RT Book, Section A1 Harper, Richard A. A1 Shock, John P. A2 Riordan-Eva, Paul A2 Cunningham, Emmett T. SR Print(0) ID 55782574 T1 Chapter 8. Lens T2 Vaughan & Asbury's General Ophthalmology, 18e YR 2011 FD 2011 PB The McGraw-Hill Companies PP New York, NY SN 978-0-07-163420-5 LK accessmedicine.mhmedical.com/content.aspx?aid=55782574 RD 2024/03/28 AB The crystalline lens is a remarkable structure that 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.