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Ophthalmology ( / ˌɒfθælˈmɒlədʒi /, OFF-thal-MOL-ə-jee) [ 1] is a clinical and surgical specialty within medicine that deals with the diagnosis and treatment of eye disorders. [ 2] A former term is oculism . An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. [ 3]
An economic theory that defines wealth by the amount of precious metals owned. [56] business cycle. Also called the economic cycle or trade cycle. The downward and upward movement of gross domestic product (GDP) around its long-term growth trend. [57] The length of a business cycle is the period of time containing a single boom and contraction ...
The economics term cost, also known as economic cost or opportunity cost, refers to the potential gain that is lost by foregoing one opportunity in order to take advantage of another. The lost potential gain is the cost of the opportunity that is accepted. Sometimes this cost is explicit: for example, if a firm pays $100 for a machine, its cost ...
In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 6/6 (or 20/20), is the ...
A good's price elasticity of demand ( , PED) is a measure of how sensitive the quantity demanded is to its price. When the price rises, quantity demanded falls for almost any good ( law of demand ), but it falls more for some than for others. The price elasticity gives the percentage change in quantity demanded when there is a one percent ...
Marginal cost. In economics, the marginal cost is the change in the total cost that arises when the quantity produced is increased, i.e. the cost of producing additional quantity. [ 1] In some contexts, it refers to an increment of one unit of output, and in others it refers to the rate of change of total cost as output is increased by an ...
Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle [1] in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision.
An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [ 1 ] Eye charts are often used by health care professionals, such as optometrists , physicians and nurses , to screen persons for vision impairment .