title: An experimental study of the elastic properties of the human Bruch's membrane-choroid complex: relevance to ageing.
abstract: OBJECTIVE
  To investigate the mechanical properties (stress-strain relation, elasticity, hysteresis, response to stress spikes and drops) of isolated human Bruch's membrane-choroid, as well as the effect of ageing and aged related macular degeneration (AMD).
  
  
  METHODS
  13 Bruch's membrane-choroid complexes were obtained from human donors (21-97 years). Two samples (aged 85 and 95) showed signs of AMD including large, soft drusen, choroidal neovascularisation, and/or disciform scars. Various hydrostatic pressures (stress) were applied to the choroidal surface of mid-peripheral samples mounted in a modified open Ussing chamber. Linear scans of the tissue were recorded by optical coherence tomography (OCT) and the pressure induced deformation (strain), elasticity, hysteresis, and response to pressure spikes and drops measured.
  
  
  RESULTS
  The elasticity of human Bruch's membrane-choroid complex decreased linearly with ageing (p<0.001) after the age of 21 with an approximate reduction of 1% per year. The decrease was not exaggerated in AMD. The recoil capacity of Bruch's membrane-choroid was not affected by ageing. The response to pressure spikes/drops was similar in age matched normal and AMD eyes. The results suggest that although the aged induced decrease in Bruch's membrane elasticity may contribute to breaks in this membrane in AMD leading to neovascularisation this is not sufficient. The presence of other factors is required for its development.
  
  
  CONCLUSIONS
  The elasticity of Bruch's membrane-choroid complex decreases with age while recoil capacity does not. The decrease was not exaggerated in AMD.
authors.affiliation: Department of Ophthalmology, St Thomas's Hospital, London, UK. mugarte@doctors.org.uk
authors.forename: M
authors.initials: M
authors.lastname: Ugarte
authors.forename: A A
authors.initials: AA
authors.lastname: Hussain
authors.forename: J
authors.initials: J
authors.lastname: Marshall
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D016570:Bruch Membrane / Q000502:physiology* / Q000503:physiopathology; D002829:Choroid / Q000502:physiology* / Q000503:physiopathology; D004548:Elasticity; D005615:Freezing; D006801:Humans; D008268:Macular Degeneration / Q000503:physiopathology; D008875:Middle Aged; D011312:Pressure; D012212:Rheology; D013314:Stress, Mechanical