What is Anisometropia?
Anisometropia is a condition that occurs when your eyes have varying refractive powers, which can cause your eyes to focus unevenly. This condition typically occurs when one eye is a different size or shape than the other and results in asymmetrical curvatures, asymmetric farsightedness, or asymmetric nearsightedness.
Anisometropia is one of the most common causes of amblyopia, which is more commonly known as “lazy eye”.
In this article, we will cover everything you need to know about anisometropia.
Root Cause & Risk Factors
We still aren’t entirely sure what causes anisometropia, but having eyes that are significantly different sizes can be a contributing factor. Individuals with normal vision may have up to a 5% difference in refractive power in their two eyes, though individuals with a greater difference than 5% are more likely to develop anisometropia.
Anisometropia affects our binocular vision. Individuals with anisometropia typically see one larger image in one eye and one smaller image in the other. This causes their vision to blur. As a result, one eye may become weaker than the other, which may prompt the brain to favor the stronger eye. This can cause amblyopia if the anisometropia is not caught and treated early. Individuals with untreated anisometropia may experience:
- Poor depth perception
- Visual discomfort
Though anisometropia can be present from birth, it is not typically diagnosed until childhood. Estimates suggest that around 6% of all children between the ages of 6 and 18 suffer from anisometropia.
There are three types of anisometropia: Simple anisometropia, compound anisometropia, and mixed anisometropia.
Simple anisometropia occurs when only one eye has a refractive error. The eye can be either hyperopic (farsighted) or myopic (nearsighted). This form of anisometropia can be treated using eyeglasses. Simple anisometropia causes one eye to see a blurry image while the other eye sees a clear image.
Compound anisometropia occurs when both eyes are either hyperopic (farsighted) or myopic (nearsighted). However, there is still a significant difference in the refractive errors of the two eyes, so they will need dramatically different prescriptions. This form of anisometropia causes both eyes to see blurry images, but one eye’s vision will be significantly blurrier.
Mixed anisometropia occurs when both eyes have refractive errors but one is myopic (nearsighted), and the other is hyperopic (farsighted).
Typical Manifestations & Symptoms
Potential Vision Manifestations
Anisometropia can affect our vision in a variety of ways. This can include:
- Amblyopia: Amblyopia, also called “lazy eye” occurs when the brain begins to favor the eye with stronger vision over the eye with weaker vision, reducing visual stimulation. This causes the brain to begin ignoring visual inputs from the weaker eye.
- Strabismus: Strabismus, also called “crossed eyes”, occurs when we are unable to keep our eyes aligned. This lack of coordination keeps us from being able to focus both eyes on the same point in space.
- Diplopia: Diplopia, also called “double vision”. Diplopia causes our eyes to send two, slightly offset images to our brain, causing double vision and confusion. Diplopia can cause eyestrain, headaches, nausea, sensitivity to light, tired eyes, and dizziness.
Untreated anisometropia can cause a variety of symptoms including:
- Poor depth perception
- Visual discomfort
Treatment & Management Options
Anisometropia needs to be treated as soon as it is diagnosed. If treatment is delayed the brain may decide to favor the eye that presents a clearer image over the other eye, leading to dependence on the stronger eye. If this occurs, the non-favored eye will become increasingly weaker.
Anisometropia can be treated using a variety of methods, which are determined based on the severity of the condition. Treatments can include corrective lenses, contact lenses, or laser eye surgery. For corrective lenses or contact lenses to be effective they will need to be different prescriptions so that each eye can have its visual needs met.
Individuals with large degrees anisometropia typically cannot rely on corrective lenses for treatment. Eyeglasses have a magnifying effect, which can significantly change the size of the image seen by each eye. As such individuals with large degrees of anisometropia may find that eyeglasses negatively affect their binocular vision.
Depending on the severity of the anisometropia it may be managed without the use of corrective lenses, contact lenses, or eye surgery. Patching, where the dominant eye is covered to encourage the weaker eye to pick up the slack, is an effective treatment for amblyopia caused by anisometropia. Some studies have also shown that children with anisometropic amblyopia may benefit from the use of prisms instead of using patching.
However, individuals with large degrees of anisometropia will likely require contact lenses or laser eye surgery.
For more information about anisometropia, or to request your next eye exam, please contact our office.