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The relationship between accommodative amplitude and the ratio of central lens thickness to its equatorial diameter in vertebrate eyes
  1. Ronald A Schachar1,
  2. Barbara K Pierscionek2,
  3. Ali Abolmaali3,
  4. Tri Le3
  1. 1Department of Physics, University of Arlington, Arlington, Texas 76019, USA
  2. 2Department of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland BT52 1SA, UK
  3. 3Department of Civil and Environmental Engineering, University of Texas at Arlington, Arlington, Texas 76019, USA
  1. Correspondence to: R A Schachar PO Box 601149, Dallas, TX 75229, USA; ron{at}2ras.com

Abstract

Aim: To determine the relationship between accommodative amplitude and central lens thickness/equatorial lens diameter (CLT/ELD) ratio in vertebrates.

Methods: Midsagittal sections of lenses from fixed, post mortem eyes from 125 different vertebrate species were photographed. Their CLT/ELD ratios were correlated with independently published measurements of their accommodative amplitudes. Using the non-linear finite element method (FEM), the efficiency of zonular traction (the absolute change in central radius of curvature per unit force [|ΔCR|/F]) for model lenses with CLT/ELD ratios from 0.45 to 0.9 was determined.

Results: Vertebrates with CLT/ELD ratios ⩽0.6 have high accommodative amplitudes. Zonular traction was found to be most efficient for those model lenses having CLT/ELD ratios ⩽0.6.

Conclusions: Vertebrates with lenses that have CLT/ELD ratios ⩽0.6 – i.e. “long oval” shapes – have the greatest accommodative amplitudes; e.g. primates, diving birds and diurnal birds of prey. Vertebrates that have oval or spherical shaped lenses, like owls and most mammals, have low accommodative amplitudes. Zonular traction was found to be most efficient when applied to model lenses with CLT/ELD ratios ⩽0.6. The implications of these findings on the mechanism of accommodation are discussed.

  • crystalline lens
  • accommodative amplitude
  • central lens thickness/equatorial lens diameter ratio
  • vertebrate

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Footnotes

  • Published Online First 31 October 2006

  • Competing interests: RAS has a financial interest in the surgical reversal of presbyopia

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