capsule, crystalline lens
Transparent elastic capsule covering the crystalline lens. It is made up of collagen fibrils embedded in a glycosaminoglycan matrix. The thickness of the capsule varies; the anterior portion is thicker than the posterior and it is also thicker towards the periphery (or equator). This variation in thickness plays a role in moulding the lens substance, contributing to an increase in the curvature of the front surface, in particular, during accommodation. The capsule increases in thickness with age, and its modulus of elasticity decreases with age, which (besides flattening of the lens, and a hardening of the lens substance) contributes to presbyopia (Fig. C2). Under electron microscopy the capsule appears to have a lamellar structure that disappears with age. The capsule receives the insertion of the zonular fibres. See lens fibres; modulus of elasticity; shagreen of the crystalline lens; Fincham's theory; zonule of Zinn.
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Fig. C2 Lens capsule of a person about 30 years old. It is thickest near the equator and at the anterior pole
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