The following are health and medical definitions of terms that appear in the Tonometry article.
Acute: Of abrupt onset, in reference to a disease. Acute often also connotes an illness that is of short duration, rapidly progressive, and in need of urgent care. See the entire definition of Acute
Analog: In biochemistry, a substance that is similar, but not identical, to another.
Analysis: A psychology term for processes used to gain understanding of complex emotional or behavioral issues.
Anesthesia: Loss of feeling or awareness. A general anesthetic puts the person to sleep. A local anesthetic causes loss of feeling in a part of the body such as a tooth or an area of skin without affecting consciousness. Regional anesthesia numbs a larger part of the body such as a leg or arm, also without affecting consciousness. The term "conduction anesthesia" encompasses both local and regional anesthetic techniques. Many surgical procedures can be done with conduction anesthesia without significant pain. In many situations, such as a C-section, conduction anesthesia is safer and therefore preferable to general anesthesia. However, there are also many types of surgery in which general anesthesia is clearly appropriate.
Anesthetic: A substance that causes lack of feeling or awareness. A local anesthetic causes loss of feeling in a part of the body. A general anesthetic puts the person to sleep.
Anomaly: A deviation from the usual, something different, peculiar, or abnormal. See the entire definition of Anomaly
Anterior: The front, as opposed to the posterior. The anterior surface of the heart is toward the breast bone (the sternum). See the entire definition of Anterior
Anticipation: A remarkable phenomenon in which a genetic disease appears earlier appearance and with increased from with each succeeding generation. Anticipation was once thought not to exist in genetics. It was chalked off as a meaningless statistical artifact. However, anticipation has now been proven to occur in a large number of important genetic disorders, including Huntington disease and myotonic dystrophy. In molecular terms, anticipation is due to the expansion of a trinucleotide repeat sequence in the DNA. This phenomenon also occurs in the fragile X syndrome, the most common inherited form of mental retardation.
Aqueous humor: In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. It is a clear, watery fluid that flows between and nourishes the lens and the cornea; it is secreted by the ciliary processes. See the entire definition of Aqueous humor
Bilateral: Having, or relating to, two sides. Bilateral is as opposed, for example, to unilateral (which means having, or relating to, one side).
Bleb: A bladder-like structure more than 5 mm in diameter with thin walls that may be full of fluid. Also called a bulla.
Blindness: Loss of useful sight. Blindness can be temporary or permanent. Damage to any portion of the eye, the optic nerve, or the area of the brain responsible for vision can lead to blindness. There are numerous (actually, innumerable) causes of blindness. The current politically correct terms for blindness include visually handicapped and visually challenged.
Brain: That part of the central nervous system that is located within the cranium (skull). The brain functions as the primary receiver, organizer and distributor of information for the body. It has two (right and left) halves called "hemispheres."
Cataract: A clouding or loss of transparency of the lens in the eye as a result of tissue breakdown and protein clumping. There are many causes of cataracts, including aging, cortisone medication, trauma, diabetes, and other diseases. Cataracts affect most people who live into an old age. Symptoms include double or blurred vision and sensitivity to light and glare. A physician can diagnose cataracts by examining the eyes with a viewing instrument. Sunglasses can help to prevent cataracts. See the entire definition of Cataract
Central vision: Straight-ahead vision. Central vision is the work of the macula, a small area in the center of the retina that contains a rich collection of cones. (The retina is made up of two types of cells, the cones and the rods. Millions of cones are packed into the macula. The cones are nerve cells sensitive to light, fine detail, and color.) Central vision permits a person to read, drive, and perform other activities that require fine, sharp, straight-ahead vision. As opposed to peripheral vision.
Chin: Medically, the mentum. The lower portion of the face below the lower lip including the prominence of the lower jaw and the line of fusion of the two separate halves of the jawbone (mandible). This line of fusion (called the symphysis menti) encloses a triangular area at tip of the chin (termed the mental protuberance). On each side, below the second premolar tooth, is the mental foramen, an opening for the passage of blood vessels and a nerve that supply the chin.
Chronic: This important term in medicine comes from the Greek chronos, time and means lasting a long time. See the entire definition of Chronic
Congenital: Present at birth. A condition that is congenital is one that is present at birth. There are numerous uses of "congenital" in medicine. There are, for example, congenital abnormalities. (For more examples, see below.) See the entire definition of Congenital
Conjunctiva: A thin clear moist membrane that coats the inner surfaces of the eyelids and the outer surface of the eye. See the entire definition of Conjunctiva
Conjunctival: Pertaining to the conjunctiva, the clear moist membrane that covers the inner surfaces of the eyelids and the front of eyeball.
Cornea: The clear front window of the eye that transmits and focuses light into the eye. See the entire definition of Cornea
Diabetes: Refers to diabetes mellitus or, less often, to diabetes insipidus. Diabetes mellitus and diabetes insipidus share the name "diabetes" because they are both conditions characterized by excessive urination (polyuria). See the entire definition of Diabetes
Diabetes mellitus: Better known just as "diabetes" -- a chronic disease associated with abnormally high levels of the sugar glucose in the blood. Diabetes is due to one of two mechanisms: (1) Inadequate production of insulin (which is made by the pancreas and lowers blood glucose) or (2) Inadequate sensitivity of cells to the action of insulin. The two main types of diabetes correspond to these two mechanisms and are called insulin dependent (type 1) and non-insulin dependent (type 2) diabetes. In type 1 diabetes there is no insulin or not enough of it. In type 2 diabetes, there is generally enough insulin but the cells upon it should act are not normally sensitive to its action. See the entire definition of Diabetes mellitus
Diagnosis:1 The nature of a disease; the identification of an illness. 2 A conclusion or decision reached by diagnosis. The diagnosis is rabies. 3 The identification of any problem. The diagnosis was a plugged IV. See the entire definition of Diagnosis
Essential:1. Something that cannot be done without. 2. Required in the diet, because the body cannot make it. As in an essential amino acid or an essential fatty acid. 3. Idiopathic. As in essential hypertension. "Essential" is a hallowed term meaning "We don't know the cause."
Etiology: The study of the causes. For example, of a disorder. See the entire definition of Etiology
Eyelid: The lid or cover of the eye, a movable fold of skin and muscle that can be closed over the eyeball or opened at will. Each eye has an upper and a lower lid. An eyelid is also called a palpebra.
Family history: The family structure and relationships within the family, including information about diseases in family members. See the entire definition of Family history
Glaucoma: A common eye condition in which the fluid pressure inside the eyes rises because of slowed fluid drainage from the eye. If untreated, it may damage the optic nerve and other parts of the eye, causing the loss of vision or even blindness. See the entire definition of Glaucoma
Hearing aid: An instrument to help in hearing. There are four common styles of hearing aids. See the entire definition of Hearing aid
Herpes: A family of viruses. Herpes also refers to infection with one of the human herpesviruses, especially herpes simplex types 1 and 2. See the entire definition of Herpes
Herpes zoster: Also called shingles, zona, and zoster. The culprit is the varicella-zoster virus. Primary infection with this virus causes chickenpox (varicella). At this time the virus infects nerves (namely, the dorsal root ganglia) where it remains latent (lies low) for years. It can then be reactivated to cause shingles with blisters over the distribution of the affected nerve accompanied by often intense pain and itching.
Humor: In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. The humors ran through an ancient theory that held that health came from balance between the bodily liquids. These liquids were termed humors. Disease arose when there was imbalance between these humors. See the entire definition of Humor
Injury: Harm or hurt. The term "injury" may be applied in medicine to damage inflicted upon oneself as in a hamstring injury or by an external agent on as in a cold injury. The injury may be accidental or deliberate, as with a needlestick injury. The term "injury" may be synonymous (depending on the context) with a wound or with trauma.
Intraocular: In the eye. The intraocular pressure is the pressure within the eye.
Intraocular pressure: The pressure created by the continual renewal of fluids within the eye. The intraocular pressure is increased in glaucoma. See the entire definition of Intraocular pressure
Intraoperative: During surgery. Literally, within surgery. Intraoperative hemorrhage is bleeding during surgery.
Iritis: Inflammation of the iris. The iris is the circular, colored curtain in the front of the visible of the eye. (The opening of the iris forms the pupil.)
Laser: A powerful beam of light that can produce intense heat when focused at close range. Lasers are used in medicine in microsurgery, cauterization, for diagnostic purposes, etc. For example, lasers are employed in microsurgery to cut tissue and remove tissue. See the entire definition of Laser
Lens: The transparent structure inside the eye that focuses light rays onto the retina (the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain). The lens was named after the lentil bean because it resembled it in shape and size. See the entire definition of Lens
Macular: Pertaining to the macula. A macula is a small spot. A macula on the skin is a small flat spot while the macula in the eye is a small spot where vision is keenest in the retina.
Macular degeneration: A disease that progressively destroys the macula, the central portion of the retina, impairing central vision. Macular degeneration rarely causes blindness because only the center of vision is affected. However, injury to the macula in the center of the retina can impair the ability to see straight ahead clearly and sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision. See the entire definition of Macular degeneration
Microscope: An optical instrument that augments the power of the eye to see small objects. The name microscope was coined by Johannes Faber (1574-1629) who in 1628 borrowed from the Greek to combined micro-, small with skopein, to view. Although the first microscopes were simple microscopes, most (if not all) optical microscopes today are compound microscopes.
Myopia: Nearsightedness, the ability to see close objects more clearly than distant objects. See the entire definition of Myopia
Nasal: Having to do with the nose. Nasal drops are intended for the nose, not (for example) the eyes. The word "nasal" came from the Latin "nasus" meaning the nose or snout.
Nerve: A bundle of fibers that uses chemical and electrical signals to transmit sensory and motor information from one body part to another. See: Nervous system.
Neuropathy: Any and all disease or malfunction of the nerves.
Open-angle glaucoma: Glaucoma in which the aqueous (fluid) that flows through the pupil into the anterior (front) chamber of the eye cannot get through a filtration system called the trabecular meshwork into the drainage canals, causing pressure to build up within the eye which can damage the optic nerve and impair vision. See the entire definition of Open-angle glaucoma
Operating room: A facility equipped for performing surgery. Abbreviated OR.
Ophthalmologist: An eye doctor. A physician practicing ophthalmology. An ophthalmologist is an M.D.
Optic: Having to do with vision.
Optic nerve: The optic nerve connects the eye to the brain. The optic nerve carries the impulses formed by the retina, the nerve layer that lines the back of the eye and senses light and creates impulses. These impulses are dispatched through the optic nerve to the brain, which interprets them as images. Using an ophthalmoscope, the head of the optic nerve can be easily seen. It can be viewed as the only visible part of the brain (or extension of it). See the entire definition of Optic nerve
Optic nerve head: The circular area in the back of the inside of the eye where the optic nerve connects to the retina.
Optometrist: A health care professional who is licensed to provide primary eye care services:
to examine and diagnose eye diseases such as glaucoma, cataracts, and retinal diseases and, in certain states in the U.S., to treat them;
to diagnose related systemic (bodywide) conditions such as hypertension and diabetes that may affect the eyes;
to examine, diagnose and treat visual conditions such as nearsightedness, farsightedness, astigmatism and presbyopia; and
to prescribe glasses, contact lenses, low vision rehabilitation and medications as well as perform minor surgical procedures such as the removal of foreign bodies.
Orbit: In medicine, the bony cavity in which the eyeball sits together with its associated muscles, blood vessels, and nerves. The orbit is formed of parts of the ethmoid, frontal, lacrimal, nasal, palatine, sphenoid, and zygomatic bones and the maxilla.
Peripheral: Situated away from the center, as opposed to centrally located. See the entire definition of Peripheral
Peripheral vision: Side vision. The ability to see objects and movement outside of the direct line of vision. Peripheral vision is the work of the rods, nerve cells located largely outside the macula (the center) of the retina. The rods are also responsible for night vision and low-light vision but are insensitive to color. As opposed to central vision.
Pigment: A substance that gives color to tissue. Pigments are responsible for the color of skin, eyes, and hair.
Prescription: A physician's order for the preparation and administration of a drug or device for a patient. A prescription has several parts. They include the superscription or heading with the symbol "R" or "Rx", which stands for the word recipe (meaning, in Latin, to take); the inscription, which contains the names and quantities of the ingredients; the subscription or directions for compounding the drug; and the signature which is often preceded by the sign "s" standing for signa (Latin for mark), giving the directions to be marked on the container.
Probe: (1) In surgery, a probe is a slender flexible rod with a blunt end used to explore, for example, an opening to see where it goes. (2) In molecular genetics, a probe is a labeled bit of DNA or RNA used to find its complementary sequence or locate a particular clone like homing in on a needle in a haystack.
Progressive: Increasing in scope or severity. Advancing. Going forward. In medicine, a disease that is progressive is going from bad to worse.
Pseudoexfoliation syndrome: An eye condition that often leads to glaucoma. Called the pseudoexfoliation syndrome because deposits on the surface of the lens look like flakes of dandruff, as if the lens capsule has exfoliated (shed the flakes). It is also called exfoliation syndrome.
Quadrant: A quarter. For example, the liver is in the right upper quadrant of the abdomen.
Refraction: In ophthalmology, the bending of light that takes place within the human eye. See the entire definition of Refraction
Resistance: Opposition to something, or the ability to withstand it. For example, some forms of staphylococcus are resistant to treatment with antibiotics.
Retina: The retina is the nerve layer that lines the back of the eye, senses light, and creates impulses that travel through the optic nerve to the brain. There is a small area, called the macula, in the retina that contains special light-sensitive cells. The macula allows us to see fine details clearly. See the entire definition of Retina
Shingles: An acute infection caused by the herpes zoster virus, the same virus as causes chickenpox. Shingles is most common after the age of 50 and the risk rises with advancing age. Shingles occurs because of exposure to chickenpox or reactivation of the herpes zoster virus. The virus remains latent (dormant) in nerve roots for many years following chickenpox. See the entire definition of Shingles
Shunt: 1) To move a body fluid, such as cerebrospinal fluid, from one place to another. 2) A catheter (tube) that carries cerebrospinal fluid from a ventricle in the brain to another area of the body. A shunt may be placed to relieve pressure from hydrocephalus, for example.
Steroid: A general class of chemical substances that are structurally related to one another and share the same chemical skeleton (a tetracyclic cyclopenta[a]phenanthrene skeleton). See the entire definition of Steroid
Sturge-Weber syndrome: A congenital, but not inherited, disorder that affects the skin, the neurological system, and sometimes the eyes and internal organs. The main sign of Sturge-Weber syndrome is a port wine stain birthmark. Neurological symptoms may include seizures and developmental delay. Also known as encephelotrigeminal angiomatosi. See the entire definition of Sturge-Weber syndrome
Surgery: The word "surgery" has multiple meanings. It is the branch of medicine concerned with diseases and conditions which require or are amenable to operative procedures. Surgery is the work done by a surgeon. By analogy, the work of an editor wielding his pen as a scalpel is s form of surgery. A surgery in England (and some other countries) is a physician's or dentist's office. See the entire definition of Surgery
Syndrome: A set of signs and symptoms that tend to occur together and which reflect the presence of a particular disease or an increased chance of developing a particular disease. See the entire definition of Syndrome
Tactile: Having to do with touch.
Tear: A drop of the salty secretion of the lacrimal glands which serves to moisten the conjunctiva and cornea.
Tear film: The liquid layer bathing the cornea and conjunctiva. It creates a perfectly smooth liquid outer layer that polishes the corneal surface, mechanically traps and flushes out foreign bodies and chemicals, contains bacteriostatic substances that inhibit the growth of microorganisms, and reduces the surface friction associated with eyelid blinking and eye movement.
Tonometry: A standard eye test that determines the fluid pressure inside the eye. Increased pressure is a possible sign of glaucoma, a common and potentially very serious eye problem if not detected and treated promptly. It is recommended that adults over age 40 have tonometry for glaucoma every 3 to 5 years by having their eye pressures measured. See the entire definition of Tonometry
Topical: Pertaining to a particular surface area. A topical agent is applied to a certain area of the skin and is intended to affect only the area to which it is applied. Whether its effects are indeed limited to that area depends upon whether the agent stays where it is put or is absorbed into the blood stream.
Trauma: Any injury, whether physically or emotionally inflicted. "Trauma" has both a medical and a psychiatric definition. Medically, "trauma" refers to a serious or critical bodily injury, wound, or shock. This definition is often associated with trauma medicine practiced in emergency rooms and represents a popular view of the term. In psychiatry, "trauma" has assumed a different meaning and refers to an experience that is emotionally painful, distressful, or shocking, which often results in lasting mental and physical effects. See the entire definition of Trauma
Uveitis: Inflammation of the uvea, the part of the eye that collectively refers to the iris, the choroid of the eye, and the ciliary body. The uvea provides most of the blood supply to the retina. Uveitis as a rule signifies inflammation involving the iris, choroid, and ciliary body -- all three components of the uveal tract. See the entire definition of Uveitis
Visual acuity: The clarity or clearness of the vision, a measure of how well a person sees. The ability to distinguish details and shapes of objects; also called central vision. See the entire definition of Visual acuity
Visual field: The entire area that can be seen when the eye is directed forward, including that which is seen with peripheral vision. See the entire definition of Visual field
Visual field test: A test which measures the extent and distribution of the field of vision. See the entire definition of Visual field test
Diabetes mellitus is a chronic condition characterized by high levels of sugar (glucose) in the blood. The two types of diabetes are referred to as type 1 (insulin dependent) and type 2 (non-insulin dependent). Symptoms of diabetes include increased urine output, thirst, hunger, and fatigue. Treatment of diabetes depends on the type.
Glaucoma is a common eye condition in which the fluid pressure inside the eye rises because of slowed fluid drainage from the eye. If untreated, glaucoma may damage the optic nerve and other parts of the eye, causing the loss of vision or even blindness.
A cataract is an eye disease that causes the eye's lens to become cloudy and opaque with decreased vision. Causes of cataracts include diabetes, hypothyroidism, certain genetic illnesses, hyperparathyroidism, atopic dermatitis, and certain medications. Symptoms and signs include a decrease in vision and a whitish color to the affected eye. Treatment depends upon the patient's specific visual needs and may involve cataract surgery.
Toxoplasmosis (toxo) is a parasitic infection that causes flulike symptoms, swollen lymph nodes, and muscle aches and pains that may last from a few days to several weeks. Toxoplasmosis can be contracted by touching the hands to the mouth after gardening, cleaning a cat's litter box, or anything that came into contact with cat feces. Toxoplasmosis can also be contracted by eating raw or partly cooked meat, especially pork or lamb, or touching the hands to the mouth after contact with raw or undercooked meat.
Many common eye disorders resolve without treatment and some may be managed with over-the-counter (OTC) products. It's important to visit a physician or ophthalmologist is the problem involves the eyeball itself or the condition hasn't improved after 72 hours of use of an eye-care OTC product.
Uveitis is inflammation of the eye. Symptoms include blurred vision, eye pain, eye redness, and floating spots before the eyes. Treatment may involve prescription eyedrops, antibiotics, and wearing dark glasses.
Herpes of the Eye is developed by the herpes simplex 1 virus that usually lives around the nerve fibers in humans. Symptoms of herpes of the eye include pain in and around only one eye, redness rash or sores on the eyelids, redness of the eye, and swelling and cloudiness of the cornea.
Age-related macular degeneration (AMD) is a disease that gradually destroys the central vision. In people over 60, AMD is a leading cause of vision loss. Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula, leaking blood and fluid and causing rapid vision loss. In dry AMD, light-sensitive cells slowly break down in the macula, resulting in gradual vision loss. Pain is not associated with either form of AMD.
Disease prevention in men includes routine screening tests that are part of basic prevention medicine. Take an active role in your own health care and discuss screening tests with your doctor early in life. Age of screening and timing of screening depends upon the condition being assessed.
A visual field test is a method of measuring an individual's entire scope of vision, that is their central and peripheral (side) vision. Visual field testing actually maps the visual fields of each eye individually. The visual field test is a subjective examination, requiring the patient to understand the testing instructions, fully cooperate, and complete the entire test in order to provide useful information.
What is a visual field test used for?
Visual field testing is most frequently used to detect any signs of glaucoma damage to the optic nerve. In addition, visual field tests are useful for detection of central or peripheral retinal disease, eyelid conditions such as ptosis or drooping, optic nerve disease, and diseases affecting the visual pathways within the brain. The visual pathways carry information from the eye to the visual or occipital cortex in the brain, where this information is proces...
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