The effect of photobiomodulation on a rat acute ocular hypertension retinal ischemia/reperfusion model

Abstract

Photobiomodulation (PBM) is a non-invasive treatment that shows potential for treating various neuronal and vascular diseases. Its biological effects include enhancing mitochondrial metabolism, improving microcirculation, decreasing oxidative stress, anti-inflammation and neuroprotection. Glaucoma is one of the leading causes of irreversible blindness worldwide. It is characterized by progressive retinal ganglion cell (RGC) degeneration, which leads to optic neuropathy and gradual visual field constriction. Glaucoma pathogenesis is multifactorial involving both mechanical damage through elevated intraocular pressure and vascular dysregulation. This leads to secondary insult involving disrupted microcirculation, excitotoxic neuronal injury and oxidative damage via various reactive oxygen species. We hypothesize that PBM may have a neuroprotective effect in glaucoma, because its biological effects coincide with the mechanisms of the secondary insult in glaucoma. A rat retinal ischemia/reperfusion injury induced by acute ocular hypertension (AOH) was used as an animal glaucoma model. Rats were randomized into receiving treatment (PBM) or no treatment (no PBM). Three cycles of 88 seconds PBM generates a fluence of 6.9 J/cm² daily. The PBM regimen was adopted with reference to major PBM studies. At 1 day after AOH, we analyzed apoptotic count. At 1 week after AOH, we conducted RGC count and electroretinography (ERG) to assess retinal function. Among eyes that underwent AOH, apoptotic TUNEL analysis showed a reduced mean apoptotic count in eyes that received PBM when compared with no PBM, which was statistically significant. For RGC count, it was significantly reduced in eyes undergoing AOH compared to those not receiving AOH. Eyes receiving PBM and AOH showed a higher RGC count than eyes undergoing AOH only, but statistical significance was not reached. For ERG analysis, AOH was shown to result in pan-retinal dysfunction. PBM did not show significant improvement in ERG measurement. In conclusion, our work suggests that PBM may have a beneficial role in glaucoma, as suggested by the reduced apoptotic count and higher RGC count observed among eyes that received PBM. General ERG may be too non-specific to assess RGC function. Suggestions for future study directions include adding longer study time points and behavioral tests for retinal function.