The human lens is truly a marvel of nature. Despite its small size, it accomplishes so much. These lenses are not visible because they reside behind the iris (the colored part of the eye). They are made up of long cells that are arranged in a perfect curvilinear pattern, which permits light to pass through. Beyond the perfect alignment of cells, the lens is pliable, which allows it to flex and bend. This movement allows our eyes to autofocus (accommodation), so we can see things near and far. The normal human lens can function perfectly for decades despite daily use. Eventually, however, this marvel of nature starts to break down. The autofocus stops working, resulting in the need for reading glasses, and the perfectly aligned cells start to misalign and cause cloudiness. A cloudy lens that does not focus well is called a cataract.