[Selection of IOL power formula for patients with cataract and high myopia]

To compare the accuracy of two IOL power formulas (SRK-T and SRK-II) in order to improve the accuracy of predicative IOL powers for patients with cataract and high myopia.

(1) Patient's axial lengths of the eye, K-readings and A-constants were input to the SRK-T and SRK-II formulas. The differences in predicative refraction between the two formulas were compared. (2) Eight six patients (130 eyes) with cataract and high myopia underwent phacoemulsification and posterior chamber IOL implantation were studied. These patients were randomly divided into two groups and received IOL whose power was determined by either SRK-T or SRK-II. Three months after IOL implantation, the postoperative refractions were recorded and compared with predictive refractions. Patients were followed-up for 3 to 24 months.

(1) When K-reading was 43.00 D, there was no statistically significant difference between the results from these two formulas (P > 0.05) and there was no correlation between the difference and the axial lengths (P > 0.05). In eyes with K-reading at 39.00 D, 41.00 D, 45.00 D, or 47.00 D, there was statistically significant difference between the results from these two formulas (P < 0.05). The difference between the two formulas was in proportional to the axial length (P < 0.05). (2) The mean error between the postoperative refraction and predictive refraction determined by SRK-T and SRK-II formula was 0.08 D and -0.79 D, respectively. The difference between these two formulas was statistically significant (P < 0.05).

Selection of IOL power formula should consider the axial length, K-reading and other related factors. SRK-T formula is appropriate for high myopia eyes with axial length longer than 26.0 mm. In this group, SRK-T formula is much more accurate than the SRK-II formula.