MAY 05, 2015
This retrospective study suggests that corneal asphericity influences the refractive outcome of IOL calculations obtained using the Haigis, Hoffer Q, Holladay 1 and SRK/T formulas.
The authors found that if not taken into account, prolate corneas tend to end up with a myopic refraction and oblate corneas with a hyperopic outcome.
Corneal asphericity is a parameter that has gained attention since it was identified as a contributing factor in refractive surprises in post-corneal refractive surgery patients. A natural consequence of this is that we are now starting to examine the corneal asphericity of all patients and not only of those with previous refractive surgery.
High-order aberration profiles should become more of a routine measurement for all cataract surgeons in order to choose the IOL that provides the least amount of postoperative high-order aberrations.
In this study, the authors calculated IOL lens power using the Haigis, Hoffer Q, Holladay 1 and SRK/T formulas for 115 eyes (115 consecutive patients) implanted with the Acrysof SA60AT.
They found a statistically significant relationship between the error in refraction prediction (the difference between expected refraction and refraction measured 1 month after surgery) and the Q-value (or asphericity) with all formulas. In all cases, a more negative Q-value (prolate cornea) was associated with a myopic outcome, whereas a more positive Q-value (oblate cornea) was associated with a hyperopic outcome.
They suggest two solutions that might help avoid the influence of asphericity on refractive outcomes of cataract surgery and IOL implantation: using corneal power measurements rather than ring measurements, thus eliminating the discrepancy between central and paracentral corneal curvature; and adjusting current formulas to include corneal asphericity.