Astigmatism is a type of refractive error in which nonspherical (variable) curvature of the cornea or lens causes light rays of different orientations (vertical, oblique, horizontal) to focus at different points. Thus, the eye failures to focus images sharply on the retina, causing blurred vision.
The following symptoms can point to astigmatism:
- Blurred or distorted vision
- Eye strain or discomfort
- Difficulty with night vision
In the normally refracted (emmetropic) eye, entering light rays are focused on the retina by the cornea and the lens, creating a sharp image that is transmitted to the brain. During accommodation, the ciliary muscles adjust lens shape to properly focus images. In astigmatism, irregular curvature of the cornea or the lens prevents the normal focusing of the image on the retina.
The goal of treatment is to compensate for the inability of your eyes to focus on nearby objects. Treatment options include wearing corrective eyeglasses or contact lenses, as well as undergoing refractive surgery.
Refractive surgery alters the curvature of the cornea to focus light more precisely on the retina. The goal of refractive surgery is to decrease dependence on eyeglasses or contact lenses.
The two most common refractive surgery procedures are femtosecond laser-assisted in situ keratomileusis (Femto-LASIK) and Small Incision Lenticule Extraction (SMILE).
In Femto-LASIK, a surgeon separates a small flap of tissue from the cornea, using a femtosecond laser. The new profile of the cornea is created with a high-precision excimer laser so that light rays will be focused exactly on the retina. After changing the cornea surface, a flap of corneal tissue, which was separated in the first stage, is turned back. The flap is replaced without suturing. Because surface epithelium is not disrupted centrally, vision returns rapidly. Most people notice a significant improvement the next day.
SMILE laser eye surgery is performed using a VisuMax femtosecond laser, which is proprietary technology of Carl Zeiss Meditec. In the SMILE procedure, the surgeon uses a femtosecond laser to create a small, lens-shaped bit of tissue (lenticule) within the cornea. Then, with the same laser, a small arc-shaped incision is made in the surface of the cornea, and the surgeon extracts the lenticule through this incision and discards it. With the tiny lenticule removed, the shape of the cornea is altered, correcting nearsightedness. The corneal incision heals within a few days without stitches, and sharper vision occurs very quickly.
In some cases, photorefractive keratectomy (PRK) is performed to correct astigmatism. In PRK, the corneal epithelium is removed and then the excimer laser is used to sculpt the anterior curvature of the corneal stromal bed. The epithelium typically takes 3 to 4 days to regenerate. PRK may be more suitable for patients with thin corneas or anterior basement membrane dystrophy.
There are many other ways to correct astigmatism, which, in particular, include intraocular lens implantation and astigmatic keratotomy. The decision to choose the most optimal treatment tactics is made by the surgeon, taking into account the individual characteristics of the patient.