title: A longitudinal study of vergence adaptation in incipient presbyopia.
abstract: BACKGROUND
  To investigate vergence adaptation during the incipient phase of presbyopia, when the amplitude of accommodation approaches the level where the first reading addition is required. The study aimed to assess the ability of the vergence system to counteract changes in the component contributions to the overall vergence response with the decline in the amplitude of accommodation in presbyopia, although previous reports on the nature of changes in accommodative, tonic and proximal vergence are equivocal.
  
  
  METHODS
  Using a 'flashed' Maddox rod technique, an assessment of vergence adaptation to 6delta base-out and 6delta base-in prism was made for 28 subjects (aged 35-45 years at the commencement of the study). The measurements were taken four times over a 2-year period.
  
  
  RESULTS
  Using a repeated measures analysis of variance, the results show that with the decline in amplitude of accommodation, there is a statistically significant reduction in the magnitude of vergence adaptation to both base-out (p < 0.05) and base-in prism (p < 0.01).
  
  
  CONCLUSIONS
  This study shows that with ageing, there is a decrease in the ability of the slow vergence mechanism to overcome a change in fusional vergence demand and would suggest that either the fast component of fusional vergence must cope with any change in fusional vergence demand or that the sum of the accommodative, tonic and proximal vergence responses are virtually stable with age.
authors: Ophthalmic and Physiological Optics Research Group, Neurosciences Research Institute, School of Life and Health Sciences, Aston University, Birmingham B4 7ET, UK.
authors: Fiona J
authors: FJ
authors: Baker
authors: Bernard
authors: B
authors: Gilmartin
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D003290:Convergence, Ocular / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D011305:Presbyopia / Q000503:physiopathology*; D013997:Time Factors