Eye care glossary
What they told you at your visit, explained in plain words. 77 terms, from visual acuity to keratoconus.
A B C D E F G H I K L M N O P R S T U V Y
A
Amblyopia (lazy eye)
One eye does not develop normal vision because the brain suppresses it. It can only be corrected in childhood, and the earlier the better. See pediatric ophthalmology and strabismus.
Anisometropia
Each eye has a very different prescription. If it is not corrected early in childhood it can lead to a lazy eye. See pediatric ophthalmology and strabismus.
Astigmatism
The cornea is oval rather than perfectly round, which makes images look distorted or shadowed at all distances. Almost everyone has some astigmatism. See laser vision correction (lasik and prk).
B
Biometry
The measurement of the eye that allows the exact power of the intraocular lens to be calculated before cataract surgery. Much of the result depends on how carefully this test is done. See diagnostic eye tests.
Blepharitis
Chronic inflammation of the eyelid margin. It causes burning, crusting on waking, and makes dry eye worse. See cornea and anterior segment.
Blepharoplasty
Surgery on excess eyelid skin. When the eyelid blocks vision, the indication is functional rather than cosmetic. See oculoplastic and tear duct surgery.
Blocked tear duct
The duct that drains tears becomes blocked and the eye waters constantly. Very common in babies and in older adults. See oculoplastic and tear duct surgery.
Blue light filter
A lens treatment that reduces glare from screens. It helps with comfort, though on its own it does not cure dry eye or eye strain. See optical shop.
C
Cataract
The crystalline lens, the eye's natural lens, turns cloudy. Vision looks like it is through a fogged window, colors fade and lights glare at night. It is the most common cause of reversible vision loss in adults. See cataract surgery.
Chalazion
A lump in the eyelid from a blocked gland. It usually does not hurt and sometimes needs draining. See oculoplastic and tear duct surgery.
Color blindness
Difficulty telling certain colors apart, almost always present from birth and more common in men. See diagnostic eye tests.
Conjunctivitis (pink eye)
Inflammation of the conjunctiva. It can be viral, bacterial or allergic, and treatment is different for each. Self-medicating with drops can make it worse. See eye exam.
Cornea
The clear window at the front of the eye. It is where the laser is applied in vision correction surgery. See cornea and anterior segment.
Corneal crosslinking
A treatment that stiffens the fibers of the cornea with riboflavin and ultraviolet light to stop keratoconus from progressing. See cornea and anterior segment.
Corneal topography
A map of the shape of the cornea. Essential before laser vision correction and for diagnosing keratoconus. See diagnostic eye tests.
Corneal transplant
Replacement of a damaged cornea with donor tissue. Today it is usually done layer by layer rather than full thickness. See cornea and anterior segment.
Corneal ulcer
An infected wound on the cornea. This is an emergency. A common cause: sleeping in contact lenses or cleaning them poorly. See cornea and anterior segment.
Cycloplegia
Drops that temporarily paralyze focusing so the true prescription can be measured without the eye compensating. Used above all in children and before laser surgery. See diagnostic eye tests.
D
Diabetic retinopathy
Damage to the retinal blood vessels caused by diabetes. It is the leading cause of preventable blindness in working-age adults and gives no symptoms until it is advanced. A yearly dilated retinal exam is essential if you have diabetes. See retina and vitreous.
Digital eye strain
Burning, intermittent blurring and headache after hours on screens. It eases with more blinking, the 20-20-20 rule and the right correction. See eye exam.
Dilated fundus exam
Examination of the retina and optic nerve, almost always with the pupil dilated. It is the only way to see inside the eye. See eye exam.
Diplopia (double vision)
Seeing double. If it starts suddenly, get seen promptly. See eye exam.
Dry eye
The eye does not produce enough tears, or the tears it makes evaporate too fast. It burns, feels gritty and, paradoxically, sometimes waters a lot. Screens and air conditioning make it worse. See cornea and anterior segment.
E
Ectropion
The eyelid turns outward and stops protecting the eye. See oculoplastic and tear duct surgery.
Emmetropia
An eye that needs no correction: it focuses well without glasses.
Entropion
The eyelid turns inward and the lashes rub against the cornea. See oculoplastic and tear duct surgery.
Epiphora
Constant watering of the eye, almost always from a blocked tear duct. See oculoplastic and tear duct surgery.
Excimer laser
The laser that reshapes the cornea with micron precision. See laser vision correction (lasik and prk).
F
Floaters
Spots or threads that drift across your vision. Most are harmless and come from aging of the vitreous. But if they appear suddenly, in numbers, and with flashes, get seen immediately. See retina and vitreous.
Fluorescein angiography
Studies retinal circulation by injecting a dye into the arm and photographing the back of the eye. See diagnostic eye tests.
G
Glaucoma
Progressive damage to the optic nerve, almost always from raised eye pressure. It does not hurt and gives no warning: it takes visual field away from the edges inward. What is lost cannot be recovered, which is why early diagnosis is everything. See glaucoma.
H
Hyperopia (farsightedness)
Focusing up close is hard and, if the error is large, so is distance. The eye is shorter than normal. In children it can go unnoticed because the eye compensates with an effort that ends in headaches. See laser vision correction (lasik and prk).
I
Intraocular lens
The artificial lens that replaces the natural lens in cataract surgery. There are monofocal lenses, toric lenses for astigmatism, and extended-depth-of-focus or multifocal lenses. See cataract surgery.
Intraocular pressure
The pressure of the fluid inside the eye. It is the main risk factor for glaucoma and the only one that can be acted on. See glaucoma.
Intravitreal injection
Medication delivered inside the eye, the standard treatment for wet macular degeneration and diabetic macular edema. Given over several sessions. See retina and vitreous.
Iridotomy
A small opening made with a laser in the iris to prevent or treat angle-closure glaucoma. See glaucoma.
K
Keratoconus
The cornea thins and bulges into a cone shape, distorting vision. It usually starts in adolescence. Catching it early allows it to be halted with crosslinking, and it is the reason not everyone can have laser surgery. See cornea and anterior segment.
L
LASIK
A laser correction technique in which a thin flap of cornea is lifted, the laser is applied underneath, and the flap is repositioned. Visual recovery is fast, one to two days. See laser vision correction (lasik and prk).
Laser vision correction
Using a laser to correct myopia, hyperopia and astigmatism and reduce or eliminate dependence on glasses. See laser vision correction (lasik and prk).
M
Macula
The central part of the retina, the one you use to read and recognize faces. It is tiny and responsible for detailed vision. See retina and vitreous.
Macular degeneration
Age-related deterioration of the macula. It distorts the center of vision: straight lines look wavy. See retina and vitreous.
Macular edema
Fluid building up in the macula, which blurs central vision. Common in people with diabetes. See retina and vitreous.
Myopia (nearsightedness)
Distance vision is blurred and near vision is clear. The eye is slightly longer than normal and the image forms before it reaches the retina. Corrected with glasses, contact lenses or laser surgery. See laser vision correction (lasik and prk).
N
Nystagmus
Involuntary, repetitive movement of the eyes. See pediatric ophthalmology and strabismus.
O
OCT scan
Optical coherence tomography. It sections the retina and optic nerve micron by micron without touching the eye. It detects glaucoma and macular disease before the patient notices anything. See diagnostic eye tests.
Ocular ultrasound
An ultrasound scan of the eye. Used when a very dense cataract or a hemorrhage prevents a view of the retina. See diagnostic eye tests.
Ophthalmology
The medical and surgical specialty that diagnoses and treats diseases of the eye. See eye exam.
Optic disc cupping
The shape of the center of the optic nerve. When it grows over time it is a sign of glaucoma damage. See glaucoma.
Optic nerve
The cable that carries the image from the eye to the brain. It is what glaucoma destroys. See glaucoma.
Optometry
Concerned with measuring vision and prescribing optical correction. It is distinct from ophthalmology, which treats eye disease. See optical shop.
P
PRK
A variant in which the epithelium is removed and the laser applied on the surface. It is more uncomfortable for the first few days, but it is the option when the cornea is thin. See laser vision correction (lasik and prk).
Pachymetry
Measures the thickness of the cornea. It determines whether there is enough tissue for laser surgery and helps interpret eye pressure. See diagnostic eye tests.
Patching
Covering the good eye to force the lazy one to work. It is the classic treatment for amblyopia. See pediatric ophthalmology and strabismus.
Phacoemulsification
The technique used for cataract surgery today. Through an incision of about 2.2 millimeters the lens is broken up with ultrasound, aspirated, and an implant is put in its place. It takes 15 to 30 minutes and is day surgery. See cataract surgery.
Photophobia
Exaggerated discomfort in bright light. See eye exam.
Posterior capsule opacification
Months or years after cataract surgery, the membrane holding the implant can cloud over and vision blurs again. The cataract has not come back: it is cleared in minutes with a YAG laser. See cataract surgery.
Presbyopia
The classic “aging eyes”. From the mid-forties the lens loses elasticity and focusing up close becomes hard: you have to hold your phone further away to read. It is not a disease, it is part of getting older. See optical shop.
Progressive lenses
Correct distance, intermediate and near vision in a single lens, with no visible line. See optical shop.
Pterygium
Tissue growing from the conjunctiva onto the cornea, very common in sunny climates. When it grows toward the center it affects vision and is removed surgically. See cornea and anterior segment.
Ptosis
The upper eyelid droops lower than normal. If it covers the pupil it reduces the field of vision and is corrected surgically. See oculoplastic and tear duct surgery.
Pupil dilation
Drops that widen the pupil so the back of the eye can be seen. They leave vision blurred and light-sensitive for four to six hours: do not drive. See eye exam.
R
Refraction
The measurement that gives the exact prescription for your glasses or contact lenses. See optical shop.
Retina
The layer at the back of the eye where the image forms, like the film in a camera. See retina and vitreous.
Retinal detachment
The retina separates from the wall of the eye. It announces itself with a sudden shower of floaters, flashes of light and an advancing shadow. This is an emergency: be seen the same day. See retina and vitreous.
Retinopathy of prematurity
Abnormal retinal blood vessels in babies born early. It requires screening in the first weeks of life. See pediatric ophthalmology and strabismus.
S
Scotoma
A blind spot within the field of vision. See retina and vitreous.
Slit lamp
The microscope an ophthalmologist uses to examine the eye layer by layer. See eye exam.
Specular microscopy
Counts the cells of the corneal endothelium. Requested before cataract surgery. See diagnostic eye tests.
Strabismus (squint)
The eyes do not point at the same place. In children it has to be treated early, because the brain can start ignoring the image from the turning eye. See pediatric ophthalmology and strabismus.
Stye
An acute infection of an eyelid gland. It hurts and reddens, and generally settles with warmth and treatment. See oculoplastic and tear duct surgery.
T
Tonometry
The measurement of intraocular pressure. Quick and painless. See diagnostic eye tests.
Trabeculoplasty
A laser that improves fluid drainage from the eye to lower intraocular pressure. See glaucoma.
U
Uveitis
Inflammation inside the eye. It hurts, reddens, and can be associated with rheumatological disease. See eye exam.
V
Visual acuity
How well each eye sees. It is what the letter chart measures. See eye exam.
Visual field test
Measures your whole field of vision, not only what you see straight ahead. It is the test that shows whether glaucoma is progressing. See diagnostic eye tests.
Vitreous
The clear gel that fills the eye. With age it liquefies and pulls away from the retina, which is what produces floaters. See retina and vitreous.
Y
YAG laser
An office laser that opens the clouded membrane after cataract surgery. It needs no operating room and no incision. See cataract surgery.
This is not a substitute for a consultation
These definitions are here to help you understand what you were told, not to diagnose yourself. If you have a symptom, book a visit: most eye conditions respond well when they are caught early.
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