Astigmatism is a common visual condition characterized by an imperfection in the curvature of the eye’s cornea or lens. Instead of a uniformly spherical shape, the surface is shaped more like a football. This irregular curvature prevents light from focusing evenly onto the retina, leading to blurred or distorted vision at any distance. Because light rays are bent differently along various axes, the resulting image lacks sharpness. This refractive error is highly treatable through various methods aimed at altering or compensating for the eye’s shape. This article explores the established and modern techniques available to correct astigmatism.
Standard Corrective Eyewear
Specialized corrective eyewear is the most common approach to managing astigmatism. Both prescription glasses and contact lenses utilize a unique lens design known as a cylindrical or toric lens. This lens incorporates different powers in different meridians, effectively compensating for the uneven curvature of the eye’s surface. The varying thickness across the lens ensures that incoming light rays are refracted properly to converge sharply on the retina.
Glasses offer a straightforward method, using the toric power ground into the lens itself. Contact lenses, conversely, must maintain a specific orientation on the eye to align the corrective cylinder with the astigmatic axis. Soft toric contact lenses are weighted or shaped to prevent rotation, ensuring the corrective power stays aligned with the irregular curvature. Rigid Gas Permeable (RGP) lenses can also be effective; these harder lenses create a new, smooth refracting surface over the cornea, neutralizing the underlying irregularity with a tear layer.
Temporary Corneal Reshaping
Orthokeratology, or Ortho-K, is a method that temporarily alters the eye’s shape. This procedure involves wearing custom-designed rigid contact lenses, typically only while sleeping overnight. These specialized lenses exert gentle pressure on the central corneal surface, causing a controlled and reversible flattening. The change in curvature effectively reduces or eliminates mild-to-moderate astigmatism.
After the lenses are removed in the morning, the reshaped cornea retains its new, more spherical form throughout the day. This allows the patient to experience clear vision without glasses or contacts during waking hours. Because the corneal tissue has an elastic memory, this effect is not permanent, meaning consistent nightly wear is necessary to maintain the corrected vision. The procedure is often considered for individuals who are not good candidates for surgery or those involved in activities where glasses or daytime contacts are impractical.
Laser Vision Correction
Laser vision correction offers several surgical options for permanent alteration. These procedures work by using an excimer or femtosecond laser to precisely remove microscopic amounts of tissue, thereby reshaping the cornea to correct its uneven curvature. Candidates for these procedures typically have a stable prescription and meet specific corneal thickness requirements.
One widely performed technique is Laser-Assisted In Situ Keratomileusis, or LASIK. This process begins with the creation of a thin, hinged flap on the outermost layer of the cornea. The flap is gently lifted, allowing the laser to ablate the tissue underneath to correct the astigmatism. Once the reshaping is complete, the flap is repositioned, adhering naturally without stitches.
An alternative surface procedure is Photorefractive Keratectomy, or PRK. Unlike LASIK, PRK does not involve creating a permanent corneal flap. Instead, the outer layer of epithelial cells is removed before the excimer laser reshapes the underlying corneal tissue. The epithelial layer must then regenerate over several days, resulting in a slightly longer recovery period compared to LASIK.
Small Incision Lenticule Extraction, or SMILE, is a newer option for certain types of astigmatism. This technique uses a femtosecond laser to create a small, lens-shaped piece of tissue, called a lenticule, inside the intact cornea. The surgeon then extracts this lenticule through a very small peripheral incision, changing the cornea’s overall shape. SMILE avoids creating the large flap of LASIK and the extensive surface healing of PRK.
Implantable Lens Procedures
When laser vision correction is not suitable due to high degrees of astigmatism or thin corneas, surgical options involving internal lens implantation are considered. These procedures bypass the need to reshape the cornea by placing a corrective device inside the eye.
The Implantable Collamer Lens, or ICL, is a permanent, artificial lens placed behind the iris but in front of the natural lens. This lens is custom-designed with toric power to correct the patient’s existing astigmatism and other refractive errors. The procedure is reversible and does not involve the removal of corneal tissue.
Another option involves the use of Toric Intraocular Lenses, or Toric IOLs. These specialized lenses are typically utilized during cataract surgery, where the eye’s natural, cloudy lens is removed. The Toric IOL then replaces the natural lens, simultaneously correcting both the cataract and any pre-existing astigmatism. This approach provides a lasting solution.