P
“P” selections in the Glossary of Terms for
Anatomy, Physiology & Pathology of the Human Eye
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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
- palpebral conjunctiva
- see conjunctiva, palpebral
- 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
- pathway, visual
- see visual pathway
- pattern discrimination perimetry (PDP)
- 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 (PDS)
- 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
- pigmentosa, retinitis (RP)
- see retinitis pigmentosa (RP)
- 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
- pink eye
- see conjunctivitis
- 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
- posterior vitreous detachment (PVD)
- see detachment, posterior vitreous (PVD)
- 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
- pressure, intraocular (IOP)
- see intraocular pressure (IOP)
- 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
- processes, ciliary
- see ciliary processes
- 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, Adie’s tonic
- see Adie’s tonic pupil
- pupil, Argyll Robertson
- see Argyll Robertson pupil
- pupil, Marcus Gunn
- see Marcus Gunn pupil
- 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
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