RT Book, Section A1 Harper, Richard A. A2 Riordan-Eva, Paul A2 Augsburger, James J. SR Print(0) ID 1144468147 T1 Lens T2 Vaughan & Asbury's General Ophthalmology, 19e YR 2017 FD 2017 PB McGraw-Hill Education PP New York, NY SN 9780071843539 LK accessmedicine.mhmedical.com/content.aspx?aid=1144468147 RD 2024/03/28 AB The (crystalline) lens contributes to focusing of images on the retina. It is positioned just posterior to the iris and is supported by zonular fibers arising from the ciliary body and inserting onto the equatorial region of the lens capsule (see Figure 1–12). The lens capsule is a basement membrane that surrounds the lens substance. Epithelial cells near the lens equator divide throughout life and continually differentiate into new lens fibers, so that older lens fibers are compressed into a central nucleus; younger, less-compact fibers around the nucleus make up the cortex. Because the lens is avascular and has no innervation, it must derive nutrients from the aqueous humor. Lens metabolism is primarily anaerobic owing to the low level of oxygen dissolved in the aqueous.