title: Entrance pupil size predicts retinal illumination in darkly pigmented eyes, but not lightly pigmented eyes.
abstract: OBJECTIVE
  We determined the effect of entrance pupil size on retinal illumination. The influence of unilateral miosis on the magnitude of the pupil light reflex was studied to ascertain how a clinically significant anisocoria influences the relative afferent pupil defect (RAPD).
  
  
  METHODS
  Miosis was induced by topical 1% pilocarpine in the right eye of 14 healthy subjects with normal eyes. The interocular difference in retinal illumination was assessed by computerized pupillometry from the stimulus response curve of the right and left eyes. The main outcome measure was the RAPD, determined by computerized pupillography, at baseline and after pilocarpine-induced anisocoria.
  
  
  RESULTS
  Induced anisocoria produced a significant change in RAPD from baseline (mean = 1.60 dB in the miotic eye, P = 0.007). However, anisocoria correlated with RAPD only in subjects with darkly pigmented irides (Pearson correlation coefficient 0.793, P = 0.05).
  
  
  CONCLUSIONS
  In darkly pigmented eyes, entrance pupil size significantly influenced the retinal illumination. However, retinal illumination of lightly pigmented eyes is relatively independent of entrance pupil size, presumably due to extrapupillary transmission of light through the iris and sclera. This has important implications in understanding the potential influence of anisocoria on the RAPD and also greater susceptibility of lightly pigmented eyes to light toxicity.
authors.affiliation: Department of Ophthalmology and Visual Science, University of Iowa Hospitals and Clinics and Iowa City VA Medical Center, Iowa City, Iowa 52242, USA. randy-kardon@uiowa.edu
authors.forename: Randy H
authors.initials: RH
authors.lastname: Kardon
authors.forename: Sungpyo
authors.initials: S
authors.lastname: Hong
authors.forename: Aki
authors.initials: A
authors.lastname: Kawasaki
mesh_terms: D000328:Adult; D005127:Eye Color / Q000528:radiation effects*; D005260:Female; D006801:Humans; D008027:Light; D008029:Lighting; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D010857:Pigment Epithelium of Eye / Q000502:physiology / Q000528:radiation effects*; D011680:Pupil / Q000502:physiology*; D012016:Reference Values; D012025:Reflex, Pupillary / Q000528:radiation effects*
keywords: light damage; pupil light reflex; pupils; retinal illumination