title: Gene-environment interactions and aging visual function: a classical twin study.
abstract: OBJECTIVE
  To elucidate the contribution of environmental versus genetic factors to the significant losses in visual function associated with normal aging.
  
  
  METHODS
  A classical twin study.
  
  
  METHODS
  Forty-two twin pairs (21 monozygotic and 21 dizygotic; age 57-75 years) with normal visual acuity recruited through the Australian Twin Registry.
  
  
  METHODS
  Cone function was evaluated by establishing absolute cone contrast thresholds to flicker (4 and 14 Hz) and isoluminant red and blue colors under steady state adaptation. Adaptation dynamics were determined for both cones and rods. Bootstrap resampling was used to return robust intrapair correlations for each parameter.
  
  
  METHODS
  Psychophysical thresholds and adaptational time constants.
  
  
  RESULTS
  The intrapair correlations for all color and flicker thresholds, as well as cone absolute threshold, were significantly higher in monozygotic compared with dizygotic twin pairs (P<0.05). Rod absolute thresholds (P = 0.28) and rod and cone recovery rate (P = 0.83; P = 0.79, respectively) did not show significant differences between monozygotic and dizygotic twins in their intrapair correlations, indicating that steady-state cone thresholds and flicker thresholds have a marked genetic contribution, in contrast with rod thresholds and adaptive processes, which are influenced more by environmental factors over a lifetime.
  
  
  CONCLUSIONS
  Genes and the environment contribute differently to important neuronal processes in the retina and the role they may play in the decline in visual function as we age. Consequently, retinal structures involved in rod thresholds and adaptive processes may be responsive to appropriate environmental manipulation. Because the functions tested are commonly impaired in the early stages of age-related macular degeneration, which is known to have a multifactorial etiology, this study supports the view that pathogenic pathways early in the disease may be altered by appropriate environmental intervention.
  
  
  BACKGROUND
  The authors have no proprietary or commercial interest in any materials discussed in this article.
authors.affiliation: Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Hogg
authors.forename: Peter N
authors.initials: PN
authors.lastname: Dimitrov
authors.forename: Mohamed
authors.initials: M
authors.lastname: Dirani
authors.forename: Mary
authors.initials: M
authors.lastname: Varsamidis
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Chamberlain
authors.forename: Paul N
authors.initials: PN
authors.lastname: Baird
authors.forename: Robyn H
authors.initials: RH
authors.lastname: Guymer
authors.forename: Algis J
authors.initials: AJ
authors.lastname: Vingrys
mesh_terms: D000368:Aged; D000375:Aging / Q000235:genetics*; D055253:Color Vision / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology; D003623:Dark Adaptation; D004777:Environment; D005260:Female; D005796:Genes / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology; D012042:Registries; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D014787:Vision Tests; D014792:Visual Acuity / Q000235:genetics*