Cataract surgery affects the pupil size and pupil constrictions, but not the late post-illumination pupil response.

Abstract

Recent research findings suggest chromatic pupillometry as a novel tool to differentiate between outer and inner retinal diseases. As many patients with retinal diseases undergo cataract surgery, we wanted to investigate whether there was a mechanical effect of unilateral cataract surgery on the pupillary light response. Bilateral pupil responses to blue light (463 nm, 2 loglux) were recorded in 11 subjects before, 1 day, 3 weeks and 3 months after unilateral cataract surgery using a binocular chromatic pupillometer (DP-2000, NeurOptics). The non-operated eye was illuminated, and the pupil response was measured in both eyes. The outcomes were baseline pupil diameter, maximum pupil contraction and post-illumination sustained pupil responses from 1 to 10 seconds (PIPR010s) and 10 to 30 seconds (PIPR1030s) after termination of the light. Cataract surgery by phacoemulsification was performed using local anaesthesia. Three patients were not examined at the 3-month follow-up due to the cataract surgery of the fellow eye. The effect of surgery was investigated by comparing the intereye differences (fellow eye – surgery eye) before and after surgery. The baseline pupil diameter was transiently affected by surgery, as the pupil was 0.37 mm (p = 0.003) smaller on the surgery eye 1 day after surgery but not at any other time-point hereafter (Table 1). Likewise, the maximum contraction was reduced minutely at 1 day (p = 0.02) and 3 weeks (p = 0.01), but not at the 3-month follow-up (p = 0.50). The PIPR010s in the surgery eye was 0.30 (±0.05) and in the fellow eye 0.31 (±0.05), and the pupils showed reduced PIPR010s in the eye having undergone surgery at each time-point, but the effect was minor. The PIPR1030s before the surgical intervention was 0.14 (±0.06) in the surgery eye and 0.13 (±0.08) in the fellow eye (p = 0.87), and there was no significant difference following the surgery. The reported transient miotic effect of cataract surgery on short term is consistent with one previous study (Hayashi & Hayashi 2004). Yet, other studies have reported decreased pupil size up to 12 months after surgery (Komatsu et al. 1997; Moller et al. 2000; Kanellopoulos & Asimellis 2014). This may be caused by different levels of inflammation, as postoperative inflammation has been shown to vary similarly. Lens thickness may also contribute to the decreased pupil size, as intraocular lens intraocular lens (IOL) is much thinner, thus protruding the iris less than the larger cataractous eye lens. Another reason for the immediate difference in baseline pupil size at 1 day is just as likely to be due to rebound effects of the mydriatic agents used during surgery, which is a well-known effect. The decreased maximum pupil contraction to blue light in the operated eye after surgery could be the result of intraoperative damage to iris sphincter or inflammation. However, the smaller baseline pupil diameter might also limit the maximal achievable pupil constriction and thus contribute a mechanical effect that could limit pupil contraction. The mechanical effect of cataract surgery on the PIPR10-30s has not been investigated before. In the present study, there was no significant effect of cataract operation on this parameter. One reason for this finding is that PIPR to blue light is the surrogate marker of melanopsin containing intrinsic photosensitive retinal ganglion cells (ipRGCs), which produce a stronger and more sustained pupil constriction (Gamlin et al. 2007); hence, PIPR1030s is not likely to be limited by the mechanical and inflammatory effects of cataract surgery. In conclusion, this study shows that the mechanical effect of cataract surgery on the dark-adapted pupil size and maximal pupil constriction is observed within 3 weeks postoperatively, recovering 3 months after the operation. Conversely, no mechanical effect of cataract surgery was found on the melanopsin-mediated pupil response.