Astigmatism is a very common type of refractive error where the eye is not perfectly spherical. This imperfect curvature typically occurs on the cornea, the clear front surface of the eye, but can also affect the lens inside the eye. When light rays enter an eye with astigmatism, they do not focus at a single point on the retina; instead, they focus at multiple points, causing vision to be blurry or distorted at various distances. Fortunately, a wide spectrum of options exists to correct this focusing issue, ranging from simple external aids to advanced surgical procedures.
Corrective Lenses: Glasses and Contacts
Corrective lenses represent the most common, non-invasive, and immediate method for correcting astigmatism. Eyeglasses use specially designed spectacle lenses, known as cylindrical lenses, which feature different curvatures in different directions to counteract the eye’s irregular shape. This unique lens design neutralizes the unequal focusing power of the astigmatic eye, ensuring light converges to a single, sharp focal point on the retina. The simplicity and accessibility of glasses make them a practical choice for correcting most levels of astigmatism.
For those preferring not to wear glasses, specialized contact lenses offer a direct correction by sitting on the eye’s surface. The most frequent option is the soft toric contact lens, which is custom-made with different corrective powers across its vertical and horizontal meridians to match the eye’s specific irregularity. These lenses incorporate design features, such as subtle weighting, to prevent rotation and maintain the precise alignment of the cylindrical power.
Another effective contact lens option, particularly for higher or more irregular astigmatism, is the Rigid Gas Permeable (RGP) lens. RGP lenses are firm and maintain their perfectly spherical shape while worn on the eye. The tear film that pools between the rigid back surface of the RGP lens and the irregular front surface of the cornea creates a new, smooth, spherical refractive surface. This tear-layer correction often results in sharper vision compared to soft lenses, although RGP lenses may require a longer initial adjustment period for comfort.
Non-Surgical Corneal Reshaping (Ortho-K)
Orthokeratology, commonly shortened to Ortho-K, is a non-surgical process that temporarily corrects astigmatism and other refractive errors. This method involves wearing specially designed, rigid gas permeable contact lenses only while sleeping. The lenses are custom-fitted based on precise corneal mapping technology to ensure optimal contact with the eye’s surface.
While worn overnight, the lenses apply a gentle, controlled pressure that subtly reshapes the front surface of the cornea. This reshaping effect flattens or adjusts specific areas of the cornea, effectively neutralizing the irregular curvature causing the astigmatism. Upon waking, the lenses are removed, and the temporarily reshaped cornea allows for clear, unaided vision throughout the day. The corrective effect is temporary, requiring consistent nightly wear to maintain the clear daytime vision.
Permanent Laser Correction Options
Laser vision correction procedures offer a permanent solution by surgically altering the corneal tissue to correct the irregular curvature. Laser-Assisted In Situ Keratomileusis (LASIK) is the most widely known procedure. It begins with the creation of a thin, hinged flap on the cornea’s surface using a femtosecond laser. This flap is lifted, and an excimer laser is then used to precisely remove microscopic amounts of underlying corneal tissue, reshaping it to correct the astigmatism. The flap is subsequently repositioned, allowing for a rapid visual recovery, often within 24 hours.
A flap-free alternative is Photorefractive Keratectomy (PRK), the original laser eye surgery. In PRK, the outer layer of the cornea, the epithelium, is gently removed before the excimer laser reshapes the underlying corneal tissue. Because the epithelium must grow back naturally, the visual recovery is slower and may involve more initial discomfort compared to LASIK. PRK is often recommended for patients with thinner corneas or those with specific lifestyle needs where a flap might be a concern.
A newer, minimally invasive technique is Small Incision Lenticule Extraction (SMILE). A femtosecond laser creates a small, lens-shaped piece of tissue called a lenticule inside the intact cornea. This lenticule is then removed through a tiny keyhole incision, which permanently reshapes the cornea without creating a large flap. Candidacy for any of these laser procedures requires a stable prescription, adequate corneal thickness, and an absence of other eye diseases.
Surgical Lens Implants
For patients with very high refractive errors, severe astigmatism, or those who are not ideal candidates for corneal laser correction, surgical lens implants offer an alternative permanent solution. One option is the implantation of a Phakic Intraocular Lens (IOL), sometimes called an Implantable Collamer Lens (ICL). These artificial lenses are implanted inside the eye, typically placed in front of the natural lens, which remains in place.
Toric models of these Phakic IOLs are designed to correct astigmatism in addition to nearsightedness or farsightedness. The procedure is reversible and does not involve removing any corneal tissue, preserving the cornea’s natural structure. The other primary lens-based procedure is Refractive Lens Exchange (RLE), where the eye’s natural lens is removed, similar to cataract surgery. This is followed by the implantation of a Toric IOL, an artificial lens containing the specific cylindrical power needed to correct the astigmatism. RLE is a common approach for older adults with high prescriptions and can prevent the need for future cataract surgery.