['To quantify the prevalence and effect on visual acuity of macular cysts in a large cohort of patients with retinitis pigmentosa.', 'In 316 patients with typical forms of retinitis pigmentosa, visual acuity was measured with Early Treatment Diabetic Retinopathy Study (ETDRS) charts, macular cysts were detected with optical coherence tomography (OCT), and retinal thicknesses was quantified by OCT. The FREQ, LOGISTIC, and GENMOD procedures of SAS (SAS Institute, Cary, NC) were used to evaluate possible risk factors for cyst prevalence, and the MIXED procedure was used to quantify the relationships of visual acuity to retinal thickness measured at different locations within the macula.', 'Macular cysts were found in 28% of the patients, 40% of whom had cysts in only one eye. Macular cysts were seen most often in patients with dominant disease and not at all in patients with X-linked disease (P = 0.006). In eyes with macular cysts, multiple regression analysis revealed that visual acuity was inversely and independently related to retinal thickness at the foveal center (P = 0.038) and within a parafoveal ring spanning an eccentricity of 5 degrees to 10 degrees from the foveal center (P = 0.004).'] Is visual acuity related to parafoveal retinal thickness in patients with retinitis pigmentosa and macular cysts?