Tuesday, March 22, 2011

Anisometropia is the condition in which each eye has different refractive power. This means that one eye can be mildly nearsighted (myopic) while the other very nearsighted; or one eye is nearsighted and the other eye is farsighted. Anisometropia causes unequal rotations thus leading to diplopia and asthenopia. This eye condition can adversely affect the development of binocular vision in infants and children if there is a large difference in clarity between the two eyes. The brain will often suppress the vision of the blurrier eye in a condition called amblyopia, or lazy eye. The opposite of anisotropia is isometropia. In isometropia, the refractive power is equal in both eyes.

The solution to the problem of anisometropia for spectacle wearers is spectacles which incorporate iseikonic lenses. Iseikonic lenses present adjusted image sizes to the eye compared to standard lenses. The formula for iseikonic lenses (without cylinder) is: Magnification = 1/(1-(t/n)P) X 1/(1-hF), where: t = center thickness (in meters) n = refractive index P = front base curve h = vertex distance (in meters) F = back vertex power (essentially, the prescription for the lens).