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Nguyen Khoi Tram, Matthew Aaron Reilly, Katelyn E Swindle-Reilly; The Presence of Accommodative Tissues Influences the Shape of the Developing Eye. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3002.
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© ARVO (1962-2015); The Authors (2016-present)
In the early developmental stages of the vertebrate eye, the cornea and sclera have similar radii. Through normal growth, the radius of the cornea becomes smaller than that of the sclera, resulting in the usual corneal bulge in the anterior of the eye. Previous experiments demonstrated that intraocular pressure drives eye growth and plays a role in corneal morphogenesis. This study investigates the hypothesis that accommodative tissues (e.g. lens, ciliary body, and iris) are contributing mechanical determinants of ocular morphogenesis, using both an experimental porcine model and a finite element method.
The pressures in porcine eyes were controlled using a custom apparatus consisting of an eye holder, a pressure transducer system, and a saline column to control the pressure. The lens, ciliary body, and iris were removed using a blunt surgical probe inserted into the posterior of the eye. Corneal curvature maps were obtained using a Keratron Scout before and after ocular tissue removal. An idealized axisymmetric representation of the ocular geometry was constructed in COMSOL Multiphysics v5.2. The unloaded corneo-scleral shell was assumed to be spherical with an inner radius of 11.5 mm and outer radius of 12.5 mm. A representative ciliary body was juxtaposed about 2/3 of the length of the eye from the anterior pole, protruding several millimeters into the eye. A uniform pressure was placed on the entirety of the interior corneo-scleral boundary.
Experimental data show that the average corneal radius of the intact eye (8.59 ± 0.10 mm) seemed to be lower than that of the eye with the annular tissues removed (8.70 ± 0.37 mm). Computer simulations show that, without the ciliary body, the corneo-scleral shell remains spherical under intraocular pressure. In contrast, the presence of the ciliary body causes increased corneal curvature, resulting in the characteristic corneal bulge required for appropriate refractive power.
Accommodative tissues seem to have a key role in the proper geometric development of the eye under intraocular pressure. This study shed some light on the mechanical interactions between the corneo-scleral shell and the annular tissues.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure 1: Experimental (top) and computational (bottom) curvature maps for the intact (left) and dissected (right) eye.
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