Eyes

Glossary of Ocular Terms

Glossary of Terms for
Anatomy, Physiology & Pathology of the Human Eye

A ,B | C,D,E | F,G,H | I | J,K, L | M,N,O | P,Q,R,S | T,U,V,W | X,Y, Z

Papillae
a collection of lymphocytes and plasma cells, usually greater than 1 millimeter in diameter; resemble cobblestones; present in large numbers on the superior conjunctival tarsal plate in giant papillary allergic conjunctivitis

Papillitis
inflammation of the optic nerve, usually unilateral, affecting the part of the nerve and the disc within the eyeball, frequently accompanied by hyperemia and/or edema of the disc, retinal edema around the nerve head, engorgement and tortuosity of retinal veins, a few exudates and hemorrhages on or near the nerve head, and central vision loss (from a small central or paracentral scotoma to complete blindness); occurs due to disorders such as multiple sclerosis, infarction of part or all of the optic nerve head in temporal arteritis or other occlusive diseases of the ciliary vessels, tumorous metastasis to the optic nerve head, toxicity from certain chemicals (such as lead and methanol), bee stings, meningitis, and syphilis

Papilledema
“choked disc”; optic disc swelling and elevation, almost always bilateral, frequently accompanied by indistinct optic disc margins, hyperemia of the optic disc, hemorrhages around the disc, engorgement and tortuosity of retinal veins, absence of the spontaneous venous pulses, Paton’s lines (circumferential retinal microfolds in the region surrounding the disc), and usually normal vision but an enlarged blind spot; occurs due to an increase in intracranial pressure from disorders such as a tumor or abscess, cerebral trauma or hemorrhage, meningitis, arachnoidal adhesions, cavernous or dural sinus thrombosis, encephalitis, space-occupying brain lesions, severe hypertensive disease, pulmonary emphysema, and pseudotumor cerebri

Pattern discrimination perimetry
a type of visual field testing in which damage is detected in large optic nerve fibers carrying information on form and motion, thus theoretically revealing glaucomatous nerve damage earlier than conventional perimetry which detects damage primarily in smaller nerve fibers using spots of light; utilizes a checkerboard pattern on a moving background of random “noise” and presented to various points of the retina

Perimetry
visual field testing of the retina, used primarily for the detection of damaged optic nerve fibers caused by glaucoma

Perimetry, pattern discrimination
see pattern discrimination perimetry (PDP)

Pernicious anemia
also known as addisonian anemia; a severe hyperchromic anemia marked by a progressive decrease in number and increase in size and hemoglobin content of the red blood cells and by pallor, weakness, and gastrointestinal and nervous disturbances and associated with reduced ability to absorb vitamin B12 due to the absence of intrinsic factor

Persistent hyaloid artery
a remnant of the hyloid artery which usually atrophies by 8½ months in the embryo but which occasionally remains postnatally, lying in the hyaloid canal or canal of Cloquet

Phacoemulsification
see extracapsular cataract extraction (ECCE)

Photon
a quantum or packet of electromagnetic radiation, usually considered as an elementary particle that is its own antiparticle and that has zero rest mass and charge and a spin of one

Photopic range
the well-illuminated range of light, above 3.4 cd/m² (candela per meters squared), in which the cones of the retina respond well; most commonly present during the day

Photoreceptors
light-sensitive cells (cones and rods) in the retina, located just intimal to the pigmented epithelium; contain chemicals (photopsin and rhodopsin) which react to specific wavelengths of light and trigger nerve impulses

Photorefractive keratectomy (PRK)
surgical procedure in which an excimer laser is used to remove corneal tissue to correct myopia (nearsightedness), hyperopia (farsightedness), or astigmatism

Piebald syndrome
a condition in which there is a white forelock and an absence of pigmentation of the medial portion of the forehead, eyebrows and chin, and of the ventral chest, abdomen, and extremities; includes hyperpigmentation at the borders of unpigmented areas; can include heterochromia iridis and, less commonly, deafness

Pigmentary glaucoma
a type of glaucoma secondary to pigment dispersion syndrome, caused by an over-accumulation of liberated iris pigment in the irido-corneal angle, thereby blocking aqueous outflow and elevating intraocular pressure; can result in glautomatous optic atrophy and associated visual field loss; best managed with topical miotics, but may require argon laser trabeculoplasty, filtering surgery, and even laser peripheral iridotomy

Pigment dispersion syndrome
liberation of iris pigment, due to a rubbing of the posterior iris by zonular fibers, and movement of the pigment through the pupil, into the anterior chamber, and into the irido-corneal angle; eventually can block aqueous outflow through the angle, elevating intraocular pressure and resulting in pigmentary glaucoma; often seen (through a biomicroscope) as a granular brown vertical band along the corneal endothelium (known as Krukenberg’s spindles), as well as pigment dusting on the lens, the surface of the iris and at Schwalbe’s line; typically encountered in young, white males between the ages of 20 and 40 years

Pigmented epithelium
supporting cells for the neural portion of the retina (photopigment regeneration, ion transport); microvilli and sheaths that surround outer segments of rods and cones; dark with melanin which decreases light scatter within the eye; digest debris from rods and cones, make melanosomes, and metabolize vitamin A

Pinguecula
a yellowish nodule in the conjunctiva at the front of the eye, usually but not always on the nasal side; thought to represent degeneration in the conjunctiva as a result of dryness, as well as of exposure to wind and dust; does not require medical or surgical treatment

Pituitary gland
a small oval endocrine organ that is attached to the infundibulum of the brain and occupies the sella turcica; consists essentially of an epithelial anterior lobe derived from a diverticulum of the oral cavity and joined to a posterior lobe of nervous origin by a pars intermedia; has the several parts associated with various hormones which directly or indirectly affect most basic bodily functions and include substances exerting a controlling and regulating influence on other endocrine organs, controlling growth and development, or modifying the contraction of smooth muscle, renal function, and reproduction

Plug, silicone
punctal plug; a tiny, tapered shaft inserted into the punctum to prevent tears from draining out of the eye, as a treatment for a dry eye

Posterior chamber
a narrow space inside the eye, located behind the peripheral part of the iris and in front of the suspensory ligament of the lens and the ciliary processes; contains aqueous humor

Posterior compartment
the large space inside the eye, located posteriorly to the crystalline lens; contains the vitreous humor

Presbyopia
a visual condition which becomes apparent most often during the age span 40 to 45 in which loss of elasticity of the crystalline lens causes reduced accommodation and the inability to focus sharply at a near distance

Prism diopter
a measurement of the angle of deviation of an eye with strabismus; a 1 prism diopter prism deflects a straight beam of light one centimeter when measured one meter away from the prism

Protanopia
a type of anomalous dichromatism color deficiency in which the spectrum is seen in tones of yellow and blue with confusion of red and green and reduced sensitivity to monochromatic lights from the red end of the spectrum, due to a lack of (or lack of function of) “L-cone” photoreceptors sensitive to long (reddish) wavelengths of light

Protoanomaly
a type of anomalous dichromatism trichromatism in which an abnormally large proportion of red is required to match the spectrum

Pseudopapilledema
optic nerve head drusen; deposits of calcium, mucopolysaccharides, hemosiderin and amino acids in the optic nerve head, causing an apparent elevation of the optic disc; an autosomal disorder which sometimes is associated with retinitis pigmentosa; generally asymptomatic, but may produce visual field loss by direct effect on optic nerve axons, subretinal hemorrhage, or subretinal neovascularization; resembles the appearance of papilledema but differs from the latter in that there is the presence of venous pulsations and the absence of hemorrhages, exudates, cotton wool spots, and Paton’s lines (circumferential retinal microfolds in the region surrounding the disc)

Pseudotumor cerebri
found most frequently in young, overweight women between the ages of 20 and 45; usually associated with signs of increased intracranial pressure, including papilledema and an enlarged blind spot; symptoms may include headaches, dizziness, nausea, and vomiting; can include transient visual obscurations and intermittent diplopia; diagnosis demonstrated by lumbar puncture

Pterygium
a triangular fleshy mass of thickened conjunctiva occurring usually on the inner aspect of the eyeball, covering part of the cornea, and often causing a disturbance of vision due to corneal distortion

Pupil
the contractile, usually round aperture in the iris of the eye which allows light to pass into the crystalline lens; see also Pupillary Defects and Conditions Affecting the Face

Punctum
the opening of either the upper or the lower lacrimal duct at the inner canthus of the eye

Pupil constriction
decrease in size of the pupil, due either to an increase in incoming light or to an increase in lens accommodation at near

Pupil dilation or dilatation
increase in size of the pupil, due either to a decrease in incoming light or to a decrease in lens accommodation at near

Pupillary block
contact between the posterior iris (at the pupillary edge) and the anterior crystalline lens, decreasing or blocking the flow of aqueous fluid through the pupil, increasing pressure on the posterior iris (causing it to bow forward and to decrease the size of the irido-corneal angle), all of which creates in increase in intraocular pressure

Pursuit
an eye movement in which the eyes smoothly follow a moving target (such as a car, a jogger, or a tennis ball) in space

Radial keratotomy (RK)
surgical procedure to correct myopia by flattening the curvature of the cornea via a series of 4 to 16 equally spaced radial cuts in the peripheral cornea; may leave extensive scars on the cornea, causing glare in bright light and possibly interfering with the wearing of contact lenses (in case the myopia is not fully corrected)

Radiation, infrared (IR)
electromagnetic radiation with a wavelength outside the visible spectrum at its violet end; used of radiation having a wavelength between about 700 nanometers and 1 millimeter

Radiation, ultraviolet (UV)
electromagnetic radiation with a wavelength outside the visible spectrum at its red end; used of radiation having a wavelength shorter than that of visible light and longer than that of x-rays

Real image
the image formed by a convex lens (or a concave mirror), on the opposite side of the lens from which the light is entering; the image is formed at the focal point of the lens, at a distance (focal length) away from the lens, in meters, equal to the inverse of the dioptric power of the lens

Rebound hyperemia
continual engorgement of blood vessels (such as those in the conjunctiva) due to chronic use of a vasoconstricting drug, due to a weakening of the smooth muscles constricting the vessels, creating a need for more of the vasoconstrictor to be used to have the same vasoconstricting effect

Rectus muscle
any of four muscles of the eyeball that arise from the border of the optic foramen and run forward to insert into the sclera of the eyeball; medial rectus inserts into the medial (nasal) aspect of the sclera; lateral rectus inserts into the lateral (temporal) aspect of the sclera; superior rectus inserts into the superior aspect of the sclera; inferior rectus inserts into the inferior aspect of the sclera

Reiter’s syndrome
a disease that usually is initiated by infection in genetically predisposed individuals and typically is characterized by recurrence of arthritis, conjunctivitis, and urethritis

Retina
layer of nervous tissue, covering the back two-thirds of the eyeball, in which stimulation by light initiates an electrochemical reaction in which electrical impulses are transmitted to the brain, producing the sensation of vision; actually an extension of the brain, formed embryonically from brain tissue and connected to the brain proper by the optic nerve

Retinal arteries
arteries in the retina; salmon to red in color; about 1 1/3 to 2 times the diameter of retinal veins; see central retinal artery

Retinal hemorrhage
bleeding into the retina; caused by such things as infections, trauma, hypertensive retinopathy, diabetic retinopathy, central vein occlusion, hematologic abnormalities, central nervous system vascular malformations, prolonged and vigorous cardiopulmonary resuscitation, or high-altitude mountain climbing

Retinal tear
a rip in the retina; caused by such things as trauma or a pulling on a weak section of retina by the attached vitreous; can result in a vitreous hemorrhage if the retina tears across a blood vessel

Retinal veins
veins in the retina; salmon to orange in color; about 1/2 to 3/4 the diameter of retinal arteries; see central retinal vein

Retinitis pigmentosa (RP)
degeneration of the retina manifested by night blindness and gradual loss of peripheral vision, eventually resulting in tunnel vision or total blindness

Retinopathy
any diseased condition of the retina, especially one that is noninflammatory

Retrobulbar optic neuritis
inflammation of the optic nerve, usually unilateral, affecting the part of the nerve behind the eyeball, sometimes accompanied by mild optic disc hyperemia but an otherwise normal retina, and almost always accompanied by central vision loss and pain on moving the eye; occurs due to multiple sclerosis and other disorders which cause papillitis, but most often due to idiopathic (unknown) causes

Rhodopsin
a bright red photosensitive pigment found in the retinal rod photoreceptors that is similar to iodopsin (in cone photoreceptors) but is less labile; contains opsin (a protein) and retinene (a light absorbing compound which is derived from Vitamin A); important in scotopic vision

Rods
the elongated, rod-shaped light-sensitive receptor cells of the retina that function in dim-light and night vision and in the perception of size, shape, and brightness of visual images; composed of an outer segment (containing the photoreceptor molecule rhodopsin), inner segment, cell body, and synaptic region; about 120 to 130 million per eye, much more than the number of cones; densest accumulation is in the retinal periphery, with none being present in the fovea; absent in the optic disc (optic nerve head)

Saccade
an eye movement in which the eyes jump from one point to another, as from one word to the next while reading or around a room when searching for something

Sarcoidosis
a rare, chronic, autoimmune disease of unknown cause that is characterized by the formation of nodules resembling true tubercles, especially in the lymph nodes, lungs, liver, eyes, bones, skin, joints, kidneys, and spleen

Schwalbe’s line
the demarcation between the cornea and the sclera; the endpoint of Descemet’s membrane

Sclera
the dense fibrous opaque white outer coat enclosing the eyeball, except the part covered by the cornea

Scleral buckle
a silicone implant or flexible band placed around the equator of the eye which “squeezes” the eye inward and to counterbalance any force pulling the retina out of place

Scleral spur
the protrusion of the sclera to which the trabecular fibers attach anteriorly and the iris root attaches posteriorly

Scotoma
a blind or dark spot in the visual field

Scotopic range
the dimly-illuminated range of light, below 0.034 cd/m² (candela per meters squared), in which the rods of the retina respond well but the cones of the retina respond poorly or not at all; most commonly present at night

Sinusitis
inflammation of a sinus of the skull

Sjogren’s syndrome
a chronic inflammatory autoimmune disease that affects especially older women; characterized by dryness of mucous membranes, especially of the eyes and mouth, and by infiltration of the affected tissues by lymphocytes; often associated with rheumatoid arthritis

Strabismus
heterotropia or tropia; inability to attain or maintain binocular vision due to some type of muscle imbalance in one eye, causing that eye to turn in, out, up, or down relative to the other eye; can be “intermittent” (occurring sometimes), “constant” (occurring all the time), and/or “alternating” (occurring sometimes with one eye and sometimes with the other eye, whether intermittently or constantly)

Stroma, corneal
substantia propria; lamellae (layers) of regularly arranged collagen fibers in the cornea, the parallel fibers in each lamella aligned at an orientation different from those of the fibers in the appropriately spaced layers above and below it such that corneal transparency is maintained; comprises 90% of the cornea’s thickness

Stroma, iridial
thick, highly vascular central layer of the iris containing delicate collagenous fibers intermixed with varying proportions of pigmented and nonpigmented cells, the amounts of the latter which provide the iris with its degree of color

Substantia propria
the layer of lamellated transparent fibrous connective tissue that makes up the bulk of the cornea of the eye

Superior oblique muscle
an extraocular muscle in the orbit, originating in the annulus of Zinn, which loops through the trochlea before inserting into the sclera; innervated by the trochlear nerve (cranial nerve IV); intorts, depresses, and abducts the eye

Superior rectus muscle
an extraocular muscle in the orbit, originating in the annulus of Zinn; innervated by the abducens nerve (cranial nerve VI); elevates, intorts, and adducts the eye

Syphilis
a chronic contagious, usually venereal and often congenital disease that is caused by a spirochete of the genus Treponema (T. pallidum) and if left untreated produces chancres, rashes, and systemic lesions in a clinical course with three stages continued over many years