Evaluation of Melbourne Edge Test contrast sensitivity measures in the visually impaired

Contrast sensitivity (CS) provides important information on visual function. This study aimed to assess differences in clinical expediency of the CS increment-matched new back-lit and original paper versions of the Melbourne Edge Test (MET) to determine the CS of the visually impaired.

The back-lit and paper MET were administered to 75 visually impaired subjects (28-97 years). Two versions of the back-lit MET acetates were used to match the CS increments with the paper-based MET. Measures of CS were repeated after 30 min and again in the presence of a focal light source directed onto the MET. Visual acuity was measured with a Bailey-Lovie chart and subjects rated how much difficulty they had with face and vehicle recognition.

The back-lit MET gave a significantly higher CS than the paper-based version (14.2 +/- 4.1 dB vs 11.3 +/- 4.3 dB, p < 0.001). A significantly higher reading resulted with repetition of the paper-based MET (by 1.0 +/- 1.7 dB, p < 0.001), but this was not evident with the back-lit MET (by 0.1 +/- 1.4 dB, p = 0.53). The MET readings were increased by a focal light source, in both the back-lit (by 0.3 +/- 0.81, p < 0.01) and paper-based (1.2 +/- 1.7, p < 0.001) versions. CS as measured by the back-lit and paper-based versions of the MET was significantly correlated to patients' perceived ability to recognise faces (r = 0.71, r = 0.85 respectively; p < 0.001) and vehicles (r = 0.67, r = 0.82 respectively; p < 0.001), and with distance visual acuity (both r = -0.64; p < 0.001).

The CS increment-matched back-lit MET gives higher CS values than the old paper-based test by approximately 3 dB and is more repeatable and less affected by external light sources. Clinically, the MET score provides information on patient difficulties with visual tasks, such as recognising faces.