Abstract
Purpose :
The main objective of this preliminary study is to test a protocol of mesopic full-field stimulus threshold (mFST) to assess rod and cone function in controls and individuals with retinitis pigmentosa (RP). Typically, in scotopic background (BG), thresholds for blue and red FST are distinct, and are used to assess the function of rods and cones, respectively. But it requires pupil dilation and dark adaptation for at least 30min. We hypothesized that distinct thresholds for blue and red FSTs can be achieved by performing mFST without either pupil dilation or dark adaptation.
Methods :
mFST at 0.1cd/m2 white BG luminance was measured (ColorDome, Diagnosys LLC) in controls (n=21) and individuals with RP (n=11). In addition, mFST at 1cd/m2 BG luminance was also measured in 10 controls. After adapting to a room light level for at least 10min, FST in two different wavelengths; blue (448nm) and red (627nm) were measured in a dark room. For each wavelength (λ), FST of one eye, with the other occluded, was measured and the test was repeated three times. The results were analyzed using ANOVA and Tukey HSD.
Results :
In controls, there was a significant main effect of BG [F(1, 10)=257.94, p<0.001], λ [F(1, 10)=561.88, p<0.001] on mFST measured thresholds. Moreover, threshold difference between blue and red mFST using 0.1cd/m2 BG (0.95 log cds/m2) was significantly larger compared to 1cd/m2 (0.22 log cds/m2) BG luminance (p<0.001). This suggested that mFST at 0.1cd/m2 has more distinct blue and red mFST thresholds. On comparing individuals with RP and controls, there was a significant main effect of groups [RP vs. controls: F(1, 19)=18.58, p<0.001]. Individuals with RP had significantly worse thresholds overall compared to controls [blue mFST (p<0.001) and red mFST (p<0.001)]. In addition, threshold difference between blue and red FST in 0.1cd/m2 BG luminance in RP (0.47 log cds/m2) was significantly less than the threshold difference noted in control participants (p<0.001).
Conclusions :
mFST at 0.1cd/m2 BG luminance can be used to assess the functions of rods and cones without pupil dilation and dark adaptation. In the future, associations between mFST and other measures such as dark adaptation, low luminance visual acuity and contrast sensitivity should be evaluated for some unique information to consider mFST as an outcome measure in clinical trials and for clinical use.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.