title: Optimal time following fluorescein instillation to evaluate rigid gas permeable contact lens fit.
abstract: OBJECTIVE
  To examine the optimum time at which fluorescein patterns of gas permeable lenses (GPs) should be evaluated.
  
  
  METHODS
  Aligned, 0.2mm steep and 0.2mm flat GPs were fitted to 17 patients (aged 20.6 ± 1.1 years, 10 male). Fluorescein was applied to their upper temporal bulbar conjunctiva with a moistened fluorescein strip. Digital slit lamp images (CSO, Italy) at 10× magnification of the fluorescein pattern viewed with blue light through a yellow filter were captured every 15s. Fluorescein intensity in central, mid peripheral and edge regions of the superior, inferior, temporal and nasal quadrants of the lens were graded subjectively using a +2 to -2 scale and using ImageJ software on the simultaneously captured images.
  
  
  RESULTS
  Subjectively graded and objectively image analysed fluorescein intensity changed with time (p < 0.001), lens region (centre, mid-periphery and edge: p < 0.05) and there was interaction between lens region with lens fit (p < 0.001). For edge band width, there was a significant effect of time (F = 118.503, p < 0.001) and lens fit (F = 5.1249, p = 0.012). The expected alignment, flat and steep fitting patterns could be seen from approximately after 30 to 180 s subjectively and 15 to 105 s in captured images.
  
  
  CONCLUSIONS
  Although the stability of fluorescein intensity can start to decline in as little as 45 s post fluorescein instillation, the diagnostic pattern of alignment, steep or flat fit is seen in each meridian by subjective observation from about 30s to 3 min indicating this is the most appropriate time window to evaluate GP lenses in clinical practice.
authors.affiliation: Ophthalmic Research Group, Life and Health Sciences, Aston University, Birmingham, UK. Electronic address: j.s.w.wolffsohn@aston.ac.uk.
authors.forename: James S
authors.initials: JS
authors.lastname: Wolffsohn
authors.affiliation: Ophthalmic Research Group, Life and Health Sciences, Aston University, Birmingham, UK.
authors.forename: Ali
authors.initials: A
authors.lastname: Tharoo
authors.affiliation: Ophthalmic Research Group, Life and Health Sciences, Aston University, Birmingham, UK.
authors.forename: Nikita
authors.initials: N
authors.lastname: Lakhlani
mesh_terms: D000328:Adult; D003261:Contact Lenses; D003287:Contrast Media / Q000008:administration & dosage; D019781:Corneal Topography / Q000379:methods*; D005260:Female; D019793:Fluorescein / Q000008:administration & dosage*; D005456:Fluorescent Dyes / Q000008:administration & dosage; D015590:Fluorophotometry / Q000379:methods*; D005740:Gases; D006801:Humans; D007322:Instillation, Drug; D008297:Male; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D010539:Permeability; D017755:Prosthesis Fitting / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D005456:Fluorescent Dyes; D005740:Gases; D009883:Ophthalmic Solutions; D019793:Fluorescein
keywords: Fit evaluation; Fluorescein; Gas permeable (GP); Rigid gas permeable (RGP)