title: Contrast sensitivity measured by 2 methods after photorefractive keratectomy.
abstract: OBJECTIVE
  To study contrast sensitivity in eyes that had flying-spot excimer laser photorefractive keratectomy (PRK) and to compare a subjective method (Vision Contrast Test System [VCTS] 6500) and an objective method (visual evoked potential [VEP]) of measuring contrast sensitivity.
  
  
  METHODS
  Istituto Clinica Oculistica, Università degli Studi, Bari, Italy.
  
  
  METHODS
  Contrast sensitivity changes over time were evaluated in 26 eyes. The baseline values were compared with measurements 3, 6, and 12 months after PRK using the VCTS 6500 and VEP. Contrast threshold and VEP amplitude were classified by myopic correction.
  
  
  RESULTS
  Contrast threshold values changed significantly over time (P <.001). Significant differences were found between mean contrast threshold preoperatively and 12 months postoperatively (P <.001) at all spatial frequencies. A significant relationship was established between baseline and 12 month measurements at 18 cycles per degree. Mean VEP amplitude measurements also changed significantly over time (P <.001) and showed a significant relationship between baseline and 12 month measurements (P <.001). A significant relationship was also established between baseline and 12 month VEP amplitude values at 100% of grating contrast. Patients with high myopia complained significantly more at a lower contrast threshold and at lower VEP amplitude values than patients with low myopia.
  
  
  CONCLUSIONS
  Three months after PRK, contrast threshold and VEP amplitude values were reduced. Partial recovery was established at 6 months, although patients reported permanent impairment under low-contrast conditions, especially if the myopia correction was more than 6.0 diopters.
authors.affiliation: Department of Ophthalmology and Otorhinolaryngology, University Hospital of Bari, Bari, Italy. m.vetrugno@oftalmo.uniba.it
authors.forename: M
authors.initials: M
authors.lastname: Vetrugno
authors.forename: G M
authors.initials: GM
authors.lastname: Quaranta
authors.forename: A
authors.initials: A
authors.lastname: Maino
authors.forename: F
authors.initials: F
authors.lastname: Mossa
authors.forename: L
authors.initials: L
authors.lastname: Cardia
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005074:Evoked Potentials, Visual; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000601:surgery; D018903:Photorefractive Keratectomy; D011184:Postoperative Period; D020127:Recovery of Function / Q000502:physiology*; D012029:Refraction, Ocular; D012189:Retrospective Studies