Low-Luminance VA and Microperimetry in AMD
The authors of the following prospective cross-sectional study sought to compare the effectiveness of low-luminance visual acuity (LLVA) and microperimetry as functional measures in early stages of age-related macular degeneration (AMD).
Included in the study were 179 participants with a clinical spectrum of non-neovascular AMD and 26 control participants. The authors measured best-corrected visual acuity (BCVA), LLVA and microperimetric retinal sensitivity on one eye of all participants. They calculated low-luminance deficit (LLD) as the difference between LLVA and BCVA. Additionally, they compared functional parameters between six clinical severity groups (from controls to non-foveal geographic atrophy [GA]), and they determined and compared the relationships and magnitude of these parameters. Visual acuity parameters (BCVA, LLVA and LLD) and central retinal sensitivity were the main outcome measures.
The authors found that BCVA, LLVA and central retinal sensitivity were reduced significantly for all AMD clinical severity groups when compared with control participants (p≤0.002), except for those with drusen between 63 µm and 125 µm (p≥0.107). However, they noted that LLD was not significantly different from control participants in all groups (p≥0.073), except in the non-foveal GA group (p=0.008). A significant positive relationship between central retinal sensitivity and LLD (r=0.613; p<0.001), but not BCVA, suggests that there is a trend for LLVA to detect a greater extent of functional deficit than BCVA in eyes with increasingly poorer retinal sensitivity. However, the results of the linear regression models estimated central retinal sensitivity to be 6.1, 3.7, and 5.1 standard deviations (SDs) less than normal by the time BCVA, LLVA and LLD, respectively, were two SDs less than normal.
To conclude, in early stages of AMD, LLVA did not detect a greater extent of functional deficit than BCVA when compared with control participants. Although there was a trend for LLVA to be more effective at detecting foveal deficits than BCVA in eyes with increasingly poorer retinal sensitivity, both VA measures were much less sensitive compared with microperimetry.