ASSOCIATION BETWEEN TOMOGRAPHIC CHARACTERISTICS OF PTERYGIUM AND PREOPERATIVE CORNEAL ASTIGMATISM MEASURED BY ANTERIOR SEGMENT OPTICAL COHERENCE TOMOGRAPHY.

The main objective of this work is to study the association between pterygium's anatomical features and its tomographic classification and the preoperative topography values using a single, fast and comfortable test for the patient, the AS-OCT.

50 eyes of 50 patients which were listed for primary pterygium surgery at an Ophthalmology Tertiary Centre were studied preoperatively by measuring the anatomical characteristics of the pterygium and performing a corneal topography with AS-OCT (Casia 2; Tomey Corp., Nagoya, Japan).

10 anatomical variables of pterygium and 13 anterior and posterior topography variables were measured with AS-OCT. Finally, statistical analysis was performed using SPSS program (SPSS Statistics®, IBM®, version 21.0.0.0) for descriptive variables and R-project (The R foundation©, version 3.0.2) for other analyses.

Pterygium classified with AS-OCT as flat pattern exhibit significantly lower preoperative mean values of flat keratometry (K1), real flat keratometry (K1r),  average keratometry (AvgK), and real average keratometry (AvgKr) compared to those classified as having a nodular pattern. Flat pattern pterygium also shows greater differences between the principal meridians increasing preoperative cylinder (CYL) and real cylinder (CLYr). In contrast, the classification using slit-lamp examination (SLE) (atrophic, intermediate or fleshy pterygium) does not reveal differences between patterns. The horizontal corneal invasion of pterygium, measured with AS-OCT, proportionally increases the difference between the principal meridians increasing preoperative CYL and CYLr. Overall, a statistically significant relationship is observed between most anatomical measurements of pterygium with AS-OCT (limbus thickness, central pterygium thickness, head pterygium thickness, epithelial thickness at 1 mm, stromal thickness at 1 mm, total thickness at 1 mm, total thickness at 2 mm, total thickness at 3 mm) and preoperative keratometry. Larger measurements in these variables result in a decrease in K1, K1r, AvgK and AvgKr values of the anterior topography and in a decrease in posterior K1 and posterior AvgK values of the posterior topography. 

This study demonstrates associations between preoperative topography, including posterior topography, and the pterygium tomographic classification (nodular or flat) and its anatomical measurements assessed only by AS-OCT, which are not assessable with SLE.