Abstract: Objective To estimate the role of the pachymetry paramerers measured with high-speed anterior segment optical coherence tomography (RTVueOCT) in the screening of  subclinical keratoconus. Design Evaluation of diagnosis technique. Participants Thirty-six cases (56 eyes) with keratoconic, 37 cases (57 eyes) with subclinical keratoconic, and 30 normal subjects (60 eyes) were enrolled. Method Kertoconus or suspected keratoconus were diagnosed based on the examinations with the slit lamp microscope and Tomey corneal topographic map. If the results of the two exams suggested to be suspect, the eyes whose KSI value and local curvature increased after the following up for 3~6 months were diagnosed as subclinical keratoconus. The pachymetry paramerers were measured by RTVueOCT and compared among the normal eyes, subclinical kertoconus group, and the kertoconus group. The parameters included superior-inferior (S-I), superonasal-inferotemporal (SN-IT), minimum(MIN), minimum-median(MIN-MED), minimum-maximum(MIN-MAX), and the location of the thinnest cornea (X-location,Y-location). Receiver operating characteristic (ROC) curves were used to analyzed the optimal cutoff points, sensitivity, and specificity of the pachymetry pamameters to differentiate the keratoconic eyes, or subclinical keratoconus eyes from the normal eyes. Main Outcome Measures S-I, SN-IT, MIN, MIN-MED, MIN-MAX, X-location,  Y-location, area under the ROC curve (AROC),  sensitivity, and specificity. Results IT-SN, I-S, MIN, MIN-MED, and MIN-MAX in the subclinical keratoconus group and keratoconic group were significantly increased than in the control group, and which were significantly increased in keratoconic group than in the subclinical keratoconus group (all P<0.05). To differentiate the subclinical keratoconic eyes from the normal eyes, the AROC of the IT-SN, I-S, MIN, MIN-MED, and MIN-MAX was 0.757, 0.732, 0.858, 0.769, and 0.790, respectively; the cutoff point was -28.5, -33.5, 487.0, -22.5, and -53.0 μm, respectively; the sensitivity was 0.632， 0.404， 0.667， 0.596 and 0.632; the specificity was 0.833， 0.967， 0.900， 0.937 and 0.917, respectively. Conclusion RTVueOCT can play an important role in the screening of the subclinical keratoconus.

Key words: RTVueOCT, pachymetric parameters, corneal topography, keratoconus/diagnosis