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The Eye Library

The Eye

Library 1The eyeball contains three layers:

  • The outer layer, formed by the cornea and sclera
  • The middle layer, holding the primary blood supply for the eye and containing the iris and pupil
  • The inner layer, comprised of the retina

The eyeball also contains three chambers of fluid:

  • Anterior chamber, between the cornea and iris
  • Posterior chamber, between the iris and the lens
  • Vitreous chamber, between the lens and the retina

The anterior and posterior chambers are filled with aqueous humour, which is a watery fluid that provides nourishment to the interior eye structures and helps to keep the eyeball inflated. The vitreous chamber is filled with a thicker fluid called vitreous humour, a transparent gel which is 99% water, which helps the eyes to stay inflated.

The Optic Nerve

The Optic NerveAs well as numerous blood vessels, the eye also contains the optic nerve. This runs from the back of the eyeball, through an opening in the orbit known as the optic foramen.

From here, the optic nerve connects to the brain and acts as a conduit, transmitting visual information into the brain. Other nerves within the eye carry non-visual information and send messages about pain or help to control motor activity within the eye.

The Cornea

The cornea is the clear portion of the eye that covers the iris and the pupil and takes up about one-sixth of the eye. The rest of the eye (the scleral segment) is opaque. Several nerves and blood vessels run through the sclera, including the optic nerve. The cornea and scleral segment come together in an area called the limbus. This contains a great deal of blood vessels.

The Iris and Pupil

Lens and RetinaThe iris and pupil are the most noticeable parts of the eye. The iris is the coloured ring of tissue that lies beneath the cornea and can be a range of colours, determined by genetics. The pupil is located in the centre of the iris and appears as a black hole that acts rather like a camera aperture, allowing light to enter the eye. This works in the same way as a camera, adjusting to control the flow of light into the eye. In bright conditions, the pupil closes down, reducing the amount of light entering the eye and protecting the delicate nerves from being damaged. In the dark, the reverse happens to allow what light there is to enter the eye.

Lens and Retina

Directly behind the iris is the lens. This focuses rays of light onto the retina, which is a light-sensitive nerve tissue that contains photosensitive cells called rods and cones. These convert light into electrical signals that are carried to the brain by the optic nerve.


Although often ignored, the eyelids play a crucial role in protecting the eyes. They help to protect the surface of the eye from scratches, dust and foreign objects and also help to lubricate the surface of the eye. When we blink, the eyelids carry secretions from the various glands across the eye.

The eyelid has several layers:

  • A fibrous layer to provide stability
  • A layer of muscle that controls the opening and closing of the eyelid. This layer can act incredibly quickly if the surface of the eye is vulnerable to attack, shutting the eyelid and protecting the surface of the eye using a reflex mechanism.
  • A layer of skin that contains glands and the eyelashes, which act as filters to stop large foreign objects entering the eyes.
  • The conjunctiva, which is a mucous membrane that connects the eyeball to the eyelid and the eyeball to the orbit.

Tear Glands

Tear GlandsTears are provided by several glands in and around the eyelids. Tears are around 99% water and keep the cornea moist, as well as protect the delicate cells on the cornea. Each gland can have as many as 12 tear ducts. On blinking tears drain away via the puncta lachrymal, a small opening in the inner corner of the eyelid.


Eye Conditions

Familiarity with the symptoms of common eye conditions can help you to prevent an initially minor infection or problem from becoming a major health issue. Some eye conditions can be indicators of deeper, underlying health problems such as diabetes or high blood pressure, which with the right treatment can be managed or even eradicated. However, it is essential that you have regular general health checks, as well as regular eye tests to ensure a healthy lifestyle.

Below you'll find summaries of common eye and vision conditions. These are just a few of the common eye conditions that can affect almost anyone.

Flashes & FloatersFlashes & Floaters

Most people will suffer from flashes or 'floaters' at some stage in their lives. These 'dots' or specks are most noticeable when looking at a white background and are simply small particles that float in the vitreous fluid inside the eye. However a sudden onset could be a sign of a more serious problem


This is the name given to a group of diseases characterised by progressive damage to the optic nerve head, sometimes due to raised intraocular pressure within the eye.

Macular DegenerationMacular Degeneration

Macular degeneration is usually found in older adults which results in a loss of vision in the centre of the visual field (the macula) because of damage to the retina.

Myopia & HyperopiaMyopia & Hyperopia

Often referred to as short and long sightedness, myopia and hyperopia are two of the most common eye defects. Both conditions are correctable. Myopia is the inability to see objects clearly at a distance, but close up objects are much clearer. Hyperopia means objects are generally clearer further away than up close.


Presbyopia describes the condition where the eye exhibits a progressively diminished ability to focus on near objects. This condition is more prevalent with age.



Astigmatism is the optical term for more than one point of focus. The condition occurs when the surface of the cornea or crystalline lens is not spherical.



A cataract is a clouding of the clear crystalline lens inside the eye. Cataracts are typically more common in people over 65.



Conjunctivitis is an inflammation of the conjunctiva. The conjunctiva is the thin layer that covers the white of the eye and the inside of the eyelids.



Diabetes can lead to a condition called Diabetic Retinopathy and other eye problems, which can ultimately lead to blindness if not diagnosed and treated early.


Dry eyeDry eye

Dry eye is a condition caused by the eyes not producing enough tears, or producing tears of a poor quality, leading to gritty, uncomfortable eyes.



For assistance in the treatment and care in the conditions above please contact us to book an appointment.