Limbal Relaxing Incision (LRI) is a minor surgical technique developed to treat corneal astigmatism, which is a common refractive error. This procedure involves making one or two shallow, precise incisions near the perimeter of the cornea, which is the clear front surface of the eye. LRI is most frequently performed concurrently with cataract surgery, offering a straightforward method to reduce a patient’s reliance on glasses or contact lenses following the implantation of an intraocular lens. The technique aims to gently reshape the cornea, moving it from an irregular curve toward a more uniformly rounded surface.
How LRI Corrects Astigmatism
Astigmatism arises when the cornea is shaped more like a football than a basketball, possessing a steeper curve along one axis and a flatter curve along the axis perpendicular to it. This uneven curvature causes light entering the eye to focus improperly on the retina, resulting in blurred or distorted vision. The LRI procedure addresses this by targeting the biomechanical properties of the corneal tissue.
The incisions are strategically placed on the limbus, the outer edge of the cornea where it meets the sclera. A surgeon carefully marks the location along the steepest axis of the astigmatism, where the cornea is under the greatest tension. These small, arc-shaped cuts allow the peripheral corneal fibers to “relax” and lengthen in that specific meridian.
This relaxation reduces the tension along the steep axis, causing it to flatten. Simultaneously, this flattening effect is coupled with a corresponding steepening effect on the flatter axis, located 90 degrees away from the incision. The combined effect is a movement toward a more spherical corneal shape, which allows light to focus more accurately onto a single point on the retina. LRI is used to correct low to moderate astigmatism, typically in the range of 0.5 to 3.0 diopters.
The Surgical Procedure
The LRI procedure begins with pre-operative measurements to determine the precise location, depth, and length of the intended incisions. Advanced diagnostic imaging, such as corneal topography, provides a detailed map of the corneal curvature, allowing the surgeon to pinpoint the exact steep axis requiring correction. These measurements are integrated into a nomogram, a mathematical guide that customizes the procedure based on the patient’s age and the magnitude of the astigmatism.
The procedure is performed in an outpatient setting, often integrated into the beginning of cataract surgery. Anesthesia is administered using topical drops or a gel to numb the eye surface, ensuring the patient experiences no pain. A specialized instrument is then used to keep the eyelids open, and the eye is carefully marked to guide the incision placement.
The incisions are generally created using either a calibrated diamond scalpel or a femtosecond laser. When a scalpel is used, it is set to a precise depth, usually targeting about 80 to 90 percent of the corneal thickness, to avoid penetrating the full depth of the cornea. The surgeon makes one or two small, curved cuts at the pre-marked limbal locations.
The length of the arc-shaped incision is determined by the amount of astigmatism being corrected, with longer arcs used for higher degrees of error. The procedure is quick, often taking only a few minutes to complete. Because the incisions are made at the edge of the cornea, they are outside the central visual field, minimizing the risk of visual disturbances like glare.
Recovery and Long-Term Outcomes
Following the LRI procedure, patients may experience minor, temporary symptoms, including a mild foreign body sensation, light sensitivity, or some tearing for the first few days. Over-the-counter pain relievers can manage any minimal discomfort. The surgeon will prescribe medicated eye drops to prevent infection and control inflammation as the incisions begin to heal.
Vision may be blurry immediately after the procedure, but it often improves significantly within the first 24 hours. Most individuals can return to their normal daily routines, including work, the day after the surgery. Patients are advised to avoid strenuous activities, eye rubbing, and exposure to water sources like swimming pools or hot tubs for a few weeks to ensure proper healing.
The stabilization of vision typically occurs over several days to a few weeks as the corneal shape settles into its new curvature. LRI is an effective method for reducing astigmatism, with results that are considered long-lasting. While the goal is to fully correct the astigmatism, there is a possibility of under-correction or over-correction due to the natural variability of individual wound healing.
In rare instances where astigmatism remains, the surgeon may perform an enhancement, which involves slightly deepening or extending the original incisions. Most patients achieve a substantial reduction in their astigmatism, which significantly improves their uncorrected vision and reduces their need for glasses, particularly for distance tasks.