Background
Ocular hypertension (OHT) can be used as a generic term referring to any situation in which intraocular pressure (IOP) is greater than 21 mm Hg, the widely accepted upper limit of normal intraocular pressure in the general population. (See the image below.) The term makes no mention of whether or not glaucomatous nerve damage is present. It also depicts no particular time frame during which the elevated pressure has been measured.
Diagram of intraocular pressure distribution. Used with permission from Survey of Ophthalmology.
The formal definition of ocular hypertension evolved in the latter part of the 20th century.
It was used as early as 1962 by Drance, but was not defined in English language publications until 1966 by Perkins and others.
Ocular hypertension is a condition in which the following criteria are met:
An intraocular pressure greater than 21 mm Hg in one or both eyes, as measured by applanation tonometry on 2 or more occasions
Absence of glaucomatous defects on visual-field testing
Normal appearance of the optic disc and nerve fiber layer
Anatomically normal, open angles on gonioscopy
Absence of ocular conditions contributing to the elevation of pressure, such as narrow angles, neovascular conditions, and uveitis
Despite early definitions, ocular hypertension has historically meant different things to different ophthalmologists.
Some glaucoma experts such as Hitchings stressed the point of not reading too much into the term.
Others, including Spaeth, advocated total disuse of the term secondary to its inherent ambiguity, preferring the term glaucoma suspect to more adequately convey uncertainty regarding the diagnosis and prognosis.
(See the image below.)
Diagram showing the relative proportion of people in the general population who have elevated pressure (horizontally shaded lines) and/or damage from glaucoma (vertically shaded lines). Notice that most have elevated pressure but no sign of damage (ie, ocular hypertensives), but there are those with normal pressures who still have damage from glaucoma (ie, normal tension glaucoma). (Diagram used by permission of M. Bruce Shields.) OHT = horizontal lines only NTG = vertical lines only POAG and other glaucomas with both elevated intraocular pressure and damage = overlapping horizontal and vertical lines
The Ocular Hypertension Treatment Study (OHTS) is a multicenter, prospective, randomized, controlled clinical trial studying more than 1800 research subjects, evaluating the safety and efficacy of medical treatment in preventing or delaying the onset of visual-field loss and/or optic nerve damage in patients with ocular hypertension who are at moderate risk for developing primary open-angle glaucoma (POAG).
In this article, ocular hypertension refers to a state in which the eye(s) meet the above 5 criteria, in the absence of identifiable causes or cardinal signs of POAG.
Ocular hypertension is a condition requiring closer observation for the potential development of glaucomatous damage.