Laboratory science
Effect of beam variables on corneal sensitivity after excimer
laser photorefractive keratectomy
a Applied Vision Research Centre, Department
of Optometry and Visual Science, City University, London, b Reta Lila Weston Institute of Neurological Studies,
University College London Medical School, c Department of Ophthalmology, St Thomas's Hospital, London
Correspondence to: Dr J G Lawrenson, Department of Optometry and Visual Science, City University, Goswell Road, London EC1V 7DD.
Accepted for publication 10 April
1997
AIM
To investigate changes in corneal touch
sensitivity following excimer laser photorefractive keratectomy (PRK)
using different beam configurations.
METHODS20 subjects were given a unilateral
3.00 D correction with either a 5 mm (26 µm, n=10) or 6 mm (42 µm, n=10) beam diameter. Thirty subjects underwent a unilateral
6.00 D correction with 5 mm (62 µm, n=10), 6 mm (78 µm, n=10),
or multizone (62 µm, n=10) treatments. The multizone treatment was 6 mm in diameter with the depth of the 5 mm treatment. Corneal
sensitivity was measured using a slit-lamp mounted Cochet-Bonnet
aesthesiometer before and at 1, 3, 6, and 12 months after PRK. Stimulus
locations included points lying within the ablated zone (central) and
outside (peripheral). These were compared with the equivalent locations
in control (untreated) eyes.
RESULTSThere was a significant reduction in
corneal sensitivity within the central (ablated) zone in all treatment
groups after PRK. In most groups a return to full sensitivity was
achieved by 6 months with the exception of the multizone treatment
group which showed significant corneal hypoaesthesia at 12 months.
Peripheral corneal sensitivity was also reduced in this group up to 3 months after the procedure. A comparison between the 3.00 D and
6.00 D treatment groups showed no significant difference. However, combining data from all treatment groups, a significant correlation was
found between the interocular difference in central corneal sensitivity
and postoperative haze at 3 and 6 months.
CONCLUSIONSFor corrections up to 6.00 D
ablation depth and treatment zone diameter do not appear to be
clinically important determinants of corneal hypoaesthesia. In
contrast, postoperative corneal haze appears to correlate with
sensitivity loss.
© 1997 by British Journal of Ophthalmology
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