A Prospective Randomized Controlled Study of How Construction and Placement of Surgical Corneal Incisions May Influence Refractive Errors and Spectacle Dependence After Cataract Surgery

Scientific Research Questions Can astigmatic refractive error after cataract surgery be reduced by tailoring surgical incision placement to the corneal astigmatism, compared with using standardized incisions without considering corneal astigmatism? How is the cornea biomechanically affected by customized surgical incisions? Can the need for, or dependence on, glasses in everyday activities be reduced after cataract surgery performed using incision placement adapted to corneal astigmatism, compared with cataract surgery performed using standardized incisions?

Background and Overview of the Field In Sweden, approximately 160,000 cataract surgeries are performed annually according to data from the National Cataract Register (2023-2025). Cataract surgery is considered one of the most cost-effective interventions for improving quality of life. However, about one in ten patients report experiencing equal or greater difficulty performing daily activities after surgery due to their postoperative vision, according to a 2023 report from the National Cataract Register.

Refractive errors after cataract surgery may lead to dissatisfaction if patients become more dependent on glasses for good visual quality than expected. Astigmatic refractive error is generally caused by the cornea not being perfectly spherical, but instead having a steeper curvature in one meridian and a flatter curvature in the meridian perpendicular (90°) to it.

For the past decade, intraocular lenses with astigmatic correction (toric lenses) have been available for implantation during cataract surgery to compensate for corneal astigmatism. These lenses require additional time for surgical planning and preparation, and incur higher costs for measurement equipment and lenses compared with non-toric lenses. According to the National Cataract Register, the proportion of toric lenses implanted has gradually increased from 0.21% of surgeries in 2011 to 2.33% in 2023. Approximately 40% of cataract patients have astigmatism greater than 1 diopter, which is considered to impair visual quality. Thus, only a small proportion of patients with visually significant astigmatism receive toric lenses.

Using complex nomograms that account for factors such as the magnitude of astigmatism and patient age, arcuate incisions can be made deep within the cornea to reduce astigmatism. Such incisions can be created using a blade or a femtosecond laser. However, there is a risk of complications, including unintended full-thickness penetration of the cornea causing leakage of aqueous humor, as well as risks of corneal or intraocular infection.