The Corneal Thickness Changes in Different Gazes in Orbscan Topography

ABSTRACT

PURPOSE: To evaluate error of corneal thickness measurement in different gazes in Orbscan topography. METHODS: Sixty eyes of 30 normal subjects were investigated using the Orbscan topography system. The central corneal thickness (Kc) and the thinnest corneal thickness (Kt) on topography map were obtained in 5 different gazes. Gaze directions were classified into center (C), nasal I (NI), nasal II (NII), temporal I (TI), and temporal II (TII), in which I means 13 degree deviation from visual axis and II means 22 degree deviation. RESULTS: Kc in right eye was 540.4+/-37.7 micro meter(mean+/-standard deviation) at central gaze (C) and 550+/-36.9 micro meter at NI ; there was no significant change, but there were in Kc at NII (563.0+/-40.5 micro meter), TI (566.5+/-32.8 micro meter), TII (595.2+/-54.5 micro meter). In addition, the same patterns were seen in left eye in Kc analysis. In contrast, Kt did not change even in 5 gaze changes. In comparison between Kc and Kt at the same gazes, there were significant differences except in central gaze (C). CONCLUSIONS: Though the gaze direction changed, the most reliable measurement for evaluation and follow up of corneal thickness is the thinnest corneal thickness (Kc) in Orbscan topography system. In case that the central corneal refractive power and thickness were needed, it is important that Orbscan topography is performed in exact central fixation.