A

accommodating IOL
An implant containing a hinge that allows for both near and far vision, thereby mimicking the movement of the natural lens of a young person.

accommodation
The process by which the natural lens changes shape, allowing it to focus on near or far objects.

adrenergic agonist eyedrops
A treatment for glaucoma. The eyedrops reduce intraocular pressure by decreasing the production of aqueous humor and increasing its drainage through the uveoscleral pathway.

age-related macular degeneration (AMD)
A loss of central vision caused by changes in the macula.

Amsler grid
A diagram of a box subdivided into smaller boxes that is used for self-monitoring by people with AMD.

angiostatic corticosteroids
Drugs being studied for treating AMD and diabetic retinopathy.

antimetabolites
Drugs sometimes used in filtration surgery for glaucoma.

aqueous humor
A watery fluid that is located in front of the lens and provides nutrients to the lens and cornea.

astigmatism
Blurred or distorted vision that is common in nearsighted people.

A-scan ultrasonography
A test that uses sound waves to measure the length of the eyeball.

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B

beta-blocker eyedrops
A treatment for glaucoma. The eyedrops reduce intraocular pressure (IOP) by decreasing the production of aqueous humor.

bifocals
A pair of glasses with lenses that correct both distant and near vision.

body mass index (BMI)
A measure of weight in relation to height. To calculate your BMI, multiply your weight in pounds by 704 and divide that by the square of your height in inches. Overweight is defined as a BMI of 25-29.9; obesity is defined as a BMI of 30 or greater.

B-scan ultrasonography
A test that uses sound waves to view structures in the back of the eye.

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C

carbonic anhydrase inhibitors
Medications used to treat glaucoma. These drugs decrease the production of aqueous humor and are available in both oral and eyedrop formulations.

cataract
A cloudiness (opacification) of the lens that can lead to visual impairment.

central vision
The middle part of the visual field.

choroid
A layer of the eye inside the sclera. It contains a dark pigment that minimizes scattering of light inside the eye.

ciliary body
A part of the eye that surrounds the lens and produces aqueous humor.

classic AMD
One of two types of neovascular AMD. Classification is based on fluid leakage patterns.

closed-angle glaucoma
A type of glaucoma caused by a blockage near the iris that prevents aqueous humor from reaching the trabecular meshwork. It results in a rapid buildup of extremely high intraocular pressure that can lead to severe, permanent vision damage within a couple of days.

cones
Nerve cells in the retina that are activated only in bright light and by the colors red, blue, and green.

conjunctiva
A thin, lubricating mucous membrane that covers the sclera and lines the inside of the eyelid.

cornea
The transparent, dome-shaped disk covering the iris and pupil.

coronary heart disease
Abnormality of the arteries that supply blood and oxygen to the heart and can lead to chest pain or a heart attack.

cortical cataract
A cataract that affects the lens cortex.

cyclodestructive surgery
A treatment for glaucoma that destroys the ciliary body with a laser.

cystoid macular edema
A specific pattern of swelling of the central retina.

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D

diabetes
A disease characterized by abnormally high glucose (sugar) levels in the blood.

diabetic retinopathy
Damage to small blood vessels in the retina resulting from the chronic high blood glucose levels in people with poorly controlled diabetes. Proliferative retinopathy is the most dangerous form.

drusen
Small accumulations of debris underneath the retina.

dry AMD
See non-neovascular AMD.

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E

endophthalmitis
An infection of the vitreous humor that develops in a small number of people after eye surgery.

extracapsular surgery
Cataract surgery that removes the front of the lens capsule along with the cortex and nucleus of the lens, while leaving the back of the lens capsule intact.

extrafoveal blood vessels
See neovascular AMD.

exudative AMD
See neovascular AMD.

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F

farsightedness
See hyperopia.

filtration surgery
A treatment for glaucoma that uses conventional surgical instruments to open a passage through the clogged trabecular meshwork, allowing excess aqueous humor to drain into surrounding tissues.

floaters
Black spots or shapes that drift through the field of vision.

fluorescein angiography
A diagnostic procedure for age-related macular degeneration and other retinal diseases. A special dye, called fluorescein, is injected into a vein in the arm. Photographs of the retina are taken as the dye circulates through the blood vessels of the eye.

fovea
The small indentation at the center of the macula. It contains the highest concentration of cones and provides the sharpest vision.

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G

ganglion cells
A type of cell in the retina. Damage to these cells is thought to play a role in the development of glaucoma.

glare
Light within the field of vision that is brighter than other objects to which the eyes have adapted.

glaucoma
An eye disease that results in damage to the optic nerve. Contrary to popular belief, it is not always caused by elevated intraocular pressure.

gonioscopy
A technique used to distinguish between open- and closed-angle glaucoma. It involves an examination of the front part of the eye to check the angle where the iris meets the cornea.

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H

hemorrhage
Leakage of blood from blood vessels.

hyperopia
Farsightedness. Distant objects can be seen clearly, but close ones do not come into proper focus.

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I

indocyanine green angiography
A test similar to fluorescein angiography, using a different dye.

intracapsular surgery
Cataract surgery that removes the entire lens (the front and back of the lens capsule, the cortex, and nucleus). Rarely performed today.

intraocular lens implant (IOL)
A plastic lens that replaces the lens removed during cataract surgery.

intraocular pressure (IOP)
The pressure exerted by the fluids inside the eyeball.

IOL
See intraocular lens implant.

iridectomy
A treatment for closed-angle glaucoma that involves removing part of the iris.

iridotomy
A treatment for closed-angle glaucoma that creates a hole in the iris with a laser.

iris
The colored circle in the middle of the eye that controls the amount of light that enters the eye.

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J

juxtafoveal blood vessels
See neovascular AMD.

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K

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L

LASEK
Laser-assisted subepithelial keratomileusis, a refractive surgery procedure that reshapes the cornea.

laser trabecular surgery
A treatment for glaucoma that involves making 80-100 tiny laser burns in the area of the trabecular meshwork. The procedure increases the drainage of aqueous humor.

LASIK
Laser-assisted in situ keratomileusis, a refractive surgery procedure that reshapes the cornea.

legal blindness
Vision that is 20/200 or worse in both eyes (20/200 vision is the ability to see at 20 feet what a normal eye can see at 200 feet).

lens
A transparent, dome-shaped disk that is responsible (along with the cornea) for the eye's ability to focus light.

lens capsule
The outermost structure of the lens.

lens cortex
The second innermost structure of the lens, it surrounds the nucleus, and its outer edge is lined with a layer of cells called the epithelium.

lens epithelium
Cells that line the outer surface of the lens cortex.

lens nucleus
The center structure of the lens. Surrounded by the cortex.

low vision aids
Items that can help people with poor vision. Examples include closed-circuit televisions, magnifying glasses, telephones with large numbers, and large-print reading materials.

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M

macula
A small area at the center of the retina that is responsible for central and fine-detail vision.

macular edema
A swelling of the macula caused by leakage and accumulation of fluid. More common in people with diabetes than in the general population.

macular nonperfusion
Closure of small blood vessels that supply the macula.

microaneurysms
Weak spots that bulge outward from blood vessels, including those of the retina.

miotic eyedrops
Used to treat glaucoma, these eyedrops increase the outflow of aqueous humor through the trabecular meshwork by constricting the pupil.

monofocal IOL
A single-focus lens used after cataract surgery to provide clear distance vision.

monovision
A process in which one eye is corrected for distance and the other for near vision. Achieved with an IOL in cataract surgery, in refractive surgery, or even with contact lenses.

multifocal IOL
A type of lens used after cataract surgery. It contains several rings with a common center that focus and adjust for either near or far vision. This allows the eye to be in focus for near and far vision simultaneously.

myocilin
A protein in trabecular meshwork cells. Mutations in the myocilin gene have been identified as a cause of glaucoma.

myopia
Also called nearsightedness, a vision deficit in which close objects can be seen clearly, but distant ones do not come into proper focus.

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N

neovascular age-related macular degeneration (AMD)
A form of AMD in which new blood vessels grow in the choroid layer of the eye. The blood vessels are classified according to their location
subfoveal blood vessels occur at the fovea, extrafoveal blood vessels are farthest away from the fovea, and juxtafoveal blood vessels are in between.

neovascularization
The growth of new blood vessels.

nonexudative AMD
See non-neovascular AMD.

non-neovascular age-related macular degeneration (AMD)
A form of AMD characterized by the breakdown or thinning of tissues in the macula and the formation of drusen and shrinkage of tissues in the retina. This form of AMD often does not impair vision.

normal tension glaucoma
A type of glaucoma that results from damage to the optic nerve although intraocular pressure is normal.

nuclear cataract
A cataract affecting the nucleus of the lens.

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O

occult AMD
One of two types of neovascular AMD, classified by fluid leakage patterns. Occult AMD is common but difficult to treat.

opacification
The process of becoming opaque or less penetrable to light. Common in the cornea and lens of the eye in people with glaucoma.

open-angle glaucoma
The most common form of glaucoma. It usually produces no obvious symptoms until late stages.

ophthalmologist
A physician who specializes in the diagnosis and treatment of eye diseases.

ophthalmoscopy
Examination of the interior structures of the eye, especially the retina, using a specialized instrument called an ophthalmoscope.

optic nerve
A nerve at the back of the eye that carries visual information from the retina to the brain.

optineurin
A protein found in the trabecular meshwork and retina. Its role is not fully understood, but defects in the gene that directs its production have been associated with glaucoma.

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P

pegaptanib
A recently approved drug used to treat neovascular AMD. Sold under the name Macugen.

perimetry
A test used to determine a person's visual fields. While the person looks straight ahead at a bowlshaped white area, a computer generates a light in fixed locations around the bowl. The patient indicates each time he or she sees the light.

peripheral vision
The ability to see objects at the edges of the visual field.

phacoemulsification
A type of extracapsular surgery that is performed with an ultrasonic device that nearly liquifies the nucleus and cortex so that they can be removed by suction through a tube.

photocoagulation
The standard treatment for neovascular AMD when the new blood vessels are outside the center of the retina. The procedure involves closing the new blood vessels with a laser. It is also used to treat diabetic retinopathy. Focal laser photocoagulation targets individual blood vessels; panretinal photocoagulation creates a grid-like pattern across a larger area of the retina.

photodynamic therapy
A newer treatment for AMD that involves the intravenous administration of a special drug to sensitize blood vessels in the eye to light. A low-power laser, directed at the new blood vessels, activates the drug and closes the vessels in a way that causes less damage to the retina than standard laser treatment.

posterior subcapsular cataract
A cataract in the rear of the lens capsule.

presbyopia
An inability to focus on near objects that commonly develops after age 45.

PRK
Photorefractive keratotomy, a refractive surgery procedure that reshapes the cornea.

pupil
The opening in the center of the iris that resembles a large black dot.

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Q

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R

retina
The innermost layer of the eye that consists of light-sensitive nerve tissue.

retinal detachment
A vision-threatening condition in which the retina becomes separated from the underlying layers of the eye.

retinal pigment epithelial cells
A layer of cells that contribute to the function of the retina.

rods
Nerve cells in the retina that are sensitive to dim light.

rubeosis iridis
New blood vessel growth on the iris that usually occurs in people with diabetes.

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S

sclera
The white outer layer that covers and protects most of the eye.

scotoma
A blind spot in the visual field.

shunt
A device that creates a new passage to drain excess aqueous humor. It is used in the treatment of glaucoma when filtration surgery is unsuccessful.

slit lamp
A table-mounted microscope that enables an eye specialist to get a three-dimensional view of the optic nerve.

subfoveal blood vessels
See neovascular AMD.

subfoveal surgery
A procedure for age-related macular degeneration in which abnormal blood vessels beneath the retina are surgically removed.

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T

tonometry
A method of measuring intraocular pressure by determining the amount of force needed to make a slight indentation in a small area of the cornea.

topical prostaglandin eyedrops
A treatment for glaucoma. These eyedrops reduce intraocular pressure by increasing the outflow of aqueous humor through the uveoscleral pathway.

trabecular meshwork
A spongy network of connective tissue through which aqueous humor drains from the eye. Blockage of the meshwork causes a buildup of intraocular pressure.

trabeculectomy
See filtration surgery.

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U

uveitis
Inflammation of the uvea, the part of the eye that contains the iris, ciliary body, and choroid.

uveoscleral pathway
An alternative drainage system for aqueous humor located behind the trabecular meshwork.

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V

vascular endothelial growth factor (VEGF)
A protein that promotes the growth of new blood vessels in the eye and elsewhere in the body.

verteporfin
A drug used in photodynamic therapy and sold under the name of Visudyne.

vitrectomy
A surgical procedure that removes the vitreous humor and replaces it with saline solution.

vitreous humor
A thick, gel-like substance that fills the back of the eyeball behind the lens.

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W

wet AMD
See neovascular AMD.

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X

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Y

YAG laser
A type of laser that contains yttrium, aluminum, and garnet used to clear blurred vision that may occur after extracapsular surgery for cataracts.

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Z

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Derived from The Johns Hopkins White Paper 2007: Vision

Look Inside the Book: Vision

copyright 2007 Johns Hopkins Health Alerts.

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Posted in Vision on April 14, 2007
Reviewed May 2007