Intravitreal dexamethasone implant (Ozurdex, Allergan) may be a valuable alternative to oral carbonic anhydrase inhibitors (CAIs) as a first line treatment for cystoid macular edema (CME) secondary to retinitis pigmentosa (RP), according to a study.

Three centers in Italy were involved, including the European Institute of Ocular Microsurgery (IEMO) and the Ophthalmology Department of the University Hospital of Udine, Italy.  A total of 91 patients with CME secondary to RP were included and divided into two cohorts, receiving either intravitreal dexamethasone implant or the standard treatment with oral acetazolamide 500 mg/day.  Patients were matched one to one in 2 treatment groups of 30 patients with similar propensity scores, followed monthly for 1 year.

A rapid and significant anatomical and functional improvement was obtained with the use of intravitreal dexamethasone implant.  At 1 year, central retinal thickness (CRT) was reduced by 327 + 110 µm in the dexamethasone group as compared with 180 + 125 µm in the acetazolamide group, with an average gain of +4.2 vs. +1.6 ETDRS letters from baseline.  With the dexamethasone implant, these results were achieved early in the course of treatment, and then maintained over time.  In the same group, a significantly lower proportion of patients showed presence of fluid within the inner nuclear layer. According to the authors, this latter finding supports the hypothesis that dexamethasone, besides reducing inflammation, may play a role in ameliorating Müller cell dysfunction, reestablishing water homeostasis in the retinal tissue. 

The study also showed that a significant and steady improvement is possible with a low number of 1 to 2 dexamethasone implant injections, on average 1.7 over 1 year.  Combination with CAIs could be considered to further reduce the need for retreatment and to better treat cases with larger cysts in the inner retinal layer, the authors noted. 

The adverse events classically associated with corticosteroids, namely IOP elevation and cataract, were relatively infrequent.  In 13% of the patients IOP elevation was reported, and was effectively controlled with short-term topical treatment.  Cataract progression requiring surgery was reported in only one case. 

This study was the first to perform a multicenter, prospective comparison of intravitreal dexamethasone implant with oral acetazolamide in CME secondary to RP.  It was able to prove that “intravitreal dexamethasone implant provides a superior anatomic improvement and a slight trend toward better functional efficacy over oral CAIs therapy in patients affected by CME secondary to RP, and therefore may represent a valuable treatment option,” the author wrote.

However, larger randomized clinical trials will be necessary to confirm these results, they concluded.

Reference:

Veritti D, Sarao V, De Nadai K, Chizzolini M, Parmeggiani F, Perissin L, Lanzetta P.  Dexamethasone implant produces better outcomes than oral acetazolamide in patients with cystoid macular edema secondary to retinitis pigmentosa. J Ocul Pharmacol Ther. 2019 Dec 30. doi: 10.1089/jop.2018.0153.