Influence of shape and gradient refractive index in the accommodative changes of spherical aberration in nonhuman primate crystalline lenses.
OBJECTIVE
To estimate changes in surface shape and gradient refractive index (GRIN) profile in primate lenses as a function of accommodation. To quantify the contribution of surface shape and GRIN to spherical aberration changes with accommodation.


METHODS
Crystalline lenses from 15 cynomolgus monkeys were studied in vitro under different levels of accommodation produced by a stretching system. Lens shape was obtained from optical coherence tomography (OCT) cross-sectional images. The GRIN was reconstructed with a search algorithm using the optical path measured from OCT images and the measured back focal length. The spherical aberration of the lens was estimated as a function of accommodation using the reconstructed GRIN and a homogeneous refractive index.


RESULTS
The lens anterior and posterior radii of curvature decreased with increasing lens power. Both surfaces exhibited negative asphericities in the unaccommodated state. The anterior surface conic constant shifted toward less negative values with accommodation, while the value of the posterior remained constant. GRIN parameters remained constant with accommodation. The lens spherical aberration with GRIN distribution was negative and higher in magnitude than that with a homogeneous equivalent refractive index (by 29% and 53% in the unaccommodated and fully accommodated states, respectively). Spherical aberration with the equivalent refractive index shifted with accommodation toward negative values (-0.070 μm/diopter [D]), but the reconstructed GRIN shifted it farther (-0.124 μm/D).


CONCLUSIONS
When compared with the lens with the homogeneous equivalent refractive index, the reconstructed GRIN lens has more negative spherical aberration and a larger shift toward more negative values with accommodation.
Instituto de Óptica "Daza de Valdés," Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain.
Alberto
A
de Castro
Judith
J
Birkenfeld
Bianca
B
Maceo
Fabrice
F
Manns
Esdras
E
Arrieta
Jean-Marie
JM
Parel
Susana
S
Marcos
D000065:Accommodation, Ocular / Q000502:physiology*; D000818:Animals; D057108:Corneal Wavefront Aberration / Q000503:physiopathology*; D007908:Lens, Crystalline / Q000503:physiopathology*; D008252:Macaca fascicularis; D012029:Refraction, Ocular / Q000502:physiology*; D041623:Tomography, Optical Coherence
GRIN; accommodation; crystalline lens; gradient refractive index; spherical aberration