Retest Variability in the Medmont M700 Automated Perimeter

To investigate the level of test-retest variability in the Medmont M700 automated perimeter. We compare the retest variability of the outer 20° test points of one test method to test points in the inner 10° of two test methods to determine whether test points from different tests and regions exhibit different retest variability. We also generate some clinically applicable coefficient of repeatability (CoR) values for M700 Overall Defect (OD) and Pattern Defect (PD) indices.

Twenty-four glaucoma patients with varying degrees of field loss were enrolled, and 21 patients (40 eyes) had usable results. The Central (30°) test and the Macula (10°) test were performed on each eye on the same day. To determine retest variability, the tests were repeated 1 week later at the same time of day.

Test points from 5 to 20 dB in the outer 20° of the 30° test showed lower retest variance than points of equal decibel value in the central 10° of the same test. For the 30° test, the OD CoR was 2.4 dB. The PD retest CoR varied with glaucoma severity, ranging from 1.24 dB for PD less than or equal to 2.8 to 3.1 dB for PD more than 5.7. The 10° test CoR for OD was 2.1 dB, and PD retest CoR ranged from 1.58 for PD less than or equal to 2.8 to 2.4 for PD more than 5.7.

In glaucoma patients, retest variance for some decibel values does not seem to increase with increasing eccentricity in the M700. The OD values as graded by the M700 do not appear to correspond well with the amount of visual field loss and are not directly comparable to mean deviation results reported by other perimeters. Pattern defect values in the M700 seem to correlate well with the degree of field loss.