The variation in axial length in office hours causes a diopter change in the intraocular lens power calculation.

Purpose: To investigate whether diurnal changes in biometric parameters at different times of the day are visible and to analyze whether the variations could have clinical significance in the process of intraocular lens (IOL) power calculation.

Methods: Phakic eyes measured by IOLMaster 700 above the age of 16 were included, with the exclusion of previous surgery. Measurements were taken between 7:00 and 15:00 and data were treated in hourly groups within this range. Data such as age, sex and biometric parameters (axial length (AL), anterior chamber depth, central corneal thickness, white-to-white distance, keratometry readings, lens thickness) were used besides the hour:minute time of the examination.

Results: Biometric data from 32,596 eyes were used (38.89% males). There were no statistically significant differences in age and biometric parameters between the office-hour groups (p > 0.05), excluding the AL. The AL at the end of the day was 0.198 mm longer for male and 0.197 mm longer for female compared to the beginning of the office day. Accordingly, the results of IOL power calculation varied between 21.0 and 20.0 D for male, and 21.5 D and 20.5 D for the female population.

Conclusion: The results suggest that the assessment of AL may be affected by the intraday time of the biometry. This variation is clinically significant and may have implications for the evaluation of AL.