Predictors of femtosecond laser intrastromal astigmatic keratotomy efficacy for astigmatism management in cataract surgery

Purpose: To evaluate the factors associated with the efficacy of femtosecond laser intrastromal astigmatic keratotomy (AK).

Setting: Moorfields Eye Hospital, London, United Kingdom.

Design: Prospective case series.

Methods: Eyes having intrastromal AK for corneal cylinder correction were analyzed. Preoperative biometric parameters included axial length, anterior chamber depth, central corneal thickness, and Ocular Response Analyzer corneal hysteresis (CH) and corneal resistance factor (CRF). Preoperative and 1-month postoperative corneal keratometry was measured using the Topcon KR8100PA topographer-autorefractor. Astigmatic analyses were performed using the Alpins method.

Results: The study analyzed 319 eyes of 213 patients with a mean target induced astigmatism of 1.24 diopters (D) ± 0.44 (SD), mean surgically induced astigmatism (SIA) of 0.71 ± 0.43 D, and mean difference vector of 0.79 ± 0.41 D. Two multiple regression models were constructed for SIA prediction. Model 1, based on previous manual limbal relaxing incision parameters, confirmed age and astigmatism meridian (with/against the rule and oblique) to be associated with SIA in addition to AK arc length, AK start depth, and preoperative corneal cylinder magnitude. Model 2, additionally considering other parameters, found only lower CH (-0.06 DC per unit CH), a higher CRF (0.04 D per unit CRF), and the astigmatism meridian to be independent predictors of greater SIA (after adjusting for intrastromal AK arc length, start depth, and preoperative corneal cylinder). With-the-rule astigmatism was associated with a 0.13 D higher SIA than against-the-rule astigmatism, holding all other variables constant.

Conclusion: Corneal biomechanical parameters and astigmatism meridian were independent predictors of femtosecond laser intrastromal AK efficacy even after adjusting for AK arc length, AK start depth, and preoperative corneal cylinder.

Financial disclosure: Dr. Stevens is a previous consultant to Optimedica, Inc. which is now part of Abbott Medical Optics, Inc. Drs. Stevens and Day have no financial or proprietary interest in any material or method mentioned.