ASTIGMATISM AND ASTIGMATIC KERATOTOMY

What is astigmatism?

Astigmatism is a condition where images are not clearly seen at any distance. Astigmatism represents an irregular corneal curvature, with steeper and flatter areas. Instead of the cornea having a spherical shape like a basketball, it has an elliptical shape like a football in Australian rules or Rugby (see below).

One means of surgically correcting astigmatism is by Astigmatic Keratotomy. The technique is well established. It is an incisional refractive surgery, which uses tangential arcuate corneal incisions to correct either congenital or induced astigmatism. Incisions are made in the peripheral cornea which cause flattening of the steeper portion of the cornea. This technique is now commonly combined with cataract surgery to improve the uncorrected visual acuity.

This technique has several advantages and disadvantages to refractive surgical techniques that directly alter corneal curvature (such as laser techniques). Advantages include the absence of a central surgery and healing process, reduced postoperative pain, and a rapid effect. Disadvantages common to incisional refractive surgical techniques include an overall reduction in the strength of the eye.

Post Operative Care

Usually little more than a scratchy eye sensation is experienced during the first day and after that nothing. Antibiotic drops (usually Chrloramphenicol) are used 4 times a day until the epithelium is healed. The refraction may fluctuate for about 1 month and at that time enhancement may be performed if necessary. A conservative approach to surgery is best to avoid overcorrection.

Possible Complications of Astigmatic Keratotomy (AK)

1. Surgical perforation of the cornea (rare).

If a microperforation occurs during the incision, the procedure may be aborted, to be completed later. If a perforation occurs, a suture may be required to close it. However in AK, or Limbal Relaxing Incisions (LRI), perforation is very uncommon because of the relative thickness of the cornea. Theoretically damage to the iris and lens could occur in a perforation. This would be very serious, but is extremely rare, and has not ocurred in the author's experience.

2. Infection (rare).

If the incision becomes infected and particularly if there is a perforation, the eye is at risk of endophthalmitis (infection involving the structures inside the eye). This condition requires intensive treatment with topical, local, and systemic antibiotics. There is a risk of complete loss of vision following endophthalmitis. The incidence of visual loss from serious infection is about 1 in 5000 cases. Full sterile precautions are taken and prophylactic antibiotic eye drops are used to minimize the risk of infection.

3. Overcorrection (uncommon) and undercorrection (common).

The exact outcome is always uncertain due to variability in individual healing response so that some patients may be overcorrected or undercorrected. Further surgery to relieve the undercorrection is necessary in about 20% of cases.

4. Instability of refraction (usual).

In the immediate post op period there is fluctuation up until about 2 months.

5. Weakening of the cornea (always).

If the cornea has several deep incisions, it is more prone to rupture if a direct blow is received. This has been reported in Radial Keratotomy but not in simple AK. In spite of the above-mentioned complications, the chance of having surgery without complications is 99%. If complications do develop, treatment is possible and nearly always successful.