Illustration of the fine structure of the eye lens. This is the internal optical component (also called the crystalline lens) of the eye, responsible for adjusting focus. The lens is composed of elongated epithelial cells, many of which have lost their nuclei (here, shown as dark blue dots). These cells, known as lamellar fibres, contain a crystalline protein giving them optical properties. The cell membranes of adjacent fibres are fused, which creates minimal interference to light. The anterior of the lens contains a single layer of cuboidal epithelium cells with nuclei. This complex pattern of cells is enclosed in a transparent membrane capsule.