P

Pachometer is an instrument attached onto the biomicroscope (slit lamp) in order to measure the thickness of the cornea and the depth of the anterior chamber of the eye. This is necessary for such cases as corneal swelling or thickening after contact lenses are worn for an extended time and may have caused damage.

Panophthalmitis is a painful condition in which inflammation or infection affects the entire globe of the eye. This may result from the inflammation of posterior uveitis or an infection due to surgery or injury. The condition also occurs when an inflammation or infection that affects the posterior chamber and center of the globe (endophthalmitis) spreads past the center to involve the anterior chamber and the sclera. The underlying condition is usually not treatable after it has reached the stage of panophthalmitis, which usually results in complete, and permanent vision loss in the affected eye. The eye may begin to shrink and may require surgical removal.

Papilledema is a swelling of the optic disc resulting from an increase in intracranial pressure. Intracranial pressure may be the result of cerebral tumor or abscess, hypertension, subdural hematoma, or hydrocephalus (an increase in cerebrospinal fluid within the cranial cavity). Papilledema is often accompanied by vomiting and headache, enlargement of the blind spot, and transient blurring or loss of vision. It almost always is bilateral and may develop over hours to weeks. Since papilledema may indicate a tumor, it is a serious condition that requires prompt medical attention. The condition may be diagnosed by a visual-field examination, ultrasonography, computerized tomography, and fluorescein angiography. Pseudopapilledema is a degeneration or abnormality of the disc that exhibits the same symptoms as those of papilledema but may actually be a misshapen disc or multiple drusen (waste particles of the optic nerve). Treatment is according to cause.

Pathsounder is an ultrasonic electronic travel aid designed for use by the visually impaired. The device is manufactured under several names, including the Russell Pathsounder and the Polaron. The device consists of a small box that may be hand held or worn at chest height from a strap around the neck. The box sends ultrasonic waves into the path of the user to detect objects up to sixteen feet away. The reflected waves are converted into an audible sound to warn the user. The pathsounder is designed to be used in conjunction with a long cane, and some manufacturer’s models may be used with a guide dog. Its use does require training from a qualified instructor.

Perimetry (See Visual Field Test.)

Peripheral Vision is the side vision of the visual field. It provides information about the area surrounding the central vision, where detail is perceived. Peripheral vision is controlled by the rods, light-sensitive cells of the retina. Because the rods are scattered throughout the retina, unlike the cones which are concentrated in the center, they are the ones responsible for peripheral vision. Diseases of the retina and other disorders of the eye may damage cones or destroy peripheral vision. Retinitis pigmentosa is a hereditary group of diseases that attack the retina and cause degeneration of the rods and cones. The rods are affected first and as they are destroyed, night vision deteriorates and peripheral vision is lost. As the disease progresses, ever-increasing tunnel vision results. Currently, there is no treatment for retinitis pigmentosa. Retinal detachment may cause sudden loss of peripheral vision. This occurs when the retina pulls away from the epithelial layer next to the choroid, which may be caused by holes or tears in the retina, by traction, or by leakage of the vitreous gel. The tears may result from aging, injury, cataract surgery, or severe myopia. As the retina detaches, it fails to function in the detached area, and vision is lost. Glaucoma is a disease that attacks and destroys peripheral vision. It is the leading cause of blindness among adults in the US.

Phoroptor is an instrument used in an ophthalmologic examination and determines the refraction errors, or the degree of inability to focus properly. It is a large butterflylike apparatus that has two round sections affixed to a vertical base. The patient faces the phoroptor, with one round section centered in front of each eye. The patient places his chin on a chin rest and looks through lenses in each round section to read a wall chart. The phoroptor holds hundreds of lenses of varying degrees in each round section. The examiner uses a dial to change the lenses in front of each eye. The patient is asked to determine which of the lenses provides the clearest vision or image of the chart. From the information provided by the patient in response to the phoroptor lenses, the examiner can prescribe the proper corrective lenses.

Photophobia is a fear of light, a condition in which the eyes have little tolerance for light. The eyes may experience pain as a result of exposure to light or may involuntarily squint or blink in response to light. Photophobia is not a disease but is a symptom or result of an ocular disease or disorder. It is the first sign of congenital glaucoma in infants. It may be caused by or seen in a multitude of disorders, including iritis, corneal lesions, albinism, cataracts, blepharitis, migraines, trachoma, uveitis, some types of drugs, and sympathetic ophthalmia. Since it is a result or symptom of a disorder, its occurrence should prompt an ocular examination.

Pleoptics, or pleoptic methods are part of orthoptic training in the use of exercises to correct or improve vision disorders. Pleoptic methods use flashing devices to improve macular and foveal orientation and fixation in cases of amblyopia. The treatment consists of producing an afterimage on which the patient is taught to focus. The macular region of the retina is stimulated with a bright or dazzling light. When the light is turned off, the patient fixates on the macula’s afterimage, encouraging the individual to use the macula. Pleoptic treatment may last several weeks to several years, but results have been disappointing in light of early expectations. The methods are now more widely used in Europe than in the US.

Pneumatic retinopexy is a fairly new procedure used to repair a retinal detachment, which occurs when the retina becomes separated from the back of the eye. Some detachments are caused by retinal holes or tears and must be surgically repaired. With pneumatic retinopexy, freezing treatment is placed around the retinal tear, after which an expanding gas bubble is injected into the eye. The gas pushes against the area of the retinal tear and closes it, eliminating the need for a scleral buckle. The procedure requires only local anesthetic and often can be done in the doctor’s office. It does not, however, work for all types of retinal detachments. Pneumatic retinopexy was first introduced in the US in 1985.

Posterior chamber of the eye is the area between the iris and the lens. It is the counterpart to the anterior chamber located between the cornea and the iris. Both chambers are filled with aqueous fluid, the clear liquid that nourishes the cornea and lens and carries away waste. The posterior chamber is the site of surgery for posterior intraocular lens implantations. As a part of cataract surgery, a plastic lens is often placed either in front of, or behind, the iris to replace the portion of natural lens lost to surgery. Posterior lens implantation places the artificial lens behind the iris. Posterior is also a term used to describe the back portion of the eye behind the lens. This area is filled with the vitreous, a clear gel-like material that makes up to 80% of the volume of the eye, as well as giving support to other organs within the globe. The expanded definition or boundaries of the posterior area may include the retina, optic nerve, and portions of the choroid and sclera, which are positioned in the back of the eye. This area may be injected with antibiotics or other medications in the treatment of a disease or infection. It may also be the site of surgery as in retinal detachment operations or vitrectomies. In retinal detachment surgery, the retina is reattached to the epithelial layer next to the choroid. During a vitrectomy, the chamber behind the lens is drained of diseased vitreous gel and filled with a sterile saline solution. The posterior section behind the lens may be subject to floaters, bits of debris or blood in the vitreous. Light passing through the vitreous casts shadows of the debris onto the retina, causing images of the debris to float through the field of vision. Floaters appear in normal vision and are not considered a symptom of a disease unelss they appear suddenly or in large numbers.

Potential Acuity Meter (PAM) is a slit-lamp attachment used to assess the potential, usable vision of those with cataractous lenses or corneal opacities. The PAM uses a prism system and self-illumination to project a small Snellen chart through a clear section of the cornea or lens and onto the retina of the person being examined. In by-passing the opacities, the examiner can efficiently use the Snellen chart to measure visual acuity. Also known as the Guyton-Minkowski Potential Acuity Meter (PAM), it was developed by two ophthalmologists at Johns Hopkins University. The PAM is mounted on a slit lamp and projects an eye chart via a tiny beam of light one-quarter the diameter of a pin, through minute clear areas of the cataract, directly onto the retina. With this method, the patient is able to read an eye chart as if the cataract were not there indicating the potential for vision after cataract surgery. Although not foolproof, it is remarkably accurate.

Presbyopia is a Greek word meaning “old sight”. The condition has been recognized for a very long time. As one ages, the lens gradually loses its elasticity and the ability to change shape, causing the vision to become progressively more blurred as time goes on. It is an age-related condition that requires eyeglasses or contacts; but, generally, after the age of 65, there is little need for changes in prescriptions.

Prisms are inexpensive optical additions to prescriptive lenses that maximize the use of remaining sight. They are used to improve such ocular conditions as nystagmus, diplopia, macular disease, or peripheral-field defects. Prisms are horizontally incorporated into frames for prescriptive lenses or noncorrective spectacles to treat nystagmus, an uncontrollable jerking of the eyes that impairs focusing on an object. The prisms may relieve symptomatic headaches and improve acuity and stabilization of vision. Vertically applied prisms are used to treat diplopia, or double vision, due to retinal surgery. The prisms compensate for the impaired abilities of the extraocular muscles. Those with macular disease may find prisms helpful. If the macula, or central vision of sight, is impaired or destroyed, prisms can be placed to move the image from the fovea (central macular region) to an area outside the fovea that is usable. Prisms such as the Fresnel, are used for peripheral-field defects. They are incorporated into prescription lenses of pressed onto noncorrective lenses in sections above and below or to the sides of the usable central visual field. By moving the eyes or head slightly, the user can see through the prims into the restricted field.

Progressive addition lenses are seamless, multifocal lenses that allow the wearer a smooth transition from the distance portion of the lens into the reading portion. No line is visible, either to the wearer or to anyone else. The power of a progressive lens gradually increases as the wearer looks from the distance portion to the reading portion, creating an appropriate lense power for every distance. A disadvantage of these is that the sides tend to become distorted, making side vision appear to be watery. Technology creating these lenses, which first appeared in the late 1970s, continues to improve, however. Wearers find the distortion to be less troublesome as they become accustomed to the lenses.

Proptosis (See Exophthalmos.)

Prosthesis, or artificial eye is used to replace an eye that has been enucleated, or surgically removed. Prosthetic eyes have been in existence for centuries. Ancient Egyptian cultures fashioned wax, plaster, or precious-stone eyes to adorn their heads. Roman surgeon priests made artificial eyes for the living out of wood, shells, bone, ivory, stone, and precious metals. In the 16th century, Venetians developed the first glass eyes, but the precursor of the modern type of prosthetic was developed in the 17th century by French surgeons. Before WWII, most prosthetic eyes were manufactured of glass in Germany and exported to other countries. After the war, plastic prosthetics were invented and manufactured throughout the world. Modern prosthetic eyes are made from glass or plastic by ocularists. They are custom shaped to match the eye socket of the individual and the coloring of the natural eye. Prosthetic eyes are generally nondistinguishable from natural eyes. Two or more days after enucleation, the eye socket is fitted with a plastic shell that will cradle the prosthesis. Three or four weeks later, the prosthetic eye is fitted. The eye is attached to the remaining extrinsic muscles in the orbit to ensure natural movement. The prosthetic eye is worn constantly to prevent contraction of the eye socket. It is cleansed daily and may be lubricated with drops for this purpose. A slight mucus discharge is a normal characteristic of the prosthesis, but profuse discharge could indicate an infection. Infection often stems from roughening of the prosthesis which should be polished once or twice a year to buff out scratches and reduce irritation. It should be checked once a year by a specialist. Most plastic prosthetics last five years on average.

Pterygium (See Conjunctiva.)

Ptosis is a weakness of the muscle that raises the upper eyelid, keeping it in an open position. The condition often runs in families; and some children are born with it, although usually in one eye only. In adults, ptosis can be the result of aging or an injury but can also appear after such conditions as nerve palsy, inflammation, styes, brain tumors, cysts, myasthenia gravis, diabetes, oculomotor palsy, Horner’s syndrome, or use of guanethidine drops. A drooping eyelid that develops suddenly requires immediate attention as it may be a sign of a stroke or another acute problem with the nervous system. Surgical correction is a complicated operation performed by a specialist but an eye doctor will determine if this treatment is necessary.sagging of the upper eyelid. The condition may be congenital or acquired and can affect one or both eyes by blocking vision. Mild ptosis that does not affect vision may require no treatment. Severe forms of the condition may affect vision by obstructing the pupil or may be cosmetically unattractive. After careful diagnosis as to the cause, ptosis may be corrected surgically in some congenital, nerve palsy, or age-related cases. Surgery may be performed on children three or four years of age or younger if the ptosis is unilateral and causing amblyopia. The surgery may be performed under local anesthetic for adults and general anesthesia for children. The type of surgical procedure used depends on the severity and underlying cause of each case.

Three surgical procedures are most commonly used:

• The Fansanella-Servat involves the removal of a portion of the lid from the inside. The outer skin is not incised. The shortened lid is lifted off the eye. This procedure is used to treat mild cases of ptosis.
• The levator resection is used to treat moderate cases. During this procedure, several incisions are made in the lid. A sling is placed inside the lid to permanently lift it.
• The frontalis suspension is reserved for severe cases of ptosis. A section of the muscle that raises the eyelid is removed. The surface skin of the eyelid is usually involved in the incision. The shortened muscle keeps the lid elevated. Complications from eyelid surgery may include infection, bleeding, scarring, and corneal drying. Over- and under-corrections may also occur.

Treatment of other forms of ptosis involves therapy for the underlying causes.

Pupil is a hole in the center of the iris which looks black. This is because it is the opening to the inside of the eye, which is dark. The “red-eye” effect in flash photography is simply the pupil as seen with light reflected off the retina. The size of the pupil varies with the amount of light entering the eye, age, and focusing tone. Light is not the only thing that can cause the pupil to enlarge. Seeing something you really like can cause the pupil to dilate an extra 45%. There are various names given to conditions involving the pupil.

• Ardie’s pupil, or tonic pupil, is usually a unilateral condition of the eye in which the affected pupil is larger than the other. It responds to accommodation and convergence in a slow, delayed fashion, and reacts to light only after prolonged exposure to dark or light.
• Argyll Robertson pupil is one that is miotic (excessive contraction of the pupil) and responds to accommodation but not to light.
• Fixed pupil refers to a pupil that does not react either to light, on convergence, or in accommodation.
• Hutchinson’s pupil is one that is dilated while the other is not.