Quantitative analysis of central visual field defects in macular edema using three-dimensional computer-automated threshold Amsler grid testing
To evaluate the central visual field (CVF) with specialized Amsler grid testing methods that include contrast sensitivity evaluation, in an attempt to detect abnormalities not identified with standard methods and to define new patterns of CVF deficits in two different diseases. 3D computer-automated threshold Amsler grid testing (3D-CTAG) was performed at five levels of contrast in one eye of 37 patients with diabetic macular edema (DME, n = 16) and exudative age-related macular degeneration (AMD, n = 21). 3D-CTAG abnormalities were detected in six patients (16%) who had no abnormalities with conventional Amsler grid testing. DME patients had more foci of CVF deficits (3.56 ± 2.92 defects/eye), than AMD patients (1.24 ± 0.89 defects/eye; P < 0.0002). The shape of the 3D-CTAG abnormality in DME was an inverted cone, while the deficits in AMD were always cylindrical. All eyes showed significant increases in CVF deficit surface area at minimum contrast levels when compared to maximum contrast (295% greater with DME, P < 0.02 and 150% greater with AMD, P < 0.03). 3D-CTAG detected CVF abnormalities not identified with conventional Amsler grid testing in 16% of subjects. Low-contrast conditions elicited a larger defect in both DME (3-fold) and AMD (1.5-fold). DME and AMD have unique 3D-CTAG profiles, enabling diagnostic discrimination. Measuring CVF defects with 3D-CTAG can quantitatively index disease severity and may be useful in longitudinal studies of the natural history of disease, as well as providing a quantitative outcome measure of the response to therapy.