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Impressum
The change in shape of the human crystalline lens with accommodation
1Dubbelman M., 1Van der Heijde G. L., 2Weeber H. A.
1VU Medisch Centrum, Klinische Fysica en Informatica, Postbus 7057, 1007MB, Amsterdam, Nederland; 2Pharmacia Groningen, van Swietenlaan 5, 9728 NX, Groningen, Nederland
Objective: To measure the change in shape of the aging human crystalline
eye lens during accommodation.
Methods: Scheimpflug images were made of 102 subjects ranging in
age between 16 and 65 years at different levels of accommodation. Accommodative
amplitude was attained by focusing on a target with the left eye. This
was controlled by placing lenses in front of this eye at 1.0 D intervals.
When focus had been achieved, an image of the right eye was made using
the Nidek Eas-1000 Scheimpflug camera. Scheimpflug images are distorted
due to the geometry of the camera and the refraction of the cornea and
anterior lens surface. To perform an accurate correction of the images,
the refractive index of the crystalline lens must be known. Therefore,
in addition, axial length was measured using the Zeiss IOLmaster, which
enabled calculation of the refractive index of the lens. Using ray-tracing,
each Scheimpflug image was corrected for distortion, which enabled an
accurate determination of the shape of the lens.
Results: With accommodation, there is a highly significant decrease
of both the anterior and posterior radius of the lens, although the rate
of decrease of the latter is much smaller. Furthermore, the increase of
lens thickness with accommodation is significantly higher than the decrease
of the anterior chamber depth. This indicates that the posterior lens
surface moves backward with accommodation. The anterior surface of the
lens becomes more hyperbolic with accommodation.
Conclusions: Our data on the shape of the lens agrees qualitatively,
but not quantitatively with earlier studies using Scheimpflug imaging
not reliably correcting for distortion. Our experimental data can be used
for the modelling of the refractive properties of the lens.