A Nomogram to Improve the Predictability of High Myopic Astigmatism in Small Incision Lenticule Extraction Surgery

To evaluate a new regression-derived nomogram for high myopic astigmatism in small incision lenticule extraction (SMILE) surgery.

In this prospective study, data from 180 eyes with myopic astigmatism ranging from -2.50 to -4.50 diopters (D) at 3 months after SMILE surgery were analyzed to construct the astigmatic nomogram. Linear regression between target induced astigmatism and flattening effect formula was derived as a nomogram to adjust astigmatic treatment. The nomogram was applied to 112 eyes with astigmatism ranging from -2.75 to -4.50 D. Subsequently, 143 eyes (manifest refraction group) with astigmatism greater than 2.50 D from 180 eyes were compared with 112 eyes (astigmatic nomogram group). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and refractive outcomes at 3 months postoperatively were recorded.

At 3 months after surgery, there was no difference in postoperative degree of astigmatism or UDVA between the two groups. In the astigmatic nomogram group, 109 (97%) of the eyes were within ±0.50 D compared with 127 (89%) in the manifest refraction group (P = .010). Target induced astigmatism and surgically induced astigmatism were strongly correlated in both groups. However, the average undercorrection in the manifest refraction group was 8.4% (R² = 0.67), whereas the astigmatic nomogram group displayed 2.7% overcorrection (R² = 0.86). Moreover, interestingly, all eyes in the astigmatic nomogram group had an angle of error within -5° to 5° compared with 137 (95.8%) of the eyes in the manifest refraction group (P = .028).

The astigmatic nomogram, based on regression between target induced astigmatism and flattening effect, could enhance the accuracy and predictability of high myopic astigmatism correction in SMILE surgery. [.