The Human Eye

The eye has many parts and functions and it can take forever to list all of them. Some parts and their functions include (refer to Appendix A to see more about the structures of the eye):

Suspensory Ligaments

Suspensory ligaments are also known as the zonular fibres that attach the lens to the rest of the eye. They grip the lens in place and function to change the focusing power of the eye. They do this by changing the tension of the fibres by contraction and relaxation of the ciliary muscle.

Fovea

The fovea, a tiny part of our retina responsible for our topmost visual acuity; it is the core of our central vision and is responsible for sharp central vision. It is located in the mascula of the retina.

Ciliary Muscle

The ciliary muscle changes the shape of the lens called accommodation. The muscle is a smooth muscle affecting the zonular fibres in the eye. The ciliary muscle relaxes to flatten the lens for long-range focus. For short-range focus the ciliary muscle contracts making the lens more spherical. This releases the tension on the lens caused by the zonular fibres.

Lens

The lens also known as the crystalline lens is transparent and is located just behind the iris. The lens is encased in a capsular-like bag and suspended within the eye by tiny zonules. The lens along with the cornea helps to focus light onto the retina.

Aqueous Humour

The Aqueous humour is a water like fluid, produced by the ciliary body; the aqueous humour fills the front of the eye between the lens and cornea. The aqueous humour also provides the cornea and lens with oxygen and nutrients. It drains back into the blood stream through the canals of Schlemm.

Pupil

The pupil is the hole or slit shaped opening in the centre of the iris that light passes through. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. The iris muscles control its size.

Vitreous Humour

The vitreous humour is a gel like liquid that fills most of the eye (from the lens back). The gel like liquid is a clear aqueous solution that fills the space between the lens and the retina of the vertebrate eyeball. The solution is 99% water, but has a gelatinous viscosity two to four times that of water. The remaining solutes include salts, sugars, phagocytes, and a network of collagen fibres. The vitreous humours purpose is to cushion the eye. As we age it changes from a gel to a liquid and gradually shrinks separating from the retina.