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Corneal biomechanics, incision width affect refractive outcomes
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Biomechanical features of the cornea and incision width influenced key refractive outcomes in cataract surgery, according to a study.
The study authors hypothesized that preoperative analysis of corneal biomechanical properties and incision width would help predict postoperative outcomes, such as surgically induced astigmatism (SIA).
“We originally reported that intrinsic biomechanical properties of the cornea directly influenced SIA after cataract surgery, thus opening new avenues based on preoperative [corneal hysteresis] analysis to better predict the final outcome,” Alexandre Denoyer, MD, PhD, the corresponding author, said in an email interview with Ocular Surgery News.
Novel metrics help surgeons predict outcomes from new surgical techniques and IOL technologies, Denoyer said.
“Premium cataract surgery that combines microincision cataract surgery with a toric and/or multifocal IOL requires a better predictability of the refractive result in order to improve the visual outcome,” he said. “New tools and formulas, including incision features but also corneal biomechanical properties, may help optimize the final result of our surgery.”
The study was published in the Journal of Cataract and Refractive Surgery.
Methods and measures
The prospective clinical study included 40 eyes of 40 patients who underwent cataract surgery. Complete ophthalmic examinations were conducted preoperatively and 1, 7 and 30 days postoperatively. Investigators assessed objective and subjective refraction, slit lamp images and fundus photographs.
“All the patients visiting for cataract surgery were included, except when corneal astigmatism was greater than 3 D,” Denoyer said. “Neither [higher-order aberrations] nor [corneal hysteresis] nor [corneal resistance factor] at baseline constituted exclusion criteria. Hence, the population included closely reflected the ‘standard’ cataract population as encountered in daily practice.”
Corneal imaging was performed with Spectralis spectral-domain optical coherence tomography (Heidelberg Engineering). The Pentacam Scheimpflug camera (Oculus) was used to perform optical analysis of corneal astigmatism and higher-order aberrations. The Ocular Response Analyzer (Reichert) was used to analyze corneal biomechanical factors.
Investigators calculated central and peripheral corneal thickness; incision width, length and architecture; and corneal hysteresis and corneal resistance factor.
Outcomes and observations
Surgically induced astigmatism correlated significantly with incision width (P < .05) and preoperative corneal hysteresis (P < .01). Corneal third-order trefoil correlated significantly with incision width only (P < .01).
“There were significant and independent correlations between corneal hysteresis and SIA and between incision width and SIA,” Denoyer said. “We could speculate that corneal intrinsic properties influence the way the cornea reacts to surgery. In other words, the more a cornea is elastic, the more it may be stretched by a surgical incision, whatever the incision width.”
Surgically induced astigmatism and higher-order aberrations were significantly lower after microincision cataract surgery (MICS) than after small-incision cataract surgery (SICS) (both P < .01).
“However, some patients still have significant SIA after MICS. Together, our results suggest that these patients presented specific biomechanical properties, which also deeply influence the final SIA,” Denoyer said. – by Matt Hasson