Factors affecting intraocular lens power calculation.

Intraocular lens power calculation is increasing in use in the United Kingdom. Primarily to avoid anisometropia, intraocular lens power calculation may also be used to provide the patient with three rather than two working distances, but to achieve this greater accuracy of IOL power calculation is required. Using the SRK regression formula, three groups of patients have been studied. The effect of inaccurate use of the formula of choice is shown and the need to modify the 'A' constant to account for variation both in technique and biometry equipment emphasised. The variation in results due to inaccurate biometry are statistically assessed. Accuracy of IOL power calculation requires consistency but not absolute accuracy in biometry. No ocular factors were found to affect the accuracy of IOL power calculation.