Abnormal stereopsis and reduced retinal sensitivity in patients with retinitis pigmentosa

Purpose: The aim of the study was to evaluate retinal sensitivity and stereoacuity (SA) in retinitis pigmentosa (RP) patients. Methods: Twenty-six patients with RP were examined, mean age 36.4 ± 7.21 (SD) years old and best corrected visual acuity better than 0.15 logMAR. The control group (CG) included 25 healthy subjects matching the RP group by age and sex. Every patient and healthy control underwent a complete ophthalmologic examination: Titmus, Lang, TNO stereotests and microperimetry (MP-1) (Nidek Technologies). Results were subjected to factor analysis using Varimax rotation, and p values < 0.05 were considered statistically significant. Results: With the Titmus stereotest, the mean SA was 136.52 ± 26.5 (SD) arcsec in the RP group and 67.2 ± 11.5 (SD) in CG; Lang SA was 391.39 ± 53.72 (SD) in RP group and 1150 ± 33.4 (SD) in CG; and TNO SA was 69.3 ± 14.39 (SD) in the RP group and 15.97 ± 3.7 (SD) in CG. Factor analysis showed significant correlation between visual acuity and SA (p = 0.0001) in RP group. MP-1 demonstrated that in RP patients, inter-ocular difference in retinal sensitivity and fixation stability was related to anomalous stereopsis (p values < 0.05). Conclusion: Progressive RP degeneration in the cone system could determine a significant impairment in the binocular vision due to anomalous inter-ocular retinal sensitivity and incomplete Panum’s area utilization, causing an incongruent retinal localization. These findings suggest a possible reason why RP patients with a central retinal involvement, even if minimal, perceive a damaged stereoscopic perception that produces a severe disability.