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Contrast sensitivity helps gauge visual function in glaucoma
Contrast sensitivity testing can be performed quickly, is less demanding than visual field perimetry and can be easily incorporated into a busy clinical practice, according to researchers in the Journal of Glaucoma.
Ninety-four patients with primary open-angle glaucoma underwent visual acuity, letter contrast sensitivity testing with the M&S Smart System II (M&S Technologies) and standard automated perimetry testing. Mean patient age was 65 years.
Subjects had a best corrected visual acuity (BCVA) of 0.3 log MAR, 20/40 Snellen equivalent or better and reliable standard automated perimetry.
The mean BCVA was 0.08 log MAR, the mean contrast sensitivity (CS) was 1.38, and the mean Humphrey Visual Field mean deviation (MD) was -7.22 dB.
The range of letter CS spanned a factor of about 10 (log CS values of 0.8 to 1.8), whereas the range of Humphrey Visual Field MD was much larger, spanning a factor of greater than 1,000 (1 dB to -32 dB). These two measures were significantly correlated when compared for all subjects.
“Reduced central field CS may, at least in part, account for some of the subjective complaints of glaucoma patients who have minimal field loss and relatively good VA,” the researchers wrote.
Researchers believe letter CS measurements may be useful for: patients who have subjective complaints of poor vision and minimal to no VA or visual field MD loss and patients who cannot reliably perform standard automated perimetry.
“Letter CS testing may provide a useful supplementary measure of visual function, particularly for patients from whom reliable visual field measurements cannot be obtained,” researchers wrote. – by Abigail Sutton
Disclosures: The researchers reported no financial disclosures.
Perspective
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Although structural damage defines glaucoma, patients are impacted by functional impairment. Whereas structural evaluation has evolved to include ancillary objective imaging, function is still routinely assessed through automated visual field analysis, a subjective test that is quite variable and relatively insensitive in detecting the loss that accompanies early disease.
Liu and colleagues have demonstrated that letter contrast sensitivity is decreased in patients with glaucoma, even those with good visual acuity and relatively minor abnormalities on 24-2 automated visual field testing (AVF) testing.
From a clinical perspective, letter contrast sensitivity (CS) may represent a complementary assessment of function that is particularly valuable in patients with early/pre-perimetric glaucoma (where the logarithmic scale of AVF analysis masks subtle loss) or initial parafoveal scotomas (where letter CS testing and 10-2 AVF analysis are guided by abnormalities detected in macular ganglion cell analysis).
Despite its limitations, AVF assessment is not going anywhere in the foreseeable future. However, better use of current analyses (including targeted 10-2 testing), complemented by subjective (letter CS) and objective (multifocal visual evoked potential, pattern electroretinogram) functional testing – all guided by sound clinical and objective assessment of structure – can provide a wealth of information to inform diagnostic and treatment decision-making through the entire glaucoma continuum.