cochrane eyes and vision group
Glossary
It is important to note that what follows are not definitions but comprise an explanation of ophthalmic terminology. The explanations are accurate but, in the interest of brevity, not complete. Most would be unacceptable to ophthalmologists, because no single term is fully defined. For details and definitions the reader should refer to an ophthalmology textbook.
This glossary is adapted from Okhravi N. Manual of primary eye care. Oxford: Butterworth-Heinemann, 1997. We are very grateful to them for allowing us to use this glossary.
A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | R | S | T | U | V
A [Top]Accommodation: The ability of the eye to change the shape of its lens and focus at different distances.
Age-related macular degeneration: degenerative disease of the central retina with no obvious cause occurring in older people
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.
Amaurosis fugax: A 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.
Aniridia: Absence of the iris.
Aniseikonia: An optical condition in which the images that fall on the retina are of different sizes in the two eyes.
Anisocoria: Pupils of unequal size.
Anisometropia: A person who is anisometropic has different prescriptions for each eye.
Ankyloblepharon: A condition in which the margins of the eyelids are fused together.
Anophthalmos: 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.
Aphakia: 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 that 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 that 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.
Astigmatism: 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.
Atrophy: Loss of cells and tissue.
B [Top]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.
Blepharitis: Inflammation of the eyelids.
Blepharoplasty: Plastic surgery of the eyelids.
Blepharospasm: Involuntary spastic closure of the eyelids.
Blindness: There are over 50 definitions of blindness worldwide. The World Health Organisation 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.
Buphthalmos: Large eyeball in infants associated with congenital glaucoma.
C [Top]
Canaliculus: 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.
Canthus: Specified as inner and outer this is what is commonly known as the inner and outer corners of the eye.
Cataract: 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 within the lens capsule (intra-capsular cataract extraction).
Chalazion: Chronic inflammation of a meibomian gland in the eyelid.
Chemosis: Conjunctival swelling which can be severe enough to protrude between the lids.
Choroid: 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 which 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.
Corectopia: Displacement of the pupil from its normal position.
Cornea: Clear window in the front of the eyeball that 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, A.I.D.S. 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.
Cycloplegia: 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 A.I.D.S. (CMV Retinitis).
D [Top]
Dacryocystorhinitis: Infection of the tear / lacrimal sac.
Dacryocystorhinostomy (DCR): An operation to bypass a blockage in the tear drainage system that 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.
Dermatochalasis: A fold of skin in the eyelid that has appeared with age and may overhang the lid margin.
Diplopia: Seeing one object as two. People sometimes confuse a blurring of an object with seeing double.
Disciform: 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.
Dacryocystitis: Infection of the tear/lacrimal sac.
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.
Drusen: 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 [Top]
Ecchymosis: the extravasation of blood underneath the skin. A bruise.
Ectropion: Eyelid falling away from the eyeball.
Endophthalmitis: Presence of extensive severe infection inside the eye.
Entropion: Turning inward of the eyelid against the eyeball.
Enucleation: Complete surgical removal of the eyeball.
Epicanthus: see Pseudo-squint.
Epiphora: Watering of the eye.
Episcleritis: Localised inflammation of the superficial tissues of the sclera.
Esodeviation/Convergent squint: Inward deviation of the eye. See also Heterotropia.
Esophoria: see Heterophoria.
Esotropia: see Heterotropia.
Evisceration: Removal of the contents of the eyeball.
Exenteration: 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.
Exophoria: see Heterophoria.
Exotropia: see Heterotropia.
Extravasation: slow leakage of fluid (as in extravasation of aqueous from the eye).
F [Top]
Field of vision: The entire area that can be seen without shifting of gaze.
Flare: See Aqueous flare.
Floater: 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 that 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.
Fundoscopy: examination of the back of the eye with an ophthalmoscope that allows the examiner to see the vitreous, retina and optic nerve head.
Fundus: The back of the eye, that is, the retina, vessels and the optic disc, seen with an ophthalmoscope.
G [Top]
Giant cell arteritis: See temporal arteritis.
Glare: The sensation of being dazzled by direct light.
Glaucoma: 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 [Top]
Haemorrhage: Bleeding.
Hemianopia: 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.
Heterochromia: Different colours - Heterochromia iridis means the patient has a different coloured iris in each eye.
Heterophoria: 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).
Heterotropia: The deviation of an eye that 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).
Hordeolum: 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 /'Far sightedness': Ability to see distance better than near when not wearing corrective spectacles or contact lenses. These people use + or convex lenses.
Hyphaema: A fluid level of blood in the anterior chamber of the eye.
Hypopyon: A fluid level of pus in the anterior chamber of the eye.
Hypertension, ocular: High pressure inside the eye.
I [Top]
Indirect ophthalmoscopy: See ophthalmoscope.
Injection: Congested blood vessels in a red eye.
Intra-ocular: Inside the eye.
Iris: 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 [Top]
Keratitis: Inflammation of the cornea.
Keratoconjunctivitis: Inflammation of the eye that has affected both the conjunctiva and the cornea.
Keratoconus: Conical distortion of the cornea that leads the eye to have severe astigmatism and blurred vision.
Keratoplasty: See corneal graft.
Keratoscopy: Examination of the shape of the cornea.
Keratotomy: 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 [Top]
Laceration: A cut that may be deep or superficial, and may need stitching.
Lacrimal gland: The source of some of the eye's 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.
Lacrimation: The production of tears from the lacrimal gland that may be profuse in response to emotion or aroma.
Lagophthalmos: 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.
Lens: 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.
Leucocoria: A white coloured pupil.
Leukoma: 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'.
Lid retractraction: The position of the upper eyelid when it is pulled back so that the very top paer of the corneo-scleral junction is visible.
Limbus: The junction of the cornea and the sclera. This is also where the conjunctiva, which covers the sclera, ends.
M [Top]
Meibomian gland: Glands in the eyelid margins that secrete an oily substance into the tears.
Metamorphopsia: Wavy distortion of vision.
Miosis: Constriction of the pupil.
Miotic: A drug causing pupillary constriction.
Mydriasis: Dilatation of the pupil.
Mydriatic: 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 [Top]
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 seen in glaucoma patients taking pilocarpine drops.
O [Top]
Ocular: Pertaining to the eye.
Opacity: Loss of clarity in something that is normally clear or transparent.
Ophthalmia neonatorum: Conjunctivitis in the new-born.
Ophthalmoscope: 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 that 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.
Orbit: The bony socket in which the eye resides. It is shaped like a pyramid that 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.
Orthophoria: The situation in which both eyes work together in full co-ordination.
P [Top]
Pannus: Infiltration of the cornea with blood vessels.
Papilloedema: Swelling of the optic disc when secondary to raised intracranial pressure.
Perimeter: An instrument for measuring the field of vision.
Peripapillary: Near or around the optic disc on fundus examination.
Peripheral vision: Ability to perceive objects when outside the direct line of vision.
Phlyctenule: Localised infiltration of the conjunctiva with white blood cells.
Photocoagulation: Using laser light to treat certain disorders at the back of the eye.
Photophobia: Abnormal sensitivity to light.
Photopsia: Seeing flashing lights out of the corner of the eye when there are none. This is usually caused by mechanical stimulation of the retina.
Pingueculum: 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.
Proptosis: Abnormal protuberance of the eyeball out of its socket.
Pseudo-exfoliation: see Exfoliation of the lens.
Pseudophakia: The presence of an intraocular lens implant inside an eye, usually after cataract extraction.
Pseudo-squint: The situation in which a person seems to have a squint but in fact doesn't. The most common cause of this is the presence of a wide nasal bridge (epicanthus).
Pterygium: A triangular growth of tissue that grows from the conjunctiva onto the cornea. If large it can cause astigmatism.
Ptosis: Drooping of the eyelid.
Punctum: The hole through which the tears pass into the canaliculi.
Pupil: 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 [Top]
RAPD: 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.
Refraction: 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.
Retina: 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.
Retinopathy: Disease of the retina. For example, Diabetic retinopathy is disease of the retina secondary to diabetes.
S [Top]
Sclera: The white part of the eye.
Scotoma: A blind or partially blind area in the field of vision.
Slit lamp: A slit beam of light and a horizontally mounted microscope that allows detailed examination of the eye.
Spastic closure: Intense and involuntary closure (of eyelids as in bepharospasm).
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.
Stye: See Hordeolum, external.
Synechiae: Adhesion of the iris to the cornea (anterior synechiae) or the pupil to the lens (posterior synechiae).
Syneresis: A degenerative process of the vitreous humour/gel that leads to shrinkage and collapse of the gel.
T [Top]
Tarsorrhaphy: 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.
Tension: Pressure.
Tertiary syphilis: Very advanced syphilis that can affect any organ of the body but particularly the brain.
Tonometer: 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.
Trabeculectomy: An operation for glaucoma that allows controlled escape of aqueous fluid from the eye.
Trichiasis: 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 [Top]
Uvea: 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.
Uveitis: 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 [Top]
Vesicles: Small blisters filled with liquid that contains virus particles.
Visual acuity: The finest detail that an eye can distinguish using LogMar or Snellen scales.
Vitrectomy: Surgical removal of the vitreous.
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.
