Anisometropia: Types, Symptoms, Causes and Treatment

Definition: Clinically Significant Refractive Condition of an Eye

Very few people are born with two eyes of identical optical power, but this difference allows the brain to compensate imperceptibly. However, when a person has anisometropia, the difference in vision between their two eyes is significant and will interfere with normal binocular vision.

These people really see a smaller image in one eye and a larger image in the other eye. The result is that your general vision is often blurry. Another potential result of anisometropia is amblyopia (lazy eye), which can occur if an eye has blurred vision for some time and becomes permanently weaker.

Sometimes, anisometropia may be present at birth, although it often will not become apparent until later in life. It has been estimated that around six percent of children between six and eighteen suffer from this visual condition.

Types of Anisometropy

  • Simple anisometropia: It is when one eye is affected while the other eye does not have any refractive error. The affected eye may be hyperopic or myopic.
  • Composite anisometropia: It is when both eyes are myopic, although there will be a significant difference in their refractive errors. This causes one eye to see a blurrier image than the other.
  • Mixed anisometropia: It is when both eyes have appreciable refractive errors, with one myopic eye and the other hypermetropic.

Symptoms of anisometropia

  • Amblyopia (lazy eye): Usually occurs when the reduction of the refractive power in an eye causes a lack of visual stimulation that results in the transmission of insufficient information through the optic nerve to the brain.
  • Strabismus (crossed eyes): Occurs when a patient can not align both eyes. This lack of coordination prevents both eyes from focusing on the same point in space.
  • Diplopia (often known as double vision): The person has visual fatigue, headaches, nausea, sensitivity to light, fatigue and dizziness.

With unequal vision measurements, you may be at higher risk for binocular vision problems, such as vague eyes or double vision. Some people can develop astigmatism too.


People who enjoy normal vision can have up to 5% difference in the refractive power of each eye. However, those with a difference of 5-20% will experience an unequal vision (anisometropia). The causes include defects in the eye at birth, as well as the unequal size of the two eyes.

Having eyeballs of different sizes can lead to their development. Most of the time, this condition affects children, especially in ages between 6 and 18 years.

Although it is rare to have an identical visual measurement in both eyes, their difference is usually minimal, which is why the brain usually manages to compensate. However, in anisometropia there are significant differences.

The power of refraction between the eyes is so great that it leaves the brain no choice but to ignore the visual cues of the weaker eye.

Another factor that can cause anisometropia is cataract. Frequently, the intraocular gas is used to help repair retinal detachment, this gas can increase the rate of cataract formation, and therefore myopia.


Anisometropia is usually detected or diagnosed when the child has an eye exam. If it occurs in an older person, they may notice that their vision is blurred and undergo an examination for a diagnosis.

During the eye exam the doctor will check how well they see things when they cover the first eye and then the other. It can also be diagnosed if it causes other conditions, such as eyestrain or double vision.


It is important to treat anisometropia as soon as it is diagnosed. If left untreated, the brain can decide to select the eye that presents the clearest image and then ignore the other eye, this can lead to a stronger eye dependence.

The neglected eye will become progressively weaker, so it is important to seek treatment before the problem becomes acute. The way in which anisometropia can be treated depends on the severity.

For some the difference between the two eyes is manageable, especially with a minimal difference. Other patients may require corrective lenses, contact lenses or corrective surgery.

When using contact lenses or corrective lenses each lens should be a different recipe to be effective. Generally speaking, lenses are not suitable for those with very large degrees of anisometropia.

Due to its magnification effect, eyeglasses can create a considerable difference in the size of the image that each eye sees and can prevent good binocular vision.

It is recommended to see an ophthalmologist for regular eye exams in adults and children. These specialists can help identify the signs of this visual disability and handle all types of ocular misalignment. They are masters of refraction (they refract babies) and most are well versed in the evaluation of adult cataracts.