The College of Optometrists

are contact lens more suitable for refractive or axial anisometropia? and why?

overcome effects of spectacle mag, thereby making images more fusible for BSV

Without goning into too much detail.

Some basic facts,

1) In uncorected refractive ammetropia, the retinal image size is constant, regardless of the ammetropia.

2) In uncorected axial ammetropia, retinal image size varies with sign and size of the ammetropia. Larger with increasing myopia and smaller with increasing hypermetropia.

3) Refractive corrections change retinal image size, smaller in myopia and larger in hypermetropia.

4) This latter change is less with CL than gls, mainly due to their reduced BVD.

As such, in refractive ammetropia, e.g. post cataract surgery , uncorrected the retinal image sizes in both eyes are the same size. CL should be worn to preserve this state of affairs - to enable fusion and lessen any aniseikonia.

In axial anisometropia, e.g. many myopes, uncorrected the most myopic eye has a larger image size. Differential minification with gls would act to reduce this and are thus to be preferred.

However...the above classical theory is more simplistic than reality as it assumes that retinal image size is commensurate with perceived image size. This is not the case, possibly due to stretching of the retinal elements in larger eyes. As such, the basic premise (2) above is often not true, and patients with anisometropia are invariably (but not always) better off with CL, regardless of whether it is refractive or axial.