Astigmatic Keratotomy

This study investigates astigmatism reduction after application of femtosecond laser-assisted arcuate incisions with the Castrop nomogram at the time of cataract surgery.

A retrospective, single-site, single surgeon, consecutive case series study. All patients were treated at the Tyger Valley Eye & Laser Centre, Bellville, Cape Town, South Africa.

A total of 51 astigmatic eyes (27 right and 24 left) of 51 patients with mean preoperative cylinder of −1.05 ± 0.45 diopters (D) (range: -0.37 to -2.35 D) underwent femtosecond laser-assisted arcuate incisions with the Castrop nomogram using the FEMTO LDV Z8 laser (Ziemer Ophthalmic Systems AG). 38 eyes (74.51%), with mean preoperative cylinder of −1.13 ± 0.46 D, received paired corneal arcuate incisions (PAK), while 13 eyes (25.49%), with mean preoperative cylinder of −0.84 ± 0.28 D, received single arcuate incision (SAK). Preoperative and postoperative objective astigmatism vectors were assessed using iTrace (Tracey Technologies Corp.). Postoperative cylinder accuracy was evaluated between 6 and 8 weeks after the surgery.

Mean total cylinder power was significantly reduced to -0.59 ± 0.40 D (p<0.001) with 56% of eyes achieving ≤ 0.50 D and 89% of eyes achieving ≤ 1.00 D. In addition, the mean postoperative manifest cylinder in PAK and SAK was reduced to -0.61 ± 0.45 D (p<0.001) and -0.54 ± 0.22 D (p<0.01), respectively. Data analysis for target-induced astigmatism (TIA) versus surgically-induced astigmatism (SIA) showed a global astigmatism corrected index (CI) of 0.69 ± 0.34. In eyes with preoperative cylinder of ≤−1.00 D the CI was 0.82 ± 0.37 (n=17), in eyes with -1.00 to -2.00 D the CI was 0.58 ± 0.28 (n=18).

Paired and single surface-penetrating keratotomies created with a low-energy femtosecond laser using the Castrop nomogram at the time of cataract surgery showed efficient astigmatism reduction. In this study the Castrop nomogram showed a good accuracy in patients with low preoperative astigmatism (CI=0.82) and a tendency for undercorrection in patients with moderate to high astigmatism (CI=0.58).