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GLOSSARY
OF OPTICAL TERMS A ACCOMMODATION The ability of the eye to change its focus from distant to near objects. ACETATE A type of plastic often used in spectacle frames. ADIE'S PUPIL A pupil that does not react normally to bright light due to impaired nerve function. It does not usually interfere substantially with vision. AGE-RELATED MACULAR DEGENERATION A disorder characterised by the gradual loss of central vision due to a damaged macular. AMAUROSIS FUGAX A temporary loss of vision in one eye - may be a sign of a transient ischaemic attack (TIA) or an impending stroke. AMBLYOPIA Also termed "lazy eye". A healthy eye with poor vision, normally due to lack of input from the eye to the brain during childhood. AMD See AGE-RELATED MACULAR DEGENERATION ANISOMETROPIA An unequal refractive power between the two eyes. ANTERIOR CHAMBER The space behind the cornea and in front of the iris and lens. AR COATING (anti-reflective coating) A coating applied to a lens to reduce the amount of reflected light and glare that reaches the eye. APHAKIA The absence of the eye's natural lens, usually after cataract surgery. AQUEOUS FLUID A clear watery fluid in the front chamber of the eye that nourishes the lens and the cornea, and also determines intraocular pressure. ARCUS SENILIS A hazy ring at the edge of the cornea where the iris meets the white of the eye. It does not impair vision. ARMD See AGE-RELATED MACULAR DEGENERATION ASPHERIC Not quite spherical. ASTHENOPIA Eyestrain or tired eyes ASTIGMATISM A condition caused by an irregularly shaped cornea, which results in a blurred image being received at the retina. B BI-FOCAL Two lenses combined into one lens area to give two different focal lengths, usually distance and reading. BINOCULAR VISION The blending of the separate images seen by each eye into a single image. This allows images to be seen with depth. BLEPHARITIS An inflammation of the eyelid that can cause irritation, discharge and blurred vision. BLIND SPOT A small area of the retina where the optic nerve enters the eye. This occurs normally in all eyes. BOWMAN'S MEMBRANE A corneal layer between the epithelium and the stroma. BRIDGE A part of a spectacle frame that extends across the nose. C CATARACT A clouding of the natural lens, usually found in older patients (but it can occur following accidental damage to the eye) which results in impaired vision. CENTRAL RETINAL ARTERY The vessel that transports blood into the eye. CENTRAL RETINAL ARTERY OCCLUSION A blockage of the main blood supply to the eye, which often causes blindness. CENTRAL RETINAL VEIN The vessel that transports blood away from the eye. CENTRAL RETINAL VEIN OCCLUSION A blockage of the main vein transporting blood away from the retina. This causes haemorrhage in the retina and usually results in permanent visual impairment. CENTRAL SEROUS RETINOPATHY A spontaneous leakage of fluid into the retina, often in young healthy people. Cause unknown. CENTRAL VISION The ability to distinguish details and shapes of objects. This is also called visual acuity. CHALAZION A bump in the eyelid caused by a clogged oil gland - may require surgical removal. CHOROID A layer of blood vessels that lies beneath the sclera which nourishes the retina. CILIARY BODY A part of the eye that contains a focusing muscle and connective tissue. CILIARY MUSCLE A muscle that enables the lens to change shape for focusing. CILIARY PROCESSES The extension of the ciliary body that secretes aqueous humour. CLIP-ON Lenses that attach to regular glasses, such as clip-on sunglasses. CMV RETINITIS (cytomegalovirus retinitis) A serious infection of the eye, usually found in those with immune problems. Symptoms include floaters, blind spots, blurring of vision and vision loss. COLOUR BLINDNESS Partial or total inability to distinguish specific colours. COMPUTOR VISION SYNDROME A condition caused by prolonged computer use. Symptoms include blurred vision, headaches, and dry or irritated eyes. CONCAVE LENS An optical lens with both surfaces curving inwards. CONE One type of specialised photoreceptors (light sensitive cells) in the retina that provide sharp central vision and colour vision. CONJUNCTIVA The thin mucous membrane that lines the visible part of the eye and the inner surface of the eyelid. CONJUNCTIVITIS Inflammation of the conjunctiva. CONTACT LENS DROPS Eye drops for contact lens wearers - regular eye drops can discolour contact lenses. CONTRAST SENSITIVITY The ability to perceive differences between an object and its background. CONVEX LENS An optical lens with both surfaces curving outwards. CORNEA The transparent membrane which covers the iris and pupil. Its main purpose is protection, but it also lets light into the eye. CORNEAL ABRASION A tearing or puncture of the cornea. CORNEAL EROSION Spontaneous loss of a part of the surface of the eye, causing pain, light sensitivity and blurred vision. CORNEAL IMPLANTS Devices placed in the eye to correct vision. CORNEAL OEDEMA A swelling of the cornea, often causing blurred vision. CORNEAL ULCER A localised inflammation of the cornea due to infection, injury or dryness caused by lack of tear production. Needs immediate treatment to prevent permanent damage. D DACRYOCYSTITIS An infection in the tear sac. DACRYOSTENOSIS A blocked tear duct. DAILY WEAR Soft contact lenses worn every day for 6 - 24 months. They require daily cleaning and disinfecting. DERMATOCHALASIS An excess of baggy skin on the eyelids. DESCEMET'S MEMBRANE A corneal layer between the stroma and the endothelium. DIABETIC RETINOPATHY A leaking of retinal blood vessels in advanced diabetes, affecting the macular or retina. DILATION A process by which the pupil is temporarily enlarged with eye drops. This allows a better view of the inside of the eye. DIOPTER The unit which measures the refractive (light-bending) power of a lens. DIPLOPIA A term meaning double vision. DISPOSABLE CONTACT LENS Any contact lens that is thrown away after a short period of time. DRUSEN Tiny yellow or white deposits in the retina. DRY EYE A lack of sufficient moisture and lubrication in the eye. E ECTROPION Loosening of the eyelid, causing it to turn outwards away from the eye. EMMETROPIA A term meaning normal vision. ENDOTHELIUM The inner layer of cells of the cornea. ENTROPION Collapsing of the eyelid, causing the edge of the lid to turn inwards towards the eye. ENZYMATIC CLEANER A cleaner that removes protein deposits and other debris from contact lenses. EPITHELIUM The outer layer of cells of the cornea. ESOTROPIA The condition in which an eye turns inwards. EXOPHTHALMOS A forward bulging of the eyes. EXOTROPIA The condition in which an eye turns outwards. EXTENDED WEAR Contact lenses that can be worn without removal for up to seven days. F FLOATERS Small specks that pass across the field of vision. These are clumps of cells inside the transparent gel in front of the retina. FOCAL LENGTH The distance between the object and the eye. FOVEA The central part of the macular that provides the sharpest vision. FREQUENT REPLACEMENT LENSES Any contact lens that is thrown away after a moderately short period of time. FUCHS' DYSTROPHY A deterioration of the cells in the cornea that maintain the cornea's clarity. FUNDUS The interior lining of the eyeball, which includes the retina, optic disc and macular. This is the part of the inner eye that can be seenduring an eye examination by looking through the pupil. G GLAUCOMA A disease characterised by excessive fluid (aqueous humour) in the eye, high intraocular pressure, and visual impairment. In most cases the onset is gradual and can be detected by regular eye examinations. GLASS A lens material (rarely prescribed these days). GRAVES OPHTHALMOPATHY A thyroid-related autoimmune disorder. Symptoms include eyelid retraction, bulging eyes, light sensitivity and vision loss. H HARD CONTACT LENSES, These are small hard lenses made of PMMA material which were popular in the 70's and 80's. Rarely worn now as they are less healthy to wear than the modern soft and rigid lenses. HEAMORRAGE A bursting of a minor blood vessel, which can sometimes be seen in the white of the eye. HEMIANOPIA The loss of one half of the visual field usually caused by brain injury. HIGH INDEX A type of material with a higher index of refraction, which produces thinner prescription lenses. HYPERMETROPIA Also known as farsightedness - the ability to see distant objects more clearly than close objects. HYPEROPIA Also known as farsightedness - the ability to see distant objects more clearly than close objects. HYPHEAMA This is bleeding inside the eye, usually due to an injury. I INTRAOCULAR PRESSURE (IOP) The eye pressure as determined by the amount of aqueous humour filling it. High IOP can be a sign of glaucoma. IRIS A diaphragm which regulates the amount of light entering the eye by controlling the size of the pupil. The colour of the iris determines the colour of a person's eye. IRITIS Inflammation inside the eye, mostly in the front of the eye which causes redness, pain, blurred vision and sensitivity to light. K KERATECTOMY The surgical removal of part of the cornea. KERATITIS Inflammation of the cornea. KERATOCONUS A progressive change in the shape of the cornea, creating a cone-shaped configuration that can result in blurring and distortion of vision. KERATOPLASTY Any of several types of corneal surgery eg corneal transplant. KERATOTOMY Incision of the cornea. L LACRIMAL GLAND A small oval shaped structure located just above the outer corner of the eye, that produces tears LACRIMAL PLUG A device to block the opening at the end of a tear duct to keep the eye moist. LASER PHOTOCOAGULATION A procedure in which a laser is used to coagulate tissue, eg to seal leaking blood vessels. LATERAL RECTUS MUSCLE The muscle that moves the eye away from the nose. LENS A transparent double convex structure suspended between the aqueous and vitreous, which helps to focus light on the retina. LENTICULAR A type of material used in certain high power lenses to reduce the thickness on the edge of the lenses. LIMBUS A boundary area connecting the cornea and sclera - the three form the eye's outermost layer. LIPID A fatty substance that can collect on contact lenses, making them uncomfortable to wear. LOW VISION Also called partial sight. Vision that cannot be corrected with glasses, contact lenses or surgery, and interferes with daily living activities. LUTEIN An antioxidant that is found in the macula and helps protect the eyes from free radical damage caused by the sun's harmful rays. M M M MACULAThe
part of the eye near the centre of the retina where the incoming rays
of light are focused. N NEARSIGHTEDNESS
Also called myopia. O OCULAR
MIGRAINE A visual disturbance usually including flashing lights and blurry
vision. OPTOMETRIST A person registered to examine eyes for eye disease, and qualified to issue prescriptions for lenses to correct abnormal vision. P PAPILLA A small bump where the optic nerve exits the eye. PERIPHERAL VISION The edges of the visual field. PUPIL The dark circular hole in the centre of the iris which opens and closes to regulate the amount of light the retina receives. Q QUADRANTANOPSIA Loss of vision in a quarter of the visual field of the eye. R RETINA The sensory membrane that lines the inside of the eye. It is composed of several layers and receives images formed by the lens and converts them into signals which reach the brain via the optic nerve. RETINAL DETACHMENT A condition where the retina becomes detached from the inner layer of the eye. RUBEOSIS The growth of abnormal blood vessels on the iris. S SCLERA The tough, outer coat of the eyeball that forms the visible white of the eye. SQUINT See strabismus. STRABISMUS Also known as a squint. A common condition mainly effecting young children, when the two eyes have difficulty in maintaining alignment. T TEARS The clear watery fluid secreted by the lacrimal gland. TONOMETER A machine to determine the fluid pressure inside the eye. See Intraocular pressure. TRICHIASIS An abnormal eyelash growth usually with the eyelash growing inwards towards the eye. U UVEA The middle coat of the eyeball. It consists of the choroid in the back of the eye, and the ciliary body and the iris in the front of the eye. UVEITIS An inflammation of the interior of the eye. V VISUAL ACUITY The ability to distinguish details and shapes of objects. VISUAL FIELD The entire area that can be seen, including peripheral vision, when the eye is looking forward. W WINK The rapid voluntary closure and opening of one eye. WRAPAROUND A type of spectacle frame that curves around the head, from the front to the side. X XANTHELASMA A lipid deposit which appears in the skin of the eyelids and may indicate high cholesterol levels. XANTHOPSIA A condition in which all objects appear of a yellow colour. Y YELLOW SPOT An area of the retina slightly below the level of the optic disc. Z ZONULES The fibres that hold the lens suspended in position, and enable it to change shape during accommodation. |