Glaucoma has traditionally been associated with progressive peripheral vision loss, followed by central visual loss only much later in the disease progression. However, a recent study points out that this idea was based on the conventional visual acuity (VA) test, a clinical measurement for assessing macular visual function. “This subjective and rough method evaluates only the resolution ability of the eye at a fixed high contrast,” researchers explained in a recent paper published in Frontiers in Medicine. “However, resolving power is only one aspect of the very complex central visual perception pathway. Many glaucoma patients have complains regarding central vision despite normal visual acuity.”
They pointed out that this conventional VA testing isn’t sensitive enough to pick up on macular damage caused by glaucoma. They found, however, that a low-contrast (1.25%) high-pass acuity chart may be.
To test the chart’s sensitivity to macular dysfunction, researchers recruited 147 subjects (118 glaucoma patients, mean age 46.08; and 29 healthy controls, mean age 39.83). Each subject underwent monocular VA testing with two charts, the conventional and the high-pass, at 100%, 50%, 10%, 5%, 2.5% and 1.25% contrast levels. The researchers used SD-OCT to image the subjects with glaucoma to determine macular retinal thickness and circumpapillary retinal nerve fiber layer (cpRNFL) thickness.
The glaucoma patients had worse VA than controls when tested with the high-pass acuity charts. According to the ROC, the 1.25% low-contrast high-pass VA test demonstrated the best method for discriminating between glaucoma patients and controls with a sensitivity of 77.33% and specificity of 96.55%. Additionally, the researchers noted that 1.25% high-pass VA testing correlated more strongly with nasal-side macular retinal ganglion cell-related parameters than conventional testing. They noted no difference in correlation strength between VA measured using different charts and cpRNFL thickness.
“VA measurements taken with low-contrast high-pass acuity charts appear to be more sensitive in detecting central visual loss in glaucoma than those taken with conventional charts,” the researchers concluded. They also noted that “nasal-side macular GCL thinning appears to be associated with low-contrast high-pass visual loss in glaucomatous eyes.”
Wen Y, Chen Z, Zuo C, et al. Low-contrast high-pass visual acuity might help to detect glaucomatous damage: A structure-function analysis. Front Med (Lausanne) May 14, 2021. [Epub ahead of print].