Relevance of pupil size in the clinical determination of retinal straylight on young healthy human eyes.

Purpose: To determine the impact of pupil size in the psychometric determination of intraocular straylight determined by the compensation comparison method in a population of young healthy adults.

Methods: Straylight was measured in 21 eyes from 11 young healthy subjects using the C-Quant (Oculus, Germany). Subjects were dilated with Phenylephrine 5%, and varying pupil size was simulated using three different diaphragms of 3, 5 and 6 mm in diameter. Three measurements were taken with each of the apertures in a randomized sequence. Mixed effects and repeated measures ANOVA was applied to test the significance of differences in straylight values for the fixed pupil diameters. Correlation analysis was applied to test relationships between the measurements for each fixed pupil diameter, and Bland-Altmann plots displayed the distribution of differences.

Results: Significant differences between the straylight values obtained for the different fixed pupil diameters were not found. Correlation analysis did not show relationships between the values obtained for different diameters either (p > 0.05 in all cases). Bland-Altmann plots show that average differences are around zero regardless of the actual value measured, but there is also a substantial individual variation, with differences going as far up as 0.5 Log(s) units in some cases.

Conclusion: In healthy human eyes, straylight values measured with the Van den Berg straylightmeter are not affected significantly by the subject's pupil size, although individual variations exist implying that no control for pupil size is required when estimating average amounts of retinal straylight from samples of eyes, but is desirable for the assessment of longitudinal variations of straylight in individual subjects, especially when assessing effects of surgical procedures and/or lens designs.