2020–2021 BCSC Basic and Clinical Science Course™
13 Refractive Surgery
Chapter 3: Incisional Corneal Surgery
Incisional Correction of Astigmatism
The outcome of AK and LRI surgery depends on several variables, including patient age; the distance separating the incision pairs (optical zone); and the length, depth, and number of incisions. Few large prospective trials have been performed. The Astigmatism Reduction Clinical Trial (ARC-T) of AK, which used a 7-mm optical zone and varying arc lengths, showed a reduction in astigmatism of 1.6 ± 1.1 D in patients with preoperative, naturally occurring astigmatism of 2.8 ± 1.2 D. Other studies of AKs have shown a final UCVA of 20/40 in 65%–80% of eyes. Overcorrections have been reported in 4%–20% of patients.
Studies of LRIs are limited, but these incisions are frequently used with seemingly good results in astigmatic patients undergoing cataract surgery. One study showed an absolute change in refractive astigmatism of 1.72 ± 0.81 D after LRIs in patients with mixed astigmatism. Astigmatism was decreased by 0.91 D, or 44%, in another series of LRIs in 22 eyes of 13 patients. Incisions in the horizontal meridian have been reported to cause approximately twice as much astigmatic correction as those in the vertical meridian (see Table 3-1).
Faktorovich EG, Maloney RK, Price FW Jr. Effect of astigmatic keratotomy on spherical equivalent: results of the Astigmatism Reduction Clinical Trial. Am J Ophthalmol. 1999; 127(3):260–269.
Price FW, Grene RB, Marks RG, Gonzales JS; ARC-T Study Group. Astigmatism Reduction Clinical Trial: a multicenter prospective evaluation of the predictability of arcuate keratotomy. Evaluation of surgical nomogram predictability. Arch Ophthalmol. 1995;113(3): 277–282.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.