Effect of pupil dilation on the accuracy of the IOLMaster

To evaluate the effect of pupil dilation on the accuracy of the IOLMaster® (Zeiss) in performing biometry and to assess test–retest variability without pupil dilation. Ophthalmic outpatient department of a district general hospital. This prospective study comprised consecutive patients presenting to a cataract clinic (study group) who had biometry performed with the IOLMaster before and after pupil dilation. A control group was recruited from consecutive patients attending a cataract preassessment clinic who had 2 sets of biometric measurements with the IOLMaster but without pupil dilation. The SRK/T formula was used to calculate intraocular lens (IOL) power. The IOLMaster showed excellent reproducibility in the control group with no significant test–retest variability between the 2 sets of readings. The study group showed a statistically significant change in K2 and average keratometry values ( P < .05) but no significant change in axial length or IOL power between undilated and dilated pupil biometry readings. No systematic errors were revealed. Dilating the pupil did not adversely affect the clinical accuracy of the IOLMaster.