title: Effect of beam variables on corneal sensitivity after excimer laser photorefractive keratectomy.
abstract: OBJECTIVE
  To investigate changes in corneal touch sensitivity following excimer laser photorefractive keratectomy (PRK) using different beam configurations.
  
  
  METHODS
  20 subjects were given a unilateral -3.00 D correction with either a 5 mm (26 micrograms, n = 10) or 6 mm (42 micrograms, n = 10) beam diameter. Thirty subjects underwent a unilateral -6.00 D correction with 5 mm (62 micrograms, n = 10), 6 mm (78 micrograms, n = 10), or multizone (62 micrograms, 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.
  
  
  RESULTS
  There 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.
  
  
  CONCLUSIONS
  For 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.
authors.affiliation: Department of Optometry and Visual Science, City University, London.
authors.forename: J G
authors.initials: JG
authors.lastname: Lawrenson
authors.forename: M C
authors.initials: MC
authors.lastname: Corbett
authors.forename: D P
authors.initials: DP
authors.lastname: O'Brart
authors.forename: J
authors.initials: J
authors.lastname: Marshall
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003316:Corneal Diseases / Q000209:etiology*; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D018903:Photorefractive Keratectomy / Q000009:adverse effects* / Q000379:methods; D010812:Physical Stimulation; D012678:Sensation Disorders / Q000209:etiology*; D012684:Sensory Thresholds