O

OD (oculus dexter) Right eye. Or, doctor of optometry.

Off label use - The permissible use of an approved drug or instrument in a way that has not been specifically sanctioned.

Optic nerve - The millions of optical nerve fibers connecting to the eye and terminating in the brain where images are created and processed.

Ophthalmologist (ahf-thal-MAH-loh-jist) - A Physician (MD) specializing in diagnosis and treatment of refractive, medical and surgical problems related to eye diseases and disorders.

OS (oculus sinister) - Left eye.

Optician = A Professional who makes and adjusts optical aids, e.g., eyeglass lenses, from refraction prescriptions supplied by an opthalmologist or optometrist.

Optometrist (ahp-TAHM-uh-trist).Doctors of optometry (O.D.s) examine eyes for both vision and health problems, prescribe glasses, and fit contact lenses. They can prescribe many ophthalmic medications and may participate in your pre- and postoperative care if you have eye surgery. O.D.s must complete four years of post-graduate optometry school for their doctorate.

OU (oculus uterque, oculus unitas or oculus uniter) Both eyes.

Overcorrection - The result achieved when the change to refractive error exceeds the attempted correction.

P

Penetrating keratoplasty - A transplant procedure in which a circular area of eye tissue, is removed from a healthy donor cornea and transferred to a recipient. The full thickness of the cornea is removed. A penetrating keratoplasty or corneal transplant may be needed in case of eye damage from injury or from eye diseases such as keratoconus.

Peripheral vision - The edges of your visual field.

Pachymetry - The process of measuring corneal thickness, usually using an ultrasonic probe.

Photorefractive keratotomy - A procedure involving the removal of the surface layer of the cornea (epithelium) by gentle scraping and use of a computer-controlled excimer laser to reshape the stroma. Acronym is PRK.

Piggy back contact lenses – The waering of soft contact lenses to "carry" a gas permeable lens
Plano - Characterized by no refractive error.

Placido Disc - Most topographers consist of a "placido disc" made up of multiple circles, which is backlit or projected onto the corneal surface. The resultant circular images are reflected and captured with a video camera and digitized.

PMMA (polymethyl methacrylate) Old-fashioned hard contacts were made of PMMA, which is not permeable; today's rigid lenses contain other polymers that allow oxygen to reach your eye.
polarized lenses Lenses that block light reflected from horizontal surfaces such as water, to reduce glare.

Practice of medicine - A regulatory body's allowance of practitioners to make decisions to best serve their patients.

Presbyopia - The natural deterioration of near vision caused by loss of flexibility in the eye's lens as one ages.

PRK - The acronym for photorefractive keratotomy. A procedure involving the removal of the surface layer of the cornea (epithelium) by gentle scraping and use of a computer-controlled excimer laser to reshape the stroma.

Protein - All living cells contain these large, complex organic molecules that include 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.

Ptosis - Droopy eyelid.

Pupil - The round, dark center of the eye, which opens and closes to regulate the amount of light the retina receives.