Straylight and Pupil Size in Cataract Patients

The decision when to operate cataract can be difficult when there are subjective visual complaints but visual acuity is intact. Straylight measurements can help to improve surgical decision making in this group of patients. It is however unclear if pupil size can affect straylight when cataract is present. In this study we investigate the effects of pupil size on intra-ocular straylight in patients with multiple types of cataract.

A total of 85 eyes from 51 participants were measured, with an average age of 66 years. Straylight was measured before and after pharmacologic mydriasis with the Oculus C-Quant device. Cataract was graded using the LOCS III classification system. Exploratory analysis using retro-illumination slit-lamp photography was performed to divide between central and peripheral lens opacities.

Mean straylight both before and after dilation was 1.57 log(s). Reliable individual effects from dilation ranged between -0.42 and +0.48 log(s). No significant differences were found between cataract subtype groups using mixed model analysis. In nuclear cataract mean straylight levels were 1.71 log(s) undilated and 1.66 log(s) dilated. Mean straylight in cortical cataract was 1.38 log(s) undilated and 1.51 log(s) dilated. Centrally and peripherally located cataracts showed a mean change after mydriasis of -0.08 and +0.07 log(s), respectively.

Straylight after pupil dilation showed varying degrees of change, with a tendency to increase in cortical cataract and decrease in nuclear cataract. However, in all forms of cataract both large increases and decreases can be found. These changes were found to be repeatable and reliably measured. Centrality determination from retro-illumination photography can only partly predict these changes.