Noninvasive mapping of the normal retinal thickness at the posterior pole

Objective: Objective and sensitive measurements of the retinal thickness at the posterior pole are useful to detect and delineate macular edema or ret inal atrophy. The authors therefore developed an instrument, the Retinal Th ickness Analyzer (RTA), to map the retinal thickness rapidly. The RTA was u sed to study the normal thickness at the posterior pole and to provide a pi lot baseline. Design: Cross-sectional study. Methods: A green (540-nm) laser slit was focused on the retina via a scanni ng mirror placed at the conjugate plane of the pupil. The intersection betw een the laser slit and the retina was viewed at an angle and recorded by a video camera. Nine scans, each acquired in 200 to 400 msec, covered the cen tral 20 degrees of the fundus. Participants: The posterior pole was mapped in 29 normal subjects 19 to 76 years of age (mean, 48 years). Results: The thickness maps matched the posterior pole anatomy. Points with maximum thickness were located in the perifovea in a C-shaped manner exten ding from the disc to above and below the fovea, The local variation (stand ard deviation) in retinal thickness among the subjects was, on average, 15 mu m. Age, gender, and race did not have a large effect (<35 mu m) on the v alues. Conclusions: Rapid scanning thickness analysis with the RTA provides a deta iled map of the retinal thickness. The relatively narrow range of thickness values in normal subjects indicates that the method may provide a sensitiv e detection of pathologic thickening or thinning of the retina.