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PLEASE READ THIS: The information contained herein is not intended as a
substitute for medical advice and care from qualified, licensed health
care providers. The reader should regularly consult a physician in matters
relating to his or her health and particularly with respect to any symptoms
that may require diagnosis or medical attention. The information is presented
here to educate and inform and to guide you to an understanding of cause,
prevention as well as treatment.
Note: This glossary is designed to assist with the reading and understanding of the report on glaucoma. There is also a more extensive general glossary available for your viewing.
Aqueous: The watery fluid produced by tissues inside the eye and which fills the forward chamber of the eye.
Automated perimeter: A computer-driven device used to plot defects in the visual field. Usuallly this is a large hemisphere shell into which the patient's head is placed. Various points of lights, sometimes of different sizes, intensities and colors are projected onto the screen. The patient then indicates whether the light is seen and the response is recorded. The computer then plots the effective visual thresholds within the targeted visual field.
Blind spot, physiological blind spot: The ONH does not itself contain photoreceptors, and therefore its location at the back of the eye is a blind spot. This small area can be measured and in glaucoma, as the nerve fibers die, the blind spot tends to enlarge and enlongate. This is one of the diagnostic hallmarks of glaucoma.
Gonioscopy: A viewing procedure utilizing a mirror/lens device placed directly upon the cornea that is used to view the drainage area called "the angle" through which aqueous fluid exits the eyeball.
Intraocular pressure (IOP): The fluid pressure created by aqueous fluid contained within the solid sphere of the eye.
Ischemia: The restriction or blockage of blood flow through a blood vessel. Ischemia is a causative agent of certain heart attacks and strokes and is involved in various types of visual field losses.
Nerve fibers/axons: The extensions of the retinal photoreceptors that form the nerve bundle that is called the optic nerve.
Ocular hypertension: Elevated fluid pressure. The normal pressure is about 10 to 20mmHg, with the majority of people falling between 13 and 19. Over 20 is considered "suspicious" over 24 "cautiously concerned" and warranting immediate investigation, and over 30 is considered to be "urgent" and a potential emergency situation.
Optic nerve, optic nerve head (ONH): The optic nerve is a bundle of nerve fibers, about the diameter of pencil, which passes through the back of the eyeball and connects to the nerve fiber layer of the retina. It can be observed directly with an instrument called an ophthalmoscope.
Retina: A multi-layered tissue lining the back surface of the eye, containing the photoreceptors called rods and cones.
Visual fields: The area projected in space that each eye "sees". There is a central visual field--that is directly in front of us, the target at which we are looking, and a peripheral visual field---that which we perceive in our "side vision". The fields of each eye partly overlap. We do not perceive the blind spots from each eye because the area that is missing in one eye is present in the other.