The Amsler grid is a suprathreshold target used to assess the central 10 degrees of the visual field; thus, it may fail to detect relative central scotomas. Low luminance conditions can be created by viewing the white grid on a black background through two cross-polarizing filters that vary light transmission and change the procedure to a threshold Amsler grid (TAG) test, thereby increasing its sensitivity. A total of 26 patients with diabetic retinopathy were tested by standard Amsler grid, TAG, and tangent screen. Four scotomas were detected by Amsler grid testing; each of these scotomas expanded in size on retesting with the TAG. TAG testing revealed 22 scotomas more than five times the number seen with conventional Amsler grid testing; tangent-screen examination confirmed 9 of these defects. In many cases, fundus photography and fluorescein angiography revealed pathology that correlated with the scotomas detected only by TAG testing. It thus appears that the TAG test is a rapid, high-yield, and sensitive means of assessing the central visual field in patients with diabetic retinopathy.