If your patients are reading late into the night or logging excess hours on their computer, their prolonged near work may be thinning their ciliary muscles. German researchers found the ciliary muscle unexpectedly thinned during 30 minutes of continuous close reading at 25 centimeters.

Their study, published in Experimental Eye Research, looked at the effect of prolonged near work on ciliary muscles and accommodation in 18 myopic and 17 normal vision subjects between the ages of 19 and 25. The researchers also found the muscle thinned in both emmetropes and myopes, but the latter showed a sustained lens power increase.

The investigation used OCT to image the ciliary muscles for far (0.25D) and near vision (4D). The study also included infrared photo-refraction to monitor changes in accommodation to a step pulse (0.25D-4D-0.25D for 15 seconds each) before and after a 30-minute reading task at the 25 centimeter mark.

Researchers reported, on average, the ciliary muscles got thinner after near work—predominantly at 0.0mm to 1.4mm posterior to the scleral spur in emmetropes and at 1.0mm to 1.9mm in myopes. Additionally, the investigators observed significant thinning after near work in the ciliary muscle thickness without any influence of the subjects’ refractive state or the target distance. The study reported the mean accommodation response was significantly increased after near work with a larger myopic shift in myopes.

“Sharing properties of striated muscles, the ciliary muscle was expected to increase its thickness, but the opposite was found,” the investigators wrote in their paper.

Currently, there is no explanation for why the ciliary muscle thins except for its sustained activity, researchers noted. They added further research is needed to explore the possible impact of sympathetic innervation that is activated during intense near work.