Eye Conditions and Disorders

Eyes and Vision

The eye is a complex organ made up of several highly specialized components. Many eye disorders do not threaten sight, but a few serious conditions may damage the eye’s components and lead to loss of vision. Eye disorders are very common, but early diagnosis usually leads to successful treatment.

This section covers disorders caused by disease, structural abnormality, or injury to the eye. Conditions that involve the front covering of the eye (the conjunctiva and cornea) are described first, followed by disorders that affect the front chamber of the eye and the structures within it, including the iris and lens.

The next group of articles discusses disorders of the light-sensitive retina at the back of the eye and conditions affecting the optic nerve, which carries nerve signals from the retina to the brain. The final articles in this section cover conditions in which the eye is displaced or injured in some way. Impaired vision, whether occurring in healthy eyes or as a consequence of serious underlying causes, is described separately (see Vision disorders), as are disorders of the eyelid and tear system and eye disorders that usually or only affect children. These include congenital blindness, cancer of the retina (see Retinoblastoma), and misalignment of the gaze of the eyes (see Strabismus).

Many major eye disorders that in the past would have ultimately progressed to blindness can now be treated successfully if detected early. For example, diabetic retinopathy is often now treated by laser surgery to prevent further sight loss. Regular eye examinations are therefore important, especially for people over the age of 40.

Key anatomy

For more information on the structure and function of the eye, see Eyes and Vision.


Subconjunctival Haemorrhage

Corneal Abrasion

Corneal Ulcer








Acute Glaucoma

Chronic Glaucoma


Vitreous Haemorrhage

Retinal Vein Occlusion

Retinal Detachment


Diabetic Retinopathy

Macular Degeneration

Retinitis Pigmentosa

Optic Neuritis



Eye Injuries

Eyelids and tears work together to protect the eye against damage. The eyelids act as shutters, closing to stop material from entering the eyes. Tears keep the surface of the eyes moist and help to prevent infection. Disorders of the eyelids or tear system can damage the eyes, but most are easily treated if detected early.

The upper and lower eyelids provide essential protection for the eyes. If anything approaches the eye or face rapidly, the eyelids close together almost instantaneously as a reflex action. Furthermore, each eyelid has two or three rows of eyelashes, which help to prevent small particles from entering the eye.

Tears are another important part of the eyes’ defences. They are made up of a salty fluid produced by the lacrimal (tear) glands, which are located above the upper eyelids. Tears lubricate the exposed surface of the eye and wash away potentially harmful materials, such as dust and chemicals. Tears also contain a natural antiseptic that helps to protect the eye against infection.

The initial articles in this section focus on conditions that affect the eyelids. These conditions include infections of the eyelid and disorders that alter the physical shape of the eyelids. The section then discusses disorders that affect the tear system, which include blockage of the tear drainage channels and problems with tear production. Disorders that affect the physical structures of the eye itself are covered elsewhere in the guide (see Eye disorders).

Key anatomy

For more information on the structure and function of the eye, see Eyes and Vision.







Watery Eye


Keratoconjunctivitis Sicca


Disorders of vision are very common; most people have a visual problem at some time in their lives. The most common disorders of vision are shortsightedness (myopia), longsightedness, (hypermetropia), and astigmatism, which are types of refractive (focusing) errors. Most refractive errors can be corrected by aids, such as glasses or contact lenses, or cured by surgical techniques.

The opening articles in this section discuss refractive errors and show how variations in the size and shape of the eye may lead to distortions of vision. Tests and treatments for refractive errors are also described. However, special tests for children’s vision are covered separately (see Vision tests in children). Presbyopia, the deterioration of vision that occurs with aging, is covered next.

The following articles describe colour blindness, a condition that is more common in men, and serious visual problems, including double vision and partial or total blindness.

Disorders that affect the structure of the eye, including glaucoma, are covered elsewhere (see Eye disorders), as are blindness at birth (see Congenital blindness) and two disorders that mainly affect children: crossed eyes (see Strabismus) and abnormal vision in an eye that is otherwise structurally normal (see Amblyopia).

Key anatomy

For further information on the structure and function of the eye, see Eyes and Vision.



Treatment: Glasses and Contact Lenses



Double Vision

Visual Field Defects


Colour Blindness


From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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