Laser Corrective Eye Surgery
Source: AOPA (Australia) magazine (Dec 95 Issue)

I am the holder of a Class-1 Medical Certificate which specifies a requirement for vision correction due to Short Sightedness. Can you please advise me of the benefits and/or problems which could be expected from Laser Corrective Surgery?

The excimer laser was introduced in 1983 and, since then, has been used to perform laser corrective surgery on the eyes of myopic (short sighted) individuals. The procedure involves using the laser to burn away (ablate) a thin layer from the 4 - 7 mm diameter central area at the front of the eye (cornea). This acts to change the shape of the front of the eye and, if all goes according to plan, correct the visual problem. This procedure is usually called Photo-Refractive Keratectomy - PRK.

Being a relatively new procedure the problems and complications of PRK surgery are not, yet, terribly well documented as are currently under intensive study. The information provided here is based on a recently published review article as well as information provided by USAF colleagues.

Astigmatism if the ablation zone is placed off centre.

If the area of ablation doesn't end up exactly as planned an alteration of the eye's visual axis (astigmatism) might result.

At night if the pupil dilates beyond the zone of ablation (the central 4 - 7 mm of the eye) then optical aberrations may ensue causing blur, halos, and decreased night vision.

The deeper the laser ablation the thinner the remaining cornea. This may compromise the biomechanical structure and reduce corneal stability. Future studies may clarify this.

Corneal healing, scarring, and regression. After the PRK procedure is performed a period of healing occurs. This healing often leads to further changes in the function of the eye - usually towards the original problem. Some surgeons try to overcorrect when performing PRK to allow for this 'regression'.

The deeper the laser ablation (i.e. the worse the myopia to start with) the greater the scarring or haze, and the greater the degree of regression of correction.

'Haze' and 'Halos' in the vision can also occur because of scarring of the front of the eye. One study reported that 10% of people who had had their first eye treated using PRK (the usual practice is to operate on the eyes separately - just in case) declined having their other eye treated a year later because of persistent haze and/or halos.

Corneal stability

A deep PRK ablation (cases of more severe myopia) may result in physical weakening of the structure of the eye. This might make other physical injuries (i.e. a piece of metal in your eye) more likely to cause more serious damage. This potential problem has currently not been substantiated and remains theoretical conjecture.

Aerospace considerations

While PRK appears to be effective, safe, and satisfactory for many of the general population some of its problems might cause a pilot second thoughts.

In one group studied 78% experienced disturbances in night vision. A pilot might not find this risk acceptable given the possible high workload and visual demands of some night flying.

A small, but not insignificant, number of PRK subjects end up with worse vision than before the procedure.

It is also theoretically possible for PRK to interfere with your visual depth perception. This could result if each eye ends up with a different degree of correction - due to the original amount of ablation or the subsequent scarring / regression process.

In conclusion

PRK offers the general population some advantages over other myopia correction options. It does, however, also have a number of side effects that might be of unacceptable risk to a pilot.

Me? I probably wouldn't consider PRK at the moment. I'd want to wait another 5 years or so until we had a much better understanding of this, relatively new, procedure.

This response to your letter is brief and quite abridged. If you'd like more information please write with your return address and I'll post you some of the literature.