Evaluation of B-mode guided biometry for IOL power calculations in high myopia

Abstract

High myopia is defined as a spherical equivalent greater than 6 or 7

or an axial length of more than 25.5 mm (Hendicott and Lam, 1991).

Biometry and calculation of the power of an intraocular lens (IOL) is sometimes difficult. Eyes with normally rounded posterior segments are not usually a problem, but eyes with staphylomas are. The fovea can be at the deepest point of the staphyloma, on its slope, or outside the staphyloma. A repeated examination with the patient fixing on the tip of

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the biometry probe is one way to establish the axial length of the refractive system, rather than to the maximum length of the eye. B-scan ultrasonography is also useful in some cases, in which the biometry is difficult to map out the shape of the posterior segment and to assist the biometer to determine the approximate placement of the visual center (Raj et al., 1998).