Corneal diameter should be determined prior to cataract surgery, as it can lead to varying degrees of corneal astigmatism depending on the type of incision used, reports a study in the January 2016 issue of Cornea.1 Other factors already known to impact postoperative astigmatism include incision size, configuration and location relative to the limbus, as well as the axis on which the main incision is performed.

Researchers observed cataract procedures performed on 330 eyes at the General Hospital of Piraeus “Tzaneio” Attiki in Greece from February 2011 to October 2013. Patients were divided into four groups according to corneal horizontal diameter, i.e., white-to-white (WTW) distance: group A ≤ 11.6mm; group B 11.7mm to 11.9mm; group C 12.0mm to 12.2mm; and group D ≥ 12.3mm. At the first postoperative month, surgically-induced astigmatism (SIA) was 0.98D ± 0.6SD in group A, 0.79D ± 0.43SD in group B, 0.68D ± 0.45SD in group C and 0.53D ± 0.32SD in group D, while at six months postoperatively, SIA was 0.77D ± 0.43SD in group A, 0.69D ± 0.34SD in group B, 0.62D ± 0.36SD in group C and 0.49D ± 0.27SD in group D. 

These data indicate that a change greater than 0.5D in corneal astigmatic power at the first and sixth months postoperatively was significantly lower in eyes with WTW distance 12.0mm to 12.2mm and ≥ 12.3mm, compared with eyes with WTW distance ≤ 11.6mm and 11.7mm to 11.9mm. In effect, the researchers note, the smaller the cornea, the larger the effect on the power of postoperative astigmatism. 

“These findings are important because it identifies an additional perioperative variable that is helpful in improving astigmatic results following cataract surgery,” Eric Donnenfeld, MD, a surgeon on Long Island, says.

Researchers also classified the participating eyes into groups of either right or left to evaluate if superior and superomedial incisions in the left eyes lead to greater SIA due to the primary incision being situated closer to the optical center of the cornea and the placement of the phaco probe against the nose and brow. They also examined whether superior and superolateral incisions produce more postoperative astigmatism in against-the-rule astigmatic eyes than in with-the-rule eyes. 

Ultimately, however, results indicated no differences in SIA between right and left eyes, and the type of astigmatism could not be accounted for, due to the unvaried patient base. The results are further limited by the evaluation of anterior surface topography, the researchers note. Research that includes posterior corneal effects is needed to more fully evaluate astigmatism-induced results.  

1. Theodoulidou S, Asproudis I, Kalogeropoulos C, et al. Corneal diameter as a factor influencing corneal astigmatism after cataract surgery. Cornea. 2016 Jan;35(1):132-6.