Reaction time as a measure of enhanced blue-light mediated cognitive function following cataract surgery

Since 2002 the discovery of a novel population of intrinsically photosensitive retinal ganglion cells, expressing the photopigment melanopsin, has attracted broad interest in human blue-light mediated non-visual effects including circadian regulation and cognitive function. Ageing is associated with insomnia and cognitive decline. It has been postulated that reduced blue-light transmission through the formation of cataract impairs melanopsin dependant non-visual brain responses mediated by intrinsically photosensitive retinal ganglion cells. We aimed to establish if any objective improvement in cognition could be demonstrated using a reaction time task (RTT) following cataract surgery and intraocular lens implantation.

Following strict inclusion and exclusion criteria, 15 patients (age range 59-87, mean 75.4 years) with bilateral cataract performed the RTT before and after surgery on one eye. The mean and the SD of two modalities of reaction time, namely complex reaction time and simple reaction time, were measured and analysed.

Responses became both quicker and more consistent following surgery, with statistically significant improvements in the complex reaction time (p=0.016) and the complex reaction time SD (p=0.055), which were not due to a learning effect or improved vision.

The results suggest that improved blue-light transmission following cataract surgery has a beneficial effect on cognitive function. We advocate the RTT as an objective platform for exploring these benefits in large sample randomised controlled trials.