Purpose: To evaluate microstructural changes in cystoid macular edema in retinitis pigmentosa after intravitreal dexamethasone implant injection.
Methods: In an extended cohort of a randomized trial of intravitreal dexamethasone implant for the management of retinitis pigmentosa-associated cystoid macular edema, microstructural changes during six months after the 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, 13 (34.2%) showed complete resolution and 12 (31.6%) showed cystoid space only in the INL at 2 months after injection, whereas others showed persistent cystoid space in both layers. After complete resolution, cystoid space recurrence was earlier in the INL than in the outer nuclear layer/Henle's layer. Multivariable analysis showed that greater cystoid space area in the INL and outer nuclear layer/Henle's layer, presence of macular leakage, and longer intact external limiting membrane at baseline were associated with greater cystoid space area decrease after the treatment.
Conclusion: Resolution and recurrence pattern of retinitis pigmentosa-associated cystoid macular edema after dexamethasone treatment showed that the INL is the primary layer of cystic change, and this suggests its pathogenesis is most likely caused by Müller cell dysfunction.