Modulation of Total Corneal Astigmatism, Corneal Thickness, and Corneal Higher-Order Aberrations Following Tear-Enhancing Drop Instillation: A Retrospective Comparative Study.

INTRODUCTION

This study aimed to quantify changes in corneal astigmatism, thickness, and corneal higher-order aberrations after instilling a tear-enhancing drop (Systane Hydration Ultra, SHU) or 0.9% saline.

METHODS

This retrospective comparative study included 56 eyes (SHU, n = 38; 0.9% saline, n = 18). Corneal pachymetry and optical parameters were assessed using CASIA2 swept-source anterior segment optical coherence tomography. Measurements were acquired immediately after a natural blink (baseline, time 0). Subsequently, one drop of SHU or 0.9% saline was instilled, and measurements were repeated at 5 and 10 min postinstillation.

RESULTS

No clinically relevant changes in mean total corneal astigmatism (TCA), apparent corneal thickness (CT), or corneal higher-order aberrations were observed following instillation of either SHU or 0.9% saline. On a case-by-case basis, changes observed in the 0.9% saline group correlated with preinstillation values. CT tended to reduce with saline and generally increase with SHU. The induced change in TCA (y) 10 min after instillation significantly correlated with preinstillation. (i) CT (t) in SHU cases, where y = 0.317-0.003t +0.006t2 (r2 = 0.361, n = 38, p < 0.001); and (ii) TCA (x) in 0.9% saline cases, where y = 0.68x-0.30 (r2 = 0.562, n = 18, p < 0.001). Overall, the induced change in TCA exceeded 0.50 D in 18% of SHU and 17% of 0.9% saline 10 min after instillation.

CONCLUSIONS

Tear supplementation induces short-term case-specific changes in astigmatism and optical parameters, particularly within the first 5 min after Systane Hydration Ultra instillation. These findings may be relevant when interpreting corneal measurements in patients with mild ocular surface dysfunction undergoing refractive or cataract assessment.