Glossary of Eye Care Terms - P
papilla Small bump where the optic nerve exits the eye.
papilledema Swelling with accompanying compression of the optic nerve head, which can be a medical emergency. Causes of papilledema can include bleeding near the vicinity of the optic nerve and abnormally high cerebrospinal fluid (CSF) pressure. Autoimmune disorders, trauma and infections of the central nervous system also can cause papilledema. Optic nerve swelling can result from central retinal vein occlusion or may occur as a side effect of medications such as lithium, tetracycline and corticosteroids.
papilloma Usually benign tumor, such as a wart or a skin tag; papillomas may be raised or flat, and can be a variety of colors, such as skin-colored, yellow, pink, brown or black. Eye papillomas are typically on the eyelid, but may also appear on the conjunctiva. The cause of papillomas is felt to be viral.
Parinaud dorsal midbrain syndrome Inability to look up, typically associated with a brain lesion, characterized by nystagmus and pupil unresponsiveness to light. Causes include hydrocephalus ("water on the brain") and tumors of the pineal gland.
Parkinson's disease Neurological disorder characterized by tremors, muscle rigidity, a shuffling walk and a mask-like appearance in the face. Parkinson's may also cause infrequent blinking.
pars plana Posterior part of the eye's ciliary body.
Patau syndrome Also called Trisomy-13. Condition caused by an extra, third copy of chromosome 13. Symptoms include severe mental retardation, a small head, microphthalmia, a cleft lip or palate, heart defects and extra fingers or toes; many patients also have an iris coloboma and retinal dysplasia (abnormal development). The majority of infants with Patau syndrome die within the first year.
pediculosis Lice infestation, typically caused by contact with an infected person or infected bedding. When lice infest the eyelid and eyelashes, they can cause such symptoms as visible lice (white or gray), eggs called nits (white or gray) or feces (reddish-brown), blue bite marks, blepharitis and conjunctivitis. Some people also develop keratitis.
penetrating keratoplasty A transplant procedure in which a circular area of surface eye tissue is removed from a healthy donor cornea and transferred to a recipient. A penetrating keratoplasty or corneal transplant may be needed in case of eye damage from injury or from eye diseases such as keratoconus.
periorbital cellulitis An infection and inflammation of the eyelid and portions of skin around the eye, caused by bacteria, viruses or other pathogens. Also called preseptal cellulitis.
peripheral vision The edges of your visual field.
phacoemulsification Also called "phako," this in-office cataract surgery procedure involves using a device with a vibrating, ultrasonic tip to break up the cataract, then suctioning the pieces out with a tiny needle. Read our article about cataract surgery.
phakic An eye that still has its natural lens. When an eye is aphakic, usually the lens has been removed during cataract or other eye surgery.
phoropter Device that provides various combinations of lenses used for tests of vision errors in eye examinations.
photoablation Procedure in which a surgeon uses ultraviolet radiation to remove tissue.
photochromic Able to change lens color or darkness/density depending upon the degree of exposure to light. Read more about photochromic lenses.
photocoagulation Use of heat from a high-energy laser to seal off bleeding in damaged tissue. Photocoagulation also may prevent formation of abnormal blood vessels (neovascularization) in eye diseases such as age-related macular degeneration or diabetic retinopathy. Photocoagulation also may be used to reattach a detached retina.
photophobia Discomfort from sun or other light. Photophobia has many causes. Read more about light sensitivity.
photopsia Flashes of light often noticed in the edges of the visual field. Photopsia can have many causes, including mechanical (rather than visual) stimulation of light-sensitive cells (photoreceptors) in the retina. For example, a detached retina can cause photopsia when the retina pulls away or detaches from tissue in the inner back of the eye. A vitreous detachment with accompanying photopsia can occur when the eye's gel-like interior begins to shrink and pull against the retina. Photopsia can be accompanied by a shower of spots and floaters.
photoreceptor A light-sensitive cell found in the retina. Photoreceptors in the human retina are classified as cones and rods. Cones are located in the central retina (the fovea) and control color vision. Rods are located outside the fovea and control black/white vision in low-light conditions.
phytochemicals Chemicals found in plants that help protect against disease.
pigment dispersion syndrome An eye condition where pigment granules that normally adhere to the colored part of the eye (iris) flake off and adhere to the posterior surface of the cornea and other structures in the anterior chamber of the eye. If the pigment accumulates in the drainage angle of the anterior chamber, it can reduce the drainage of aqueous from the eye, causing ocular hypertension and (potentially) pigmentary glaucoma.
pinguecula A yellowish, thickened lesion on the conjunctiva near the cornea. Pingueculae represent a benign degenerative change in the conjunctiva caused by the leakage and deposition of certain blood proteins through the permeable capillaries near the limbus. Read more about pinguecula and pterygium.
placebo A "false" but harmless treatment that has no proven medical value. Placebos usually are incorporated into clinical trials to measure how patients respond to an authentic therapy that is being tested. Some patients are given placebos, and others are given the actual therapy, to provide objective comparisons and assessments.
plano A term eye care professionals use to describe lenses with no corrective power. The term is most often applied to nonprescription sunglasses or contact lenses that are worn for cosmetic purposes only.
PMMA (polymethyl methacrylate) Old-fashioned hard contacts were made of PMMA, which is not oxygen-permeable; today's rigid lenses contain other polymers that allow oxygen to reach your eye. Some intraocular lenses are made of PMMA because the material is well tolerated inside the eye.
polarized lenses Lenses that block light reflected from horizontal surfaces such as water, to reduce glare. More about polarized lenses.
porphyria Disorder in which the body produces too much of a compound called porphyrin and releases it in the urine, causing a reddish color. Other symptoms include light sensitivity, skin that swells or is sensitive to sunlight, abdominal pain, blisters and muscle weakness.
polycarbonate Plastic that is very impact-resistant, and is thus sometimes used for spectacle lenses and frames. Read more about polycarbonate lenses.
posterior chamber Part of the eye behind the iris and in front of the lens.
posterior capsular opacification Haziness that develops behind the artificial intraocular lens inserted during cataract surgery. A common complication following cataract removal, a PCO can be removed with a YAG laser capsulotomy.
presbyope Person who has difficulty reading print and seeing near objects.
presbyopia Condition in which the aging eye beginning at around age 40 is unable to focus at all distances, often noticed when print begins to blur. Additional symptoms include eye strain, headaches, and squinting. Read our article about presbyopia.
prescription lenses Lenses that provide vision correction as prescribed by an eye care practitioner.
prism In optics, a lens that can have precise geometric configurations enabling light to be bent or reflected in certain ways. A prism also can split white light into different wave lengths and colors.
PRK (Photorefractive Keratectomy) Surgical procedure in which an excimer laser is used to remove corneal tissue to correct vision problems.
progressive lenses Also called progressive addition lenses or PALs. Multifocal lenses whose corrective powers change progressively throughout the lens. A wearer looks through one portion of the lens for distance vision, another for intermediate vision, and a third portion for reading or close work. Each area is blended invisibly into the next, without the lines that traditional bifocals or trifocals have. Read an article about progressive lenses.
proliferative vitreoretinopathy (PVR) A common complication of surgery for retinal detachment, which causes scarring of the retina. PVR may require a vitrectomy and intricate surgical removal of scar tissue.
propionate A soft, flexible material that is sometimes used in goggles.
prosthetic Refers to a prosthesis, which is an artificial replacement for a part of the body. Read more about prosthetic contact lenses. Or read about losing an eye and replacement with a prosthetic eye.
protective eyewear Eyewear made with impact-resistant lenses, usually polycarbonate, that protects the eyes, especially in working situations or sports.
protein Large, complex organic molecules found in all living cells. These molecules contain enzymes, antibodies, hormones and other elements that help organisms function. Proteins are present in human tears and can collect on contact lenses, resulting in discomfort and cloudy vision.
pseudoexfoliation syndrome A condition of unknown cause in which light gray, dandruff-like material forms on the pupil margin and anterior lens capsule in the eye. This material also can lodge in the trabecular meshwork causing an increase in internal eye pressure and pseudoexfoliative open-angle glaucoma.
pseudotumor cerebri A condition whose symptoms mirror those of a brain tumor: increased intracranial pressure, headache, nausea, brief periods of vision loss (graying or blurring) and double vision. The cause is unknown, but patients are often obese women.
pseudophakic Describes an eye that has an artificial lens implant following cataract surgery or refractive lens exchange. ("pronounced sue-doh-FAY-kik")
pterygium Triangular fold of tissue on the white of the eye that can eventually grow over part of the cornea; the cause may be irritation from sun (i.e., UV rays), dust and wind. Some people have no symptoms, while others may have redness or blurred vision. Pterygia that are chronically inflamed can become itchy. Read more about pterygium and pinguecula.
ptosis Drooping eyelid. Congenital ptosis is caused by a problem with the levator muscle (which lifts the eyelid). In adults, ptosis is commonly caused by the aging of the levator's connective tissue.
puncta Tiny openings through which tears drain away from the eyes. Four puncta are in the nasal corner of the eye — two in the upper inner eyelid and two in the lower inner eyelid. Punctal plugs sometimes are used to block these openings so that more tears are retained as a treatment for dry eye syndrome.
punctal cautery A procedure that uses heat or laser energy to permanently close channels from which tears drain. Punctal cautery increases the accumulation of moisture as a treatment for dry eye.
punctal plugs Tiny inserts often made of plastic that are placed in channels or ducts of the eye where moisture drainage occurs. Punctal plugs can help stop excessive drainage to keep the eye moistened in conditions such as dry eye syndrome.
pupil The round, dark center of the eye, which opens and closes to regulate the amount of light the retina receives.
pupillary distance This is the distance between the center of each pupil. Opticians use a special ruler to measure your pupillary distance before ordering your eyeglasses. It is an essential measurement because the optical center of each eyeglass lens must be positioned directly over the center of each pupil. An incorrect measurement means you would have difficulty focusing when wearing the glasses.
Page published in April 2019
Page updated in November 2021