How Do Prismatic Lens Glasses Work?

doctor holding glasses and lenses box

Nearsightedness and farsightedness are the most common reasons for wearing glasses. People who wear glasses don’t all suffer from impaired vision. Some people may have perfectly aligned eyes and 20/20 vision, yet they don’t operate well together. 

This issue is better known as binocular vision dysfunction (BVD) and is responsible for creating concerning problems such as double vision or eye strain.

Normally, light falls on the same portion of the retina in both eyes, so we see the same picture in both our eyes. Double vision is caused by light refracting in two separate locations on the retina, causing BVDs to appear.

That’s where prismatic lens glasses come into play. Prism correction in eyeglasses is prescribed for people who have diplopia or double vision. The prism assists in aligning the two pictures so that only one image is visible.

This article will cover the most frequently asked questions about prismatic lenses that occur with patients who are introduced to them. 

Why Are Prismatic Lens Glasses Different From Regular Ones?

Prismatic lens glasses use lenses that bend light in different ways. They help people with BVD more than the glasses that are usually worn for correcting vision. 

When you have BVD, your eyes look in two different directions instead of at the same point. Prismatic lenses help your eyes work together, which can reduce or even completely get rid of problems like double vision, eye strain, and headaches that come back over and over again.

With fewer symptoms, you’ll be more able to concentrate and enhance your productivity. Children who wear lenses with prisms might also be able to focus better and achieve better results in school.

What Do Prism Glasses Look Like?

Prisms have a broad base and a pointed tip, like a pyramid. When light hits the lens, the prism bends it towards its base while allowing the picture to rise. As a result, you are able to form a clear, coherent picture of what you perceive. 

In certain cases, a thin press-on vinyl sticker known as a Fresnel prism is attached to the front or rear of your glasses. Although Fresnel prisms aren’t an ideal long-term solution, they can be employed when the prism prescription is uncertain and is likely to alter.

Prism correction can be ground into the lens of your eyeglasses if it is required for an extended period of time. Prismatic lens glasses have lenses that are bigger and more prominent on one side, but otherwise, they seem like any other pair of spectacles. You may want to try a thicker frame to cover this part of the lens if you’re concerned.

glasses fractioning the light
Black glasses photo created by freepik –

When Should I Start Wearing Prism Glasses?

Most commonly, prism lenses are prescribed to people who have serious binocular vision disorders and double vision.

Typical problems include:

  • BVD
  • Strabismus
  • Strabismus Convergence insufficiency
  • Grave’s disease;

Symptoms like:

  • Dizziness or lightheadedness 
  • Eye strain and fatigue
  • Double vision
  • Headaches
  • Difficulty concentrating or focusing

And injuries to the brain that are caused by:

  • Stroke
  • Head injuries
  • Migraines
  • Diabetes
  • Multiple sclerosis

If you or someone in your family suffers from any of the above mentioned signs, it would be ideal for making an appointment with your eye doctor as they can prescribe you adequate eyewear. 

What Does a Prism Lens Prescription Look Like?

A typical lens prescription contains two numbers:

  1. Prism: just like with normal eyeglasses, diopters calculate the prism correction amount, indicating how misaligned your eyes are (from 0.5PD and up.)
  2. Base: The prism is placed vertically, horizontally, or diagonally in the lenses, depending on your double vision. The “base” of the prism is the broadest edge and indicates where the light is diverted. It might be on the lens’s outer (Base Out, BO) or inner (Base In, BI) edge, or even at the top (Base Up, BU) or bottom edge (Base Down, BD).

Are Prismatic Lens Glasses a Long-Term Solution?

Although prism lenses can help ease double vision while you’re wearing your glasses, they can’t help you after you take them off. As a result, prisms are only a temporary cure.

Usual symptoms like eye strain, headaches, or poor concentration due to BVD can be treated with adequate eye exercises.

But, if you desire a long-term solution to your binocular vision problems, talk to your eye doctor about vision therapy. Vision therapy involves training your eye-brain connections in order to enhance your visual abilities, allowing you to see well with or without glasses.