Irregular Astigmatism

Corneal topography showing Irregular Astigmatism in a patient’s eye.

Corneal topography showing Irregular Astigmatism in a patient’s eye.

What is irregular astigmatism?

Astigmatism refers to the shape of your cornea.  It is perfectly normal for people to have regular astigmatism that can be corrected with glasses, contact lenses or laser eye surgery.

Irregular astigmatism cannot be corrected by glasses or normal contacts lenses.  It generally occurs after pterygium surgery, in corneal diseases such as keratoconus or pellucid marginal degeneration or after corneal transplants such as penetrating keratoplasty or deep anterior lamellar keratoplasty. 

How is Irregular Astigmatism treated?

Irregular astigmatism can be treated with a topography guided photo-therapeutic keratectomy or T-PTK.  It is sometimes also called a corneal regularisation.  In this procedure the irregular shape of your cornea is mapped with an extremely high-resolution mapping system.  The laser then analyses the map and reshapes your cornea to a more regular shape to minimise your irregular astigmatism.  Sometimes there may be a refractive component to the laser to minimise or remove your need for glasses, however, generally the treatment is designed to give you good vision in glasses, so that you no longer need hard or rigid contact lenses. 

When a topography guided PTK is performed on patients with keratoconus or pellucid marginal degeneration it is often called an “Athens Protocol” procedure.  In these conditions the laser corneal regularisation is combined with corneal collagen cross linking to strengthen the cornea.