Development And Validation Of A Regression-Based Nomogram For Correcting With-The-Rule Astigmatism In Small Incision Lenticule Extraction Surgery

To evaluate a regression-derived nomogram for correcting moderate to high with-the-rule astigmatism in small incision lenticule extraction (SMILE). 

Guangzhou Aier Eye Hospital, China

Data from 428 eyes with WTR astigmatism ≥1.00 diopters (D) after SMILE surgery (2020-2023) were grouped into the model group (376 eyes) and the control group (82 eyes) at a 4:1 ratio. The model group developed a personalized nomogram based on the linear regression between targeted induced astigmatism and surgically induced astigmatism, as well as between the original input SE and the achieved SE. These two formulas were derived as new input correction formulas for SE and astigmatism. The nomogram was applied to a validation group (86 eyes) with WTR astigmatism ≥1.00 D from January to June 2024. Safety, efficacy, predictability and vector analysis at 3 months postoperatively were compared between the control group and the validation group.

At 3 months postoperatively, the mean postoperative SE was 0 ± 0.19 D in the validation group, better than the control group’s -0.09± 0.27 D (P = 0.015). Linear regression between TIA and SIA revealed 2.7% undercorrection (R² =0.8514) in the validation group, compared to 11.4% undercorrection in the control group (R² = 0.7154). In the validation group, 95.3% of the eyes (82/86) achieved postoperative astigmatism within 0.50 D, significantly higher than 85.4% (70/82) in the control group (P = 0.028). Correction index (CI: 1.00 ± 0.13) and magnitude of error (ME: 0 ± 0.15 D) were significantly better in the validation group compared to the control group (CI: 0.95 ± 0.17, ME: -0.07 ± 0.24 D) (P = 0.033, P = 0.022).

The nomogram based on linear regression between targeted induced astigmatism and surgically induced astigmatism, as well as between input SE and achieved SE, significantly improved the accuracy and predictability of astigmatism correction in SMILE, particularly for moderate to high WTR astigmatism.