Effect of photobiomodulation on mice with acute ocular hypertension

Abstract

Glaucoma is one of the main causes of irreversible blindness worldwide. It is an optic neuropathy characterized by both optic disc damage and thinning of retinal neuronal layers. The characteristic damage in glaucoma is substantial RGC death in the inner retina and loss of their axon in the optic nerve. However, current treatment options focus mainly on intraocular pressure reduction, which is not always effective. Photobiomodulation is a novel non-invasive treatment option utilizing the healing properties of the red light. It has been shown to exhibit anti-inflammatory, analgesic and tissue repair property in diseases such as stroke, nerve injuries and dermatological wounds among others. Biologically, PBM was shown to enhance mitochondrial metabolism, decrease oxidative stress and exhibit antiinflammatory properties. We therefore hypothesize that PBM may have a role in treatment of glaucoma. Acute ocular hypertensive (AOH) model in mice was adopted in our study. Anterior chamber cannulation to an elevated normal saline reservoir was used to elevate intraocular pressure, inducing acute ocular hypertension in mice. This model simulates the hypoxic condition that retinal ganglion cells experiences in acute glaucoma. Photobiomodulation (PBM) treatment was given by a 670nm LED device and energy of 9J/cm2 was delivered per day for 7 days. Retinal ganglion cell count, electroretinogram and histological analysis of retina was performed 7 days after AOH injury. In AOH mice after PBM treatment, retinal ganglion cell count was significantly higher by 23.6%. Amplitudes of a-wave and b-wave were increased by 41.0% and b-wave amplitude by 25.7%, whereas implicit times of a-wave and b-wave showed decline of 8.91% and 1.97% respectively after PBM treatment. The ERG result is however statistically insignificant. For retinal histology, significant reduction in GCL thickness was seen after AOH injury. Reduced thinning of GCL thickness was seen after PBM treatment in AOH mice, this result is however statistically insignificant. Photobiomodulation showed significant salvaging effect on retinal ganglion cells and a trend of improving retinal function in AOH mice. We therefore conclude PBM as a potential treatment for ameliorating retinal ganglion cell death in ischemic retinal diseases, such as glaucoma and diabetes.