The Cochrane Collaboration Glossary 


It is important to note that what follows is not a definition but more of an explanation of ophthalmic terminology. The explanations are accurate but, in the interest of brevity, not complete. Most would be unacceptable to ophthalmologists and optometrists, because no single term is fully defined. For details and definitions the reader should refer to related textbooks or dictionaries of eye terminology.

- A -

The ability of the eye to change the shape of its lens and focus at different distances

Albinism / Albino
A lack of colour in the skin, eyes and hair that runs in families, that is white skin and hair with pale blue or pink eyes

Accommodative reflex
Automatic response to near visual target which includes accommodation and contraction of the pupil

Age-related macular degeneration
Degenerative disease of the central retina with no obvious cause occurring in older people

Amaurosis fugax
Sudden severe transient loss of vision in one eye, which may be recurrent

Amblyopia / 'lazy eye'
Reduced visual acuity in one eye that is not correctable with lenses when the deficit is not secondary to any eye disease but to incomplete development of the visual system on one side

Absence of the iris

An optical condition in which the images that fall on the retina are of different sizes in the two eyes

Pupils of unequal size

A person who is anisometropic has different prescriptions for each eye

A condition in which the margins of the eyelids are fused together

Total absence of the eyeball

Anterior capsule
The anterior part of the bag in which the lens of the eye normally resides

Anterior chamber
The fluid filled space at the front of the eye

A person who has no lens inside their eye (whether their own or an artificial one) is aphakic

Aqueous cells
The presence of cells in the aqueous fluid which can be counted and monitored on slit-lamp examination

Aqueous flare
The characteristic appearance of a beam of slit-lamp light when shone through the anterior chamber. It signifies an excess of cells and protein in the aqueous fluid for example in anterior uveitis

Aqueous humour / fluid
The clear fluid which fills the anterior and posterior chambers of the eye. These chambers are both in the front part of the eye. (Note the vitreous cavity fills the body of the eye)

Argyll-Robertson Pupil
Characteristic finding of loss of pupillary light reflex and preservation of the accommodative reflex to light, associated with tertiary syphilis

Instead of the front surface of the eye being round it is more oblong. This prevents the light being focused in the right way and leads to blurring. Astigmatism can be secondary to the shape of the cornea or the lens, and is usually correctable with spectacle or contact lenses

Asteroid hyalosis
A condition in which there are asymptomatic opacities in an otherwise normal vitreous, composed of calcium and lipids

Asthenopia / 'eye strain'
Ill-defined ocular discomfort arising from use of the eyes

Loss of cells and tissue

- B -

Band keratopathy
Deposition of calcium in the cornea associated with degenerative corneal disease, high blood calcium levels and juvenile arthritis

Bells palsy
Weakness of the nerve that supplies the muscles of facial expression on one half of the face (right or left)

Bells phenomenon
The normal outward and upward movement of the eyes on forceful closure of the eyelids or during sleep

Binocular vision
Each eye looking at the same object sees a slightly different image. Binocular vision is the ability to fuse these two images into one and gives us the ability to perceive depth and judge distances. See also stereopsis

Inflammation of the eyelids

Plastic surgery of the eyelids

Involuntary spastic closure of the eyelids

There are over 50 definitions of blindness world-wide. The World Health Organization definition of blindness is less than 3/60 in the better seeing eye. This means that the better seeing eye cannot read the top letter on the Snellen visual acuity chart at three metres

Blind spot
The area in the visual field that corresponds to the area where the optic nerve leaves the eye. Objects in this area are not seen

Branch retinal artery/vein occlusion
Occlusion of one of the branches of the central artery/vein which supply the retina leading to a field defect which if small and peripheral may go unnoticed by the person

Large eyeball in infants associated with congenital glaucoma

- C -

Small tube situated in the inner aspect of each of the upper and the lower lids that allows the tears to pass into the common canaliculus, from there to the tear sac and then to the nose

Specified as inner and outer this is what is commonly known as the inner and outer corners of the eye

Opacity of the lens inside the eye

Cataract extraction / Cataract surgery
Removal of the lens usually after opening the lens capsule (extra-capsular cataract extraction) or less frequently with the lens capsule (intra-capsular cataract extraction)

Chronic inflammation of a meibomian gland in the eyelid

Conjunctival swelling which can be severe enough to protrude between the lids

The choroid is the posterior portion of the uveal tract and lies between the retina and the sclera. It is darkly pigmented. When the overlying sclera is thinned it is the colour of the underlying choroid which gives rise to the term 'blue sclera'

Colour blindness
Diminished ability to perceive differences in colour - never a complete absence of colour vision

Commotio retinae
Swelling and haemorrhage of the retina following blunt injury to the front of the eye

Confluent dots
Description of a certain type of early cataract - small opacities in the lens of the eye that are continuous with one another

Consensual light reflex
Constriction of the pupil in the fellow eye when a light is shone in one eye

Convergent squint
Inward deviation of the eye. See also Heterotropia

Displacement of the pupil from its normal position

Clear window in the front of the eyeball which together with the lens focuses light on the retina

Corneal graft (keratoplasty)
Operation to restore vision by replacing a diseased portion of the person's cornea with healthy cornea from a donor. The operation may involve the full thickness of the cornea (penetrating keratoplasty) or only a superficial layer (lamellar keratoplasty)

Cotton wool spots
Fluffy white retinal areas seen on fundoscopy that signify infarction of the superficial retinal layers. Characteristically associated with micro-vascular disease such as diabetic retinopathy, AIDS retinopathy

Cup-disc ratio
This is a term used to communicate the extent of disc cupping. In the healthy disc, the ratio of the vertical diameters of the cup to the optic disc rim should be 0.4 or less, i.e. the height of the inner rim (the cup) should be 30% of the height of the outer rim (the disc). The size of the disc (and subsequently the cup) is dependent on several factors, including the person's refractive error and the presence of glaucoma

Paralysis of the ciliary muscle leading to a paralysis of accommodation

Cytomegalovirus (CMV)
A virus of the herpes family that, in the ophthalmic context, causes infection and inflammation of the retina in patients with AIDS (CMV Retinitis)

- D -

Infection of the tear/lacrimal sac

Inflammation of the tear / lacrimal sac

Dacryocystorhinostomy (DCR)
An operation to bypass a blockage in the tear drainage system which involves opening a new passageway for the tears to pass into the nose

Degenerative corneal disease
Chronic disease of the cornea that alters its shape and or transparency thereby reducing vision

Dendritic ulcer
Corneal ulcer caused by the herpes simplex virus (a secondary infection of the corneal epithelium). This is evidence of previous (primary) exposure to herpes which usually occurs in childhood / adolescence

A fold of skin in the eyelid that has appeared with age and may overhang the lid margin

The bending or breaking up of a ray of light into its component parts

Seeing one object as two. People sometimes confuse a blurring of an object with seeing double

This is a descriptive term. In relation to retinal disease it is most commonly used to signify age-related macular degeneration with poor prognosis for retaining central vision. In relation to corneal disease this term is most commonly used to describe characteristic appearances of viral inflammation of the cornea for example that caused by herpes virus

Discrete dots
Description of a certain type of early cataract. Opacities in the lens of the eye which are not continuous or separate from one another

Divergent squint
Outward deviation of the eye. See also Heterotropia

'Dot and Blot' Haemorrhages
These are haemorrhages in different layers of the retina as seen on fundoscopy and are associated with diabetic retinopathy

These are accumulation of waste products of metabolism under the retina, which are associated with age-related macular degeneration. They are white / yellow and may be discrete or confluent dots

- E -

The extravasation of blood underneath the skin. A bruise

Eyelid falling away from the eyeball

Presence of extensive severe infection inside the eye

Turning inward of the eyelid against the eyeball

Complete surgical removal of the eyeball

See Pseudo-squint

Watering of the eye

Localised inflammation of the superficial tissues of the sclera

Esodeviation/convergent squint
Inward deviation of the eye. See also Heterotropia

See Heterophoria

See Heterotropia

Removal of the contents of the eyeball

Evacuation of the eye socket leading to removal of the eyeball and the eyelids

Exfoliation of the lens capsule
Condition in which the anterior lens capsule degenerates and appears to be rubbed from the anterior surface of the lens by the movements of the iris. True exfoliation is secondary to infra-red light exposure. Pseudo-exfoliation syndrome has no known cause, is a systemic disease and can be associated with glaucoma

Exodeviation / Outward deviation of the eye
See also Heterotropia

See Heterophoria

See Heterotropia

Slow leakage of fluid (as in extravasation of aqueous from the eye)

- F -

Field of vision
The entire area that can be seen without shifting of gaze

See Aqueous flare

These are black or opaque objects that float across the line of vision. People describe them as spiders, flies, hairs or nets. They change position with eye movements, and are seen most clearly against a white or bright background

Fluid level
When blood enters the front of the eye, it may be visible in the front part of the eye as a level of dark red fluid beneath the clear aqueous fluid (hyphaema) or whitish material with pus (hypopyon)

Fluorescent dye/Fluorescent
A dye which will absorb light of one colour such as blue and emit another colour such as green

Fluorescein Angiography
This is a tool for examination of the back of the eye. It involves photographs being taken at the same time as a dye is injected intravenously. The test is usually performed on an out-patient basis, and takes 10 minutes once both eyes are dilated

Examination of the back of the eye with an ophthalmoscope that allows the examiner to see the vitreous, retina and optic nerve head

The back of the eye, that is, the retina, vessels and the optic disc, seen with an ophthalmoscope

- G -

Giant cell arteritis
See temporal arteritis

The sensation of being dazzled by direct light

A disease characterised by defects in the visual field, damage to the nerve at the back of the eye, and usually raised pressure inside the eye

Granulomatous uveitis
See Uveitis

- H -

Blindness of one half of the visual field of each eye. The prefix 'bitemporal' indicates that the hemi-field affected is the outer half field of each eye and 'homonymous' indicates that the hemi-field defect is on the same side of the field of each eye

Herpes virus
A family of viruses that include Herpes simplex, Herpes zoster, and Cytomegalovirus

Different colours - Heterochromia iridis means the patient has a different coloured iris in each eye

Tendency for one or both eyes to wander away from the position where both eyes are looking together in the same direction. Esophoria means a tendency for the eye to deviate inwards (towards the nose), and exophoria means a tendency for the eye to deviate outwards (towards the ear)

The deviation of an eye which is constant and usually easy to spot. Esotropia indicates that the eye is deviated inwards (towards the nose), and exotropia indicated that the eye is deviated outwards (towards the ear)

External - infection of a lash follicle (stye); Internal - infection of a meibomian gland

Horizontal meridian
The horizontal midline of the retina that separates the nerves supplying the upper and lower halves of the retina

Hypermetropia / Hyperopia / 'Farsightedness'
Ability to see distance better than near when not wearing corrective spectacles or contact lenses. These people use + or convex lenses

A fluid level of blood in the anterior chamber of the eye

A fluid level of pus in the anterior chamber of the eye

Hypertension, ocular
High pressure inside the eye

- I -

Indirect ophthalmoscopy
See Ophthalmoscope

Congested blood vessels in a red eye

Inside the eye

The coloured muscular membrane which lies behind the cornea and in front of the lens which by opening or closing determines the size of the pupil and hence the amount of light entering the eye

- K -

Inflammation of the cornea

Inflammation of the eye that has affected both the conjunctiva and the cornea

Conical distortion of the cornea that leads the eye to have severe astigmatism and blurred vision

See corneal graft

Examination of the shape of the cornea

An incision in the cornea. Radial keratotomy is a procedure in which partial thickness incisions are made in the cornea to correct short sightedness

- L -

Lacrimal gland
The source of some of the eyes tears, this gland sits in the upper outer part of the socket just inside its outer rim

Lacrimal sac
Tear sac. Collects the tears from the canaliculi and drains into the nose

The production of tears from the lacrimal gland which may be profuse in response to emotion or aroma

The failure of the eyelids to protect the eye (even when the person tries to close their eye)

Lash follicle
Pocket in the eyelid margin that contains the hair bulb and out of which each eyelash grows

A medium which will bend light. The eye has its own crystalline lens that helps focus light. Spectacle lenses help bend the light in such a way that once it reaches the eye it can then be focused. Contact lenses do the same except that they are in contact with the eyeball

A white coloured pupil

White opacity of the cornea

Lid retraction
The position of the upper eyelid when it is pulled back so that the very top part of the corneo-scleral junction is visible. Lid retraction is commonly seen in people with anxiety states and thyroid disease and may affect upper and lower lids

Lid lag
When the person is asked to slowly look down, there is a delay in initiation of movement of the upper lid downwards, such that the eyelid looks like it is 'being left behind'

The junction of the cornea and the sclera. This is also where the conjunctiva, which covers the sclera, ends

- M -

Meibomian gland
Glands in the eyelid margins that secrete an oily substance into the tears

Wavy distortion of vision

Constriction of the pupil

A drug causing pupillary constriction

Dilatation of the pupil

A drug causing pupillary dilatation

Myopia / Near sightedness
The ability to see near objects better than distant ones when not wearing corrective spectacles or contact lenses

- N -

New vessels
This term is used to signify the abnormal growth of vessels in the eye in response to a need for more oxygen. On the cornea - pannus, on the iris - rubeosis, on the disc - new vessels disc 'NVD', on the retina - new vessels elsewhere 'NVE'

Night blindness
The inability of the eye to adapt to reduced illumination, therefore leading to a complaint of not being able to see in the dark. Characteristically associated with the disease retinitis pigmentosa and with vitamin A deficiency and seen in glaucoma patients taking pilocarpine drops

- O -

Ophthalmia neonatorum
Conjunctivitis in the new-born

An instrument specially designed to allow visualisation of the back of the eye and lens

Optic atrophy
Loss of cells and tissue from the optic nerve from whatever cause, which results in poor vision

Optic disc
Portion of the optic nerve seen with an ophthalmoscope which is also called the optic nerve head

Optic nerve
The nerve that carries visual information from the eye to the brain

Optic neuritis
Inflammation of the optic nerve

Optic neuropathy
Any disease process that might damage the optic nerve

The bony socket in which the eye resides. It is shaped like a pyramid which is lying on its side with the tip pointing backwards and inwards towards the centre of the brain. The orbit is described as having a roof, floor, apex, inner (medial) and outer (lateral) wall

Orbital cellulitis
Inflammation of the tissues surrounding the eye

Orbital floor
See Orbit

Orbital tumour
A tumour (from whatever origin) that is arising from or situated in the orbit

The situation in which both eyes work together in full co-ordination

- P -

Infiltration of the cornea with blood vessels

Swelling of the optic disc when secondary to raised intracranial pressure

An instrument for measuring the field of vision

Near or around the optic disc on fundus examination

Peripheral vision
Ability to perceive objects when outside the direct line of vision

Localised infiltration of the conjunctiva with white blood cells

Using laser light to treat certain disorders at the back of the eye

Abnormal sensitivity to light

Seeing flashing lights out of the corner of the eye when there are none. This is usually caused by mechanical stimulation of the retina

Fleshy white mass of tissue located between the limbus and the canthus under the conjunctiva

Posterior capsule
The back of the bag in which the lens normally sits in the eye. This can become opaque some time after cataract surgery leading the patient to complain of mistiness of vision

Posterior chamber
A space filled with clear fluid (called aqueous humor) behind the iris and in front of the lens

Presbyopia / Old sight
Increasing distance at which text can be read usually occurs after the age of about 40. This is an entirely normal process and signals the need for reading glasses. As a general rule presbyopia occurs at an earlier age in far-sighted people and at a much later age (if ever) in short-sighted people

Abnormal protuberance of the eyeball out of its socket

See Exfoliation of the lens capsule

The presence of an intra-ocular lens implant inside an eye, usually after cataract extraction

The situation in which a person seems to have a squint but in fact does not. The most common cause of this is the presence of a wide nasal bridge (epicanthus)

A triangular growth of tissue that grows form the conjunctiva onto the cornea. If large it can cause astigmatism

Drooping of the eyelid

The hole through which the tears pass into the canaliculi

The round hole in the centre of the iris that corresponds to the lens aperture in a camera. The pupil varies in size according to whether the environment is bright (small pupil) or dark (large pupil)

Pupillary light reflex
The pupil contracts or gets smaller in response to a bright light being shone into it and automatically causes the pupil of the other eye to contract

- R -

Relative afferent pupillary defect

Recession and resection
The moving of muscles from their original position to new positions on the eyeball in order to either weaken (recession) or strengthen (resection) their pull for the surgical correction of squints

The deviation of light in passing obliquely from one medium to another of different density. In ophthalmic practice, refraction describes the process by which the prescription of spectacle lenses for an eye is measured

Refractive error
When the eye fails to focus light correctly and needs a lens (for example spectacles or contact lens) to correct it

The light sensitive part of the back of the eye that corresponds to the film in a camera

Retinal detachment
The falling away of the retina from its correct position at the back of the eye, which leads to a defect in the field of vision and ultimately loss of vision

Disease of the retina, for example, diabetic retinopathy is disease of the retina secondary to diabetes

- S -

The white part of the eye

A blind or partially blind area in the field of vision

Slit lamp
A slit beam of light and a horizontally mounted microscope which allows detailed examination of the eye

Spastic closure
Intense and involuntary closure (of eyelids as in blepharospasm)

Squint / Strabismus
A condition in which the two eyes do not point in the same direction when the patient is looking at a distant object

Squint surgery
See Recession and resection

See Hordeolum, external

Adhesion of the iris to the cornea (anterior synechiae) or the pupil to the lens (posterior synechiae)

A degenerative process of the vitreous humour / gel that leads to shrinkage and collapse of the gel

- T -

A surgical procedure in which the outer parts of the upper and lower lids are joined

Temporal arteritis
An inflammatory condition that affects arteries in the body and a blinding, life-threatening disease


Tertiary syphilis
Very advanced syphilis that can affect any organ of the body but particularly the brain

An instrument for measuring the pressure inside the eye

Trabecular meshwork
The area inside the front part of the eye through which the aqueous fluid leaves the eye. Failure of this system leads to a rise in intra-ocular pressure, as in certain types of glaucoma

An operation for glaucoma which allows controlled escape of aqueous fluid from the eye

Rubbing of inturned eyelashes against the eyeball

Trigeminal nerve
The nerve that supplies sensation to the skin of the face and eye amongst other functions

- U -

The uveal tract is composed of the iris, ciliary body and the choroid. It is the middle vascular layer of the eye and is protected by the cornea and sclera

This indicates inflammation of the uveal tract. It is divided into anterior, intermediate and posterior according to which part of the eye is involved. There are two main forms: granulomatous and non-granulomatous uveitis. The granulomatous form is has characteristic appearances on slit-lamp examination and is associated with sarcoidosis, syphilis and tuberculosis among other conditions

- V -

Small blisters filled with liquid that contains virus particles

Visual acuity
Measurement of the finest details that an eye can distinguish often estimated using LogMar or Snellen charts

Surgical removal of the vitreous

Soft gelatinous material that fills the back of the eye and sits behind the lens. See also Syneresis

Vitreous haemorrhage
Bleeding into the vitreous cavity

Vitreous detachment
The falling away of the vitreous gel from the retina (also called posterior vitreous detachment or PVD). This usually results in floaters and flashing lights and is occasionally associated with vitreous haemorrhage or tearing of the retina