Measurement of axial length in the calculation of intraocular lens power.

Purpose: Accurate measurement of ocular axial length is essential for accurate intraocular lens (IOL) power calculation. Although it is common practice to average several axial length measurements to improve accuracy, it has been suggested that a single high-quality A-scan ultrasonographic measurement is adequately accurate owing to the high test-retest reliability of A-scan biometry. The aim of this study was to compare the accuracy of a single high-quality A-scan measurement with that of the average of three acceptable measurements in the calculation of IOL power.

Method: We studied 103 eyes of 103 patients who underwent cataract-IOL surgery. All these patients underwent pre-operative ocular biometry, a standardised extracapsular cataract extraction with posterior chamber IOL implantation, and clinical refraction between 10 and 14 weeks post-operatively.

Results: There was no statistically significant difference between the two study groups in measured axial length (p > 0.01), calculated emmetropic IOL power (p > 0.05) or the prediction of post-operative refraction (p > 0.99).

Conclusion: The use of a single high-quality axial length measurement was as accurate as the mean of three acceptable axial length measurements in the calculation of IOL power.