Intraocular pressure
Intraocular pressure (IOP) is the fluid pressure of the aqueous humor inside the eye. In ophthalmology, tonometry is the measurement eye care professionals use to determine the fluid pressure inside the eye. IOP is an important aspect in the evaluation of patients with glaucoma. Most tonometers are calibrated to measure pressure in millimeters of mercury (mmHg).
Contents
Physiology and measurement
Intraocular pressure is mainly determined by the coupling of the production of aqueous humor and the drainage of aqueous humor mainly through the trabecular meshwork located in the anterior chamber angle.
Intraocular pressure is measured with a tonometer.
Influencing factors
Intraocular pressure measurement is also influenced by corneal thickness and rigidity.[1][2]
Fitness
Studies have been conducted on both healthy and sedentary individuals to determine if intraocular pressure could be reduced with exercise. Some forms of exertion have been found to result in a decrease in intraocular pressure. Exercises studied included; walking, jogging, and running. These studies indicate the possibility that other exercise may also reduce intraocular pressure such as yoga, tai chi, pilates, and aerobics[3][4]
Significance
Ocular hypertension (OHT) is defined by intraocular pressure being higher than normal, in the absence of optic nerve damage or visual field loss.[5][6] Current consensus among optometrists and ophthalmologists define normal intraocular pressure as that between 10 mmHg and 20 mmHg.[7][8]
The average value of intraocular pressure is 15.5 mmHg with fluctuations of about 2.75 mmHg. Intraocular pressure varies throughout the night and day. The diurnal variation for normal eyes is between 3 and 6 mmHg and the variation may increase in glaucomatous eyes. During the night, intraocular pressure usually decreases due to the slower production of aqueous humour. Intraocular pressure also varies with a number of other factors such as heart rate, respiration, exercise, fluid intake, systemic medication and topical drugs. Alcohol consumption leads to a transient decrease in intraocular pressure and caffeine may increase intraocular pressure.[9]
An important quantitative relationship is provided below:
- IOP = F / C + PV
Where, F = aqueous fluid formation rate,C= outflow rate, PV = episcleral venous pressure. The above factors are those that drive IOP. In the general population, IOP ranges between 10 and 21 mm Hg with a mean of about 15 or 16 mm Hg (plus or minus 3.5 mm Hg during a 24-hour cycle).
Ocular hypertension is the most important risk factor for glaucoma.
Differences in pressure between the two eyes is often clinically significant, and potentially associated with certain types of glaucoma, as well as iritis or retinal detachment.
Because of the effect of corneal thickness and rigidity on measured value of intraocular pressure, some forms of refractive surgery (such as photorefractive keratectomy) can cause traditional intraocular pressure measurements to appear normal when in fact the pressure may be abnormally high.
Intraocular pressure may become elevated due to anatomical problems, inflammation of the eye, genetic factors, as a side-effect from medication, or during exercise.[10] Intraocular pressure usually increases with age and is genetically influenced.[11]
Hypotony, or ocular hypotony, is typically defined as intraocular pressure equal to or less than 5 mmHg.[12][13] Such low intraocular pressure could indicate fluid leakage and deflation of the eyeball.
Case History
 | This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2007) |
One of the most extensive intraocular pressure case history records assembled to date is available online.[14] As 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.
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.[15]
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. 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.
References
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<references />, or <references group="..." />14. Acute Dynamic Exercise Reduces Intraocular Pressure, Departments of1 Ophtalmology, 2Physiology,Faculty of Medicine, Atatürk University,Erzurum- Turkey, July, 1999
15. Effects of mild, moderate and severe exercise on intraocular pressure of sedentary subjects, I.A. Qureshi, Rawalpindi Medical College, Rawalpindi, Pakistan
External links
bs:Intraokularni pritisakcs:Nitrooční tlak de:Augeninnendruck es:Presión intraocular hr:Intraokularni pritisak it:Pressione intraoculare nl:Oogdruk ja:眼圧 pl:Ciśnienie wewnątrzgałkowe fi:Silmänpaine sv:Ögontryck
zh:眼压- ↑ Effect of Central Corneal Thickness on Dynamic Contour Tonometry and Goldmann Applanation Tonometry in Primary Open-angle Glaucoma by Matthias C. Grieshaber, MD; Andreas Schoetzau, MS; Claudia Zawinka, MD; Josef Flammer, MD; Selim Orgul, MD in Arch Ophthalmol. 2007;125:740-744.
- ↑ Corneal Pachymetry: A Prerequisite for Applanation Tonometry? by Tanaka in Arch Ophthalmol.1998; 116: 544-545
- ↑ Acute Dynamic Exercise Reduces Intraocular Pressure, Departments of Ophthalmology, Physiology, Faculty of Medicine, Atatürk University, Erzurum- Turkey, July, 1999. http://journals.tubitak.gov.tr/medical/issues/sag-00-30-2/sag-30-2-20-9907-19.pdf.
- ↑ Effects of mild, moderate and severe exercise on intraocular pressure of sedentary subjects, I.A. Qureshi, Rawalpindi Medical College, Rawalpindi, Pakistan [1]
- ↑ Archives of Ophthalmology
- ↑ American Optometric Association
- ↑ webMD
- ↑ Glaucoma Overview from eMedicine
- ↑ Intraocular pressure measure on normal eyes by Pardianto G et al., in Mimbar Ilmiah Oftalmologi Indonesia.2005;2:78-9.
- ↑ Intraocular Pressure Variation During Weight Lifting by Vieira et al., in Arch Ophthalmol.2006; 124: 1251-1254.
- ↑ Intraocular pressure measure on normal eyes by Pardianto G et al., in Mimbar Ilmiah Oftalmologi Indonesia.2005;2: 80.
- ↑ eMedicine - Ocular Hypotony : Article by Sheila P Sanders
- ↑ Arch Ophthalmol - Abstract: Elevated Intraocular Pressure and Hypotony Following Silicone Oil Retinal Tamponade for Complex Retinal Detachment: Incidence and Risk Factors, February 1999, Henderer et al. 117 (2): 189
- ↑ fiteyes.com/blogs/dave
- ↑ Combining-Timoptic-and-Xalatan
