What is an astigmatism?
An astigmatism is a refractive error caused by asymmetrical meridians of the eyes' lenses. It may be in the cornea, crystalline lens or we have even heard of an astigmatism in the retina.
In general, this asymmetry occurs in the cornea, which has an oval or melon shape. As the corneal lens is not regular, it leads to incorrect focus of the images in the retina.
When are incisions indicated?
In patients who have had a cornea transplant, the astigmatism is usually 4 dioptres on average and we come across cases with many more dioptres to correct.
This is due to the sutures, the cicatrisation of the cornea, etc. One of the techniques we have for correcting the astigmatism or at least trying to reduce the dioptres is relaxing incisions.
How are they performed?
The relaxing incisions are performed with a laser or a slit knife. Some incisions are made in the more curved meridians to try relax them and restore the cornea's normal spherical shape.
When they are made with a laser, the treatment is simple, usually lasting 3 or 4 minutes. It is performed with topical anaesthesia and the patient can go home immediately after surgery.
The relaxing incisions made with the slit knife are usually undertaken in the surgical theatre during other operations like cataract surgery.
The results are good but the patient must be informed of the amount of astigmatism they have and the amount we expect to correct.
They are not techniques with 100% precision. Normally, a result of 50% of correction and 70% of the patient's refractive error is obtained, which largely improves the eyesight without correction and on many occasions allows the patients to wear suitable glasses or tolerate contact lenses better.