To find the most common etiology for anisometropia in pre-op cataract cases: axial or refractive?

Etiologies of the difference more than 0.33mm between the 2 eyes' axial length should be evaluated when calculating IOL power, in whom want to undergo cataract surgery .In this cross-sectional study 41 pre-op cataract eyes with more than 0.33 difference between axial lengths of 2 eyes were enrolled.For long eyes( AXL more than 25),each 1mm difference between AXL was expected 1.75-2.00 D of anisometropia, for normal eyes(AXL: 22- 25):2.50D and for short eyes (AXL less than 22):3.50-3.75D of axial anisometropia . If there are more or lesser anisometropia , we recorded them as refractive anisometropias.

Average of anisometropia :4.24 D, prevalence of PK or LK :1(2.38%),scleral buckling 0, kc:1(2.38% ), glaucoma surgery :1( 2.38% ), and pseudophakic status of the opposite eye 8(19.04%). Prevalence of axial anisometropia:21 (52.4%) and refractive anisometropia 20(47.6% ).On basis of this study results we can rely on the patient’s refraction before phaco for evaluation of axial length differences between the 2 eyes, because the most of the anisometropias are axial and so result the difference.

In most cases , cataract does not induce a significant change in refractive error(secondary myopia)and AXL difference between the 2 eyes are correlated with anisometropia.so we can rely on pre-op refraction when ocular biometry. Pre-cataract refraction is a valuable variable should be measured and recorded in routin eye examination especially in the aged patients.