Perelman School of Medicine at the University of Pennsylvania

Center for Preventive Ophthalmology and Biostatistics (CPOB)

CPOB Glossary of Terms

Amblyopia is reduced visual acuity in one or both eyes not improved solely with refractive error correction (i.e., prescription glasses) and not attributable to other structural abnormalities.  This condition is also sometimes called lazy eye and occurs when the vision in one of the eyes is reduced because the eye and the brain are not working together properly.  The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye.  Amblyopia is the most common cause of visual impairment in childhood.  Unless it is successfully treated in early childhood, amblyopia usually persists into adulthood, and is the most common cause of monocular (one eye) visual impairment among children and young and middle-aged adults.

Age-related macular degeneration (AMD) is the leading cause of blindness in the United States and most Western countries.  The macula is the center of the retina and is responsible for central vision.  AMD is frequently categorized as either “early” (with drusen and pigmentary changes in the macula) or “late”, which is characterized by choroidal neovascularization (CNV), serous detachment of the retinal pigment epithelium (SPED), or geographic atrophy (GA) of the retinal pigment epithelium.  Many people with early AMD have good visual acuity but may have problems with night vision, require bright light for reading and experience mild impairment in contrast sensitivity (the ability to discern subtle degrees of contrast).  The magnitude of these problems varies with the severity of the disease.  For more information on AMD, click here.

Anisometropia, a type of refractive error, is an unequal spherical or cylindrical refractive error between the two eyes, usually defined as more than a 1-diopter difference.

Astigmatism, a type of refractive error, is an optical defect in which refractive power is not uniform in all directions (meridians).  Light rays entering the eye are bent unequally by different meridians, which prevent formation of a sharp image focus on the retina due to the presence of an elliptical (egg or football shaped) rather than spherical shape of the refracting surfaces of the eye.  Slight uncorrected astigmatism may not cause symptoms, but a large amount may result in significant blurring and headache.

Choroidal neovascularization (CNV) is the most severe form of late age-related macular degeneration.  It is characterized by the growth of abnormal, leaking choroidal blood vessels through Bruch’s membrane and under the retina. CNV can be categorized as classic CNV or occult CNV.

Classic CNV is characterized by well-demarcated areas of increased accumulation of dye on fluorescein angiography.

Disciform scar (natural scar) is dull, white fibrous tissue that may accompany choroidal neovascularization or replace it over time.

Drusen are yellowish deposits under the retina that are the hallmark of early age-related macular degeneration.  Larger drusen increase the risk of more advanced disease.

Dry Eye Disease is a condition that occurs when tears are unable able to provide adequate lubrication for the eyes. Dry eyes may occur if eyes don’t produce enough tears or if eyes produce poor-quality tears. The result is discomfort, visual disturbance and tear film instability with the potential to damage the ocular surface.

Fluorescein angiogram (FA) is a dye study where fluorescein dye is injected into a vein in the patient’s arm.  A series of photographs are taken in quick succession showing the flow of fluorescein dye through the blood vessels of the eye.  Special filters on the camera allow visualization of the dye carried by the blood stream.

Foveal avascular zone is the center of the macula that is responsible for the central “straight ahead” vision used for activities like reading, driving, and sewing.

Geography atrophy (GA) is a form of late age-related macular degeneration characterized by relatively large areas in which the retinal pigment epithelium is thinned and depigmented, allowing visualization of underlying choroidal vessels. Central geographic atrophy (CGA) causes vision loss through loss of photoreceptors (rods and cones) in the central part of the eye. Geographic atrophy (GA) from age-related macular degeneration (AMD) is responsible for approximately 20% of the legal blindness cases in North America.

Hyperopia (farsightedness) is a type of refractive error which occurs when light enters the eye and the point of focus is behind the retina which results in blurred vision.  The hyperopic eye is not able to see the objects that are nearby.

Laser photocoagulation is a technique employed by retinal surgeons to treat a number of eye conditions, one of which is the exudative (wet) form of AMD.  In the Complications of AMD Prevention Trial (CAPT) very low intensity laser photocoagulation was applied to eyes at high risk of developing abnormal blood vessels with the hopes of preventing the growth of new vessels.  For more information on CAPT, click here.

Laser scar is the area of damage to the retina from laser photocoagulation treatment for CNV.

Meibomian glands are large sebaceous glands in eyelids that produce and secrete an oily substance called meibum. Meibum, water, and mucus form the three layers of tear film, the fluid that keeps the eyes moist.

Myopia (nearsightedness) is a type of refractive error which occurs when light enters the eye and the point of focus is in front of the retina which results in blurred vision.  The myopic eye is not able to see the objects that are far away.

Occult CNV is characterized by poorly-demarcated areas of increased accumulation of dye on fluorescein angiography.  The timing and appearance of dye accumulation is different from the pattern seen in classic CNV. 

Refractive Error occurs when light entering the eye is not precisely focused on the retina, causing blurred vision.  Refractive errors are the most easily corrected vision disorder.  Anisometropia, astigmatism, hyperopia and myopia are types of refractive errors.

Serous detachment of the retinal pigment epithelial detachment (SPED) is one of the forms of late age-related macular degeneration.  Clinical examination and fluorescein angiography show evidence of leakage of fluid under the retinal pigment epithelium; however, the angiographic signs of choroidal neovascularization are absent.

Strabismus is an "eye misalignment" or inability to direct the two eyes in the same direction simultaneously.  Strabismus can result in amblyopia and poor to absent binocular function.  Most strabismus develops in early childhood and some types may not be cosmetically obvious. Detection of strabismus is especially important in young children because of its strong association with amblyopia.

Subfoveal CNV is angiographic evidence (fluorescein leakage) of choroidal neovascularization under the geometric center of the foveal avascular zone.

Uveitis (intraocular inflammation) is the 5th or 6th leading cause of blindness in the United States.  Intraocular inflammation can be caused by infections, but in most cases results from immunologic disturbances (autoimmunity).

Visual acuity (VA) is a measure of central vision.  Typically, normal vision is considered as 20/20 in both eyes.  Visual impairment is considered as 20/40 or worse in each eye. Legal blindness is considered as 20/200 or worse in each eye.

Vitreous (VIT-ree-us).  Transparent, colorless genatinous mass that fills the rear two-thirds of the eyeball, between the lens and the retina.