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Eye Health Glossary

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PAL

Progressive Addition Lenses (PAL); popular no-line bifocal lenses that are used to correct for presbyopia.

papilla

Small, fleshy, nipple-like extension from the skin.

papilledema

Swelling of the optic nerve head caused by a rise in intracranial pressure. Papilledema is an important risk factor for brain tumors, as 50% of brain tumor cases have papilledema.

papilloma

Benign skin tumor that may project out from the skin surface; also known as a wart. Warts are caused by the papilloma virus and resolve spontaneously without need for treatment.

pars plana

Flattened portion of the ciliary body. In a pars plana vitrectomy procedures, instruments enter the eye through the area of the pars plana.

patching

The classical treatment for amblyopia (lazy eye) in children. In theory, by patching the “good” eye, the amblyopic eye is forced to work harder and as a result perform better. While patching has shown improvement in many cases, it is difficult to force a child to wear a patch and the amount of time that the patch should be worn varies among individuals, so it is a very inexact science. Use of atropine drops is a popular alternative to patching for amblyopia.

pediculosis

Lice (Pediculosis humanus) infestation, resulting in severe itching. Lice can be found among the eyelashes as well as on top of the head.

perimetry

Measurement of the field of vision. See Field Testing for more information.

peripheral vision

Side vision; usually classified as vision outside of the central 30 degrees. Detection of movement is enhanced in our side vision while formation of high resolution images are not possible using peripheral vision.

phacoemulsification

The process by which ultrasonic vibrations are used to break up the crystalline lens during cataract extraction surgery, making it easier to remove the cataract.

phakic

An eye that possesses a natural crystalline lens. Following cataract surgery with an IOL implant, individuals become pseudo-phakic.

phoria

Tendency towards a misalignment of the eyes (horizontal or vertical). Most people do have some type of phoria. This minor misalignment of the eyes is perfectly normal and only evident upon inspection of the eyes in a disassociated state (ie. with the other eye covered).

phoropter

Instrument used by eyecare professionals to determine the prescription of glasses needed by each individual. When measuring a person's refraction, optometrists will put the phoropter up to a person's eyes so that they look through it at an eye chart.

photochromic lenses

Lenses that change tint with changes in light intensity. Most photochromic lenses depend on changes in UV radiation to change tint (Transitions are like this). For this reason, photochromic lenses tend not to work in the bright sunlight when you are in a car because the windows of the car have UV protection.

photocoagulation

Application of lasers to burn (coagulation occurs so there is no bleeding) intraocular structures in an attempt to stop progression of diabetic retinopathy.

photodynamic therapy

Treatment involving the injection of a drug that is then activated by shining a laser beam in the eye. PDT is an up-and-coming therapy used in the treatment of wet macular degeneration. Learn more about macular degeneration treatment.

photokeratitis

Painful “sunburn” of the cornea. Exposure to the intense light of a welder's torch (“welder's flash”), or to the bright reflections from snow (“snow blindness”) are examples of photokeratitis. Symptoms include pain, blurred vision, and light sensitivity. Though painful, the condition is temporary as the epithelial cells slough off and regenerate.

photophobia

Light sensitivity; low tolerance to bright light.

photoreceptors

Light-sensitive cells located in the retina. The human eye contains two types of photoreceptors: cones and rods. All photoreceptors are wavelength sensitive, responding preferentially to particular wavelengths, which is the way in which color vision is possible. Once photons of light are absorbed by photoreceptors, visual information is then transferred down the visual pathway in the form of electrical signals to the brain.

pinguecula

Yellowish fleshy lesion formed from degenerated connective tissue that becomes deposited on the conjunctiva. Learn more about Pinguecula.

plano

Without power (no refractive power). An emmetropic individual would have a prescription of (or close to) plano in both eyes. Anyone who has perfect vision but wishes to buy color contact lenses would want to buy contacts with a plano (0.00) prescription.

PMMA

PolyMethyl MethAcrylate (PMMA); rigid, non-permeable plastic material that was formerly used as a hard contact lens and also as an intraocular lens implant.

polarized lenses

Lenses that allow only allow certain rays of light that are oscillating in a particular direction to pass through. Light that is reflected off surfaces such as water and a flat road are principally oscillating in the horizontal direction – polarized lenses cut out these horizontal rays of light and as a result, significantly reduce glare from such surfaces.

polycarbonate

Extremely hard and durable plastic that is often used for safety glasses and safety goggles. The strength of polycarbonate lenses also makes them a popular choice for the lenses used in children's glasses. Polycarbonate can be scratched easily, but this can be fixed by using a scratch resistant coating.

posterior capsulotomy

Laser procedure that is performed using a Nd:YAG laser on cataract surgery patients who have developed a small growth of cloudy membrane behind the IOL implant. The YAG laser is used to vaporize this tissue membrane, with few complications and great success, restoring vision. Learn more about Cataract Surgery procedures.

posterior chamber

The area within the eye between the iris and the crystalline lens. The posterior chamber is filled with aqueous humour.

posterior subcapsular cataract

One of three types of cataract in which an opacity forms at the outer edge of the crystalline lens, adjacent to the posterior lens capsule (thin membrane in which the crystalline lens sits). A posterior capsular cataract occurs directly in the path of the visual axis and as such, usually causes the most problems with blurred and distorted vision earlier on in development. Learn more about Cataracts.

power

A measure of the strength of an optical system, whether it be the lenses in the eye or lenses such as those found in contacts and eyeglasses. Power is measured in Diopters.

presbyopia

A normal process of aging; gradual loss of flexibility of the crystalline lens such that it loses its ability to accommodate and to produce clear vision of near objects. Learn more about Presbyopia.

primary open angle glaucoma

Most common type of glaucoma. Unlike in angle closure glaucoma, the anterior angle in POAG is open, so some other process is occurring to build pressure within the eye. Learn more about how Primary Open Angle Glaucoma occurs.

prism

Optical device that bends light. Useful in the management of some binocular vision conditions.

PRK

Photorefractive Keratectomy (PRK); laser surgical procedure in which the outermost layer of the cornea is taken off (debrided) and a pulsed laser is used to reshape the corneal surface beneath. Learn more about PRK and other laser surgeries.

progressives

Popular name for Progressive Addition Lenses. No-line bifocals used in the correction of presbyopia.

proliferative retinopathy

The stage of diabetic retinopathy in which retinal blood vessels have weakened and become blocked to the point of ischemia (oxygen starvation), and neovascularization is occurring. Learn more about the stages of Diabetic Retinopathy.

proparacaine

Opioid anesthetic used by optometrists and ophthalmologists to numb the cornea so that such techniques as tonometry and gonioscopy can be performed. Alcaine is one of the commercial brands of proparacaine.

pseudotumor cerebri

“False brain tumor;” most common among young, overweight women between the ages of 20 and 40, pseudotumor cerebri mimics the signs and symptoms of a brain tumor. Headache, dizziness, and vomiting may all occur. Pseudotumor cerebri is a diagnosis of exclusion.

ptosis

Drooping of the upper eyelid.

pterygium

Triangular patch of fleshy growth that develops on the conjunctiva and grows towards the cornea. If it grows to the point where it impairs vision, a pterygium may be surgically removed, but otherwise it is left alone.

punctum

A very small hole. There is a punctum on the inside rim of both the upper and lower eyelids of both eyes, through which tears drain into the lacrimal sac.

pupil

The opening through which light enters the eye. The iris is responsible for regulating the amount of light that enters through the pupil.

pupillary distance

Distance between the pupils of the two eyes. Important measurement for determining the proper fitting of progressive addition lenses and bifocals.

pursuit

The act of following the movement of a slow-moving target with the eyes. A simple test called a Broad H is performed in each regular eye exam to test the tracking ability of the eyes and to ensure the eyes are working well together.

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