A chart-based test of contrast sensitivity in noise: reference ranges, effects of age and optical abnormality.

CLINICAL RELEVANCE: Contrast sensitivity plays an important role in the comprehensive assessment of visual function; however, measurement with standard eye charts can be affected by age and optical abnormality.

BACKGROUND

This study describes a novel chart-based test of letter contrast sensitivity (CS) in luminance noise (the Illinois Eye and Ear Noise CS test), defines normal reference ranges, estimates test-retest repeatability, and assesses the effects of age and simulated optical abnormalities.

METHODS

Seventy-five individuals with normal visual function (age 18-85 years) participated. Subjects identified letter optotypes that spanned a broad contrast range (0.9% to 59.6%) printed in a book-based test. Letters were presented against a grey background (no-noise condition) and in luminance noise that consisted of light and dark checks (noise condition). A subset of 10 subjects repeated the test to define short-term variability and performed the test under three additional conditions: simulated cataract, +2.00D defocus, and low room illuminance.

RESULTS

In the no-noise condition, CS was independent of age (mean log CS of 1.74) until approximately 54 years, and declined for older subjects (CS loss of 0.1 log unit/decade). CS measured in noise was independent of age across the range of ages tested (mean log CS of 0.91). The 95% limits of agreement for test-retest repeatability was 0.19 log units. Simulated cataract, +2.00D defocus, and reduced illumination significantly reduced CS in the no-noise condition (F = 102.6, p < 0.001), whereas these optical manipulations did not significantly affect CS in noise (F = 2.58, p = 0.074).

CONCLUSIONS

Measurements of CS in luminance noise may be valuable, as these measures are largely independent of age and certain forms of optical degradation. CS measurements in noise may provide useful insight into visual function in patients who have combined neural and optical abnormality, as noise minimises CS loss from optical defects.