Increased Variability of PC-Based Visual Acuity and Visual Field is Partly Related to Reduced Macular Thickness in Retinitis Pigmentosa

Abstract

Purpose: : We explored whether decreased reliability of PC-based visual acuity (VA) and visual field (VF) in retinitis pigmentosa (RP) was related in part to reductions in macular thickness with ocular coherence tomography (OCT).

Methods: : 20 RP patients (mean age 48, range 23-58) completed 12-28 at home weekly PC-based VA and VF tests with the better eye ~10 years ago. Macular thickness was assessed 2-5 times during the PC-based test period with the Humphrey OCT 2000. In the past year, 24 RP patients (mean age 53, range 20-77) were tested once with the Heidelberg Spectralis SD-OCT and performed 12-18 biweekly PC-tests binocularly. Foveal, parafoveal and perifoveal thicknesses were defined by 2, 3, and 6mm rings. 39% of eyes had CME. Mean PC-based VA was 0.3 (range -0.2,0.8) and 0.5 (range (0.1,1.5) logMAR in the Humphrey 2000 and SD-OCT groups, respectively. Multiple linear regressions were used to analyze associations between variability of PC-based vision tests and macular thickness, while adjusting for age, CME, gender, and mean level of vision.

Results: : For the SD-OCT subjects with a wide range of vision, there was a stronger association between variability of VA and mean VA, than for variability of VA and macular thickness. The Humphrey 2000 subjects had better mean VA and less variable VA. For these subjects (and a subset of 18 SD-OCT subjects with less variable VA, SD<0.13) there was a statistically significant 8.7% decrease in the average variability of VA per 10% increase in foveal thickness (95%CI:2.3-14.8%; p=0.01; R²=0.32). For SD-OCT subjects, there was a 23% decrease in the average variability of VF area per 10% increase in perifoveal thickness (95%CI:5-39%; p=0.02; R²=0.45). Among Humphrey 2000 subjects, there was a statistically significant 17.8% decrease in the average variability of VF radius per 10% increase in parafoveal thickness (95%CI:1.8-31%; p=0.03; R²=0.40).

Conclusions: : Decreased macular thickness appears to be significantly associated with a greater variability in PC-based VF in RP. There was a significant relationship with perifoveal thickness across a wide range of VFs; and with foveal and parafoveal thickness in patients with smaller VFs. In patients with better VA and less variable VA, reductions in foveal thickness explain some of the variability. These findings support the hypothesis that more advanced RP is associated with less reliable vision.

Keywords: retinal degenerations: hereditary • low vision • imaging/image analysis: clinical