The relationship between accommodative amplitude and the ratio of central lens thickness to its equatorial diameter in vertebrate eyes

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 [|DCR|/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.

MRI study of the changes in crystalline lens shape with accommodation and aging in humans

“…The increase in the lens thickness to equatorial diameter ratio shows that the crystalline lens becomes more rounded with age. Across vertebrate species, a flattened lens shape in the unaccommodated state leads to greater change in lens shape with an effort to accommodate (Fisher, 1969;Schachar, Pierscionek, Abolmaali, & Le, 2007). Schachar suggested that lens central thickness to lens equatorial diameter ratio of e0.60 is commonly seen in animals that have the capacity to accommodate (Schachar et al, 2007).…”

“…Across vertebrate species, a flattened lens shape in the unaccommodated state leads to greater change in lens shape with an effort to accommodate (Fisher, 1969;Schachar, Pierscionek, Abolmaali, & Le, 2007). Schachar suggested that lens central thickness to lens equatorial diameter ratio of e0.60 is commonly seen in animals that have the capacity to accommodate (Schachar et al, 2007). In the current study, while the LT/ED ratio of the crystalline lens increases with age (0.50 at 65 years of age compared to 0.41 at 22 years), it is still within the limits seen for accommodating animal species (i.e., e0.60).…”

Comparison of Lens Thickness Measurements Using the Anterior Segment Optical Coherence Tomography and A-scan Ultrasonography

“…[1][2][3] Thickening and anterior positioning of the lens is recognized as a major anatomic predisposing factor for the development of angle closure. 2,4,5 A-scan ultrasonography (A-scan US) and Scheimpflug photography are the techniques commonly used for the LT measurement in vivo.…”

Topographical changes of biconvex objects during equatorial traction: an analogy for accommodation of the human lens

“…Human and primate lenses have a similar ratio of their central thickness to equatorial diameter after birth, always ⩽0.6 49. Interestingly, animals that have minimal accommodative amplitude—such as mice, dogs, cats, rabbits, goats, sheep, cows, and horses—have lenses with minor axis to major axis ratios greater than 0.6 52 – 56…”