

Gaussian beamdivergence

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

Because they were used for imaging purposes they have quite fine "groove" pitch (that is, small facet size) - typically on the order of 0.2mm. This fine pitch ...

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

Feb 6, 2021 — Nosepiece holds the objective lenses and is sometimes called a revolving turret. You choose the objective lens by rotating to the specific lens ...

by NI Zheludev · 2008 · Cited by 251 — What diffraction limit? ... Several approaches are capable of beating the classical 'diffraction limit'. In the optical domain, not only are superlenses a ...

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

Jul 22, 2015 — The ROOT TH1::SetDirectory function allows you to set the output directory for histograms created in ROOT. This means that any histograms ...

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.

Laser beamdivergenceand spot size

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

Abstract: Free-space optical (FSO) communication is widely used in satellites, ships, aircraft, and ground stations due to its advantages of high speed, large capacity, good confidentiality, and strong anti-interference ability. Variable-beam divergence angle (VBDA) technology makes FSO systems more flexible; this has the benefits of higher acquisition probability, stronger tracking ability, wider communication link range, and lower energy consumption. In other words, the study of VBDA has both theoretical significance and practical relevance. This paper conducts a comprehensive search of relevant scientific databases, journals, conference proceedings, patents, and books to identify publications related to VBDA technology. We analyze these publications, classify and organize various VBDA techniques based on their respective methods. To the best of our knowledge, this is the first review of VBDA technology. In this paper, we first explain the basic principle of changing the beam divergence angle by employing the ABCD matrix, and further furnish a detailed overview of the methods used for VBDA along with their corresponding advantages and disadvantages. In addition, we provide a comprehensive summary of the research conducted using VBDA technology across different link types. Lastly, we identify the challenges and potential future research directions for VBDA technology. Keywords: 6G; free-space optical (FSO) communication; variable-beam divergence angle

Divergence angleof beam

Zhang, G.; Wu, J.; Li, Y.; Wang, X.; Yu, X.; Gao, S.; Ma, L. A Review of Variable-Beam Divergence Angle FSO Communication Systems. Photonics 2023, 10, 756. https://doi.org/10.3390/photonics10070756

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

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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Focal length determines angle of view and magnification. When light enters a lens, glass elements within the lens serve to converge the light to a single point, ...

Zhang, G.; Wu, J.; Li, Y.; Wang, X.; Yu, X.; Gao, S.; Ma, L. A Review of Variable-Beam Divergence Angle FSO Communication Systems. Photonics 2023, 10, 756. https://doi.org/10.3390/photonics10070756

Microscope objectives are generally designed with a short free working distance, which is defined as the distance from the front lens element of the ...

Zhang G, Wu J, Li Y, Wang X, Yu X, Gao S, Ma L. A Review of Variable-Beam Divergence Angle FSO Communication Systems. Photonics. 2023; 10(7):756. https://doi.org/10.3390/photonics10070756

Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive positive feedback from the reviewers.

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