Ophthalmic Dictionary of Eye Conditions & Terms

accommodation

Adjustment of the shape of the lens to change the focus of the eye.  This occurs through the ciliary muscles contracting and zonular relaxation that causes the elastic like lens to “round up” and increase its optical power.  There is a natural loss of accommodation with increasing age and this is called presbyopia.

achromatopsia

Complete colour blindness that can be congenital (born with it), or through disease or injury.

acne keratitis

Inflammation of the cornea that is associated with acne rosacea.

acne rosacea

A disease of the skin that causes redness of the forehead, nose and cheeks due to chronic dilatation of the capillaries under the skin; this becomes permanent with the intermittent formation of pustules in the affected areas.

acute

A sudden attack of a disease which is severe and of short duration.

after-cataract

Pieces of an opaque lens remaining in the eye or opacities forming in the capsule of the eye following cataract surgery.

after-image

A visual impression that remains briefly after sensory stimulation, e.g. after starring at a light bulb.

age-related macular degeneration (ARMD)

Group of conditions that includes the deterioration of the macula resulting in the loss of sharp central vision. There are two general types;

1. Dry this is the more common.
2. Wet in which new abnormal blood vessels grow under the retina and leak fluid & blood further disturbing the macular function.

albinism

A condition in which there is a congenital absence of pigment in the skin, hair and eyes which may be partial or complete as in Albinos.

ALK

See automated lamellar keratoplasty.

ametropia

A condition in which there is an abnormal refractive power of the eye: myopia, hyperopia or astigmatism.

amblyopia

Sometimes known as “lazy eye”.  Decreased vision in one or both eyes without a detectable disease of the eyeball or visual pathway.

Amsler grid

A test card or grid of black lines on a white background or white lines on a black background used for the detection of central visual field distortion or defects such as in macular degeneration.

aniridia

Lack of the whole iris (or part of the iris).

anisocoria

Inequality of the pupil size between the right & left eyes.

anisometropia

A difference in the refractive power of the two eyes.

anomalopia

A form of colour blindness where reds and greens look much the same.

anterior chamber  (ac)

Fluid filled space inside the eye between the iris and the innermost corneal surface (endothelium).

anterior chamber angle

Junction of the front surface of the iris and the back surface of the cornea where aqueous fluid passes out of the eye.

aphakia

Absence of the eye’s crystalline lens such as after cataract extraction.

aqueous humour (aqueous)

Clear, watery fluid that fills the space between the back space of the cornea and the front surface of the vitreous, bathing the lens.  The fluid is produced by the ciliary process and it nourishes the cornea, iris and lens and maintains the intraocular pressure.

arcuate

Arched, bow shaped.

argon laser

A type of Laser that produces an intense beam of light, used in eye surgery to treat disease of the retina, such as diabetic retinopathy, or glaucoma as in laser trabeculoplasty.

A-Scan

A radar like ultrasound device that emits very high frequency waves that are reflected by the ocular structures and converted into electrical impulses which are used for differentiating normal and abnormal eye tissue or for the measuring of the eyeball prior to intraocular lens implantation (cataract surgery).

asthenopia

Vague eye discomfort arising from the use of the eye which may consist of eye strain, headache and/or brow ache.  It may also be related to uncorrected refractive error.

astigmatism

Inequality of the refractive power of an eye due to different curvatures of its corneal meridians (like the side of a Rugby Ball).

asymmetry

Inequality in the size or shape of two structures that are normally the same.

asymptomatic

Without symptoms.

atopy

A state of hypersensitivity to certain antigens (e.g. pollens) causing an allergic reaction:
Asthma, Eczema, Hay fever.

automated lamellar keratoplasty (ALK)

Excision of the outer corneal layers (lamellae) with a mechanical keratome (knife) usually as part of a refractive keratoplasty procedure.

axis

A line through the centre of a structure.

Bell’s palsy

Facial paralysis which can result in the failure to close the eye.

beta blocker

A group of drugs used to block the action of epinephrine (adrenaline) and nor epinephrine (noradrenalin) at the nerve endings.
They are used in the eye to treat glaucoma e.g. timolol, betaxolol.

bifocals

Spectacles that incorporate two different powers in each lens usually for near and distance corrections.

binocular vision

Blending of the separate images seen by each eye into one composite image.

bipolar cells

Retinal cells that each have two long “tails” that receive nerve signals from the rods and cones and pass them on to the ganglion cells.

blane

See Stye.

blepharitis

Inflammation of the eyelids.

blepharon

The eyelid.

blepharophimosis

Abnormal narrowing of the opening between the eyelids.  Usually congenital but may arise from chronic inflammation.

blepharoptosis

Drooping of the upper eyelid.

blepharospasm

Involuntary spasm of the muscles of the eyelids.

blepharoplasty

An operation to repair or re-construct the eyelid.

blind

Without sight.

blind registration

Now known as “Severe Sight Impaired”.  Unable to read the top letters of the vision chart or to “do a job for which vision is essential”.

blind spot

The point where the optic nerve leaves the retina; it is insensitive to light.

bruit

An abnormal sound or “murmur” heard on listening to the heart and large blood vessels.

B-Scan

Type of ultrasound that provides a cross-section view of the tissues that cannot be seen directly.  High frequency waves are reflected by the eye tissues and orbital structures and converted into electrical impulses which can be displayed or printed out.

buphthalmos

A condition seen in infants where the intraocular tension is raised (congenital glaucoma).

canaliculus

Small tube draining tears from the eyelid punctum into the lacrimal sac and the naso-lacrimal duct [plural: canaliculae].

canaloplasty

A primary open angle glaucoma surgical procedure that begins as a viscocanalostomy with the addition of the passage of a micro-catheter 360° through Schlemm’s canal with visco-dilation and the placing of a circumferential tension device/suture within the canal.  Also known as an Enhanced Viscocanalostomy (see also Viscocanalostomy).

canthus

The angle formed by the junction of the upper and lower eyelids.

capillary

The smallest blood vessel (smaller than a human hair).

capsule or capsular bag

The outermost layer of the crystalline lens “The Lens Capsule” or “bag”.
A fine “Clingfilm like” membrane which is left in the eye in most cases of cataract surgery to “shrink rap” the IOL and keep it in position.

capsulotomy

Cutting a gap in the lens capsular membrane, usually with a YAG Laser.

cataract

Opacity or cloudiness of the crystalline lens which may prevent a clear image from forming on the retina.  May be caused as part of the aging process, as a result of injury or disease, or may be congenital.

cataract extraction

Surgical removal of the opaque crystalline lens.

central retinal artery

First branch of the ophthalmic artery which supplies nutrition to the inner two-thirds of the retina of the eye.

central retinal artery occlusion (CRAO)

Blockage of the central retinal artery.  Most common causes are: hardening of arteries, high blood pressure, heart disease and diabetes.

central retinal vein

Blood vessel that collects retinal venous blood drainage; it exits the eye through the optic nerve.

central retinal vein occlusion (CRVO)

Blockage of the retinal vein.  Commonly associated with hardening of the arteries with or without blood abnormalities, systemic diseases or glaucoma.

central vision

Results from stimulation of the fovea and macular areas which provide detailed vision, used for reading and discriminating fine detail and colour.

chalazion

Inflamed lump (cyst) in the meibomian gland (of the eyelid) that may resolve without treatment or require surgical removal.  (See Meibomian Gland/Cyst).

choroid

The pigmented and vascular layer of the eye lying between the retina and sclera; it provides nourishment to the outer layers of the retina.

choroiditis

Inflammation of the choroid.

ciliary muscle

A ring of very small muscles which change the shape of the lens to allow focusing.

coloboma

A congenital gap in the eye affecting the iris, choroid and the retina.
May give rise to a “keyhole pupil”.

colour blindness

Reduced ability to discriminate between colours, especially shades of red and green; usually hereditary.

cone

Light sensitive receptor cell in the retina that provides sharp visual acuity and colour discrimination.  A normal retina has 7 million cones.

congenital

Existing before birth or at birth.

conjunctiva

Clear mucous membrane (moist skin) covering the outer surface of the eyeball, except the cornea, and lining the inner surface of the eyelids.

conjunctivitis

Sometimes called “pink eye” it is the inflammation of the conjunctiva usually associated with discharge, grittiness, redness and swelling. May be contagious.

contact lens

Small specially shaped lens used to correct a visual problem that sits in front of the eye, in front of the cornea.

convergence

Inward movement of both eyes toward each other in an effort to maintain single binocular vision as an object approaches.

cornea

Transparent front part of the eye that covers the iris, pupil and anterior chamber and provides most of the eye’s optical power (a fixed focus lens).

cornea guttata

Protuberances of the corneal endothelium.  May occur in the early stages of corneal dystrophy or as a result of aging or inflammation (particularly if confined to the peripheral cornea).

corneal graft/transplant

Surgical replacement of a damaged or diseased cornea (see keratoplasty).

cross eyes

See esotropia.

crystalline lens

The natural lens of the eye; it is the transparent, biconvex intraocular tissue that helps bring rays of light to a focus on the retina (a variable focus lens).

cyclitis

Inflammation of the ciliary body of the eye.

cycloplegia

Paralysis of the ciliary muscle of the eye.

cycloplegic refraction

Assessment of an eye’s refractive error after lens accommodation has been paralysed with cycloplegic eye drops to eliminate variability in optical power caused by accommodation.

cyclpentolate

An eye drop that paralyses the ciliary muscles and dilate the pupils.

dacryocystography

X-ray examination of the lacrimal duct using a radio-opaque contrast medium.

dacryoadenectomy

Surgical removal of a lacrimal gland.

dacryocystorrhinostomy (DCR)

An operation to create an opening between the lacrimal sac and the nasal cavity (for the treatment of watering eye).

dacryolith

A calculus (stone) in a lacrimal duct.

dacryoma

A benign tumour which arises from the lacrimal epithelium.

Deep Anterior Lamellar Keratoplasty  (DALK)

See Lamellar Keratoplasty.

Deep Endothelial Keratoplasty   (DEK)

A form of Posterior Lamellar Keratoplasty in which only the very deepest layers of the cornea are transplanted/grafted.

Deep Lamellar Keratoplasty

A deep partial thickness anterior corneal transplant/graft (see DALK).

descemet’s membrane

The elastic membrane lining the posterior surface of the cornea,
Between the corneal stroma and the endothelial cells.

descemet’s stripping automated endothelial keratoplasty

A form of Deep Endothelial Keratoplasty in which only the very deepest layers of the cornea are transplanted/grafted (see DSAEK).

diabetic retinopathy

Spectrum of retinal changes associated with long standing diabetes mellitus.

dichromatic

Relating to colour blindness where there is the ability to see only two of the three primary colours.

dilatation

The reflex widening of the pupil of the eye, in poor light, to admit more light onto the retina.

dilated pupil

Enlarged pupil resulting from the contraction of the dilator muscle or the relaxation of the iris sphincter; it can occur naturally or may be produced by certain drugs or as a result of blunt trauma (injury).

dioptre

Unit to designate the refractive power of a lens.

diplopia

Double vision.  The perception of two images from one object caused by lack of co-ordination of the external eye muscles.

divergence

Abduction of the eyes (turning outward).

DLK

Deep Lamellar Keratoplasty (see Lamellar Keratoplasty).

drusen

Tiny white hyaline deposits on Bruch’s membrane (of the retinal pigment epithelium); common after the age of 60 and is sometimes and early sign of macular degeneration.  (See also optic nerve drusen).

Dry Eye Syndrome

Corneal and conjunctival dryness caused by deficient tear production which can cause a “foreign body” sensation of ‘gritty’ or ‘burning eyes’ (see kerato-conjunctivitis [sicca]).

DSAEK

Descemet’s Stripping Automated Endothelial Keratoplasty.
A form of Deep Endothelial Keratoplasty in which only the very deepest layers of the cornea are transplanted/grafted.

dyscoria

Abnormal formation of the pupil of the eye.

ecchymosis

Black eye, usually caused by trauma.

ectopia lentis

Abnormal position of the lens of the eye.

ectropion

Outward turning of the upper or lower eyelid so that the lid margin does not rest against the eyeball but falls or is pulled away.  This can create corneal exposure with excessive drying, tearing, irritation and ulceration of the cornea.  Usually associated with aging.

emmetropia

Refractive state of having no refractive error when accommodation is at rest; images of distant objects are focused sharply on the retina without the need for corrective lenses.

endophthalmitis

Inflammation of the interior of the eye.

enophthalmos

When the eyeball is abnormally sunken into its socket.

enhanced viscocanalostomy

See viscocanalostomy & canaloplasty.

entropion

Inward turning of the upper or lower eyelid that results in the lid margin resting and rubbing against the eyeball producing irritation and ulceration of the cornea.  Usually associated with aging.

enucleation

The removal of the eyeball either surgically or through trauma (injury).

epiblepharon

A congenital condition in which an excess of skin of the eyelid folds over the lid margin so that the eyelashes are pressed against the eyeball.

epilation

Removal of eyelashes with their roots.

epithelium

Tissue that covers the external surface of the body and some organs (skin).

epiphoria

Persistent overflow of tears often due to an obstruction in the lacrimal passages or due to ectropion.

episcleritis

Inflammation of the outer coat of the eyeball.

epicanthus

Vertical fold of skin from the upper eyelid that covers the inner corner of the eye.

esophoria

Latent convergent strabismus (squint) where one or both eyes turn inwards only when one is covered up.

esotropia

Convergent strabismus (squint) where one or other eye turns inwards resulting in double vision.

excimer laser

Excited Dimer Laser; a class of ultraviolet lasers that removes tissues accurately.  In refractive corneal surgery, controlled by computer, the Excimer Laser is used to make a precise pre-programmed removal of corneal tissue to produce a given optical correction.

exophoria

Where the eyes have a tendency to turn outwards.

exophthalmos

Protrusion of the eyeball which may be caused by injury or disease and is often seen in hyperthyroidism.

exotropia

Divergent strabismus (squint) where the eyes turn outwards.

extra capsular

Outside the capsule of the eye.

extraocular

Outside the eye.

extraocular muscles

Six muscles that move the eyeball (lateral rectus, medial rectus, superior oblique, inferior oblique, superior rectus and inferior rectus).

eyelids

Structures covering the front of the eye which protect the eye, limit the amount of light entering the pupil and distribute tear film over the exposed corneal surface.

far sightedness

See hyperopia.

femtosecond laser

An “ultrashort pulsed laser” used to cut the cornea in place of a mechanical blade in e.g. LASIK and Keratoplasty.

field of vision

The area that can be seen without moving the eyes.

floaters

Particles that float in the vitreous and cast shadows on the retina and may be seen as “spots, cobwebs, spiders” etc. occurs normally with aging or with vitreous detachment, retinal tears or inflammation.

fluorescein angiography

A technique used for visualising and recording the location and size of blood vessels and any eye problems affecting them.  Fluorescein dye is injected into a vein in the arm then rapid sequential photographs are taken of the eye as the dye circulates.

focus

The point where rays of light meet after passing through a lens.

follicle

A very small sac or gland.

fovea

The central pit in the macula that produces the sharpest vision and contains a high concentration of cones but no retinal vessels.

fundus

The interior posterior surface of the eyeball that includes the retina, optic disc, macula and posterior pole.  It can be seen with an ophthalmoscope.

ganglion cells

Nerve cells in the retina that transfer messages from the rods and cones to the nerve fibres that pass messages to the brain.

glaucoma

Group of diseases characterised by increased intraocular pressure resulting in damage to the optic nerve and retinal nerve fibres.  It is a common cause of preventable vision loss and may be treated with prescription drugs or surgery.

• Primary Glaucoma: occurs without any previous disease.  Common cause of blindness, partial or complete, in the elderly.
• Closed Angle Glaucoma: Occurs when there is a mechanical defect in the drainage angle and may be primary or secondary.  It may be acute when there is pain and blurring of vision or chronic when there may be no pain but a gradual loss of vision.  Associated with hyperopia.
• Open Angle Glaucoma: Chronic primary glaucoma where the angle remains open but drainage becomes gradually diminished
• Secondary Glaucoma: Occurs when some ocular disease is complicated by an increase in intraocular pressure.
• Normotensive Glaucoma: Occurs in eyed with apparently normal intraocular pressure.

gonioscopy

Examination of the anterior chamber angle through a special contact lens incorporating mirrors called a goniolens.

guttae (gut/gt)

Drops: usually used to deliver medication to the eyes.

guttata

See Cornea Guttata.

halo

Coloured ring or rings seen around lights by people with glaucoma.

hemianopia

Partial blindness where the patient can only see one half of the normal field of vision in both eyes.  It arises from disorders of the optic tract and of the occipital lobe.

herpes zoster ophthalmicus

Shingles affecting the first division of the 5th cranial nerve.  The forehead, face and nose are affected with the cornea also usually involved.  Neuralgic pain may be severe and vesicles (very small blister containing clear fluid) may appear on the nostrils.  Keratitis may occur and the pain may persist to lesser degree for several months.

Hess Screen test

A test performed for paralytic squint.  The degree of diplopia is recorded on a chart.

heterochromia

A difference in colour in the irides of the two eyes; may be congenital or secondary due to inflammation.

heterophoria

A tendency to squint when fusion is interrupted; occurs mainly when the person is tired or in poor health.

hippus

Alternate contraction and dilatation of the pupils.

hordeolum

External hordeolum:  A stye, Inflammation of a sebaceous gland of an eyelash.
Internal hordeolum: Infected meibomian cyst.

Humphreys field analyzer

Instrument used to assess visual fields.

hyalitis

Inflammation of the hyaloid membrane or vitreous (humour) in the eyeball.

hyaloid membrane

A delicate transparent membrane surrounding the vitreous humour of the eye.

hypermetropia (hyperopia)

Long sighted; the light rays entering the eye converge beyond the retina.  Clear vision can be obtained by the wearing of corrective convex spectacles or contact lenses or with laser surgery or Intraocular Implants.

hyphaema

Haemorrhage (bleeding) into the anterior chamber of the eye.

hypometropia

See Myopia.  Short sightedness.

hypopyon

An accumulation of pus in the anterior chamber of the eye.

image

The optical picture transferred to the brain cells by the optical nerve.

inferior

Lower.

intracapsular

Within a capsule; usually a joint.
Intracapsular Extraction – the removal of the whole lens with its capsule in the treatment of cataracts.

intraocular

Within the eyeball.

Intraocular Lens Implant

An artificial “plastic” lens which is implanted into the eye.  Most commonly in association with cataract extraction.

IOL

Acronym for Intraocular Lens (Implant).
(See also Phakic IOL).

intraocular pressure (IOP)

Pressure within the eye.

iris

Pigmented ring shaped muscular screen lying behind the cornea that gives colour to the eye (e.g. blue eyes) and controls the amount of light entering the eye by varying the size of the pupillary opening (iris diaphragm).

iritis

Inflammation of the iris causing pain, photophobia, contraction of the pupils and discolouration of the iris.  (See uveitis).

Ishihara colour charts

Patterns of dots of the primary colours on similar backgrounds that can be seen by normal sighted people but those who are colour blind will only be able to identify some of them.

keratectasia

Protrusion of the cornea following inflammation.

keratectomy

Excision of a portion of the cornea.

keratic

Relating to the cornea

• Keratic precipitates: inflammatory exudates adhering to the back of the cornea.  A sign of iritis and cyclitis.

keratitis

Inflammation of the cornea

• Interstitial Keratitis – deep chronic keratitis usually arising out of congenital syphilis.
• Striate keratitis – inflammation that appears in lines due to the folding over of the cornea after injury or operation, particularly one for cataract.

kerato-conjunctivitis

Inflammation of both the cornea and the conjunctiva of the eye.
kerato-conjunctivitis sicca  = Dry Eye Syndrome

kerato-iritis

Inflammation of both the cornea and iris of the eye.

keratoconus

Conical cornea; a degenerative condition in which the cornea becomes thin and protruded into a cone shape (like the tip of a rugby ball).

kerato-malacia

Softening of the cornea.

keratome

A knife with a triangular shaped blade for incising the cornea.

keratometry

Obtaining accurate corneal curvature measurements with a keratometer.

keratoplasty

An operation on the cornea including corneal graft/transplantation,
May be “full thickness” or “partial thickness” (see Lamellar Keratoplasty).

lacrimal

Relating to tears.

• Lacrimal Apparatus:  the structures secreting the tears and draining the fluid from the conjunctival sac
• Lacrimal Gland: A gland that secretes tears which drain through two small openings in the eyelids (Lacrimal Puncta) into a pair of ducts (Lacrimal Canaliculi) into the lacrimal sac and then into the nasal cavity through the naso-lacrimal duct

lamellar keratoplasty

A partial thickness Corneal Transplant/Graft. (See Deep Lamellar Keratoplasty).

LASER

An acronym of Light Amplification by Stimulated Emission of Radiation.  A high energy light source that uses light emitted by the natural vibrations of atoms (of a gas or solid material) to cut, burn or dissolve tissue for various clinical purposes.

LASEK

An acronym of Laser Epithelial Keratomileusis.  Type of refractive surgery where the cornea is re-shaped to change its optical power.
The outermost layer of the cornea, the corneal epithelium, is softened with alcohol and pushed to one side and then an excimer laser is used to reshape the inner part of the cornea, before the epithelium is replaced, to correct myopia, hyperopia and astigmatism.  

LASIK

An acronym of Laser in Situ Keratomileusis.  Type of refractive surgery where the cornea is re-shaped to change its optical power.
The top of the cornea is first sliced with either a microkeratome or a femtosecond laser to create a “flap” and then an excimer laser is used to reshape the inner part of the cornea, or “bed”, to correct myopia, hyperopia and astigmatism.

lazy eye

See amblyopia.

legal blindness

Meets the criteria for Registration on “The Blind Register” (see Blind Registration & Partial Sighted Registration).

lens

See crystalline lens.

lens implant

A plastic lens which is implanted into the eye.  (See Intraocular Implant: IOL).

light adaptation

The changes that take place in the eye when the intensity of light increases or decreases as in “night vision”.

light coagulation

A method of treating retinal detachment by directing a beam of strong light from a carbon arc through the pupil to the affected area.

limbus

An edge or border; Corneal Limbus: The border where the cornea joins the sclera.

lipaemia retinalis

Condition in which the retinal blood vessels appear to be filled with “milk” due to the presence of an excess of fat in the blood.

lithiasis (conjunctival)

The formation of small white chalky area on the inner surface of the eyelids.

long sight

See hypermetropia, hyperopia.

loupe

A magnifying lens which may be used in eye examination.

lysozyme

A natural disinfecting agent which is produced in tears; it kills micro-organisms which could otherwise grow on the cornea.

macrophthalmia

A congenital condition of abnormally large eyes.

macula

Small central area of the retina surrounding the fovea; area of detailed central vision [a noun].  (Macular: Adjective).

Maddox Rod test

A test for muscle balance of the eyes using a lens comprised of red glass cylinders.

• Maddox Wing Test: a method of measuring the amount of heterophoria.

meibomian glands

Small specialised sebaceous glands situated beneath the conjunctiva of the eyelids and responsible for the oily constituent of the tear film.

• Meibomian Cyst: a small swelling of the gland caused by an obstruction of its duct; if untreated it may become infected (see chalazion).

meibomitis

A chronic inflammation of the meibomian glands.

meiosis

The process of cell division.

meniscus

A lens having on convex and one concave surface.

microcornea

A condition in which the cornea is smaller than normal producing hypermetropia and sometimes causing glaucoma.

microkeratome

A cutting or slicing device used in corneal surgery (see LASIK, epi-LASIK).

microphthalmos

A condition in which one or both yes are smaller than normal; their function may or may not be impaired.

migraine

Paroxysmal attacks of severe headaches, often with nausea, vomiting and visual disturbance.

miosis

Contraction of the pupil of the eye to less than 2mm.

miotic

A drug which causes contraction of the pupil of the eye e.g. pilocarpine, morphine.

mm/Hg

Millimetres of mercury: unit of measurement that is used to measure intraocular pressure.

molluscum contagiosum

Benign tumour, arising in the epidermis, caused by a virus and transmitted by direct or indirect contact.

monochromatic vision

Seeing in black, white and shades of grey; a rare form of colour blindness.

monocular

Pertaining to or affecting one eye only.

mydriasis

Abnormal dilatation of the pupil of the eye; usually caused by injury to the pupil sphincter or by the use of mydriatic drugs.

mydriatic

Any drug which causes mydriasis; they are used in the examination of the eye and the treatment of inflammatory conditions e.g. atropine, cyclopentolate, tropicamide.

myopia

Short Sighted, Hypometropia, Near Sighted.  The light rays focus in front of the retina Clear vision can be obtained by the wearing of corrective concave spectacles or contact lenses or with laser surgery or Intraocular Implants.

naevus

A birthmark; an area of pigmentation of tissue often associated with dilated blood vessels.

• Choroidal Naevus: an unusual pigmented area on the choroid of the eye.

nasolacrimal

Concerning both the nose and lacrimal apparatus.

• Naso-lacrimal Duct: The duct draining the tears from the canaliculae at the inner aspect of the eye into the inferior meatus of the nose.

neovascularisation

Abnormal formation of new blood vessels, usually in or under the retina or iris surface or angle of the eye.  May develop in diabetic retinopathy, blockage of the central retinal vein, retinopathy of prematurity or macular degeneration.

neuromyelitis

A disease in which there is bilateral optic neuritis and paraplegia.

Nd-YAG Laser

See YAG Laser.

night blindness

Loss of visual purple due to a deficiency in vitamin A which makes it difficult to see in dark or dim conditions.  [Nyctalopia] (See Retinitis Pigmentosa).

nyctalopia

Night blindness.

nystagmus

Involuntary rhythmic side to side or up and down (oscillating) eye movements that are faster in one direction than the other.

oblique

Slanting

• Oblique Muscles: a pair of muscles, the inferior and superior, which turn the eye upwards and downwards and inwards and outwards.

occlusion

Closure

• Occlusion of the eye: covering a good eye to improve the visual acuity of the other, lazy eye.
• Occlusion of the pupil: Occlusion Pupillae.  Obstruction of the pupil which may be congenital or occur in iridocyclitis or after injury.
• Central Retinal Vein Occlusion.
• Central Retinal Artery Occlusion.

ocular

Relating to the eye.

ocular prosthesis/implant

An artificial eye which is inserted into the socket after enucleation of the eyeball.

oculentum
abbreviated to Oc or Occ.

Eye ointment.

oculogyric

Causing movement of the eyeball.

oculomotor

Relating to movements of the eye.

• Oculomotor Nerves: The third pair of cranial nerves which control the eye muscles.

opacity

Cloudiness, lack of transparency.  Opacities occur in the lens of an eye when a cataract is forming; they also occur in the vitreous humour and appear as floating objects (floaters).

ophthalmoscope

Illuminated instrument for visualising the interior of the eye.

ophthalmia

Inflammation of the eye, involving especially the conjunctiva.

ophthalmitis

Inflammation of the eyeball.

ophthalmologist

A specialist in diseases of the eye.

ophthalmology

The study of the eye and its diseases.

ophthalmometer

An instrument for the accurate measurement of corneal astigmatism (Keratometer).