Identification of a Horizontal Invasion Length Threshold Predicting Posterior Corneal Flattening after Pterygium Excision

PURPOSE: To characterize perioperative changes in posterior corneal curvature (PCC) following pterygium excision using anterior segment (AS) swept-source optical coherence tomography (SS-OCT), and to identify the critical threshold of horizontal invasion length (HIL) predicting significant PCC alterations. METHODS: This retrospective cohort study included 85 eyes of 77 patients with primary nasal pterygium. PCC parameters, including posterior keratometry (K) average, posterior steep K, posterior flat K and posterior corneal astigmatism, were measured preoperatively and postoperatively using AS SS-OCT (Anterion). Perioperative PCC changes were analyzed in relation to HIL and postoperative duration. Subgroup analyses were performed to identify the HIL cutoff value associated with statistically significant changes in posterior K average. RESULTS: Significant postoperative flattening was observed in both posterior K average (from -6.27 ± 0.24 to -6.23 ± 0.23 diopters [D], p < 0.001) and posterior flat K (from -6.14 ± 0.23 to -6.09 ± 0.23 D, p < 0.001), accompanied by a significant increase in posterior corneal astigmatism (from -0.25 ± 0.12 to -0.29 ± 0.17 D, p = 0.003). The magnitude of posterior flattening showed a significant positive correlation with HIL (r = 0.384, p < 0.001) but was not correlated with postoperative duration (p = 0.428). In subgroup analysis, eyes with HIL ≥3.5 mm exhibited a significant change in posterior K average (p < 0.001), whereas those with HIL