lens

The lens is the magnifying glass inside our eye that controls fine focusing. The lens is located immediately behind the iris (the colored part of the eye). Like the cornea, it is living tissue yet it is clear. When light enters the eye, it travels through the pupil, then through the lens, before striking the retina in the back of the eye. The lens is held in place by little springs called zonules.  These are arranged in a 360-degree ring around the lens “equator” and suspend the lens like a trampoline. A muscle called the ciliary body pulls on the zonules which controls the lens shape. This shape-changing ability is called accommodation, which is how we focus to see things close up. In youth, the lens is naturally soft and can change shape like a piece of Jell-O or gummy candy. This gives children a very wide range of focus as their lens can flatten like a ‘pancake’ to give far distance vision, or the lens can become round like a ‘marble’ to focus on the tip of a nose.  As we age, the clear lens tissue begins to stiffen, and has a harder time changing shape. This process is called presbyopia, and explains why we start needing reading glasses around age 40.  The lens eventually becomes cloudy, forming a cataract. When we repair a cataract, we create a hole in the front layer of the lens and remove the inner layers of the lens. A new plastic implant lens is then placed inside the husk of the original cataract lens. This new implant is optically clear, but made of plastic that can’t change shape, so most are therefore set for one focus (to give good distance vision).