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Cover tests. There are three types of cover tests. With the cover/uncover test, one eye is covered and one is left uncovered. The doctor looks for any movement in the eye that is uncovered. The prism and alternate cover test alternates the cover over both eyes while a prism is placed in front of one eye. This measures the offset (difference) between the two eyes to find the right prism to fix your double vision. With the Maddox Rod test, each eye sees a vertical or horizontal line. The offset of these images allows the doctor to determine what type of double vision you have. Prisms are also used to measure the distance between the two images and provide the prescription value.

The NOA bond can be separated in chlorinated solvent such as methylene chloride. The bonded area must be soaked in the solvent and normally will separate overnight if only precured. Longer times may be necessary depending upon the extent of the cure and the size of the bond area.

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Just like regular eyeglasses, you need an in-person exam to test your vision. This is the only way to get the right prescription.

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The NOA 63 can withstand temperatures of-15 to 60° C when used to bond glass optics. In some cases, temperatures to 90° C are possible when the adhesive is used as a film or coating. The latter would depend upon the application.

Double vision has many causes, and a prism isn't helpful for all types of double vision. Because it can be a sign of a serious health condition, it's important to find out what's causing your double vision.

If prism correction is needed for a longer period, it can be ground into (made part of) the lens of your eyeglasses. Eyeglasses with a prism look like any other glasses without a prism, although the lens on one side may be thicker and more noticeable. If this is a concern to you, consider a thicker frame to hide that portion of the lens.

Normally, we see one image through two eyes because light falls on the same part of the retina in each eye. With double vision, two images are seen because the light falls on different parts of the retina.

Shelf life of the liquid is at least 6 months from the date of shipment if stored in a cool (5-22° C), dark place in the original container. If refrigerated, allow the adhesive to come to room temperature prior to use.

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Prism correction is used in eyeglasses for some people with diplopia, or double vision. This is when someone sees two separate images of one object. The prism helps align the two images, so that only one image is seen. Why Do People See Double?  Normally, we see one image through two eyes because light falls on the same part of the retina in each eye. With double vision, two images are seen because the light falls on different parts of the retina. How Do Prism Glasses Fix Double Vision? A prism added to eyeglasses bends light before it travels through the eye. The light is redirected to the right place on the retina in each eye. The brain then fuses the two images together to produce one, clear picture. Will Prism Glasses Fix My Double Vision? A prism may fix double vision from eye misalignment when caused by: Eye muscle problems, such as myasthenia gravis, Graves’ disease, or strabismus (crossed eyes or wall eyes) Neurological (brain-related) issues, such as head injuries, stroke, migraine, or tumor. Nerve-related problems, like multiple sclerosis or diabetes mellitus Double vision has many causes, and a prism isn't helpful for all types of double vision. Because it can be a sign of a serious health condition, it's important to find out what's causing your double vision. See a doctor immediately if your double vision: is new is caused by eye misalignment or happens for unknown reasons How Do I Get Prism Put in My Glasses? Just like regular eyeglasses, you need an in-person exam to test your vision. This is the only way to get the right prescription. During the exam, your ophthalmologist may do one or more of these tests to evaluate whether you need prism: Hirschberg test. This basic test helps check for strabismus. A pen light is aimed at the eyes. The light's reflection should appear in the center of the pupil in each eye. If the reflection is off-center in either or both eyes, there may be strabismus. Off-center corneal reflection of light in left eye, showing possible strabismus Krimsky test. This test helps measure the degree of misalignment. This is like the Hirschberg test, but with a prism. While looking at the pen light, prisms of different strengths are placed in front of the eye. When a prism brings the reflection in each eye to the center, the correct prism measurement has been found. Cover tests. There are three types of cover tests. With the cover/uncover test, one eye is covered and one is left uncovered. The doctor looks for any movement in the eye that is uncovered. The prism and alternate cover test alternates the cover over both eyes while a prism is placed in front of one eye. This measures the offset (difference) between the two eyes to find the right prism to fix your double vision. With the Maddox Rod test, each eye sees a vertical or horizontal line. The offset of these images allows the doctor to determine what type of double vision you have. Prisms are also used to measure the distance between the two images and provide the prescription value. What Does a Prescription for Prism Look Like? A prescription for prism typically has two numbers: Prism. Like normal eyeglasses, diopters measure the amount of prism correction (from 0.5PD, 1.0PD, 1.5PD, and so on) and indicate how misaligned your eyes are. Base. Depending on your double vision, the prism is placed vertically, horizontally or diagonally in one or both lenses of your eyeglasses. The “base” is the thickest edge of the prism and tells you where the light is redirected. It may be on the outer edge of the lens (Base Out, BO), the inner edge (Base In, BI), or at the top (Base Up, BU) or bottom edge (Base Down, BD). What Do Prism Eyeglasses Look Like? Sometimes, a temporary Fresnel prism (a thin press-on vinyl sticker) is fitted over the front or back of your eyeglasses. With a Fresnel prism lens, the prism is slightly visible. This isn't ideal for long-term use, but it allows you to test drive a prism and see how it works. Fresnel prisms are also used when the prism prescription isn't stable and may change soon. Eyeglasses with a temporary Fresnel prism on left lens. If prism correction is needed for a longer period, it can be ground into (made part of) the lens of your eyeglasses. Eyeglasses with a prism look like any other glasses without a prism, although the lens on one side may be thicker and more noticeable. If this is a concern to you, consider a thicker frame to hide that portion of the lens. Eyeglasses with prism built into the lens. Do Prism Eyeglasses Cause Side Effects? It may take a few days to get used to wearing new prism eyeglasses or those with an updated prescription. You may have some eye strain during this time. Rare symptoms include: double vision headache nausea eye pain If you have any of these symptoms, call your eye care professional who prescribed the glasses. You may need the frame refit or a new prescription.

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If you have any of these symptoms, call your eye care professional who prescribed the glasses. You may need the frame refit or a new prescription.

Hirschberg test. This basic test helps check for strabismus. A pen light is aimed at the eyes. The light's reflection should appear in the center of the pupil in each eye. If the reflection is off-center in either or both eyes, there may be strabismus.

Sometimes, a temporary Fresnel prism (a thin press-on vinyl sticker) is fitted over the front or back of your eyeglasses. With a Fresnel prism lens, the prism is slightly visible. This isn't ideal for long-term use, but it allows you to test drive a prism and see how it works. Fresnel prisms are also used when the prism prescription isn't stable and may change soon.

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It may take a few days to get used to wearing new prism eyeglasses or those with an updated prescription. You may have some eye strain during this time.

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NOA 63 is recommended for the bonding of achromats, prisms and all other precision compound optics. The outstanding characteristics of the adhesive are its low fluorescence and its excellent transmission in the near UV range. After full cure, the adhesive has good transmission from 320 to 3,000 nanometers. This adhesive is also suitable for bonding glass to metal. The high viscosity of NOA 63 allows it to be applied as a self-supporting drop or bead along the edge of a precision component to bond it to the substrate. The adhesive cures well in thick sections and has low shrinkage and a slight resiliency to minimize strain.

Prism correction is used in eyeglasses for some people with diplopia, or double vision. This is when someone sees two separate images of one object. The prism helps align the two images, so that only one image is seen.

Krimsky test. This test helps measure the degree of misalignment. This is like the Hirschberg test, but with a prism. While looking at the pen light, prisms of different strengths are placed in front of the eye. When a prism brings the reflection in each eye to the center, the correct prism measurement has been found.

Some of the light sources that can be used to cure the adhesive are sunlight, mercury lamps, and fluorescent black lights.

NOA 63 is cured by ultraviolet light with maximum absorption in the range of 350 to 380 nanometers. The recommended energy required for full cure is 4.5 Joules/sq. cm of long wavelength UV light. In most optical applications, curing is done in two steps. First a short exposure, or precure, is used. This cures the adhesive enough to allow it to be handled without disturbing the alignment, and keeps the number of alignment fixtures to a minimum. At this time, parts can be inspected, and excess adhesive can be cleaned up with an acetone or alcohol moistened cloth. Any rejected pieces are most easily separated at this stage. Cure is completed by exposure for the remainder of the cure time.

A prism added to eyeglasses bends light before it travels through the eye. The light is redirected to the right place on the retina in each eye. The brain then fuses the two images together to produce one, clear picture.

Norland Optical Adhesive 63 (NOA63) is a clear, colorless, liquid photopolymer that will cure when exposed to ultraviolet light. Since, it is a one part system and 100% solid, it offers many advantages in bonding of optical elements where the bonding surface can be exposed to light. The use of NOA 63 eliminates premixing, drying, or heat curing operations common to other optical adhesive systems. Curing time is remarkably fast, and is dependent upon the thickness applied and the amount of ultraviolet light energy available.

Member of Meridian Adhesives Group, the company Epoxy Technology Europe SRL (formerly known as Gentec Benelux) is a solutions provider addressing problems related to precision assembly, adhesives, encapsulants, coatings, UV curing and UV light measurement for a wide range of industries.

Care should be taken in handling this material. The Material Safety Data Sheet should be read for this product as well asfor any associated products such as alcohol, acetone or methylene chloride. Prolonged contact with skin should be avoided and affected areas should be thoroughly washed with copious amounts of soap and water. If the adhesive gets into eyes, flush with water for 15 minutes and seek medical attention. Use the material in a well ventilated area, otherwise a NIOSH approved organic vapor mask is recommended.