Purpose: Considering that peripheral corneal thinning occurs in keratoconus (KC), the 14 anterior scleral thickness (AST) profile was measured to compare thickness variations in healthy 15 and KC eyes across several meridians. Methods: This cross-sectional case-control study comprised 16 111 eyes of 111 patients, 61 KC eyes and 50 age- and axial length-matched healthy eyes. The AST 17 was explored at three scleral eccentricities (1, 2 and 3 mm from the scleral spur) across four scleral 18 zones (nasal, temporal, superior and inferior) using swept-source optical coherence tomography. 19 The AST variations among eccentricity, scleral regions within and between groups were investi- 20 gated. Results: AST significantly varied with scleral eccentricity in healthy eyes over temporal 21 (p=0.009) whereas in KC eyes over the nasal (p=0.001), temporal (p=0.029) and inferior (p=0.006) 22 meridians. The thinnest point in both groups was 2 mm posterior to scleral spur (p<0.001). The sclera 23 was thickest over the inferior region (control 581 ± 52µm, KC 577±67µm) and thinnest over the su- 24 perior (control 448±48µm, KC 468±58µm) sclera in both populations (p<0.001 for all eccentricities). 25 The AST profiles were not significantly different between groups (p>0.05). The inferior-superior 26 thickness asymmetry was different at 2mm between groups (p=0.009), specifically with subclinical 27 KC (p=0.03). There is a trend where the asymmetry increases not significantly with KC degree 28 (p>0.05). Conclusions: KC eyes presented significant thickness variations among eccentricity over 29 the paracentral sclera. Although AST profiles not differed between groups, the inferior-superior 30 asymmetry difference demonstrated scleral changes over the vertical meridian in KC that need fur- 31 ther investigations. 32 Keywords: Anterior scleral thick
