Cornea

The cornea is the clear, dome-shaped portion at the front of the eye. It helps focus light by bending it as it enters the front of the eye. In fact, the cornea is responsible for 70% of the eye’s focusing power.

Iris

The iris is the coloured part of the eye. The iris adjusts the size of the pupil to control the amount of light reaching the back of the eye. Muscles in the iris cause the pupil to constrict (become smaller) in bright light and dilate (become larger) in dim light.

Trabecular meshwork

The trabecular meshwork is the spongy tissue located in the eye’s drainage angle – the space where the the iris and the cornea meet. The trabecular meshwork acts as the eye’s drainage system. Most of the fluid produced inside the eye (called the aqueous humour) drains out of the eye via the trabecular meshwork and eventually makes its way back into the body’s circulatory system.

Pupil

The pupil is the opening in the middle of the iris that allows light to enter the eye.

Lens

The lens is a clear part of the eye that sits directly behind the iris and pupil. The lens’ job is to help focus light correctly onto the retina at the back of the eye.

Sclera

The sclera is the “white” of the eye. It’s a strong layer of protective tissue that covers most of the surface of the eyeball.

Conjunctiva

The conjunctiva is a thin, clear membrane that covers the sclera and lines the inner surface of your eyelids. It protects your eye from irritants and helps keep moisture in.

Retina

The retina is a layer of light-sensitive tissue that lines the back of the eye. It contains special cells called photoreceptors, which turn light into electric signals that travel to the brain through the optic nerve.

There are two types of photoreceptors: rods and cones. Rods perceive light levels, enabling vision in low light and at night. They’re concentrated in the outer areas of the retina and help give us our peripheral vision. Cones, which are concentrated at the centre of the retina, detect colour and provide central detailed vision.

Macula

The macula is a small area at the centre of the retina. It’s responsible for sharp central vision that allows us to clearly see details like faces and written text.

Vitreous

The vitreous (or vitreous humour) is a jelly-like substance. It fills the vitreous cavity, which is the space in the middle of the eye, between the lens and the back of the eye.

Optic nerve

The optic nerve is at the back of the eye and connects to your brain. It’s made of millions of nerve fibres that transmit electic impulses from the retina to the visual cortex – the part of our brain responsible for vision.

Retinal conditions

Two of the Big 5 serious eye conditions affect the retina. 

Age-related macular degeneration (AMD)
AMD is a progressive condition that affects the macula, which is the small area at the centre of the retina that allows us to see fine details clearly. AMD happens when cells in the macula gradually begin to deterioriate, leading to loss of central vision.

Keep learning about AMD or hear from AMD expert Dr. Maberley.

Diabetic retinopathy
Diabetic retinopathy is an eye disease that commonly affects people with diabetes. Over time, high blood sugar levels caused by diabetes can damage blood vessels in the retina. There are various stages/types of diabetic retinopathy, but all will lead to vision loss if left untreated.

Keep learning about diabetic retinopathy.

Retinal tear

As we get older, the vitreous gel inside the eye changes to a more liquid consistency and separates from the retina, creating a posterior vitreous detachment (PVD). Usually, this happens without any issue. In rare cases however, as the vitreous separates from the retina, it pulls with enough force to cause the retina to tear. This can cause a sudden onset of floaters and/or light sensitivity. Retinal tears can lead to retinal detachment.

Retinal detachment
Retinal detachment happens when the retina is pulled away from the back wall of the eye. This can happen when the vitreous passes through a retinal tear and lifts the retina off the back of the eye.

Signs of a retinal detachment include the sudden onset of floaters, flashes, or a gray curtain moving across the field of vision. A retinal detachment is very serious and usually causes blindness if not treated urgently.

Glaucoma

Glaucoma is a disease characterized by damage to the optic nerve. This damage is usually related to an increase in pressure inside the eye.

The aqueous humour is a fluid that is produced inside the eye and drains out of the eye at the trabecular meshwork. If too much fluid is being produced, or if it is not draining properly (for example, if there is a problem with the trabecular meshwork), fluid builds up inside the eye, leading to a rise in pressure.

Click on the trabecular meshwork to learn more about it.

When eye pressure is too high, the nerve fibres of the optic nerve become damaged, which can cause blind spots and vision loss.

Keep learning about glaucoma or read our article featuring glaucoma expert Dr. Saheb.

Cataracts

As you age, the normal proteins in the eye’s lens begin to break down, causing the lens to become cloudy. This prevents light rays from passing clearly through the lens, resulting in hazy or blurry vision. When the lens becomes cloudy enough to obstruct vision to a large degree, it’s called a cataract.

Keep learning about cataracts.

Eye injury

Eye injuries are common and cause anything from minor corneal scratches to vision loss or even blindness. They can affect any part of the eye or surrounding structures (like the eyelid or orbital bone), depending on the nature of the injury.

Keep learning about eye injury.

Posterior Vitreous Detachment (PVD)

PVD is when the vitreous gel inside the eye pulls away from the retina. This happens because the vitreous becomes more liquid and shrinks slightly as we get older.

Many people with a PVD will not notice any symptoms, but some will notice a sudden increase in floaters and flashes in their vision. These are actually shadows cast on the retina by clumps of vitreous gel.

For most patients, these symptoms usually subside within 3 months of the PVD.

Rarely, PVD can result in serious complications like vitreous hemorrhage, retinal detachment, or macular hole. In these cases, flashes and floaters may be accompanied by decreased or distorted vision. This should be evaluated by an eye care professional immediately.

Conjunctivitis (“pink eye”)

Conjunctivitis refers to inflammation of the conjunctiva. It can caused by infection (either viral or bacterial) or by allergies. The small blood vessels in the conjunctiva become dilated, making your eyes look red. Symptoms can also include a burning or gritty sensation and a watery or sticky discharge.