Vector Analysis Of Astigmatic Correction After Smile Pro With And Without Digital Cyclotorsion Compensation Using The Oculign® System And Femtosecond-Assisted Lasik

To compare astigmatic correction following SMILE PRO with digital cyclotorsion compensation using the OcuLign® System (SP-Oculign), SMILE PRO with manual marking (SP-MM), and femtosecond-assisted LASIK (FL) in eyes with ≥1.00 D of myopic astigmatism. 

This retrospective comparative study evaluated mean absolute angle of error (MAE) and difference vector (DV) as the primary outcome measures.

Secondary outcome measures included postoperative uncorrected distance visual acuity (UDVA), residual refractive astigmatism, the percentage of eyes within ±0.50 D of residual astigmatism, target-induced astigmatism (TIA), surgically induced astigmatism (SIA), correction index (CI), index of success (IOS), and flattening index (FI).

In this retrospective comparative study, 149 myopic eyes with astigmatism ranging from -1.00 to -5.00 D undergoing SP-Oculign (n=49), SP-MM (n=50), or FL (n=50) were analyzed. Only the right eye of each patient was included in the analysis to avoid inter-eye correlation bias. Uncorrected and corrected distance visual acuity, manifest refraction, and refractive cylinder were recorded preoperatively and at 3 months postoperatively. Astigmatic correction was evaluated using Alpins vector analysis, including target-induced astigmatism (TIA), surgically induced astigmatism (SIA), difference vector (DV), correction index (CI), index of success (IOS), flattening index (FI), and mean absolute angle of error (MAE).

No significant difference in postoperative UDVA was observed at 3 months. The percentage of eyes within ±0.50 D of residual cylinder was 88% in FL, 77.6% in SP-OcuLign and 72% in SP-MM. Compared with FL, SP-MM had a significantly lower likelihood of achieving ±0.50 D (p=0.016), whereas SP-OcuLign did not differ significantly from FL (p=0.084).Vector analysis showed no significant difference in TIA or SIA between groups. MAE was significantly higher in the SP-MM (5.05°±3.26) compared with the FL (3.28°±2.92; p=0.004). The SP-OcuLign showed a lower MAE than the SP-MM (4.39±2.98 vs 5.05°±3.26; p>0.05) and a higher MAE than the FL (p=0.071); however, neither comparison reached statistical significance. Mean DV, CI, IOS, and FI were comparable. 

Our results showed that SMILE PRO with manual marking was associated with less favorable astigmatic correction compared with femtosecond-assisted LASIK. Digital cyclotorsion compensation using the OcuLign® System reduced rotational misalignment; however, statistical equivalence to femtosecond-assisted LASIK was not achieved at 3 months postoperatively.