To better understand eye conditions and diseases, knowledge of basic eye structures is essential. We explore parts of the human eye below.
Structures of the human eye, National Cancer Institute.
The eye rests in the orbit. It is a protective bony socket containing six extraocular muscles that move the eye up and down, side to side, and rotate the eye. These extraocular muscles are attached to the sclera, or the white part of the eye that is a strong layer of tissue that envelops almost the entire surface of the eyeball.
Illustration of the 6 eye muscles (Source: American Academy of Ophthalmology)
The Surface of the Eye
A clear membrane called the conjunctiva envelops the eye surface as well as the inner surface of the eyelids.
Tears that lubricate the eye comprise three layers, collectively known as the tear film. In the tear film, the conjunctiva makes the mucous layer. The lacrimal gland that sits under the outside edge of the eyebrow (away from the nose) in the orbit makes the watery part of the tears. The meibomian gland makes the oil that becomes another part of the tear film. The tear duct helps tears drain from the eye.
Tear gland and duct (Source: Imperial Healthcare)
Also, the cornea, the clear, dome-shaped front portion of the eye focuses light into the eye and provides 70% of the eye’s focusing power.
The fluid-filled (containing aqueous humor) space behind the cornea is called the anterior chamber. The anterior chamber lies behind the cornea but in front of the lens and iris. This chamber contains aqueous humor and enables it to drain properly from the eyes into the bloodstream, in an area called the drainage angle, Such a mechanism ensures that eye pressure remains constant.
(Source: American Academy of Ophthalmology)
The iris is the coloured part of the eye and the pupil is the dark hole in the middle. The amount of light reaching the back of the eye is determined by muscles in the pupil dilating (widening) or the pupil constricting (narrowing).
The lens is located right behind the pupil and focuses light toward the back of the eye. The lens alters its shape to focus on nearby objects. By focusing light as it enters the eye, the cornea and the lens help give us clear vision.
The Back of the Eye
Between the lens and the back of the eye lies the vitreous cavity, a jellylike substance.
Light that is directed into the eye via the cornea and lens goes through the vitreous onto the light-sensitive tissue lining the back of the eye, otherwise known as the retina.
The macula is a tiny specialised area of the retina that is in charge of providing detailed central vision. The retina contains cells known as photoreceptors that convert light into energy that is transmitted to the brain. The retina also transmits light as electrical impulses to the brain via the optic nerve that comprises millions of nerve fibers. These nerve fibers transport impulses to the visual cortex, the area of the brain in charge of vision.
Understanding different parts of the human eye will equip you to understand what happens during an eye check up. To maintain optimal eye health, it’s important to attend regular eye check ups and it’s just a click away! Book your appointment today via planoEyecheck.
American Academy of Ophthalmology. 2021. Eye Anatomy: Parts of the Eye and How We See. [online] Available at: <https://www.aao.org/eye-health/anatomy/parts-of-eye> [Accessed 14 December 2021].
Allabouteyes.com. 2021. [online] Available at: <https://allabouteyes.com/understanding-different-parts-eye/> [Accessed 15 December 2021].