Ocular Neuromodulation as a Novel Treatment for Retinitis Pigmentosa: Identifying Rod Responders and Predictors of Visual Improvement

Abstract

Starvation of photoreceptors induced by reduced dysregulated ocular blood flow (OBF) is proposed as a common pathway for pathogenesis of retinitis pigmentosa (RP). The current study evaluated the safety and efficacy of ophthalmic nerve stimulation (ONS) as an OBF neuromodulator, combined with ascorbic acid (AA) as a potent anti-oxidant in treatment of RP. Additionally, the initial characteristics of rod responders were identified. Forty participants with simple RP, were enrolled in a prospective open-label intervention. The severity of the disease was clinically graded into five stages. Patients with established diagnosis of RP; aged ≥ 4 years, with BCVA ≥ 20/400 were included. All participants were daily treated with bilateral ONS sessions combined with systemic AA for two weeks. The primary efficiency endpoint was 6 months’ changes in scotopic vision as measured by a 10-items, 100 points, Low Luminance Questionnaire- (LLQ-10). The secondary efficiency points included best corrected visual acuity (BCVA) and contrast sensitivity (CS). Rod responders were defined by ≥ 25points increment of LLQ-10 score. The results showed that ONS combined with AA treatment significantly improved night vision, BCVA and CS in patients with RP. At 6-month visit, twenty-four (60%) patients were identified as rod responders and 16 (40%) patients were non-responders. The mean change in LLQ-10 score was (46.35 ±16.81) in rod responders versus (4.9 ± 7.6) in non-responders (P < 0.0001). A clinically significant improvement of BCVA (≥0.2 logMAR) and CS (≥0.3 log unit) were demonstrated in 44.4% and 56.1% of eyes of rod responders respectively. Collectively, this study sheds light on determinants of rod responsiveness which include patients’ age, duration of night blindness and the stage of RP. It also highlights two therapeutic scenarios; an early disease -modifying intervention that restore night vision and reverse the disease process and a late cone rescue intervention that improve/maintain central vision.