Astigmatic Outcomes of Single, Non-Paired Intrastromal Limbal Relaxing Incisions During Femtosecond Laser-Assisted Cataract Surgery Based on a Custom Nomogram

Carter W Lim; Sohel Somani; Hannah H Chiu; Raj Maini; Eric S Tam

doi:10.2147/OPTH.S238016

Astigmatic Outcomes of Single, Non-Paired Intrastromal Limbal Relaxing Incisions During Femtosecond Laser-Assisted Cataract Surgery Based on a Custom Nomogram

Clin Ophthalmol. 2020 Apr 22:14:1059-1070. doi: 10.2147/OPTH.S238016. eCollection 2020.

Authors

Carter W Lim^{1

2

3}, Sohel Somani^{3

4

5}, Hannah H Chiu^{3

4

5}, Raj Maini^{3

4

5}, Eric S Tam^{3

4

5}

Affiliations

¹ Faculty of Medicine, University of Ottawa, Ottawa K1H 8M5, Canada.
² Eye Foundation of Canada, Toronto M3N 2V6, Canada.
³ William Osler Health System, Brampton L6R 3J7, Canada.
⁴ Uptown Eye Specialists, Brampton L6Y 0P6, Canada.
⁵ Faculty of Medicine, University of Toronto, Toronto M5S 1A8, Canada.

Abstract

Purpose: To determine astigmatic changes of intrastromal limbal-relaxing incisions (LRIs) performed during femtosecond laser-assisted cataract surgery (FLACS).

Design: Retrospective case series.

Patients and methods: Patients undergoing FLACS with adjunctive astigmatism management with intrastromal LRIs were included. All eyes had preoperative corneal cylinder (Kcyl) ≥0.20 D on ocular biometry. An intrastromal LRI nomogram of single, non-paired LRIs placed at the 9 mm optical zone was used. Keratometry was measured preoperatively, and postoperatively at 1 week, 1 month, and 3 months (POM3). Alpins astigmatism analysis was used to calculate target-induced astigmatism (TIA, equivalent to preoperative Kcyl), surgically induced astigmatism (SIA), difference vectors (DV), and correction indices (CI). Secondary analysis included multivariable binary logistic regression to determine clinical factors associated with corrections >125% (CI > 1.25).

Results: A total of 154 eyes (125 patients) were studied. Mean preoperative Kcyl was 0.87±0.42 D (SD), which did not significantly differ from POM3 Kcyl (0.87±0.51 D, p=0.470). Only the against-the-rule (ATR) subgroup demonstrated a small but significant reduction in Kcyl from preoperative (0.96±0.51D) to POM3 (0.89±0.55D, p=0.032). Sixteen eyes (10.4%) had Kcyl ≤0.5 D preoperatively, compared to 46 eyes (29.9%) at POM3 (p<0.0001). Mean SIA was 0.80±0.52 D. Mean DV was 0.85±0.47. Mean CI was 0.79. Fifty-one eyes (33%) had astigmatism correction >125%. On multivariable regression analysis, ATR astigmatism class (p=0.026) and lower arc lengths (30º) (p=0.005) were associated with correction >125%. Lower preoperative corneal astigmatism was inversely correlated with CI (p<0.001).

Conclusion: Although intrastromal LRIs can be conveniently performed during FLACS and appear safe, only patients with ATR astigmatism demonstrated a significant reduction in corneal astigmatism 3-months postoperatively under the current nomogram. Areas for future refinements to the nomogram were identified.

Keywords: astigmatic keratotomy; astigmatism; refractive laser-assisted cataract surgery.