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Ocular hypertension (OHT) is defined by intraocular pressure being higher than normal, in the absence of optic nerve damage or visual field loss. [ 13 ] [ 14 ] Ocular hypotension, hypotony, or ocular hypotony , is typically defined as intraocular pressure equal to or less than 5 mmHg.
The higher the intraocular pressure, the harder it is to push against and indent the cornea. For very high levels of IOP, extra weights can be added to make the plunger push harder. [ 14 ] The movement of the plunger is measured using a calibrated scale. [ 14 ]
Ocular hypotony is divided into statistical and clinical types. If intraocular pressure is low (less than 6.5 mm Hg) it is called statistical hypotony, and if the reduced IOP causes a decrease in vision, it is called clinical. [4]
The standard definition of normal visual acuity (20/20 or 6/6 vision) is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc. The terms 20/20 and 6/6 are derived from standardized sized objects that can be seen by a "person of normal vision" at the specified distance.
The diagnosis is clinical. The intraocular pressure (IOP) can be measured in the office in a conscious swaddled infant using a Tonopen or hand-held Goldmann tonometer. Usually, the IOP in normal infants is in the range of 11-14 mmHg. [7] Buphthalmos and Haab's striae can often be seen in case of congenital glaucoma. [citation needed]
For most individuals, the normal range of intraocular pressure is between 10 mmHg and 21 mmHg. [3] It is estimated that approximately 2-3% of people aged 52-89 years old have ocular hypertension of 25 mmHg and higher, and 3.5% of people 49 years and older have ocular hypertension of 21 mmHg and higher.
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The Schiotz tonometer consists of a curved footplate which is placed on the cornea of a supine patient. A weighted plunger attached to the footplate sinks into the cornea. A scale then gives a reading depending on how much the plunger sinks into the cornea, and a conversion table converts the scale reading into IOP measured in mmHg.