Intraocular pressure
From Wikipedia, the free encyclopedia
Intraocular pressure (IOP) is the fluid pressure inside the eye. It may become elevated due to anatomical problems, inflammation of the eye, genetic factors, as a side-effect from medication, or during exercise.
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[edit] Significance
Ocular hypertension (OHT) is intraocular pressure higher than normal in the absence of optic nerve damage or visual field loss. Current consensus in ophthalmology defines normal introcular pressure as that between 10 mmHg and 21 mmHg. Because IOP is the most important risk factor for glaucoma, those with ocular hypertension are frequently considered to have a greater chance of developing the condition.
Differences between the pressure in the two eyes is often clinically significant, and potentially associated with certain types of glaucoma, as well as iritis or retinal detachment.
Ocular hypotony, or hypotony, is typically defined as intraocular pressure equal to or less than 5 mmHg. [6] [7]
[edit] Physiology and measurement
Intraocular pressure is determined by the coupling of the production of aqueous humor from the eye's ciliary body and its drainage through the trabecular meshwork and Schlemm's canal located in the anterior chamber angle. It is measured with a tonometer.
Some forms of refractive surgery (such as photorefractive keratectomy) can have a traditional intraocular pressure measurement appear abnormally high when in fact they it may be normal.
[edit] Case History
One of the most extensive intraocular pressure case history records assembled to date is available online at fiteyes.com/blogs/dave. At of December 29, 2006, this case history included over 12,755 intraocular pressure measurements over a period of 170 days under a wide variety of real life situations. For background information about this intraocular pressure case history see the site's about.htm page.
Additional intraocular pressure measurements are continuing to be recorded at a rate of up to 100 per day and this case history web site is updated regularly. The size of the data set and the frequency with which measurements are recorded may lead to additional insights into intraocular pressure changes in response to a diverse number of factors. One interesting recent discussion that arose directly from data mining the large data set involved the timing of using glaucoma eye drop medications. The link to this discussion is available here: Combining-Timoptic-and-Xalatan.
Another question that is extensively discussed in the patient's commentary at the Case History site is the relationship between psychological stress and intraocular pressure. According to conventional wisdom, a patient's stress (e.g., nervousness, or anxiousness) does not increase the patient's intraocular pressure the way it might increase their blood pressure. For a discussion of this topic with Dr. Elliot Werner, a glaucoma specialist, see "Stress and Glaucoma" at the Wills Glaucoma support group web site. The data of the Case History challenges this convention wisdom, although a single case history will certainly not settle the question. What can be said at this point is that stress can seemingly increase intraocular pressure in at least the one individual being followed in this ambitious Case History project. Researchers will have to continue investigating the connection between stress and intraocular pressure.
[edit] References
- ↑ Archives of Opthalmology
- ↑ American Optometric Association
- ↑ American Academy of Ophthalmology
- ↑ webMD
- ↑ eMedicine - Glaucoma Overview
