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Joshua A. Morrison-Reyes, Sam Mansour, Lindsay Smithen; The Effect of Pan-Retinal Photocoagulation on Macular Inner Retinal Thickness in Proliferative Diabetic Retinopathy. Invest. Ophthalmol. Vis. Sci. 2012;53(14):364.
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Panretinal photocoagulation (PRP) for patients with proliferative diabetic retinopathy (PDR) improves visual outcomes and prevents vision loss. Studies using Time-Domain Ocular Coherence Tomography (TD-OCT) have shown an increase in edema and overall macular thickness following the procedure, but the TD-OCT lacks the resolution to accurately measure the individual layers of the retina. It has not yet been investigated using Spectral-Domain OCT (SD-OCT) whether certain layers of the retina may thin even while overall thickness may increase.The purpose of this study is to conduct a retrospective analysis on patients with PDR who have undergone PRP and had SD-OCT before and after the procedure to determine the change in thickness of the retinal layers after treatment at 1, 3, and 6 month intervals.
All 99 patients with PDR who underwent a total of 202 sessions of PRP over a 2 year period were identified using the electronic medical record. Of these, 27 eyes from 18 patients met the criteria for inclusion, including no prior PRP, scans at the appropriate intervals using SD-OCT, and clarity of optical media to permit adequate quality scans. Baseline scans were obtained before PRP, then at 1, 3, and 6 months following. All patients were scanned using the Optovue RTVue system and scans were analyzed to determine the total, inner or "ganglion cell complex," and outer retinal thickness; each measurement was taken at the fovea, 1.5mm (parafoveal) and 3mm (perifoveal) from the center. Additionally, charts were reviewed to determine visual acuity, number of laser spots, years since diagnosis of diabetes, age, sex, race, and presence of CSME or glaucoma.
Ages ranged from 35-75 years; the average age was 54. 89% were African-American and 11% were Hispanic. The baseline average total central foveal thickness was 282.96µ; this increased at the 1 month visit, then decreased at the 3 month (258.58µ) and 6 months visits (234.88µ; p=0.061). Total parafoveal thickness and perifoveal thickness did not change significantly. Average central inner retinal thickness decreased from a baseline 85.8µ to 71.3µ at 6 months (p=0.101). Average central outer retinal thickness decreased from 197.12 µ to 163.55 µ at 6 months (p=0.093). Patients with CSME showed a 12.7% decrease in total thickness at 6 months, while patients without showed a 20.67% decrease in total thickness.
The inner and outer retinal layers both decrease in thickness over the 6 months following PRP in a pattern that trends towards but does not meet statistical significance. Interestingly, this trend is seen in patients both with and without CSME, suggesting that the thinning effect is independent of resolution of concurrent macular edema.
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