Eye Dictionary

Eye Dictionary - P

Dictionary Links A B C D E F G H I K L M N O P R S T U V W Y

pachymeter: Ultrasound machine used in measuring thickness of the cornea. Especially important in determining treatment depth in refractive surgery.
See Refractive Surgery in Eye Care Encyclopedia.
pachometer: Instrument that uses optical principle of split images to measure corneal thickness or anterior chamber depth.
pallucid macular degeneration: Pallucid is an out-of-date, seldom used term.
See Free Eye Tests.
palpebral glands: Little glands in the eyelids that make a fatty lubricant which they discharge through tiny openings in the edges of the lids. The meibomian glands can become inflamed, a condition termed meibomianitis or meibomitis. Chronic inflammation of the meibomian glands lead to a cyst, also called chalazion, which is a pimple in the margin of the eyelid. The meibomian glands are also known as the meibomian glands, tarsal glands, or tarsoconjunctival glands.
Pediatric Wellness: see Pediatric Wellness in Eye Care Encyclopedia.
See Free Eye Tests.
Pediatric Evaluation (link to free online eye test)
perimeter: Instrument used for determining central or peripheral field of vision.
perimetry: Method of charting extent of visual field as seen by the stationary eye. Aids in the detection of damage to the sensory visual pathways.
See Free Eye Tests.
peripheral vision: Side vision; vision not in the straight-ahead direction.
phacoemulsification: Technique for removing eye’s natural crystalline lens in cataract surgery or clear lens extraction. Procedure makes use of an ultrasonic instrument called a phaco machine, which produces vibrations at a rate of 40,000 cycles per second, thereby dissolving the lens into small fragments. Using a hand piece, the surgeon then uses the same machine to aspirate (suck out) the contents of the lens and irrigate the eye.
See Cataracts in Eye Care Encyclopedia.
phaco machine: Ultrasonic instrument used in phacoemulsification technique for removing the natural lens of the eye during cataract or clear lens extraction surgery. Using a hand piece connected to the phaco machine, the surgeon dissolves the lens into small fragments, aspirates the contents and irrigates the eye.
See Cataracts in Eye Care Encyclopedia.
photopic: Bright light conditions where only the cones are functional.
phoropter: An instrument used by the eye doctor to determine the degree of myopia (nearsightedness), hyperopia (farsightedness) or astigmatism that is present in the patient’s eye.
photocoagulation: A surgical process of sealing off, or clotting, tissue by means of a laser beam. It is used in cancer treatment to destroy blood vessels entering a tumor and deprive it of nutrients, in the treatment of a detached retina, to destroy abnormal blood vessels in the retina, to treat tumors in the eye; etc.
photochromatic: Eyeglass lenses that darken when exposed to short wavelength radiation or ultra-violet light. These are the “transition” lenses that change from clear to dark when exposed to sunlight.
photophobia: Abnormal sensitivity to, and discomfort from, light. Frequently associated with excessive tearing and often due to inflammation of iris or cornea.
photoreceptor: Cells specialized for receiving light.
Photorefractive Keratectomy (PRK): Refractive eye surgery procedure that employs a computer-controlled Excimer laser system to sculpt by ablation (vaporize) the central corneal zone, or visual axis. By changing the shape of the patient’s cornea, the eye care surgeon can correct some cases of nearsightedness, farsightedness and astigmatism.
See Photorefractive Keratectomy, Refractive Surgery in Eye Care Encyclopedia.
See Free Eye Tests.
pigmentary retinopathy: Any of several hereditary progressive degenerative diseases of the eye marked by night blindness in the early stages, atrophy and pigment changes in the retina, constriction of the visual field, and eventual blindness. Also called retinis pigmentosa.
pink eye: Also known as conjunctivitis. Inflammation of conjunctiva or membrane that covers the white of the eye and inner surfaces of the eyelid. Characterized by discharge, grittiness, redness and swelling. May result from virus, bacteria, allergens, chemical exposure, or ultraviolet light exposure. Can be contagious.
See Free Eye Tests.
plano: Term used by eye care professionals to describe lenses with no focusing power. The term is most often applied to nonprescription sunglasses or contact lenses that are worn for cosmetic purposes only.
plastic surgery of the eyelids: Also known as blepheroplasty. Surgery to improve the appearance of the eyelids. In addition to detracting from overall appearance, drooping eyelids may cause functional problems such as impaired field of vision or difficulty wearing glasses. Blepharoplasty is usually outpatient surgery performed by ophthalmic plastic and reconstructive surgeons.
See Blepheroplasty in Eye Care Encyclopedia.
See Free Eye Tests.
PMMA: Acronym for polymethylmethacrylate. Original material used in the manufacture of “hard” contact lenses. In today’s rigid contact lenses, PMMA is often used in combination with other polymers to increase the oxygen permeability and allow longer wearing times.
polarized lenses: Eyeglass lenses designed to protect the eye against UV rays and reduce the glare of reflected light. May be constructed of glass, plastic or lightweight, hi-index plastic.
See Free Eye Tests.
pole: Posterior pole refers to back curvature of eyeballs, usually to the retina between optic nerve and macular area. Anterior pole refers to center of front surface of cornea.
polycarbonate: Plastic marked by a high softening temperature and high impact strength, sometimes used for eyeglass lenses and frames.
posterior: Back area of an object.
posterior chamber: In referring to the eye, that space between the back which is filled with aqueous fluid between the iris and front face of the vitreous.
posterior capsulotomy: Laser surgical procedure which is sometimes necessary to clear vision after cataract surgery. During cataract surgery the front part of the capsule which contains the eye’s natural lens is removed, but the rear of the capsule (posterior capsule) is left intact. This membrane sometimes becomes cloudy after cataract surgery and requires a return trip to the ophthalmologist for treatment. Treatment comprises a very brief, in-office, painless laser procedure that opens a new pathway allowing light to reach the back of the eye. Vision improvement is very fast, usually within a day or two.
presbyope: Person who has difficulty reading print and seeing nearby objects because of age-related loss of elasticity of the eye’s natural crystalline lens.
See Free Eye Tests.
presbyopia: Deterioration in the ability of the eye’s natural crystalline lens to expand or contract in order to focus on close objects.
See Free Eye Tests.
prescription lenses: Eyeglass or contact lenses that provide vision correction as prescribed by an eye care practitioner.
See Free Eye Tests.
PRK: Acronym for Photorefractive Keratectomy. Refractive eye surgery procedure that employs a computer-controlled Excimer laser system to sculpt by ablation (vaporize) the central corneal zone, or visual axis, to change its shape in order to correct some cases of nearsightedness, farsightedness and astigmatism.
See Photoreactive Keratectomy, Refractive Surgery in Eye Care Encyclopedia.
propionate: Flexible, soft material that is sometimes used in eye goggles.
prosopagnosia: The inability to recognize faces.
protective eye wear: Eyewear made with impact-resistant lenses, often polycarbonate, to protect the eyes, usually sports or working situations.
protein: Common form of soft contact lens deposits which, if not removed, may lead to reduced lens wearing comfort, decreased visual acuity and general reduction in ocular health.
ptosis: Condition in which the upper eyelid(s) sag. May be congenital or caused by a later problem associated with a nonfunctioning levator muscle. Usually hereditary.
See Free Eye Tests.
pupil: Black opening behind the cornea in the center of the iris that regulates the amount of light entering the inner lens of the eye.
punctum plug: Small, nondissolvable silicone plugs inserted in the tear draining ducts to close the openings of the tear draining system in order to slow drainage and loss of tears. Used to provide dry eye relief and/or reduce or eliminate the major cause of contact lens discomfort.
See Free Eye Tests.
pupil dilation: Enlarged pupil resulting from contraction of dilator muscle or relaxation of iris sphincter. Normally occurs in dim illumination conditions. Comprehensive examination of the interior of the eye requires pupil dilation through the administration of appropriate eye drops by the examining eye professional. Dilation can also be caused by injuries, including blunt trauma.