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Grace Tsai, Peter A Campochiaro, Xiangrong Kong; Macular function response to N-acetylcysteine Treatment in patients with Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1909.
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In Retinitis Pigmentosa (RP), mutation-related death of rod photoreceptors results in oxidative stress leading to degeneration of cone photoreceptors. The FIGHT-RP phase-1 trial showed improved cone function in RP patients treated with oral N-acetylcysteine (NAC). In a secondary analysis, we assessed the effect of NAC on fovea cone function (central 4-degrees) versus 20-degrees macular sensitivity by microperimetry (MP).
MP was tested monthly for 9 months in 30 RP patients, including 6 months of NAC treatment and subsequently 3 months without treatment. The subjects (n=10 per cohort) received 600 mg (cohort 1), 1200 mg (cohort 2), or 1800 mg (cohort 3) NAC BID for 3 months and then TID for 3 months. The Macular Integrity Assessment (MAIA) MP device was used testing 68 loci distributed in the central 20°. The fovea mean sensitivity (FMS) was calculated as the mean of the 4 loci in the central 4°.Piecewise Linear mixed effects model was used to estimate the rates of changes during and after treatment.
Previously reported rates of change in MS of the central 20° were 0.05 dB/month (95%CI -.07 to .17), 0.04db/month (95%CI -.08 to .16) and 0.15dB/month (95%CI .04 to 2) in cohort 1, 2 and 3, respectively during the treatment period. The FMS of the central 4° change rates were 0.21dB/month (95%CI: 0.01 to 0.41) in cohort 1, 0.13 dB/month (95%CI: -0.08 to 0.34) in cohort 2, and 0.16dB/month (95%CI: -0.03 to 0.34) in cohort 3 during treatment. During the 3 month post-treatment period, the improvements in FMS in the central 4-degrees regressed in cohort 1 (rate: -0.26dB/month) and cohort 3 (rate: -0.31dB/month), compared with cohort 2 (-0.02dB/month).
This is the first clinical study showing preliminary evidence of improved cone function in RP patients treated with an antioxidant. There was greater improvement in MS in the central 4-degrees versus 20-degrees across all cohorts. It is possible that foveal cones may be more responsive to reduced oxidative stress than more eccentric cones. A hypothesis that deserves testing is that cones along the border of surviving cones which have lower MS at baseline than foveal cones, may have less capacity to improve when oxidative stress is reduced. Assessment of MS in the central 4-degrees may provide greater sensitivity for detection of an antioxidant treatment effect in RP and can be considered for use as a secondary outcome measure.
This is a 2020 ARVO Annual Meeting abstract.
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