Microstructural Changes in Cystoid Macular Edema in Retinitis Pigmentosa after Intravitreal Dexamethasone Implant Injection

Purpose: To evaluate microstructural changes in cystoid macular edema (CME) in retinitis pigmentosa (RP) after intravitreal dexamethasone implant injection.

Methods: In an extended cohort of a randomized trial of intravitreal dexamethasone implant for the management of RP-CME, microstructural changes during six months after treatment were evaluated using spectral domain optical coherence tomography.

Results: Forty-two eyes were included, and all had cystoid space in the inner nuclear layer (INL) at baseline. No eyes showed subretinal fluid, and 28.6% showed hyperreflective foci. Among 38 eyes with cystoid space both in the INL and outer nuclear layer/Henle's layer (ONL/HL), 13 (34.2%) showed complete resolution and 12 (31.6%) showed cystoid space only in the INL at 2 months after injection, while others showed persistent cystoid space in both layers. After complete resolution, cystoid space recurrence was earlier in the INL than in the ONL/HL. Multivariable analysis showed that greater cystoid space area in the INL and ONL/HL, presence of macular leakage, and longer intact external limiting membrane at baseline were associated with greater cystoid space area decrease after treatment.

Conclusion: Resolution and recurrence pattern of RP-CME after dexamethasone treatment showed that the INL is the primary layer of cystic change, and this suggests its pathogenesis is most likely due to Müller cell dysfunction.