Flashes
photopsia; the brief perception of light that is purely subjective and accompanies a pathological condition, especially of the retina or brain
Floaters
muscae volitantes; bits of optical debris (such as dead cells or fibrils), usually in the vitreous humor, that may be perceived as spots before the eyes
Fluorescein angiography
a procedure in which a fluorescent yellow dye, injected into the vein of an arm, circulates into the eye within a few seconds, at which time a sequence of retinal photographs detect pooling of the dye in a certain location or leakage of the dye outside of blood vessels, confirming some type of retinal disorder
Focal length
the distance away from a lens at which an image focuses, when parallel light rays enter the lens; the inverse, in meters, of the dioptric power of a lens
Follicles
hyperplasia of the lymphoid tissue within the conjunctival stroma; resemble “Rice-a-Roni” embedded in the inferior conjunctiva; seen primarily in adenoviral and chlamydial infections, as well as in toxic reactions
Fornix
the portion of the conjunctiva forming the junction between the posterior eyelid and the eyeball
Fovea centralis
fovea; a small shallow depression or pit at the center of the macula, caused by an almost complete absence of inner retinal layers, containing only cones (and no rods) and which affords the most acute vision
Ganglion cells
nerve cells having their bodies outside of the central nervous system, such as those located in layer 8 of the retina
Giant papillary conjunctivitis (GPC)
inflammation of the conjunctiva, most commonly associated with soft contact lens wear and marked by the presence of giant bumps or papillae (greater than 1 millimeter in diameter) on the posterior surface of the upper eyelids, as well as redness, itching, burning, mucous discharge, and blurred vision; may be related to irritation due to excess protein build-up on the lenses and/or to chemicals (such as preservatives) in the cleaning and sterilization solutions used to care for the lenses; treatment consists of decreasing (or even ceasing) contact lens wear, more frequent enzymatic cleaning of lenses (to remove protein deposits), discontinuance of preserved solutions, storage in unpreserved saline solutions, sterilization by hydrogen peroxide, and possibly obtaining new contact lenses
Gland, lacrimal
tear gland; a gland, about the size and shape of an almond, that is the major producer of a watery secretion which forms the middle (lacrimal), thickest layer of the tear film; situated laterally and superiorly to the eyeball in a shallow depression on the inner surface of the frontal bone
Glands, tear
glands located near the eye and in the eyelids which produce the lipid, lacrimal, and mucoid layers of the tear film coating the anterior surface of the cornea; consist of the lacrimal gland, Meibomian glands, Zeis glands, Krause glands, Wolfring glands
Glands, Meibomian
elongated sebaceous glands in the eyelids that discharge a fatty, oily secretion which forms the most exterior (lipid) layer of the tear film, preventing tear evaporation
Glands, Krause
small glands in the eyelids that discharge a watery secretion which forms the middle (lacrimal), thickest layer of the tear film
Glands, Wolfring
small glands in the eyelids that discharge a watery secretion which forms the middle (lacrimal), thickest layer of the tear film
Glands, Zeis
sebaceous glands in the eyelids that discharge a fatty, oily secretion which forms the most exterior (lipid) layer of the tear film, preventing tear evaporation
Glaucoma
a progressive optic neuropathy (a disease of the optic nerve) characterized by a specific pattern of retinal ganglion cell, axon, and optic nerve damage, resulting in a reduction in the visual field (beginning in the periphery and gradually moving inward) and even blindness; most significant risk factor is elevated intraocular pressure (IOP), which results from less fluid leaving the eye than is entering the eye; other possible risk factors, most of which have been as yet little explored, may include low blood pressure, abnormally low intracranial pressure, autoimmune phenomena, sleep apnea, sleeping with the pillow or one’s knuckles pressed against the eye, an abnormally hard or soft lamina cribrosa (the stack of platelike “perforated wafers” through which the optic nerve fibers pass through the eye), inherited or acquired abnormalities of the connective tissue of the lamina cribrosa, primary ganglion cell degeneration, and other as yet unconsidered possibilities.
Glaucoma, open angle
most common glaucoma commonly caused by a blockage or malfunction of the trabecular meshwork (the “drainage” channel in the irido-corneal angle through which aqueous fluid leaves the eye), leading to elevated intraocular pressure; also may be due to a weakened lamina cribrosa, making it susceptible to even normal pressures (“low tension” glaucoma), thereby causing it to compress or pinch the optic nerve fibers passing through it, resulting in optic nerve damage or destruction; also may be due to a “pupillary block” where there is an adherence between the iris and the crystalline lens, preventing the normal flow of aqueous fluid through the pupil and causing an increase in pressure on (and subsequent damage of) the ganglion cells and axons in the retina
Glaucoma, closed angle
narrow angle glaucoma; less common type of glaucoma in which the trabecular meshwork (the “drainage” channel in the irido-corneal angle through which aqueous fluid leaves the eye) is compromised due to the iris’ being moved forward and narrowing or blocking the irido-corneal and/or compressing the trabecular meshwork, preventing fluid from leaving the eye at a normal rate, increasing intraocular pressure, and damaging or destroying ganglion cells and axons in the retina and optic nerve; can cause intraocular pressures of 60 mm Hg or more, as well as severe eye pain, nausea, vomiting, redness, blurred vision with halos or rainbows around lights, and sudden loss of vision
Glycosaminoglycan
mucopolysaccharide; any of various polysaccharides derived from an amino hexose that are constituents of mucoproteins, glycoproteins, and blood-group substances
Goblet cells
mucous-secreting epithelial cells (as of columnar epithelium) located on the bulbar conjunctiva of the eye
Graves’ disease
a common form of hyperthyroidism characterized by a goiter (enlargement of the thyroid gland), an increased basal metabolism due to excessive thyroid secretion, and often a slight to moderate exophthalmos (protrusion of the eyeballs)
Guttata
thickened areas in the posterior caused by abnormal production of Descemet’s collagen by the endothelial cells; has an “orange peel” or “beaten metal” appearance; associated with Fuch’s dystrophy
Hemorrhage subconjunctival
leakage of blood from blood vessels underneath the conjunctiva, often due to a sudden jolt from blunt trauma, coughing, or sneezing; normal reabsorption of blood usually takes 1-2 weeks
Heterochromia iridis
a difference in color between the irises of the two eyes or between parts of one iris (heterochromia iridium); usually a congenital (autosomal dominant) trait, but can result from pathologies such as pigment dispersion syndrome, Horner’s syndrome (with the affected side being blue), Waardenburg syndrome, Fuch’s heterochromic cyclitis, and piebald syndrome, as well as injury to an eye, bleeding or inflammation within an eye, or eye tumors
Histoplasmosis
a respiratory disease caused by a fungus of the genus Histoplasma (H. capsulatum) with symptoms like those of influenza; endemic in the Mississippi and Ohio river valleys of the U.S.; and is marked by benign involvement of lymph nodes of the trachea and bronchi, usually without symptoms or by severe progressive generalized involvement of the lymph nodes and the reticuloendothelial system with fever, anemia, leukopenia and often with local lesions (as of the skin, mouth, throat, or retina)
Hordeolum
sty or stye; an inflamed swelling of a sebaceous gland at the margin of an eyelid; treated with warm compresses or antibiotics
Horner’s syndrome
an interruption of the oculosympathetic nerve pathway somewhere between its origin in the hypothalamus and the eye; typically causes ptosis, pupillary miosis and facial anhidrosis, as well as possibly apparent enophthalmos, increased amplitude of accommodation, heterochromia of the irides (if it occurs before age two), paradoxical contralateral eyelid retraction, transient decrease in intraocular pressure, and changes in tear viscosity
Hyaloid artery
a branch of the primitive dorsal ophthalmic artery; extends, in the fetus, from the optic cup of the optic nerve into the vitreous cavity and forward to the lens to aid its development; regresses during the last trimester of fetal formation, leaving behind the “Cloquet’s canal” through the vitreous
Hyaluronic acid
a viscous glycosaminoglycan that occurs especially in the vitreous humor, the umbilical cord, and synovia and as a cementing substance in the subcutaneous tissue
Hyperopia
farsightedness, hypermetropia; a condition in which visual images come to a focus behind the retina of the eye and vision is better for distant than for near objects; may be due to the surface(s) of the cornea and/or crystalline lens having reduced (too flat) curvature, an eyeball which is too short, and/or an index of refraction of one of the ocular media that is too low
Hypertension
abnormally high arterial blood pressure; can occur without apparent or determinable prior organic changes in the tissues, possibly because of hereditary tendency, emotional tensions, faulty nutrition, or hormonal influence; also can be associated with demonstrable organic changes (as in nephritis, diabetes, and hyperthyroidism); uncontrolled, can cause mild to severe changes in the retina: cotton wool spots, flame-shaped hemorrhages, arteriosclerosis, retinal or macular edema, macular star, and papilledema (optic disc edema)
Hyperthyroidism
thyrotoxicosis; excessive production of thyroxine by the thyroid gland, as well as the resulting condition marked by increased metabolic rate, enlargement of the thyroid gland (goiter), rapid heart rate, high blood pressure, and exophthalmos (protruding eyes)
Hypertonic
having a higher osmotic pressure than a surrounding fluid or medium
Hypertropia
a strabismus where the deviating eye turns upward, as compared to the other eye which remains pointing straight ahead
Hyphema
a hemorrhage in the anterior chamber of the eye
Hypopyon
an accumulation of white blood cells (pus) in the anterior chamber of the eye
Hypothyroidism
deficient production of thyroxine by the thyroid gland, as well as the resultant bodily condition characterized by a lowered metabolic rate, weight gain, and general loss of vigor
Hypotonic
having a lower osmotic pressure than a surrounding fluid or medium
