Cornea

The cornea is the clear window to the eye. It is at the front of the eye just in front of the coloured part of the eye, the iris. It has no blood vessels in it, and normally is completely transparent. When it is scarred or infected, it may appear white in some areas. When a person gets a "scratch" to the eye or a corneal abrasion, the superficial layer of the cornea is torn off. This can be very painful but heals quickly with the proper treatment. People who have permanent corneal scarring may be candidates for a corneal transplant. When people wear contact lenses, these lenses sit on top of the cornea. The cornea is the structure that is lasered during procedures like LASIK or PRK, which help people see without glasses (Refractive Laser).

Anterior Chamber

The anterior chamber is the area just in front of the iris inside the eye. It is filled with watery fluid called aqueous. Aqueous is produced in the cilary body muscle (in the posterior chamber) and flows through the pupil, into the anterior chamber angle or drainage canal, to exit the eye. This is a very important pathway of study in glaucoma research.

Posterior Chamber

The posterior chamber is behind the iris and includes the ciliary body muscle and the lens complex. The aqueous is produced in this chamber and flows to the front of the eye to be drained in the anterior chamber angle.

Iris

The iris is the part of the eye that gives us the colour of the eye, whether it be blue, brown, green or hazel. It acts like the diaphragm of a camera and expands (dilates) and contracts (constricts) to allow more or less light into the eye.

Sclera

This is the white leathery shell around the eye which is connected to the cornea at the front of the eye. It protects the internal eye structures and holds the eye together.

Inflammation of the sclera can occur in some people with autoimmune conditions, which may appear as a deeply red, painful eye with a mild change in vision. It differs from "pink eye" because it is an inflammation of a deeper layer of the eye, and can be very painful.

When an eye is injured with blunt trauma, the sclera may split, causing a rupture to the eyeball. This is a significant sight-threatening injury that requires emergent surgery.

Conjunctiva

The conjunctiva is a thin membranous layer of tissue on top of the sclera. It covers the eyeball up to the lids and then folds under the lids and covers the underside of the upper and lower lids. You can never lose a contact lens behind the eye, since the conjunctiva creates a natural barrier.

The conjunctiva is what gets inflamed and red when we have any infection or allergic reaction of the eyes giving the appearance of "pink eyes" or "conjunctivitis". This condition causes mildly blurred vision and discomfort and usually resolves without treatment within a couple of weeks. In contrast, "scleritis", an inflammation of the deeper white layer of the eye, is very painful, often associated with a systemic illness and and requires treatment to resolve.

Sometimes, people get a red spot under the conjunctiva, which can be a bit of blood, that can arise spontaneously or with minor trauma, and usually clears up within a week to 10 days. This is called a "subconjunctival hemorrhage". It is very common and is benign in most cases.

Pupil

The pupil is the hole in the iris. The pupil gets larger when it is dark - letting more light into the eye, and smaller when it is bright - letting less light into the eye. When your eye doctor dilates your eyes with dilating eye drops, the pupil becomes large for a few hours and near vision becomes blurry until the effect of the drops wears out in about 4-6 hours (this varies and can be much longer in some patients). This allows more visibility inside your eyes to enable your eye doctor to do a more thorough examination of the inside of your eyes.

Lens

This is the natural lens of the eye. Just as a camera has a lens, so does the eye. This lens is clear for most of our lives, and changes shape as we try to focus on things up close and things in the distance.

With some medications or diseases, the ability of our lenses to change shape becomes temporarily (or permanently) impaired. For example, pregnant women may notice that their glasses prescription changes during pregnancy, and then stabilizes after giving birth. This is due to hormonal changes that affect the shape of the lens during pregnancy.

As we age, our lenses become harder and cloudier forming a "cataract". Cataracts can develop at a younger age when using with particular medications (like steroids) and with certain diseases (like diabetes), or lifestyle issues (such as smoking or excessive exposure to UV radiation). Cataracts can also be present at birth (congenital cataracts). Cataracts can be treated successfully to restore vision (in most cases barring other eye problems) with cataract surgery.

Ciliary Body, Ciliary Muscle and Aqueous

The ciliary body and muscle enables the iris to move back and forth to change the shape of the pupil. It also produces the fluid of the eye called "aqueous". Aqueous is important since it bathes the structures in the front of the eye including the lens and cornea and delivers much needed nutrients and oxygen and picks up waste. There structures do not have blood vessels to do this, therefore the aqueous is vitally important.

However, if there is a problem with the drainage of aqueous, which occurs in different types of glaucoma, the aqueous can build up causing a build-up in eye pressure. Treatments for glaucoma mostly focus on lowering the eye pressure by improving the drainage of aqueous, or decreasing aqueous production. For example, Diode laser is a treatment for glaucoma that targets the ciliary body to decrease the production of aqueous thereby decreasing the build-up of fluid and pressure in the eye. Most glaucoma eye drops function to decrease aqueous production from the ciliary body.

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Vitreous

The vitreous is a clear gel that fills the bulk of the eyeball. It is solid when we are born and is attached to the retina. As we get older, the vitreous becomes loose, and "floaters" are formed. Floaters are pieces of more solid vitreous, floating in the more liquid vitreous, and creating shadows on the retina. Overtime, the vitreous detaches from the retina abruptly (posterior vitreous detachment), and creates sudden floaters and a flashing light sensation. The flashing is from the vitreous pulling on the retina.

Sometimes, the retina is torn during this spontaneous event. This is called a retinal tear, which is a risk factor for a retinal detachment. A retinal tear can be lasered (laser retinopexy) to prevent the development of a retinal detachment.

Retina

The retina is the "photo film" of the eye, if you think if the eye as a camera. It is a very thin layer of nerve tissue. If a person has a retinal detachment, this means that this layer has come loose and is not attached to its circulation. This is an eye emergency that needs to be surgically treated to prevent permanent vision loss.

Macula

The macula is the centre of the retina that is responsible for our central, reading vision. The retina outside the macula provides us with our peripheral or side vision. Macular degeneration is degeneration of this central, very important part of the retina. Although people with macular degeneration may lose their central, reading vision, they will still have their peripheral vision, if the rest of the retina is okay.

Retinal vessels

The retina is provided with oxygen and nutrients by vessels both within it and underneath it (in the choroid layer). The retinal layers need both sets of circulation to function properly.

Sometimes, people may have a "stroke" in the eye. This means that the circulation in either a main or branch artery of the eye has been blocked. This is often due to "atherosclerosis". Veins can also become blocked, especially from uncontrolled high blood pressure.

Choroid

This layer is mostly full of blood vessels between the retina and the sclera.

Optic Nerve

The optic nerve is like a large fibre optic cable, bringing together all the nerve endings from the retina and connecting them to the brain for interpretation of the pictures that have been taken by the eye. The brain is our "super computer " that translates these photo messages for us.

In glaucoma, the optic nerve degenerates over time, and we lose this vital connection to the brain. The result is weakening and loss of vision, without proper treatment. OCT imaging is used to track changes in the optic nerve over time that may be too subtle for the naked eye to detect.

About Basic Eye Anatomy