The effect of cataract on circadian phototentrainment

Abstract

Purpose: Stimulation of intrinsically photosensitive retinal ganglion cells (ipRGC) by blue light is essential for the photoentrainment of circadian rhythm. Natural lens ageing is characterized by yellowing. Lens yellowing works as an efficient color filter, blocking the very parts of the visible spectrum that is required for photoentrainment resulting in sleep disturbances. It has been reported that cataract surgery may improve sleep quality. The aim of the present study was to examine the effect of cataract surgery on photoentrainment of the circadian using blue light pupillometry, actigraphy and saliva melatonin measurements.

Methods: Patients with cataract and no other significant ocular or systemic diseases were included. Patients were examined before and after cataract surgery. Stimulation of ipRGC was assessed by chromatic pupillometry using the consensual pupillary constriction and postilluminatic redilation after blue light as the primary outcome. The circadian rhythm was assessed by questionnaires (Pittsburg Sleep Quality Index & and Morningness Eveningness Questionnaire) and direct activity measurements (actigraphy). In addition biological circadian markers were measured as a 24 hour profile of saliva melatonin concentration.

Results: Postilluminatic pupillary constriction to blue light increases after cataract surgery (P<0.001) whereas the pupillary response to red light did not change. Peak melatonin concentration also increases after surgery, although not significantly (P=0.097). No change was found in sleeping patterns evaluated by actigraphy and questionnaires.

Conclusions: We found that cataract surgery increases the pupillary response to blue light and a more distinct nightly melatonin peak. However an effect on sleeping habits was not discovered. None of the patients reported sleeping difficulties prior to cataract surgery and in addition, it may take time to change sleeping habits and a longer follow-up period than 3 weeks may be needed to rule out an effect on sleep quality by cataract surgery. In conclusion the discovered increase in pupillary response and nightly peak melatonin concentration suggest an enhancement of circadian photoreception. However, further studies are needed before we may conclude what the implications are.

Keywords: 445 cataract • 458 circadian rhythms • 668 pupillary reflex