What Is Anisometropia?
If you are wondering, 'what is Anisometropia?' then you have come to the right place. The definition of anisometropia, more commonly known as vision imbalance, is a condition where your eyes have varying refractive power – i.e. your ability to focus is different in each eye. Anisometropia means you have a different prescription for each eye.
Typically caused by unevenly sized or shaped eyes, anisometropia symptoms include asymmetric longsightedness or asymmetric shortsightedness. Anisometropia can result in an induced differential prism between the eyes as they move away from the centre of the correcting lens.
Several studies show that only around 6% of young people have this refractive error, which generally occurs more frequently as they age.
What are the types of Anisometropia?
There are different types of anisometropia, with patients being affected differently by each of them. However, most types of anisometropia share the same symptoms.
1) Simple anisometropia
Simple anisometropia occurs when one eye has regular vision, but the other affected eye is short-sighted (myopia) or long-sighted (hyperopia). If you have one normal eye and one nearsighted eye, you have simple myopic anisometropia i.e. blurrier image in one eye.
2) Hyperopic anisometropia
Hyperopic anisometropia, also known as compound anisometropia, occurs when both eyes have the same refraction problem, but one eye is worse. If your pair of eyes are nearsighted, but one has a higher prescription than the other, you have compound myopic anisometropia. This can cause the eyes to be unable to work together and fuse the image into one, causing double vision. Double vision, also known as diplopia, causes people to see two of the same image.
4) Simple astigmatic anisometropia
Astigmatism is when the curvature of your eye's cornea or lens is shaped like a football, which means your vision is blurred at all distances. The shape of your eye causes light to refract unevenly, which means the light changes direction when it enters your eye at an angle.
5) Compound astigmatic anisometropia
This refractive error means you have astigmatism in both eyes, but one eye requires much more correction. For compound astigmatic anisometropia, both eyes are either farsighted or nearsighted and require refraction correction.
6) Mixed astigmatic anisometropia
If you have this type of anisometropia, you have astigmatism in both eyes. However, one eye is farsighted, and the other is nearsighted.
Another kind of anisometropia is a rare refractive condition called antimetropia, also known as mixed anisometropia. This condition is when one eye is myopic and the other is hyperopic, which means there is a significant difference in vision between the two eyes.
Is Antimetropia rare?
Antimetropia is rare, but in most cases that it occurs is in post-cataract refractive surgery patients.
Symptoms of anisometropia
‘How do I know if I have anisometropia?' You may be asking at this point. Anisometropia has a number of noticeable symptoms. These can include:
Amblyopia (also called lazy eye)
Frequent blurred vision
Diplopia (double vision) and dizziness
Strabismus (crossed eyes)
Difficulty with 3D vision, poor depth perception and loss of balance
Lack of coordination
If you suffer from any of these or other mild vision problems, you should ask your doctor for a comprehensive eye exam and diagnosis. An eye exam will generally include various tests to check the health of your eye and distinguish any diseases or conditions. Even if you do not have any symptoms, an eye screening is recommended for adults at the age of 40 to identify vision change and any signs of various sight impairments.
What causes Anisometropia?
Most people with ‘normal vision' can experience up to a 5% difference in the refractive power of each eye. However, those with a larger difference in refractive power (5-20%) will experience uneven vision, which can cause a lack of coordination.
There is no definitive answer as to what causes refractive errors that lead to developing anisometropia. There are likely genetic and environmental risk factors for this, such as defects in the eye at birth or an uneven size of the two eyes. Other potential causes can include injury to the eye, eye trauma and refractive surgery.
Anisometropia after cataract surgery
Cataract surgery is when the natural lens of an eye is replaced with an artificial one to help improve visual stimulation without wearing glasses or stopping cataract development.
The majority of people will copy very well following cataract surgery. However, some people will experience symptoms of anisometropia in more severe cases.
Anisometropia in children
Anisometropia can result in anisometropic amblyopia (lazy eye) in young children. Amblyopia can occur in children because the brain tells the eyes to focus the same amount in each eye. However, if the eyes don't have the same refractive power, one eye will produce a blurry image compared to the other eye.
Furthermore, if your child does not have a wandering or crossing eye (strabismus), it can be difficult to determine the condition. Young children often do not present outward signs of issues, as they function well using one eye, so it is more difficult to notice. However, older children are likely to complain. We recommend booking your child an eye test to diagnose the condition and to be treated.
There are different methods of treatment for anisometropia, which vary from person to person. It is important to consult your eye doctor to understand and seek treatment. Treatments you may be offered include:
Corrective lenses (wear glasses or contact lenses) can be worn to improve overall vision and produce a clear image.
Special filters in glasses help train the brain to use the weaker eye.
Covering the dominant eye with an eye patch (the same treatment for a lazy eye), also known as patching, helps the brain use the neglected eye.
Eye drops can blur the vision in the dominant eye, which helps force the brain to use the neglected eye.
LASIK is a common corrective surgery for treating anisometropia, depending on your prescription.
Can anisometropia be corrected with glasses?
If you're asking, ‘can anisometropia be corrected?', you'll be pleased to hear that there are treatment options. One kind of treatment for anisometropia is corrective lenses. While you are correcting short-sightedness in both eyes using prescription glasses that are the same over each eye, anisometropia requires a different kind of lens to correct it.
When deciding which route to take when it comes to eyewear, consider the wide range of options available:
1. Prescription glasses with bifocal or progressive addition lenses (PALs) are a common option for treating anisometropia symptoms and are often the first step. You can get an up-to-date spectacle prescription from your optician or use our Lens Scanner to reveal your current prescription.
2. Bifocal lenses are glasses constructed with two points of focus, which simultaneously correct refractive errors for both distance and near vision.
3. Progressive lenses are similar to bifocal lenses but offer a gradual transition between the two prescription lenses, so there is no visible line on your prescription spectacles.
4. Reading glasses are another option for anisometropia symptoms. You can have these glasses fitted with your unique prescription so you can wear these glasses while you read or work. There are also non-prescription reading glasses that you can typically try out and purchase in high-street shops.
A patient with severe anisometropia is not generally not recommended to wear glasses. Glasses have a magnification effect that can cause a large difference in the image size seen by each eye. Therefore, wearing glasses with severe anisometropia can prevent exceptional binocular vision.
Therefore, those with severe anisometropia are generally advised to wear contact lenses instead, as they ensure optimal vision in both eyes.
Anisometropia Treatment: Contact Lenses
Additionally, there is a range of contact lenses available to treat anisometropia symptoms. Multifocal are available in both gas-permeable and soft lens material, depending on your preference. Another possibility is monovision contact lenses, where you use a distance vision lens for one eye and a different contact lens for close-up usage in the other. The type a patient chooses depends on the type of anisometropia and the spectacle prescription.
How serious is Anisometropia?
The severity of anisometropia varies in adults and children. It is essential to treat anisometropia as soon as it is diagnosed and not ignore it. If anisometropia is left untreated, the brain can select the better eye that presents a clearer image, thus ignoring the other eye.
This can then lead to dependence on the stronger eye over exam time. Eventually, the weaker eye will progressively worsen, so it's important to get an appointment with your ophthalmologist before the refractive error becomes acute.
At your appointment, your eye doctor will recommend the best eye treatment going forward.
Does Anisometropia get worse?
In some cases, anisometropia can worsen. Anisometropia shows an exponential increase in prevalence with increasing age in life.
Furthermore, if you do not treat your anisometropia, this can worsen the condition.
Therefore, it's important to ensure that you seek the correct treatment from your eye doctor before the condition can develop or lead to complications.