Екі көздің көру қабілетінің әртүрлі болуы

Term used when two eyes have unequal refractive power

Anisometropia is a condition in which a person's eyes have substantially differing refractive power. Generally, a difference in power of one diopter (1D) is the threshold for diagnosis of the condition Patients may have up to 3D of anisometropia before the condition becomes clinically significant due to headache, eye strain, double vision or photophobia. In certain types of anisometropia, the visual cortex of the brain cannot process images from both eyes simultaneously (binocular summation), but will instead suppress the central vision of one of the eyes. If this occurs too often during the first 10 years of life, while the visual cortex is developing, it can result in amblyopia, a condition where, even when correcting the refractive error properly, the person's vision in the affected eye may still not be fully correctable to 20/20. The name of the condition comes from its four Greek components: an "not", iso "same", metr "measure", ops "eye". Antimetropia is a rare sub type of anisometropia in which one eye is myopic (nearsighted) and the other eye is hyperopic (farsighted). This condition occurs in about 0.1% of the population.

Anisometropia is caused by common refractive errors, such as astigmatism, far sightedness, and myopia, in one eye. Anisometropia is likely the result of both genetic and environmental influences. Some studies suggest, in older adults, developing asymmetric cataracts may cause worsen anisometropia. However, anisometropia is associated with age regardless of cataract development: a rapid decrease in anisometropia during the first years of life, an increase during the transition to adulthood, relatively unchanging levels during adulthood but significant increases in older age. For early detection in preverbal children, photoscreening can be used. In this brief vision test specialized cameras detect each eye's light reflexes, which the equipment's software or a test administrator then interprets. If photoscreening indicates the presence of risk factors, an ophthalmologist can then diagnose the condition after a complete eye exam, including dilating the pupils and measuring the focusing power of each eye. (see: Refractive surgery).

A determination of the prevalence of anisometropia has several difficulties. First of all, the measurement of refractive error may vary from one measurement to the next. Secondly, different criteria have been employed to define anisometropia, and the boundary between anisometropia and isometropia depend on their definition. Several studies have found that anisometropia occurs more frequently and tends to be more severe for persons with high ametropia, and that this is particularly true for myopes. Anisometropia follows a U shape distribution according to age: it is frequent in infants aged only a few weeks, is more rare in young children, comparatively more frequent in teenagers and young adults, and more prevalent after presbyopia sets in, progressively increasing into old age. Notwithstanding research performed on the biomechanical, structural and optical characteristics of anisometropic eyes, the underlying reasons for anisometropia are still poorly understood. Anisometropic persons who have strabismus are mostly far sighted, and almost all of these have (or have had) esotropia. However, there are indications that anisometropia influences the long term outcome of a surgical correction of an inward squint, and vice versa. More specifically, for patients with esotropia who undergo strabismus surgery, anisometropia may be one of the risk factors for developing consecutive exotropia and poor binocular function may be a risk factor for anisometropia to develop or increase.