The influence of different corneal diameters on Belin/Ambrósio enhanced ectasia display of Pentacam corneal topography

Abstract

Objective: To investigate the effect of corneal diameter on Belin/Ambrósio enhanced ectasia display (BAD). Methods: Retrospective case series study. The subjects were 6 744 myopic patients, including 3 341 males and 3 403 females, who had undergone corneal refractive surgery or had completed preoperative examination but had not undergone corneal refractive surgery at the Army Medical Center and Chongqing Vision Institute in Chongqing from June 2017 to June 2019. Age was (23.74±5.73) years old. No patients had keratoconus. One eye of each patient was randomly included, and the patients were divided into groups according to the corneal diameter measured by Pentacam. Group A included 630 patients (630 eyes) with corneal diameter ≤ 11.1 mm. In group B, there were 4 063 patients (4 063 eyes) with corneal diameter of 11.2 to 11.8 mm. In group C, there were 2 051 patients (2 051 eyes) with corneal diameter ≥11.9 mm. Preoperative BAD parameters of deviation of front elevation difference map (Df), deviation of back elevation difference map (Db), deviation of average pachymetric progression index (Dp), deviation of minimum thickness (Dt), deviation of Ambrósio's relational thickness maximum (Da) and overall deviation value (Do) were measured by Pentacam. One-way analysis of variance was used for preoperative BAD parameters comparison between groups. The distribution of normal, suspicious and pathological results of Df, Db, Dp, Dt, Da and Do in each group was tested by chi-square test. Results: In groups A, B and C, Df was 0.73±1.14, 0.48±1.02, and 0.11±0.91, Db was 1.09±1.07, 0.23±0.83, and-0.34±0.62, Dp was 1.57±0.91, 1.14±0.86, and 0.68±0.75, Dt was -0.11±0.84, -0.2±0.82, and 0.03±0.78, Da was 0.78±0.61, 0.64±0.64, and 0.48±0.64, and Do was 1.65±0.64, 1.24±0.60, and 0.86±0.55, respectively. The BAD parameters of Df (F=129.549), Db (F=829.491), Dp (F=344.373), Dt (F=7.249), Da (F=68.637) and Do (F=524.877) were all significantly different between groups (P<0.01). The proportion of suspicious and pathological BAD parameters [Df (χ²=161.8), Db (χ²=611.75), Dp (χ²=478.84), Da (χ²=44.636), and Do (χ²=553.11)] suggested the distribution in each group was significantly different (P<0.01). Conclusions: Corneal diameter had a significant influence on BAD. Compared with eyes with large corneas, the false positive rate of BAD was higher in eyes with small corneas.(Chin J Ophthalmol, 2020, 56: 761-767).