The Physics
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Pressure in a Human Eye

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The Merk Manual of Diagnosis and Therapy. Whitehouse Station, NJ Merck Research Laboratories, 1999: 733. "Normal intraocular pressure (IOP) ranges between 11 and 21 mm Hg: however, this level may not necessarily be healthy for all people." 1.5–2.8 kPa
Hofstetter, Henry W; Griffin, John R.
Dictionary of Visual Science. 4th ed. Newton, MA: Butterworth-Heinemann, 1997: 551.
"Intraocular pressure within the range of values obtained in normal, healthy eyes, usually considered to represent an ocular tension of approximately 25 mm of mercury." 3.33 kPa
Guttman, Cheryl. Selective laser trabeculoplasty as effective as ALT. Opthamology Times, 2000 "Mean IOP at baseline was 23.6 mm Hg in both groups." 2.98 kPa
Gay, Wolf-Rudiger and Rothen burger, Astried Color Atlas of Physiology. 4th ed. New York: Thieme Medical Publishers, Inc., 1991: 300. "The form of the ocular bulb is maintained by its tough sclera (-> A and C1) and by its internal pressure, which is higher than that of the environment (normally 2-3 kPa = 15-22 mm Hg)." 2-3 kPa
Hately, Jeanne F. Treating Glaucoma with Drainage devices and Pericardial Grafts. Denver; AORN Journal, 2001: 3. "Aqueous humor, which helps in lens metabolism and nourishes the lens and cornea, maintains normal intraocular pressure (ie, normal IOP is 10 to 22 mm Hg) by the rate of its secretion and the resistance to outflow by the trabecular meshwork." 1.3–2.9 kPa

The human eye is a delicate system which consists of a few components that must be maintained at an optimum to ensure a production of an undistorted image. These components are transparency, constancy of form and smoothness of surface. The constancy of form of the ocular bulb is maintained by the sclera and the IOP (Intraocular pressure). This pressure is higher than that of the environment and is produced by the flow of the aqueous humor.

The aqueous humor is a fluid produced by the active transport of electrolytes. It flows through the anterior chamber and is drained away every hour by the venous blood flow. If the drainage of the aqueous fluid front he eye is sufficiently prevented by a physical obstacle or production exceeds the outflow, then IOP builds up and a condition known as glaucoma is developed.

Glaucoma consists of pain in the eye and visual disturbances. Glaucoma can be diagnosed by measuring the IOP with the use of a manometer or by visualization of the angle of glaucoma (open-angle or closed-angle) by a contact lens (gonioscopy). Elevated IOP (> 3 kPa) does not immediately ensure glaucoma, but a referral to an ophthalmologist for a deeper examination is recommended.

Zlata Golubitskaya -- 2001