Anisometropic Amblyopia

Anisometropic Amblyopia

Having already discussed amblyopia in general, its molecular basis and the ways of treating it, we shall now discuss perhaps the most tricky of all amblyopias – anisometropic amblyopia.

The eyes of children with anisometropic amblyopia appear perfectly normal to the naked eye

While anisometropic amblyopia might not be the most prevalent – according to some authors, its prevalence is second to the strabismic one, although others report that up to 50 % of cases of amblyopia are due to anisometropia – it is one of the hardest to recognize. In deprivation amblyopia, for instance, lens opacification is rather apparent by white pupillary reflex (leukocoria) on screening eye examination. Similarly, when the amblyopia etiology is strabismic, eye misalignment is usually easily recognized and children are soon referred to an ophthalmologist for examination.

In anisometropic amblyopia, though, there are no apparent abnormalities evident to the naked eye. Thus, in many cases, it is only recognized and addressed late which is why it often requires more aggressive treatment. That being said, in most countries vision screening examinations at the pediatrician’s office or in the school system catch those children and refer them to an ophthalmologist so that amblyopia caused by anisometropia can be addressed early enough.

Differences in refraction between the two eyes can lead to the development of amblyopia

But what exactly is anisometropic amblyopia then? As the name suggests it is amblyopia that arises due to anisometropia. You are probably asking yourselves what anisometropia is then. Well, it is simply an expression that describes the difference in the refractive power of the two eyes. Click here for more details about refraction. If there is a notable difference in the refractive power of the two eyes, one retina gets a much clearer image than the other, which leads to the development of amblyopia in the eye with the lesser image quality.

Due to high brain plasticity in children, the lesser quality image can be easily suppressed and children usually do not notice any abnormalities. According to the American Academy of Ophthalmology, anisometropia is likely to trigger amblyopia if refractive differences between the two eyes are greater than 1.50 D of hyperopia (plus diopter), 2.00 D of astigmatisms (cylinder diopter), and 3.00 D of myopia (minus diopter). 

Once diagnosed, the treatment approach for anisometropic amblyopia is like any other amblyopic etiology, with an emphasis on the refractive correction that will eliminate amblyogenic anisometropia. Some children will respond to refractive correction alone, others will benefit from the addition of patching, penalization and/or vision training. Prognosis is generally very good if the condition is recognized early and addressed soon. Frequent and thorough screenings are thus crucial in order not to leave the refractive differences unrecognized.