Macular edema reduces B cone sensitivity in diabetics

A simple clinical test of B cone pathway sensitivity shows that a group of 45 diabetics (of which 31 have VA >/= 20/20) are 40 times less sensitive than a group of 57 normals. By contrast, the diabetic group is less than 2.2 times less sensitive than the normals for R and/or G cone pathway sensitivity. The selective B cone sensitivity loss is seen even in patients who have no macular edema; however, the presence of edema is associated with significantly greater sensitivity loss. Age differences between the groups cannot account for the differences seen between normals and diabetics.