Topography Guided Laser Surface Ablation & Collagen Cross Linking for Keratoconus

There have been interesting developments in the treatment of corneal ectasia with topography guided laser surface ablation and collagen cross linking .

Consider this recent example case – a 26 year old truck driver who is having difficulty driving. He has noticed increased glare, haloes and particularly difficulty with night vision. The right eye is unaffected, whilst the left eye has poor vision. Without glasses, the right eye sees 6/5, at the bottom of the eye chart. The left eye sees 6/60 (20/200), the top letter on the chart. The left eye sees poorly with spectacles, but can be corrected to see well with a hard contact lens. Unfortunately this man finds the contact lens to uncomfortable to wear.

The cause for the poor vision in the left eye is a condition known as keratoconus, where the cornea bulges and becomes egg shaped instead of being round. There are a number of treatment options, with more advances keratoconus requiring transplantation of the cornea from a donor. Whilst corneal transplantation offers very good results, the recovery is slow and there are risks such as rejection of the transplant. 

A relatively new development is the use of the excimer laser, used for laser vision correction, to correct keratoconus and similar conditions knwon as corneal ectasias – pellucid marginal degeneration and post LASIK ectasia. Traditionally, laser vision correction has not been an option to treat corneal ectasia. Until relatively recently the ability of the laser to customise the treatment was limited. The use of corneal topography – a map of the shape of the cornea – allows the eximer laser to improve the shape of the eye and improve vision in corneal ectasia.

The other problem with the excimer laser is  that excimer laser vision correction reduces the strength of the cornea as the laser thins the cornea to a degree. Combining laser vision correction with collagen cross linking allows the treatment to be performed in weak corneas with a greater degree of safety. Collagen cross linking increases the strength of the cornea which reduces the risk of further bulging of the cornea. 

So combining corneal topography, the excimer laser and collagen cross linking gives a new treatment option for corneal ectasia. Back to the example:

Corneal Topographic Map – Left before treatment, middle after treatment, right showing the “difference” map of how the laser has changed the corneal shape.

The corneal map on the left side shows an irregular corneal shape. The colours represent different curvatures of the cornea similar to isobars on a weather map. Following treatment with topography guided laser surface ablation and collagen cross linking the shape has become much more regular. The vision improved to 6/12 three weeks following the treatment, and to 6/9 (or 20/30 in imperial measure) with a small spectacle prescription. The left eye now has much more useful vision, and the patient can keep his licence. 

This treatment is not suitable for all patients with ectasia, for example severe ectasia is not suitable. For selected patients this treatment can offer a significant improvement in vision. This treatment is not the same as typical laser vision correction where the eye is otherwise normal – the risks are greater, and the improvement in vision is less predictable. However where the alternative is a corneal transplant, it is an option worth considering.

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