What Is Prism Correction?

Published on 10/30/2023
what is prism correction

Eyeglasses are usually designed to correct a refractive error - when the shape of your eye keeps light from focusing correctly on your retina, compromising your vision. This is the most common type of vision loss, resulting in blurred vision - often seeing double or triple of something. 

However, some patients have blurred or double vision due to light falling on different parts of the retina, but it is unrelated to their eye shape. In these cases, prism correction may restore vision.

How Prism Lenses Treat Prism Correction

Multiple conditions cause light to fall on different parts of the retina that have nothing to do with the shape of the eye. Some of them are due to issues with the eye muscle or optic nerve, and others may be related to an existing disease, a brain injury, or another cause of neurological problems.

Prism lenses use triangular prisms to redirect the light entering the pupil. The angles of the triangular prism are customized to correct light refraction proportionally. A simple example of this type of technology is the way light can bend by reflecting off the transparent cover of a watch face (incidentally, these are also “prims” made from crystal, glass, or plastic). The light refracts in different directions depending on how you angle your wrist.

In the case of prism lenses, the light refracts such that the eye thinks an object is in a slightly different location than it is or to make the eyes work in better alignment. By doing so, a double (blurred) image becomes clear. Prism lenses do not magnify or have any “focusing” power, so they are not the same type of lens we use for nearsightedness, farsightedness, or astigmatism. 

Conditions Treated Using Prism Lenses

Conditions causing blurred or double vision treated by prism lenses include:

Issues affecting the eye muscles

Light may not be able to focus on a single point on the retina if the eye muscles are weak or not functioning properly. If the issue prevents the eyes from aligning properly, prism lenses may be an option. Examples are:

  • Myasthenia gravis: This is an autoimmune disease that affects specific muscle receptors. The first symptoms of myasthenia gravis often include blurred vision and drooping eyelids. However, other muscles are also affected over time, including muscles in the face, arms, and the rest of the body. People with myasthenia gravis often have spells where symptoms are minimized, and then those with weaker muscles.
  • Grave’s disease. Another autoimmune disease, Grave’s, affects the thyroid gland and can also attack the eyes. In addition to muscle inflammation, which leads to double vision, patients with Grave’s disease are also at higher risk for nerve-related vision loss as well as developing dry eye.
  • Crossed eyes (strabismus). Depending on the cause of crossed eyes or strabismus, prism lenses may be used to help muscles work together and align vision focus. Usually, this condition is diagnosed shortly after birth and easily corrected using a combination of prism lenses (if necessary) and other types of eye exercises and eye therapy. However, adults may develop crossed eyes due to health conditions like Grave’s disease, diabetes, stroke, head trauma, and other medical conditions.
  • Neurological issues. Certain neurological issues in the brain may result in uncoordinated eye muscle movements that alter how the eyes focus. These include things like a stroke, head injury, or tumors. Some people experience uncoordinated eye muscles during a migraine episode, in which case temporary glasses with prism lenses may help.
  • Nerve-related issues. Similarly, any issues affecting the optic nerves outside the brain can alter muscle control and eye coordination. If that is causing blurred vision, without refractive error, the right prism lenses may improve focus. 

Prism Correction Diagnosis & Treatment

A complete eye exam is critical if you or a loved one is experiencing a sudden or fast-onset of blurred vision. Typically, refractive errors creep up on you over time. Any sudden vision change should always trigger immediate contact with your optometrist or ophthalmologist. 

If you have existing health conditions or newly diagnosed conditions that put you at risk for needing prism corrections, we recommend more frequent eye exams. If your child is born with strabismus (lazy eye) or crossed eyes and prism lenses are deemed a potential treatment, that will happen. Noticing any signs your child has blurred vision (watery eyes, frequent eye rubbing, struggling to read, not paying attention in class, etc.)

Otherwise, it’s only through annual eye exams that we notice signs of eye or eye-muscle coordination issues requiring correction via prism lenses.

What are prism lenses?

Prism lenses aren’t different from regular eyeglasses in how they look and feel once the right prism is given. The difference is the addition of a prism - made from plastic or glass - embedded into the lens. The first pair of lenses may look different because we fit a temporary Fresnel prism (a thin press-on vinyl sticker) over the front or back of the eyeglasses. This initial sticker is somewhat visible.

However, the temporary Fresnel prism is essential to ensure correct prism placement. Once we dial the placement in, you’ll choose frames for your new prism lenses. In most cases, prism lenses do not permanently treat the condition leading to blurred vision (young children with crossed eyes or with some eye muscle issues are an exception). So, the lenses work when they’re on, but you’ll continue experiencing blurred vision without them. Also, prisms are not yet able to be embedded in contact lenses. Unless you also have a refractive error, eyeglasses are the only option for correcting blurred vision treated with prism lenses. 

Don’t forget about lifestyle choices that support healthy vision

Since certain health issues are a leading cause of blurred vision requiring prism correction, we like to emphasize the importance of healthy lifestyle choices. The healthier you live and the better you manage underlying health conditions, the more you’ll support healthy eye and vision health.

Correct Blurred Vision At Eye to Eye Family Vision Care

Is blurred vision making it more difficult for you to read, drive, or complete daily tasks? Then, it’s time to schedule an eye appointment with Eye to Eye Family Vision Care. The sooner you have a complete eye exam, the sooner we can get you back on track and focused. If blurred vision is a new or sudden onset situation, call our office ASAP at 918-227-3937 to prioritize scheduling.