[Correlation between corneal topography and subjective refraction in idiopathic and surgery-induced astigmatism].

Purpose: To study the correlation between subjective refraction and corneal topography. To compare the topographic analysis of surgically induced astigmatism (cataract and penetrating keratoplasty) with that of idiopathic astigmatism.

Methods: Subjective astigmatism, subjective spherical equivalent, best spectacle-corrected visual acuity (LogMAR units), and videokeratoscopy using the EyeSys 2000((R)) device (axial, tangential, and refractive power) were recorded in 100 eyes with idiopathic astigmatism, 100 eyes after cataract surgery, and 100 eyes after penetrating keratoplasty. Topographies were classified according to pattern (Bogan classification) and asphericity (shape factor: prolate or oblate).

Results: The asphericity shape distribution was significantly different between the 3 groups (p<0.001). The shape of idiopathic astigmatism was almost always prolate (90%) whereas the oblate shape was more frequent in the penetrating keratoplasty group (75%). There was no significant difference in topographic pattern distribution between the 3 groups (p=0.11). The asymmetric bow tie pattern was the most common topographic pattern. Topography pattern classification was significantly correlated with the subjective astigmatic cylinder. (r(s)=0.60, p<0.001). Unlike the round and oval patterns, the bow tie pattern was associated with the high subjective cylinder. Correlation between the subjective cylinder, the refractive power cylinder, and the axial power cylinder was strong (r(s)=0.92 p<0.001), but it was weak for the tangential power cylinder (r(s)=0.72 p<0.001). The correlation between the subjective spherical equivalent and central cornea power was poor (r(s)<0.37, p<0.001). Subjective astigmatic cylinder showed the strongest correlation with best spectacle-corrected visual acuity (r(s)=0.70, p<0.001), whereas the predicted corneal acuity, corneal uniformity index, asphericity, and refractive power symmetry index were poorly correlated with it (r(s)<0.54, p<0.001).

Conclusion: Despite the difference in the asphericity shape, the topographic pattern was similar in the 3 groups. The pattern type was significantly correlated with the subjective astigmatic cylinder. Topographic indices failed to predict visual acuity, while the subjective cylinder showed a strong correlation with visual acuity.