Retinal nerve fiber layer thickness measured by optical coherence tomography predicts visual recovery after orbital decompression for dysthyroid optic neuropathy

Purpose To determine the prognostic value of optical coherence tomography (OCT) measurement of the peripapillary retinal nerve fiber layer (RNFL) thickness in visual recovery after orbital decompression of patients with dysthyroid optic neuropathy (DON). Methods A total of 52 eyes of 37 patients who underwent orbital decompression for DON between 2013 and 2019 were retrospectively reviewed. We examined peripapillary RNFL thickness, best-corrected visual acuity (BCVA), visual field (VF) for mean deviation (MD) and pattern standard deviation (PSD), and pattern-reversed visual evoked potential (PVEP) for P100 latency and amplitude before and after surgery. Black and white checkerboard square sizes of PVEP were 15 and 60 arcmin (arcminute and minute of angle). Changes in RNFL overall thickness and by quadrant and interocular differences were evaluated and studied regarding changes in BCVA, VF and PVEP. Results There was a significant improvement in BCVA, VF, and PVEP, whereas a dramatic reduction in RNFL thickness of all DON patients in global average, temporal, superior, and inferior quadrants (P = 0.005, P = 0.024, P = 0.016, and P = 0.001, respectively) after decompression surgery, except for nasal quadrant (P = 0.057). The preoperative RNFL thickness in each quadrant was negatively correlated with postoperative changes of BCVA and PSD and positively correlated with changes of MD and P100 amplitude at 60 arcmin (all P < 0.05). Except for temporal quadrant (P = 0.125), the preoperative RNFL thickness in other quadrants was positively correlated with postoperative changes of P100 amplitude at 15 arcmin (all P < 0.05). The nasal RNFL thickness was an excellent predictor for improvement in BCVA by 20/25 or better and in MD by 10 dB or more after surgery, whose cutoff value was 73.50 mu m, while the inferior and superior RNFL thickness could act as a predictor for improvement in P100 amplitude by 5 mu V or more at 60 arcmin and at 15 arcmin, respectively, whose cutoff value was, respectively, 143.00 mu m and 130.50 mu m (all P < 0.05). Conclusion RNFL thickness measured by OCT was correlated with visual function recovery after decompression surgery in patients with DON, which could also act as a predictor for better visual prognosis.