Voluntary Exercise for Neuroprotection in Glaucoma

Abstract

Purpose : To investigate whether voluntary exercise benefits individuals with glaucoma to slow or protect against vision loss. To date, all treatments for glaucoma involve lowering intraocular pressure (IOP), and complementary therapies are needed. If effective, exercise could be inexpensively and readily implemented for individuals at risk of glaucoma. Crowston et al. recently showed benefit from exercise in glaucoma but used an involuntary exercise paradigm, potentially introducing stress as a confounding factor.

Methods : Female retired breeder Brown Norway rats were housed in 24-hour constant low light with a free-spinning running wheel for voluntary exercise (n=4), a locked wheel (n=3), or no wheel (n=4). Ocular hypertension (OHT) was unilaterally induced via injection of hypertonic saline after 3 months’ acclimation to exercise. Rats were followed for 4 weeks after OHT induction, with IOP measured twice weekly via Tonolab. We performed optical coherence tomography (OCT), pattern electroretinography (PERG), and optokinetic tracking (OKT) assessments at baseline and after 4 weeks of OHT to monitor visual function and optic nerve head/retinal anatomy. 3-factor nested ANOVA was used to compare the effects of exercise to controls.

Results : In this preliminary study, we found that exercise may offer modest protection of the retina against glaucomatous damage, although additional study is needed to increase statistical power. Comparing control eyes to contralateral OHT eyes at week 4, OCT-measured retinal thinning was slightly less in exercised rats (Avg±SD: 5.4±20 µm exercise wheel, 34±35 µm locked wheel, 50±47 µm no wheel, p=0.116), but functional differences were not detected by PERG (implicit time, p=0.336) or OKT (contrast sensitivity, p=0.780; spatial frequency, p=0.938). To achieve a power of 0.8 to detect the main effect of exercise, we need 20 rats/group.

Conclusions : Although we did not detect statistically significant changes within our small initial cohort of rats performing voluntary exercise, additional studies for a longer duration (8 weeks) may provide more information about whether exercise is beneficial in glaucoma. We will also quantify axon count in the optic nerve as an additional measure of RGC preservation.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

OCT measurements at Week 4 suggest exercised animals have less retinal thinning in hypertensive eyes than inactive animals. Within this small preliminary cohort, differences are not significant. Error bars: standard deviation.