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Description ( notes ) AC. Anterior chamber. fluid-filled space between the iris and the endothelium. AC 4/4. Grade 4 anterior chamber angle. open angle between cornea and iris. AC 3/4. Grade 3 anterior chamber angle.
Distance PD is the separation between the visual axes of the eyes in their primary position, as the subject fixates on an infinitely distant object. [ 2] Near PD is the separation between the visual axes of the eyes, at the plane of the spectacle lenses, as the subject fixates on a near object at the intended working distance. [ 3]
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 ...
The Strehl ratio is a measure of the quality of optical image formation, originally proposed by Karl Strehl, after whom the term is named. [1] [2] Used variously in situations where optical resolution is compromised due to lens aberrations or due to imaging through the turbulent atmosphere, the Strehl ratio has a value between 0 and 1, with a hypothetical, perfectly unaberrated optical system ...
Debye length. In plasmas and electrolytes, the Debye length ( Debye radius or Debye–Hückel screening length ), is a measure of a charge carrier 's net electrostatic effect in a solution and how far its electrostatic effect persists. [ 1] With each Debye length the charges are increasingly electrically screened and the electric potential ...
The cup-to-disc ratio (often notated CDR) is a measurement used in ophthalmology and optometry to assess the progression of glaucoma. The optic disc is the anatomical location of the eye's "blind spot", the area where the optic nerve leave and blood vessels enter the retina. The optic disc can be flat or it can have a certain amount of normal ...
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 .