Contrast sensitivity is also a major concern for PRK patients. Researchers at Moorfield’s Eye Hospital in London reported that 30 per cent of its PRK patients suffered a loss of contrast sensitivity within two years of surgery (Refractive Surgery Symposium, London 2001) - and the same symposium heard that half of all LASIK patients suffered a similar loss, one year after surgery.

The LASIK technique can cause the cornea to weaken in up to 40 per cent of all cases (Lancet, 2003; 361: 1225-6) and, sometimes, the weakened cornea resumes its original shape - so the myopia returns.

One study reported on a variety of complications following LASIK surgery. Of the 24 cases, 13 of the complications occurred during the procedure, and the rest afterwards. The technique, the researchers concluded, could result in serious complications that can lead to visual loss (Eur J Ophthalmol, 2003; 13: 139-45).

Patients may also have to go through a second, corrective operation. In one study of 1306 LASIK patients, over 10 per cent had to have a second operation, a likelihood that increases with age, the degree of initial correction and the extent of astigmatism (Ophthalmology, 2003; 110: 748-54).

As with PRK, postoperative infection is also a concern for the LASIK patient. One study found that keratitis could occur up to 450 days after surgery, and was serious enough to threaten vision (Ophthalmology, 2003; 110: 503-10).

The US Food and Drug Ad-ministration (FDA) is equally unsure of the LASIK technique. According to its website (www. fda.gov), LASIK is 'an option for risk takers'.

LASEK is a newer technique, so there are fewer studies into its efficacy and safety. However, one recent study from Japan urges caution. After studying the progress of 42 LASEK patients, the researchers reported postoperative complications such as pain, delayed recovery of visual sharpness and corneal haze (Nippon Ganka Gakkai Zasshi, 2003; 107: 249-56).

Compared with PRK, LASEK may result in less discomfort in the early postoperative period, faster visual recovery and less haze, but these claims, made by LASEK proponents, need to be vindicated in long-term trials, say researchers at the University of Washington (Semin Ophthalmol, 2003; 18: 2-10).

In general, complications that can develop after any of these three procedures have included:

* Eye infections (Ophthalmology, 2003; 110: 743-7; J Cataract Refract Surg, 2002; 28: 722-4; J Cataract Refract Surg, 2001; 27: 471-3)

* Dry eye with compromised tear function (Am J Ophthalmol, 2001; 132: 1-7)

* Strabismus (‘cross-eyes’) (Yonsei Med J, 2000; 41: 404-6)

* Detached retina (Am J Ophthalmol, 1999; 128: 588-94)

* Macular damage (Am J Ophthalmol, 2001; 131: 666-7)

* Vision disturbance due to optic nerve damage (Am J Ophthalmol, 2000; 129: 668-71)

* Irregular astigmatism (a misshapen cornea, causing blurred or distorted vision) caused by surgical complications (Rev Optom, May 1999)

* Impaired night vision and loss of contrast sensitivity, making it hard to see objects against a similarly coloured background (Med Post, 8 June 2000)

* Long-term weakening and thinning of the cornea, leading to a risk of further myopia (Ophthalmology, 2001; 108: 666-72).

Corneal weakening and corneal distortion are ‘serious’ complications, according to Dr Jory. They cause myopia that, in some cases, becomes progressively worse. 'No one knows the rate of risk or the timescale,' he says.