Distinct Morphological Progression Patterns in Primary Versus Recurrent Pterygium: Vertical Attenuation Versus Deep Stromal Invasion

Purpose: To compare progression patterns between primary and recurrent pterygium using quantitative imaging. Methods: This retrospective cohort study included 114 primary and 24 recurrent pterygium eyes. Clinical severity was assessed via T grade, V grade, and loss of vertical length of plica semilunaris (LPS). Morphological parameters, including horizontal invasion length (HIL), height, thickness, and the residual corneal thickness to central corneal thickness (RCT/CCT) ratio, were measured using anterior segment swept-source optical coherence tomography. Clinical severity and HIL-adjusted morphological parameters were compared, and correlation analyses assessed structural progression. Results: Recurrent pterygia exhibited higher clinical severity (T3 and V3 grades, P < 0.001) and greater LPS (P < 0.001). After adjusting for HIL, recurrent cases showed lower height (P = 0.048) and thickness (P = 0.012) compared to primary cases. In primary pterygium, HIL negatively correlated with height (r = -0.478, P < 0.001), thickness (r = -0.191, P = 0.042), and the RCT/CCT ratio (r = -0.483, P < 0.001), suggesting a pattern of "vertical attenuation." Conversely, in recurrent pterygium, HIL demonstrated a much stronger negative correlation with the RCT/CCT ratio (r = -0.704, P < 0.001) but no correlation with height, indicating a pattern of "deep stromal invasion". Conclusions: Primary pterygium demonstrates an association consistent with vertical attenuation, whereas recurrent pterygium exhibits a structural pattern consistent with deep stromal invasion while maintaining its vertical bulk. Translational Relevance: Characterizing the distinct pathways provides an objective basis for tailored surgical planning and optimized patient care strategies.