Micro-Prisms and BVD

Dr. Russel Lazarus, April 20, 2021
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Has your eye doctor prescribed micro-prism lenses?

Micro-prisms lenses are fast becoming the optimal treatment for people with Binocular Visual Dysfunction, BVD.

With healthy binocular vision, light enters the two eyes by passing through the cornea and focusing onto the retina in the back of the eye. The brain then interprets the information it receives from the retina of each eye, and produces a single image.

A single image can only be produced if the eyes are perfectly aligned and working together.

In an eye condition, known as Binocular Visual Dysfunction, the eyes are misaligned and is a common reason for the eye doctor prescribing micro-prism lenses.

Double vision or other symptoms occur when the brain tries needs to work hard to compensate for the misalignment of the two eyes.

Prism lenses bend light before it passes through the eye, to redirect the light onto the correct retinal area in each eye. The brain can then accurately interpret the information and produce a single image. 

If you suspect your child has an eye condition, contact an eye doctor near you, who can diagnose and treat the condition.

SEE RELATED: 2021 Update: Treatments for BVD

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How is a prism prescribed?

Hirschberg test. This test is used to identify the presence of strabismus, or a turned eye. Your doctor will aim a small light at your eyes and look for a corneal reflection in the center of each pupil. If your reflection is off-center in either one or both eyes, you may have strabismus.

Krimsky test. This test is used to measure the degree of eye misalignment. Your doctor will aim a small light at your eyes, and place prisms of varying strengths in front of your eye. To determine which prism is appropriate for you, your doctor will look for the prism that is able to bring the corneal reflection to the center of your pupil.

Cover tests. There are three types of cover tests:

  1. Cover/uncover test: One eye is covered while your doctor looks for any movement in the eye that is uncovered.
  2. Prism and alternate cover test: A prism is placed in front of one eye while your doctor alternates the cover over your two eyes. This test measures the difference between the two eyes to determine what type of prism is appropriate for you.
  3. Maddox test: Each eye sees a vertical or horizontal line. Your doctor will use prisms to measure the difference between each of the images. This test is used to determine which type of double vision you have (vertical or horizontal).

What is micro-prism?

Prisms are measured and prescribed with a unit of measurement called prism diopters, for example, 4 prism diopters (PD) or 8PD. The prism is added to your regular eyeglass prescription, in one or both of your lenses. The way the prism is situated depends on the type of double vision you have— either horizontal or vertical.

Micro-prisms is just a small amount of prism, usually under 2 PD.

Even though the amount of prism may be small, the impact on your visual system can be significant, resulting in comfortable vision and alleviating the symptoms of BVD.

Vision therapy

Vision therapy may also be a solution recommended by your eye doctor for your double vision or binocular visual dysfunction.

Vision therapy retrains your eye-brain connections to improve your visual skills for clearer, single vision, with or without your eyeglasses.

If you suffer from double vision or binocular vision difficulties, micro-prism lenses can be prescribed to improve your clarity of vision— enabling a more comfortable way of seeing.

LEARN MORE:  Guide to Binocular Visual Dysfunction (BVD)

Contact an eye doctor near you to find out if prism lenses could be the solution you have looking for.