SIA Vector Analysis and Keratometry Prediction in Temporal SICS with 350 µm Scleral Incision Depth.

OBJECTIVES: The magnitude and axis of surgically induced astigmatism depend on the sclera-corneal tunnel dimensions. Often, the incision depth is subjective, and standardization is rarely emphasized. This study attempts to evaluate a fixed scleral incision depth of 350 µm at 1-week post-op. The aim is to determine the SIA vector and centroid using the Pythagorean theorem and keratometric measurements. MATERIALS AND METHODS: This study was conducted from January to July 2025 and recruited 42 patients at a tertiary health institution. All patients received scleral incisions to a depth of 350 µm after preoperative auto-keratometry measurements. Preoperative astigmatism was classified into WTR, ATR, and oblique types. RESULTS: The overall mean age was 67.14 (± 9.23) years, with 27 (64.29%) males and 15 (35.71%) females. A positive correlation (r = 0.93, 0.69) was found for pre- and post-operative keratometry. T-test for pre- and post-operative vertical keratometry revealed statistical significance (p < 0.0009). The mean SIA magnitude and axis were 2.05 (± 1.75) D and 77.94º (± 59.68º), respectively. The Wilcoxon signed-rank test showed statistical significance for SIA magnitude (p=0.0003). The centroid was at 22.3º. A 28.57% conversion rate from ATR to WTR was observed, with 71.43% remaining unchanged postoperatively. High prediction accuracy was observed for preoperative horizontal and vertical keratometry (R2 values of 0.93 and 0.74, respectively). DISCUSSION: This work adds a unique dimension to the literature by explicitly linking a fixed tunnel depth to the SIA vector and keratometric prediction. These results provide a platform for future research exploring scleral incision depth as a determinant of astigmatic outcomes. CONCLUSIONS: This study finds a statistically significant difference in vertical keratometry with moderate SIA magnitude. Astigmatic axis transition was unchanged in most patients, likely due to a standardized scleral incision depth. Centroid demonstrated a minimal SIA magnitude on horizontal keratometry. An excellent postoperative keratometry prediction was determined.