Unequal Vision: Anisometropia and Aniseikonia
Anisometropia is a condition in which you have a different refractive power in each eye. This can be as drastic as being nearsighted in one eye and farsighted in the other. People with anisometropia are also prone to aniseikonia. Aniseikonia causes you to see images that differ in size or shape with each eye. Both conditions can be corrected or improved by LASIK surgery.
Anisometropia can be as mild as requiring a slightly different prescription for each eye, or as extreme as causing one eye to be very nearsighted and the other to be very farsighted. Glasses can be made with a different prescription for each eye, but if the difference is extreme this can cause its own problems including double vision. Contact lenses tend to work better than glasses for people with this condition, but some people cannot tolerate or wear them. Children often cannot or will not wear glasses or contact lenses. LASIK can correct the condition by making refractive power equal in the eyes.
When anisometropia is not addressed, the brain chooses the best of the two images and the eye which has better vision will become the dominant eye. Over time the non-dominant eye can worsen, due to lack of use, leading to amblyopia and strabismus. For this reason, even though refractive surgery is normally considered to be inappropriate for children because their vision is not fully developed and has not stabilized, it is recommended for children with anisometropia in order to prevent vision loss in the non-dominant eye.
Anisometropia is also a potential complication of refractive surgery, but it can be corrected by follow up surgery.
Aniseikonia is most common in people with anisometropia, but can also occur in people with equal refractive power for a number of reasons. Eyes which are two different sizes, certain retinal conditions and their treatments, and some eye surgeries including refractive surgery and lens replacement, can cause aniseikonia. Patients who have refractive surgery in one eye at a time typically experience temporary aniseikonia between surgeries. Long-term aniseikonia can be very unpleasant and, for some, debilitating. Symptoms include:
- Eye strain
- Light sensitivity
- Difficulty reading
- Double vision
- Impaired depth perception
Aniseikonia is sometimes addressed by wearing glasses with an iseikonic prescription. This means changing magnification without changing refractive power. In the past, correct iseikonic prescriptions have been very difficult to achieve. Although modern technology has greatly improved accuracy, the glasses are often bulky and unattractive, and therefore go unworn. Contact lenses can also be used to correct aniseikonia, but sometimes make the condition worse. Depending on the cause, refractive surgery can often correct the condition.
Anisometropia and aniseikonia are easy to confuse and they often occur together. Both are possible complications of refractive surgery, but can occur naturally. Naturally occurring anisometropia often appears in early childhood and should be treated as young as possible to prevent vision loss. When aniseikonia is caused by anisometropia it can also be corrected by correcting anisometropia.