Study protocol for a prospective natural history registry investigating the relationships between inflammatory markers and disease progression in retinitis pigmentosa: the RP-PRIMARY study.

Purpose: The Retinitis Pigmentosa Progression and Inflammatory Marker Registry (RP-PRIMARY) is intended as a prospective observational study aimed at establishing sensitive outcome measures to detect the efficacy of anti-inflammatory agents in future clinical trials. The following is the RP-PRIMARY study protocol.

Study design: Prospective, multicenter study.

Methods: We will recruit 100 patients with typical RP (any genetic mutation) and the following characteristics: age 20-70 years; mean retinal sensitivity ≥ 10 dB at 12 central points on Humphrey 10-2 visual field tests; central foveal thickness ≤ 250 μm on optical coherence tomography (OCT); and no ocular complications unrelated to RP or serious systemic complications. Early Treatment Diabetic Retinopathy Study (ETDRS). visual acuity, Humphrey 10-2 visual field tests, OCT, and fundus autofluorescence imaging will be performed every 3 months for 2 years. Inflammatory indices such as aqueous flare values, high-sensitivity C-reactive protein (CRP), serum IL-8, and CD14/16 inflammatory monocyte proportion will be measured every year. The primary endpoint will be the progression rate of retinal sensitivity loss on the Humphrey 10-2 visual field tests. The secondary endpoints will be the rate of decline of each parameter and its association with inflammatory indices. Standard-operation-procedure documents were prepared for all study procedures, and consultations with the regulatory agency were conducted to ensure the data reliability for future use in clinical trials.

Conclusions: Detailed registry data on the natural history and inflammatory profile of RP will be useful in designing study protocols for anti-inflammatory therapy for RP and as natural history data for drug applications.