A Prospective Randomized Controlled Study of How Construction and Placement of Surgical Corneal Incisions May Influence Refractive Errors and Spectacle Dependence After Cataract Surgery
A Prospective Randomized Controlled Study of How Construction and Placement of Surgical Corneal Incisions May Influence Refractive Errors and Spectacle Dependence After Cataract Surgery
Astigmatism is a common cause of continued dependence on glasses after cataract surgery and may lead to patient dissatisfaction with surgical outcomes. As the corneal curvature is the main source for astigmatism after cataract surgery, our aim is to investigate whether postoperative astigmatism can be reduced by tailoring the location of surgical incisions according to the curvature of the cornea. We also wish to investigate whether this in turn reduces the need for glasses following cataract surgery.
In the planned study, one group of patients with cataracts and concurrent corneal astigmatism will undergo surgery using customized incision placement, while a control group will be operated on using standard incision placement without consideration of corneal astigmatism. Astigmatism will be measured before surgery and again at 3 and 12 weeks postoperatively. We will also assess how tailored incisions affect corneal biomechanics and shape, as well as measure visual quality and the need for glasses during daily activities before and after surgery.
Approximately 160,000 cataract procedures are performed annually in Sweden. Around 40% of these patients (64,000 individuals) have astigmatism greater than 1 diopter and could potentially achieve improved surgical outcomes based on the results of this study. The method is cost-effective and associated with a low risk of complications compared to other approaches for reducing astigmatism.
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.
Both of the above methods require additional resources in terms of time, measurement equipment, and treatment technology, resulting in increased costs. For example, a cataract surgery with toric lens implantation performed at a private clinic costs the patient approximately SEK 18,000 per eye, whereas reimbursement to a public provider for cataract surgery with a standard intraocular lens (without astigmatism correction) amounts to SEK 6,407 per eye. A Dutch cost-effectiveness study found that the improvement in quality of life achieved with toric lenses was too small relative to their cost, and therefore recommended a co-payment model, meaning that toric lenses should not be part of publicly funded healthcare but instead paid for out-of-pocket by patients who choose them.
An alternative approach, which we aim to investigate in this project, takes advantage of the fact that corneal incisions made during surgery can alter corneal curvature and thus its refractive power. During cataract surgery, a self-sealing incision is made at the corneal periphery-a clear corneal incision (CCI). By aligning the incision with the axis of corneal astigmatism, and when necessary adding a second incision opposite the original one, corneal astigmatism can be reduced. This method is referred to as placing the incision on the steep meridian and may be combined with an opposite clear corneal incision (OCCI).
Both toric lenses and customized incision techniques (CCI/OCCI) must be aligned precisely at the correct axis. Misalignment reduces the corrective effect, and deviations greater than 30º may worsen astigmatism. Toric lenses may rotate from their intended position both during surgery and postoperatively, potentially leading to increased astigmatism and reduced visual quality, sometimes requiring additional surgery. This risk does not exist with customized incision techniques. Taken together, both economic considerations and complication profiles support the need to explore cost-effective, simple methods with low complication risk to reduce astigmatic refractive errors after cataract surgery.
Project Description and Work Plan The research group has established collaboration with two private healthcare providers within the regions of Östergötland and Jönköping, who have agreed to assist in the recruitment of study participants. This will significantly increase the number of eligible participants, as many cataract patients treated at Linköping University Hospital have comorbid eye conditions that preclude study inclusion.
The two participating private providers collectively perform more than 3,000 cataract surgeries annually. Since nearly 40% of cataract patients have astigmatism greater than 1 diopter, this provides a potential screening pool of approximately 1,200 patients per year. Based on power calculations indicating a required sample size of 40 operated eyes in the treatment group and 40 in the control group (α = 0.05, power = 80%), we estimate that sufficient recruitment can be achieved within one year (total of 100 eyes, 50 per group, accounting for potential dropouts).
Patients with visually significant cataracts and astigmatic refractive error greater than 1 diopter (cylinder) will be invited to participate. Informed consent will be obtained during the preoperative examination, conducted by a specialist physician involved in the project as part of their doctoral training.
In addition to standard clinical ophthalmic examination, including biometry to determine appropriate intraocular lens power, astigmatism will be measured using an autorefractokeratometer (KR-800, Topcon), optical biometry (IOLMaster 700, Carl Zeiss Meditec), and corneal topography (Pentacam, Oculus). Corneal biomechanical properties, structure, and curvature will be assessed using high-speed Scheimpflug imaging (Corvis ST + Pentacam, Oculus). Current spectacle prescription, as well as subjective and objective refraction, will be recorded.
Participants will complete a structured questionnaire on spectacle dependence and use in daily activities prior to randomization. The surgeon (principal investigator or collaborating investigator in consultation with the principal investigator) will then plan incision placement based on preoperative corneal astigmatism according to an algorithm taking into account magnitude and axis of the corneal astigmatismus.
Cataract surgery is performed using standard technique through a 1.8 mm wide surgical incision. Prior to cataract surgery with customized incisions, the surgeon marks the planned incision site on the seated patient using a cannula tip, guided by the degree scale integrated into the corneal microscope. In cases of astigmatism >1.5 diopters (cylinder), the main incision-and, where applicable, the OCCI-is enlarged to 2.75 mm prior to implantation of the intraocular lens. Follow-up visits, including measurements corresponding to the preoperative assessment, are scheduled at 3 weeks and 12 weeks after cataract surgery.
The magnitude and axis of astigmatism before and after cataract surgery will be vector-analyzed using Naeser's polar value method and presented using double-angle plots (see preliminary results). Differences in astigmatism magnitude (in diopters) before and after surgery will be compared between the control group and the group treated with customized incisions using the chi-square test. Subgroup analyses will be performed for the four different incision-planning strategies included in the algorithm.
Timeline Spring 2026: Ethical approval, statistical consultation, and development of the study protocol.
Autumn 2026: Enrollment of study participants begins. Study surgeries commence following randomization.
Autumn 2027: Completion of study surgeries. Preliminary results presented at national and international meetings.
Spring 2028: Data analysis and manuscript preparation. Preliminary Results In a retrospective chart review, data from 87 cataract surgeries performed using customized incisions have been collected and compared with an equally large control group in which patients with corneal astigmatism greater than 1 diopter underwent surgery using standardized incision placement (2 mm incision at 170°).
Preliminary results show that the effect on measured astigmatism ranges from no effect to a highly favorable outcome, in which corneal astigmatism is completely eliminated postoperatively and no astigmatic correction is required. At the group level, a statistically significant increase is observed in the proportion of patients with reduced astigmatism after cataract surgery with customized incisions compared to standardized incisions.
Corneal astigmatism is not routinely measured after cataract surgery in standard clinical practice. Therefore, retrospective studies must rely on postoperative refractive astigmatism (spectacle prescription), which is documented in the medical records after most cataract surgeries. Since a non-toric intraocular lens is implanted during surgery, the postoperative refractive astigmatism can be considered equivalent to astigmatism originating from the cornea.
Preoperative refraction in the presence of cataract is imprecise due to the visual impairment caused by the cataract. Therefore, preoperative corneal astigmatism measurements provide a more accurate reference for comparison with postoperative refractive astigmatism in retrospective studies based on medical record data.
Astigmatism magnitude (in diopters) and axis (in degrees) can be illustrated using double-angle plot diagrams, in which a semicircle of 180° is expanded into a full circle-resulting in a total of 180° rather than 360°. The distance of each data point from the center represents the magnitude of astigmatism, while its angular position reflects the astigmatic axis.
Significance
Societal Relevance and Impact The project is clearly patient-centered and focused on sustainability. Ophthalmic care is evolving rapidly, enabling treatment of larger patient populations for conditions that were previously left untreated. However, as in many other medical specialties, this development unfortunately creates an imbalance between available resources and the needs that can potentially be met. The medical technology industry is actively developing and marketing new treatment options, which may contribute to substantially increased healthcare costs. It is therefore highly relevant that independent clinical research explores approaches that make it possible to achieve good clinical outcomes at lower cost.
Methods that reduce the cost of achieving good treatment outcomes improve the balance between limited resources and growing needs. Cost savings that can be achieved without compromising medical outcomes create financial space that can be allocated to other healthcare priorities.
Originality and Interdisciplinarity A small number of studies have been published regarding the effect of customized surgical incisions on corneal astigmatism in cataract surgery (4, 5). This project is the first to investigate outcomes following the use of customized incisions in the context of micro-incision cataract surgery (MICS), i.e., cataract surgery performed through incisions of 2 mm or less.
The project involves collaboration between a university hospital, academia, and the private healthcare sector. As an increasing majority of uncomplicated cataract surgeries are performed in private practice, such collaboration will become an increasingly important prerequisite for conducting effective clinical research on cataract surgery and its outcomes.
Inclusion Criteria:
Exclusion Criteria:
bjorn.johansson@regionostergotland.se+46 10 1031254
helen.setterud@regionostergotland.se+46 10 1038682