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Ocular hypertension is the presence of elevated fluid pressure inside the eye (intraocular pressure), usually with no optic nerve damage or visual field loss. [1] [2]For most individuals, the normal range of intraocular pressure is between 10 mmHg and 21 mmHg. [3]
Palpation is one of the oldest, simplest, and least expensive methods for approximate IOP measurement, however it is very inaccurate unless the pressure is very high. [3] Intraocular pressure is measured with a tonometer as part of a comprehensive eye examination. Contact lens sensors have also been used for continuous intraocular pressure ...
The tonometer tip rests on the cornea with a constant appositional force of one gram. When the sensor is subjected to a change in pressure, the electrical resistance is altered and the tonometer's computer calculates a change in pressure according to the change in resistance. A complete measurement cycle requires about eight seconds of contact ...
For eye pressures, a value of 28 hPa (21 mmHg) above atmospheric pressure 1,010 hPa (760 mmHg) is often used, with higher pressures leading to a greater risk. [2] [26] However, some may have high eye pressure for years and never develop damage. [2] Conversely, optic nerve damage may occur with normal pressure, known as normal-tension glaucoma. [27]
Hypotony may occur either due to decreased production of aqueous humor or due to increased outflow. Hypotony has many causes including post-surgical wound leak from the eye, chronic inflammation within the eye including iridocyclitis, hypoperfusion, tractional ciliary body detachment or retinal detachment. [5]
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The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter. [19] [20] [21] (that is it has a range of 10 14, or one hundred trillion 100,000,000,000,000, about 46.
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