Previous research has shown mixed results in the treatment of patients with cystoid macular edema secondary to RP or Usher’s syndrome with a topical carbonic anhydrase inhibitor (CAI). In this retrospective case series, Dr. Mohamed A. Genead and Dr. Gerald A. Fishman of the department of ophthalmology and visual sciences at the University of Illinois, Chicago, investigated whether sustained topical therapy with dorzolamide hydrochloride (2%) would improve visual acuity and improve the size and extent of cystic macular lesions on optical coherence tomography. Dorzolamide is approved for the treatment of open-angle glaucoma.
The investigators enrolled 26 patients who had retinitis pigmentosa and 6 who had Usher’s syndrome (18 men, 14 women). There were 27 white patients (84%), 4 black patients (13%), and 1 Asian patient (3%). The age range was 19-67 years (mean, 38 years) at baseline and 20-68 years (mean, 40 years) at follow-up.
Patients received topical dorzolamide 2% t.i.d., although this was decreased to b.i.d. in four patients after a mean 11.3 months. Follow-up ranged from 6 to 58 months and from 3 to 14 visits. Patients underwent a complete eye examination and optical coherence tomography (OCT) throughout follow-up.
Mean logMAR visual acuity went from 0.33 at baseline visit to 0.28 at the most recent follow-up. Best-corrected visual acuity improved by seven or more letters on the ETDR chart in at least 1 eye in 10 patients (31%), or in 13 eyes (20%) at the most recent follow-up visit. Nine patients reported subjective improvement in central vision.
OCT revealed improvement in macular cystic changes in at least one eye in 20 patients (63%) or 33 eyes (51%), and in both eyes in 13 patients (41%). In all, 12 eyes (36%) showed a sustained improvement over a mean 39.5 months, 7 (21%) showed an initial response followed by a rebound of cystoid macular edema over a mean 8.8 months, 19 (30%) showed no response to treatment and no worsening of the macular cysts, and 12 (19%) showed no response to treatment and worsening of the macular cysts.
At the most recent follow-up, 42 eyes (66%) of 24 patients (75%) had a degree of improvement in cystic macular lesion thickness in at least 1 eye following treatment, whereas 18 patients (56%) showed a positive response in both eyes (Arch. Ophthalmol. 2010;128:1146-50).
The overall mean central foveal zone (CFZ) thickness was 356 mcm at the initial baseline visit and 326.1 mcm at the most recent follow-up visit. In all, 25 eyes (60%) showed more than an 11% decrease in the CFZ thickness from the initial baseline level in at least 1 eye, and nine patients (38%) showed this in both eyes.
“Currently, we know of no way to predict which patients will have failed therapy,” the researchers said. “An explanation for this finding may be related to different genetic mutations causing different mechanisms of protein dysfunction in such disorders. It may also depend on the residual function of the retinal pigment epithelial cells in individual patients as a CAI has been shown to affect the pumping mechanism in these cells.”
They suggest that a future study correlate the different genetic mutations in such patients with a response to the topical dorzolamide.
One limitation of the study is that it was retrospective in nature, and the manufacturer’s data for the spectral-domain OCT was not corrected for age. Also, some patients were initially followed with time-domain-OCT and then switched, meaning that researchers could not precisely calculate longitudinal change in CFZ thickness.
The researchers reported no financial disclosures. Foundation Fighting Blindness, Grant Healthcare Foundation, and the National Institutes of Health provided support for this study, and Research to Prevent Blindness provided an unrestricted departmental grant
