title: The effects of photochromic lenses on visual performance.
abstract: BACKGROUND
  The purpose of the current study was to evaluate the effects of filtering by an activated photochromic lens on visual performance in healthy adults. Glare disability, glare discomfort, heterochromatic contrast thresholds and photostress recovery time were assessed.
  
  
  METHODS
  A subject-masked, randomised, cross-over design was employed. Seventy-five healthy adults were recruited, aged 19 to 73 years (mean = 45.61 ± 13.24 years). Visual functions were measured using three different photochromic lenses that were partially activated with a steady state transmittance of 63 per cent T (Gray1), 71 per cent T (Gray2), and 71 per cent T (Brown). These lenses were compared with a clear (92 per cent transmission) polycarbonate lens. Glare disability was assessed as the intensity of a white (xenon)-light annulus necessary to obscure a central grating target. Heterochromatic contrast thresholds were measured as absolute thresholds for a monochromatic 570 nm target superimposed on a 460 nm circular background. Glare discomfort was quantified using bio-imaging of the squint response as well as a Likert-based self-report scale. Photostress recovery time was recorded as the time necessary to regain sight of a grating target after intense light exposure. Glare discomfort and photostress recovery were only assessed for the Gray1 lens compared to placebo. Lens order was randomised between subjects and conditions.
  
  
  RESULTS
  All visual functions measured were significantly improved (p < 0.05) for all of the activated photochromic lenses tested versus the clear lens. In the glare disability and heterochromatic contrast conditions, numeric differences (p < 0.09) were also seen between each of the three different activated photochromic lens types. Glare discomfort and photostress recovery times were improved in the Gray1 condition, as quantified by both the squint and subjective responses (p < 0.05).
  
  
  CONCLUSIONS
  Adding filtering via a photochromic lens significantly increased subjects' abilities to cope with intense broadband and shortwave lighting conditions and to adapt back to normal viewing after being presented with an intense photostressor.
authors.affiliation: Human Biofactors and Vision Sciences Laboratories, Behavioral and Brain Sciences Program, Department of Psychology, The University of Georgia, Athens, Georgia, USA.|Harmonized Scientific Consulting, LLC, Watkinsville, Georgia, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Renzi-Hammond
authors.affiliation: Human Biofactors and Vision Sciences Laboratories, Behavioral and Brain Sciences Program, Department of Psychology, The University of Georgia, Athens, Georgia, USA. bhammond@uga.edu.
authors.forename: Billy R
authors.initials: BR
authors.lastname: Hammond
mesh_terms: D000328:Adult; D000368:Aged; D015350:Contrast Sensitivity; D018592:Cross-Over Studies; D005135:Eye Protective Devices; D005139:Eyeglasses; D019466:Glare; D006801:Humans; D008875:Middle Aged; D011446:Prospective Studies; D014792:Visual Acuity
keywords: chromatic contrast; glare; photochromic lenses; photostress; visual performance