The eye is one of the most complex structures in the human body. It is made up of may different parts, all of which work together in order to allow us to see.
The following diagram (illustrated by Dr Santiago Ortiz Pérez) shows the eye situated in its socket and the surrounding structures.
As you can see the eye itself is held in place by several muscles including the lateralmuscle and the superior rectus muscle. There are in fact 6 muscles responsible for moving the eye. The levator muscle is responsible for moving the eyelid upwards, and hence governs opening the upper eye lid. The levator muscle is assisted by the minute Muller’s muscle. A separate muscle is responsible for closing both eyelids and blinking.
The eyelids help to spread tears that are produced from the lacrimal gland around the eye to keep it lubricated, comfortable and clean. The eyelashes help to keep dust and dirt out of the eye.
Below is a detailed diagram of the upper eyelid.
The frontalis muscle lifts the eyebrow.
The fat pad gives the eyelids volume.
The orbital septum is the foremost boundary of the orbit.
The levator aponeurosis is the thin part at the front of the levator muscle which connects to the eyelid tarsal plate.
The orbicularis assists closing the eyelids.
The tarsal plate is a dense layer of tissue, providing support and structue to the eyelid.
The diagram below demonstrates the structure of the eye itself.
The cornea protects the rest of the eye from dust and dirt. It is also the outermost lens of the eye and focusses light that enters.
The iris controls the amount of light that enters the eye. It shapes the pupil and by expanding and contracting it allows mor or less light in.
The pupil is the ‘hole’ through which the light actually enters the eye.The lens, in addition to the cornea, focusses the light entering the eye.
The vitrous gel is transparent and adds structure to the eyeball as well as allowing light to pass through it and reach the retina.
The retina is the structure of the eye that converts the ‘raw’ light entering the eye into elcectrical impulses – the starting point for the brain to actually interpret what the eye is focussing on. The macula refers to the center of the retina onto which light is focussed, and where there are special cells which appreciate colour (the cones). The areas of retina away from the macula appreciate black and white vision and movements (the rods).
The optic disc is where all the nerves of the retina converge and form the beginning of the optic nerve. It is also the place where the central retinal artery and vein enter and exit that supply the retina with blood.
The optic nerve transmits the electrical impulses created by the retina to the brain for processing and interpretation.
The lacrimal system
The are two lacrimal glands, one for each eye. Their function is to secrete tears that lubricate the eyes and keep them clean and comfortable. Tears pass over the eye with each blink.
Tears drain through pinpoint holes (puncta) at the inner-most corner of each eyelid into the lacrimal canaliculi, which are very fine lacrimal ducts.
The lacrimal sac connects the canaliculi with the nasolacrimal duct; its function is to drain the tears.
The nasolacrimal duct carries tears away from the canaliculi and lacrimal sac to the back of the nasal cavity.
The middle turbinate is a structure on the lateral wall of the inside of the nose, a useful surgical landmark for the nearby lacrimal sac. Its shape is believed to help warm and circulate the air inside the nose.
The inferior turbinate conceals the opening of the nasolacrimal duct into the nose.