The Effect of Tinted Filters on the Visual Function of Patients with Retinitis Pigmentosa

To investigate the effect of tinted filters on contrast threshold (CT) and visual evoked potentials (VEPs) in patients with retinitis pigmentosa (RP).

In this cross-sectional study, RP patients with best corrected visual acuity better than 1 log MAR were evaluated. The CT was measured using the Freiburg Acuity and Contrast Test, and pattern reversals were analyzed for both time and frequency components. The effects of gray (15% light transmission, 410 nm cutoff), brown (18% light transmission, 410 nm cutoff), and yellow (27% light transmission with a 470 nm cutoff) tinted filters were evaluated and compared.

Eighteen participants (mean age 32.78 $\pm$ 7.35 years; 72.2% male) were evaluated. The mean CT of Weber was 3.46 $\pm$ 3.2%. Yellow filters decreased CT (mean difference [MD]: -0.597%, P = 0.054). Brown filters did not produce a significant change in the CT (MD: 0.233%, P = 0.620), while the gray filters caused a significant increase in the CT (MD: 1.423%, P = 0.004). Mode frequency (Fmod) decreased with gray filters (MD: -2.33%, P = 0.004). The latency and amplitude of VEPs improved with yellow filters (P $<$ 0.05) but worsened with gray filters (P $<$ 0.05). Additionally, the spherical equivalent showed an inverse correlation with CT in patients with RP (r = -0.997, P $<$ 0.001).

Using tinted filters as a low-vision aid can modify contrast sensitivity and both frequency and time domains of VEPs in patients with RP. Yellow filters appear to improve visual function, whereas gray filters may worsen it.