Cataracts, a clouding of the eye’s lens, and astigmatism, an imperfect curvature of the eye’s cornea or lens, are distinct conditions that both cause blurry vision. While they arise from different parts of the eye, the development of a cataract can directly influence the other.
How Cataracts Can Change Your Prescription
The formation of a cataract can directly cause or worsen astigmatism. As a cataract develops, proteins in the eye’s lens clump together, making it cloudy, dense, and less flexible. This process alters the lens’s shape and thickness, which can modify how light passes through it. This induces what is known as lenticular astigmatism, originating from the lens itself.
Certain types of cataracts are more likely to induce these changes. Nuclear sclerotic cataracts, which form in the central part of the lens, can harden and change the lens’s refractive index. This alteration means light rays bend incorrectly as they pass through, preventing them from focusing onto a single point on the retina. The result is the development or worsening of astigmatism.
This change happens gradually, and many people might not realize the underlying cause of their worsening vision. They may notice an increase in blurriness or a greater need for frequent updates to their glasses prescription. The progressive thickening of the lens can also cause it to shift slightly, contributing to changes in the degree and axis of astigmatism.
The Impact of Cataract Surgery on Astigmatism
Cataract surgery presents an opportunity to address astigmatism. The procedure involves removing the clouded natural lens and replacing it with an artificial intraocular lens (IOL). For patients with pre-existing astigmatism, surgeons can use specialized IOLs to correct it during the same operation.
Toric IOLs are a specific type of premium lens designed to correct astigmatism. A toric lens has different powers in different meridians to counteract the eye’s irregular shape. Before surgery, detailed measurements of the eye’s curvature are taken to calculate the precise power and orientation needed for the toric IOL. During the procedure, the surgeon carefully aligns the lens to offset the patient’s astigmatism.
While surgery can correct astigmatism, the procedure itself can sometimes induce it. This is known as surgically-induced astigmatism (SIA), and it occurs when the corneal incision slightly alters its curvature. Modern surgical techniques have minimized this risk. Surgeons now use very small incisions that are self-sealing and have a negligible impact on the cornea’s shape.
Managing Astigmatism After Surgery
Following cataract surgery, the goal is to provide the clearest possible vision, but sometimes a small amount of astigmatism, known as residual astigmatism, may remain. This can happen if a standard IOL was used in a patient with minor pre-existing astigmatism or if there were slight variations in healing. Even with advanced toric IOLs, perfect correction is not always achieved, leaving patients with some degree of blurriness.
For most people, managing residual astigmatism is straightforward. A mild prescription for glasses or contact lenses is often sufficient to sharpen vision for specific tasks like reading or driving at night. Many patients find that they can function perfectly well for most daily activities without any correction and only use glasses when they need the sharpest possible focus.
In cases where the residual astigmatism is more significant and bothersome, other corrective procedures are available. A surgeon can perform limbal relaxing incisions (LRI), which are small incisions made on the outer edge of the cornea to make its shape more spherical. Another option is laser vision correction, such as LASIK or PRK, which can be performed months after the eye has fully healed from cataract surgery to fine-tune the vision by reshaping the cornea. These secondary procedures can further reduce or eliminate dependence on glasses.