Cataracts and astigmatism are common eye conditions that cause blurry or distorted vision by affecting how light travels through the eye. A cataract occurs when the natural lens becomes cloudy, blocking light from reaching the retina. Astigmatism is a separate issue caused by an irregular, uneven curvature of the cornea or lens, which prevents light from focusing properly. Modern surgical techniques allow surgeons to address both conditions simultaneously during a single procedure.
Defining Cataracts and Corneal Astigmatism
A cataract is the progressive clouding of the eye’s crystalline lens, typically occurring as a natural part of aging. This cloudiness makes vision seem foggy, hazy, or muted. The lens, located behind the iris, is responsible for about one-third of the eye’s total focusing power.
Astigmatism is a refractive error that arises when the cornea, the clear front surface of the eye, is shaped more like a football than a spherical basketball. This oval shape causes light rays to focus at multiple points instead of a single, precise point on the retina. This results in vision that is stretched, blurred, or distorted.
How Standard Surgery Affects Astigmatism
Cataract surgery involves phacoemulsification, where the cloudy natural lens is removed and replaced with an artificial intraocular lens (IOL). If a standard, spherical IOL is implanted, it does not correct the pre-existing irregularity of the cornea. The primary goal of a standard IOL is simply to replace the clouded lens and restore a clear light pathway.
While removing the natural lens might slightly change the overall refractive error, a standard IOL cannot counteract corneal astigmatism. Patients with significant astigmatism who receive a standard IOL will still need corrective eyeglasses or contact lenses after the procedure. Failing to correct astigmatism during surgery can reduce uncorrected visual acuity and patient satisfaction.
Methods for Simultaneous Astigmatism Correction
Toric Intraocular Lenses (IOLs)
The most effective solution for correcting astigmatism during cataract surgery involves implanting a Toric Intraocular Lens (IOL). Unlike standard lenses, a Toric IOL has different powers in different meridians to neutralize the uneven curvature of the astigmatic cornea. The surgeon must precisely align the Toric lens to the steep axis of the cornea to ensure the correction is positioned correctly.
Toric IOLs are recommended for patients with moderate to high levels of astigmatism, typically one diopter (D) or more, as they offer predictable and stable correction. These lenses successfully treat both the cataract and the refractive error in one procedure. Low-powered Toric IOLs can now correct astigmatism as low as 0.75 D.
Limbal Relaxing Incisions (LRI)
Another technique used to manage astigmatism is Limbal Relaxing Incisions (LRI), which may be performed manually or with a femtosecond laser. This involves making small, partial-thickness incisions in the peripheral clear tissue of the cornea, called the limbus. These incisions cause the cornea to relax and flatten along its steepest meridian, making the overall corneal shape more spherical.
LRI is generally used for patients with lower levels of astigmatism, often less than 1.5 D, or as a supplementary adjustment with a standard IOL. While LRI is a quick procedure, Toric IOLs often provide a higher chance of achieving a target astigmatism correction of 0.5 D or less.
Expected Visual Results After Combined Procedures
Patients who correct their astigmatism simultaneously with cataract removal can expect significant improvement in uncorrected distance vision. The goal is to reduce or eliminate the need for glasses for most daily activities, especially for viewing distant objects. Patients receiving Toric IOLs frequently achieve a residual astigmatism of 0.5 D or less, which is considered an optimal outcome for sharp vision.
A small amount of residual astigmatism is still possible, particularly in cases of severe pre-existing error or if the Toric lens slightly rotates after implantation. This minor remaining error can usually be corrected with a weak pair of distance glasses. If a monofocal Toric lens is selected, patients typically still require reading glasses for close-up tasks, as the lens is focused for distance. Vision stabilization usually takes between three and ten weeks.