Glossary
Vision and Eye Care Glossary
Plain-language definitions of the terms you will actually hear at an eye exam.
A
- Accommodation
- The eye's ability to change focus between distance and near by changing the shape of its internal lens. It weakens with age, which is presbyopia.
- Amblyopia
- Reduced vision in one eye because the visual system did not develop normally, often called lazy eye. Treatable in childhood and much harder to treat after about age eight. Read more.
- Anti-reflective coating
- A lens coating that eliminates reflections within the lens, improving clarity, cutting night-driving glare, and letting people see your eyes rather than reflections. Read more.
- Aqueous deficient dry eye
- Dry eye caused by insufficient production of the watery layer of the tear film, as distinct from evaporative dry eye. Read more.
- Astigmatism
- An eye whose surface is curved unevenly, more like a football than a basketball, so light focuses at more than one point. Read more.
B
- Base curve
- The curvature on the back surface of a contact lens, which must match your cornea for the lens to fit and move correctly.
- Binocular vision
- How the two eyes work together as a pair. Problems here cause double vision, eye strain and reading difficulty even when each eye sees clearly alone.
- Blepharitis
- Chronic inflammation of the eyelid margins. Very common, often undiagnosed for years, and a frequent underlying driver of dry eye. Read more.
C
- Cataract
- Clouding of the natural lens inside the eye. Universal with age and highly treatable with surgery. Read more.
- Convergence insufficiency
- Difficulty turning the eyes inward and holding that position for near work, producing double vision, headaches and reading avoidance. Very treatable with vision therapy. Read more.
- Cornea
- The clear front surface of the eye. It does most of the eye's focusing and is where conditions like keratoconus occur.
- Corneal cross-linking
- A procedure that strengthens the chemical bonds within corneal tissue using riboflavin and ultraviolet light. The only treatment that halts keratoconus progression. Read more.
- Corneal topography
- A detailed contour map of the corneal surface. The key test for diagnosing keratoconus and for fitting specialty contact lenses.
D
- Dilation
- Using drops to widen the pupil so the retina can be examined thoroughly. Causes several hours of light sensitivity and blurred near vision. Read more.
- Diopter
- The unit of measurement for lens power. A prescription of minus three means three diopters of nearsightedness.
E
- Evaporative dry eye
- The most common form of dry eye, caused by meibomian gland dysfunction letting tears evaporate too quickly. Read more.
G
- Glaucoma
- Progressive damage to the optic nerve, usually associated with raised eye pressure. Painless, takes peripheral vision first, and permanent. Read more.
H
- High-index lens
- A lens material that bends light more strongly, allowing a thinner and lighter lens at the same prescription. Worth it from roughly minus four onward.
- Hyperopia
- Farsightedness. Distant objects are typically clearer than near ones, and sustained near work causes fatigue.
I
- Intraocular pressure
- The fluid pressure inside the eye. Raised pressure is the main modifiable risk factor for glaucoma, though glaucoma can occur at normal pressure.
- Invisalens
- Our branded name for our orthokeratology programme, an overnight retainer lens that reshapes the cornea while you sleep. Read more.
K
- Keratoconus
- Progressive thinning and bulging of the cornea into a cone shape, distorting vision in ways glasses cannot correct. Read more.
M
- Macula
- The small central area of the retina responsible for detailed vision, reading and face recognition.
- Macular degeneration
- Deterioration of the macula causing loss of central vision while typically sparing peripheral vision. Read more.
- Meibomian glands
- Oil glands in the eyelid margins that produce the outer layer of the tear film. Their dysfunction is the leading cause of dry eye.
- Monovision
- Correcting one eye for distance and the other for near, used in contact lenses and in cataract lens implants.
- Myopia
- Nearsightedness, caused by the eye growing too long so light focuses in front of the retina. Read more.
O
- Optomap
- Ultra-widefield retinal imaging capturing over 80 percent of the retina in a single image without dilating drops. Read more.
- Optometrist (OD)
- A doctor of optometry who examines eyes, prescribes correction, fits contact lenses, and diagnoses and medically treats eye disease. Read more.
- Ophthalmologist (MD)
- A medical doctor specialising in eye care who also performs eye surgery. Read more.
- Orthokeratology
- Wearing a rigid lens overnight to reshape the cornea, giving clear vision the next day without correction. Also called corneal refractive therapy. Read more.
P
- Presbyopia
- Age-related stiffening of the eye's internal lens, reducing the ability to focus up close. Universal from around age forty.
- Progressive lens
- A lens whose power varies continuously from distance at the top through intermediate to near at the bottom, with no visible line. Read more.
- Pterygium
- A growth of tissue across the cornea, strongly associated with sun and wind exposure. Common in desert climates.
- Pupillary distance
- The distance between the centres of your pupils. Required to position lens optics correctly in front of your eyes.
R
- Refraction
- The part of an eye exam that determines your exact prescription.
- Retina
- The light-sensitive tissue lining the back of the eye. The only place a doctor can directly observe blood vessels and a nerve without an incision.
- Retinal detachment
- The retina separating from the back of the eye. A surgical emergency, typically preceded by sudden floaters, flashes or a curtain across the vision.
S
- Scleral lens
- A large rigid contact lens that vaults over the cornea and rests on the white of the eye, with saline filling the space between. Read more.
- Slit lamp
- A specialised microscope used to examine the eye under high magnification with a controllable beam of light.
T
- Toric lens
- A lens designed to correct astigmatism. In contact lenses, designed to stay in a stable rotational orientation.
V
- Visual acuity
- How clearly you see detail, measured on a chart. Twenty-twenty is a standard reference, not a measure of eye health.
- Visual field
- The full extent of what you can see including peripheral vision. Its loss is the key measure in glaucoma.
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