Compensatory efficacy and bilateral symmetry of ocular residual astigmatism in myopic astigmatism adults.

OBJECTIVE

To investigate the characteristics of distribution patterns, compensatory efficacy, and bilateral symmetry of ocular residual astigmatism (ORA) across varying degrees of myopia.

METHODS

This cross-sectional study evaluated 2390 eyes of 1195 participants with myopic astigmatism before refractive surgery. Preoperative exams measured total astigmatism (TA) and anterior corneal astigmatism (ACA) using cycloplegic refraction and corneal topography. ORA was computed using Alpins Statistical System for Ophthalmic Refractive Surgery Techniques (ASSORT) ORA calculator.

RESULTS

In the study population, the incidence rate of ORA was 99.9 %, with ATR astigmatism representing the predominant manifestation (89.4 %). Stratification by myopia severity revealed significantly higher TA and ACA in high myopia versus moderate/low groups (P<0.001), but lower ORA (high: 0.59 ± 0.31 D; moderate: 0.65 ± 0.32 D; low: 0.68 ± 0.31 D; P=0.002 high vs. others). Compensatory effects (ORA offsetting ACA) predominated across all groups (82.3-87.8 %, P=0.169), though efficacy decreased with myopia severity (compensation factor: high 0.43 ± 0.25 vs. low 0.60 ± 0.30, P<0.001). Mirror symmetry was superior to direct symmetry for all astigmatic components (P<0.001), with ORA exhibiting the poorest mirror symmetry (16.84± 16.53°), worsening in high myopia (18.65± 16.90°, P=0.006).

CONCLUSION

This study established a hierarchical relationship between ORA and myopia severity. ORA's compensatory effect on ACA attenuated significantly with higher myopia. High myopia patients exhibited lower ORA magnitude and reduced interocular ORA symmetry compared to lower myopia groups.