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  • Writer's pictureAtanas Bogoev M.D. and Maria Cholakova

Anisometropia: When One Eye Sees Better Than the Other

Anisometropia is a condition where the eyes have different refractive powers (the ability to focus light). Meaning that both eyes bend light differently and produce different images on the retina. In simple words, one eye may be more nearsighted or farsighted than the other eye.

Essentially, when one eye sees better than the other that leads to blurry vision, eye strain, headaches, and depth perception difficulty. The condition is treatable with glasses, corrective lenses, or other methods to help the eyes work better together.

Table of Content:

1.1. Types

1.2. Symptoms

1.3. Diagnosis

Discover more about anisometropia, the causes, symptoms, and treatment of unequal refraction in this Ophthalmology24 article. You will also learn whether is it permanent, and what to expect if you get the diagnosis.

More about Anisometropia

Medically speaking, anisometropia is an asymmetric refraction between both eyes with a difference of 1 or more diopter (D). The eye condition can affect people of any age but it is more common in children and can lead to amblyopia (lazy eye) if left untreated.

The vision disparity between the eyes is not rare. In fact, it is quite common and according to an article by Cleveland Clinic, it affects up to 28% of people.

Anisometropia Example scheme
Anisometropia Example

Types of Anisometropia

There are two different types of uneven eyesight, depending on which part of the eye has an abnormality:

  • Axial anisometropia

  • Refractive anisometropia

The most common type is axial anisometropia, where one eye is longer or shorter than the other, resulting in nearsightedness or farsightedness.

The other type is refractive anisometropia, where the cornea or lens of one eye has a different shape or curvature compared to the other eye.

Anisometropia Symptoms

The symptoms vary, depending on the condition's severity. In some cases, there may be no symptoms at all. In particular, if the difference in refractive power between the two eyes is small. In other cases, though, anisometropia may cause a range of problems, including:

  • Blurry vision

  • Eye strain

  • Headaches

  • Depth perception problems

If one eye is significantly more nearsighted or farsighted than the other, there will be a noticeable difference in the visual clarity between the eyes. Moreover, unequal vision can make it difficult for the eyes to work together properly, often leading to blurry sight.

Naturally, when one eye is working harder than the other to focus light, the patient may experience eye strain and headaches. That is most evident in tasks requiring a lot of visual concentration, such as reading or computer work. Anisometropia can also make it difficult to judge distances accurately.

Getting a Diagnosis

Anisometropia is detectable through a comprehensive eye exam. During the exam, an eye doctor will measure the refractive power of each eye and check for any differences between the two. They may also perform tests to check how well the eyes are working together.

vision chart

What Causes Differences in Eyesight Between Eyes?

Vision differences between eyes may result from a variety of factors.

While genetics could play a significant role in the development of uneven eyesight, hereditary factors alone cannot explain it. There is evidence to suggest that anisometropia can run in families, but this is not always the case. Even if it is passed on, the condition may not necessarily manifest in the same way in all family members.

Here are a few of the most commonly suspected causes of developing imbalanced eyesight:

  • Refractive errors

  • Eye diseases

  • Eye injuries

  • Amblyopia

Nearsightedness, farsightedness, and astigmatism are refractive errors that occur when the shape of the eye causes light to focus incorrectly on the retina. These errors can naturally vary between the eyes, causing differences in diopters and vision.

Eye diseases such as cataracts, glaucoma, and macular degeneration, macular edema can affect one eye more than the other and cause vast disparities in the sharpness of vision. At the same time, injuries to one eye can also affect its visual acuity and lead to changes in vision, compared to the other eye.

Lazy eye (Amblyopia) occurs when one eye has weaker vision than the other due to a lack of visual stimulation during development. As a result, the eyes can see differently.

If you are experiencing differences in eyesight between your eyes, you should visit an eye doctor for an eye exam to determine the underlying cause of anisometropia. Depending on the cause, treatment options may include corrective lenses, vision therapy, or surgery.

measuring refractive error

Anisometropia Treatment

If you have the condition, you are probably wondering, is anisometropia permanent? The refractive difference between eyes would not go away on its own. On the brighter side, it can be corrected.

The treatment depends on the severity and type of the condition. As well as the age and preference of the patient. Some possible treatments that tend to be medically effective include:

  • Glasses

  • Contact lenses

  • Laser eye surgery

  • Intraocular lens implantation

Glasses or contact lenses

In some cases, wearing glasses or contact lenses with different prescriptions for each eye may improve vision in the weaker eye and reduce differences in eyesight between the eyes. Glasses and contacts can correct the refractive error of each eye and help them focus on the same point.

However, some people may experience aniseikonia (a difference in the perceived size or shape of objects) when wearing glasses or contact lenses for anisometropia. Especially if the difference between the two eyes is substantial.

Laser eye surgery

This procedure can reshape the cornea of one or both eyes to correct the refractive error and eliminate the need for glasses or contact lenses. However, laser eye surgery is not suitable for everyone. It may also have some risks and complications. Consult an eye doctor to get treatment recommendations for asymmetric vision and individual information about the risks.

Intraocular lens implantation

Lens implantation involves replacing the natural lens of one or both eyes with an artificial lens that has a different power or shape. This can correct the refractive error and also treat cataracts if present. However, intraocular lens implantation is an invasive procedure that may have adverse complications. Please talk to your ophthalmologist to learn more about the risks.

Ophthalmologist offering glasses and contact lenses to anisometropia patient

Anisometropia in Children

Children with anisometropia may not realize that their vision is abnormal. The reason is they have adapted to it since birth. They may also not show any obvious signs of eye problems in children like squinting or tilting their head.

This is a bit concerning because untreated pediatric anisometropia can lead to amblyopia (lazy eye). Lazy eye is a condition where the brain favors one eye over the other and ignores the weaker eye's input. It might result in permanently reduced vision if you don't correct it before the age of 8.

The solution for on-time diagnosis, in this case, is simple - pediatric eye exams. The condition is easily diagnosable by an eye doctor using visual acuity, refraction, and eye alignment tests.

Some factors that may contribute to differences between the eyes diopters in children include genetics, premature birth, eye injuries, and diseases such as cataracts or glaucoma.

If you suspect that you or your child may have anisometropia, consult an eye doctor for a pediatric eye exam and diagnosis. Non-uniform vision affects the quality of life, school performance, and visual development of your child. Early detection and intervention can prevent long-term complications. So it is best to seek treatment as soon as possible.

Prevention of Anisometropia

It is not always possible to prevent eyes from having different refractive power. Sometimes if one eye sees better than the other, the reason may be factors outside of your control. For example, differences in eye shape or size.

However, there are steps you can take to slightly reduce the risk of developing anisometropia, especially in children. These include:

Variations in refractive powers in both eyes are more common than you would think. With proper medical care and appropriate treatment, most patients with anisometropia successfully adjust to the diopter difference and achieve clear, comfortable vision.

For more information about how to improve your eyesight and take care of your eye health, check out our patient's blog.

All medical facts in this article are checked by Atanas Bogoev M.D.

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