Editing Intraocular pressure

{{Short description|Fluid pressure inside the eye}}
[[Image:Patient and tonometer.jpg|thumb|250px|A patient in front of a [[tonometer]]]]
'''Intraocular pressure''' ('''IOP''') is the fluid [[pressure]] inside the [[human eye|eye]]. [[Ocular tonometry|Tonometry]] is the method [[eye care professional]]s use to determine this. IOP is an important aspect in the evaluation of patients at risk of [[glaucoma]].<ref name="pmid25400274">{{cite journal | last1=Farandos | first1=Nicholas M. | last2=Yetisen | first2=Ali K. | last3=Monteiro | first3=Michael J. | last4=Lowe | first4=Christopher R. | last5=Yun | first5=Seok Hyun | title = Contact lens sensors in ocular diagnostics | journal = Advanced Healthcare Materials | volume = 4 | issue = 6 | pages = 792–810 | date = April 2015 | pmid = 25400274 | doi = 10.1002/adhm.201400504 | s2cid=35508652 }}</ref> Most tonometers are calibrated to measure pressure in millimeters of mercury ([[mmHg]]).

==Physiology==
Intraocular pressure is determined by the production and drainage of [[aqueous humour]] by the [[ciliary body]] and its drainage via the [[trabecular meshwork]] and uveoscleral outflow. The reason for this is because the [[Vitreous body|vitreous humour]] in the [[Posterior segment of eyeball|posterior segment]] has a relatively fixed volume and thus does not affect intraocular pressure regulation.

An important quantitative relationship (Goldmann's equation) is as follows:<ref name="pmid27477112">{{cite journal | vauthors = Aptel F, Weinreb RN, Chiquet C, Mansouri K | title = 24-h monitoring devices and nyctohemeral rhythms of intraocular pressure | journal = Prog Retin Eye Res | volume = 55 | pages = 108–148 | date = November 2016 | pmid = 27477112 | doi = 10.1016/j.preteyeres.2016.07.002 | s2cid = 24677841 }}</ref>

:<math>P_o = \frac{F - U}{C} + P_v</math>

Where:
* <math>P_o</math> is the IOP in millimeters of mercury (mmHg)
* <math>F</math> the rate of aqueous humour formation in microliters per minute (μL/min)
* <math>U</math> the resorption of aqueous humour through the uveoscleral route (μL/min)
* <math>C</math> is the facility of outflow in microliters per minute per millimeter of mercury (μL/min/mmHg)
* <math>P_v</math> the episcleral venous pressure in millimeters of mercury (mmHg).

The above factors are those that drive IOP.

==Measurement==
[[File:TONOMETER DIATON 2011.jpg|thumb|right|upright|Diaton transpalpebral tonometer]]
Palpation is one of the oldest, simplest, and least expensive methods for approximate IOP measurement, however it is very inaccurate unless the pressure is very high.<ref>{{Cite journal|last1=Heidary|first1=Fatemeh|last2=Gharebaghi|first2=Reza|last3=Heidary|first3=Roghayeh|date=2010-07-30|title=Palpation by blind examiners: A novel approach for glaucoma screening|journal=Clinical Ophthalmology|volume=4|pages=671–672|doi=10.2147/opth.s11167|issn=1177-5483|pmc=2915851|pmid=20689781 |doi-access=free }}</ref> Intraocular pressure is measured with a [[Ocular tonometry|tonometer]] as part of a comprehensive [[eye examination]]. [[Contact lens]] sensors have also been used for continuous intraocular pressure monitoring.<ref>{{cite journal |last1=Baghban |first1=R |last2=Talebnejad |first2=MR |last3=Meshksar |first3=A |last4=Heydari |first4=M |last5=Khalili |first5=MR |title=Recent advancements in nanomaterial-laden contact lenses for diagnosis and treatment of glaucoma, review and update. |journal=Journal of Nanobiotechnology |date=2 November 2023 |volume=21 |issue=1 |pages=402 |doi=10.1186/s12951-023-02166-w |pmid=37919748|doi-access=free |pmc=10621182 }}</ref>

Measured values of intraocular pressure are influenced by [[cornea]]l thickness and rigidity.<ref name=Grieshaber>{{cite journal | vauthors = Grieshaber MC, Schoetzau A, Zawinka C, Flammer J, Orgul S | title = Effect of central corneal thickness on dynamic contour tonometry and Goldmann applanation tonometry in primary open-angle glaucoma | journal = Arch. Ophthalmol. | volume = 125 | issue = 6 | pages = 740–4 | date = June 2007 | pmid = 17562982 | doi = 10.1001/archopht.125.6.740 | doi-access = free }}</ref><ref name=Tanaka>{{cite journal | vauthors = Tanaka GH | title = Corneal pachymetry: a prerequisite for applanation tonometry? | journal = Arch. Ophthalmol. | volume = 116 | issue = 4 | pages = 544–5 | date = April 1998 | pmid = 9565063 }}</ref> As a result, 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. A newer transpalpebral and transscleral tonometry method is not influenced by corneal biomechanics and does not need to be adjusted for corneal irregularities as measurement is done over upper eyelid and sclera.<ref name="pmid26167293">{{cite journal | vauthors = Cacho I, Sanchez-Naves J, Batres L, Pintor J, Carracedo G | title = Comparison of Intraocular Pressure before and after Laser In Situ Keratomileusis Refractive Surgery Measured with Perkins Tonometry, Noncontact Tonometry, and Transpalpebral Tonometry | journal = J Ophthalmol | volume = 2015 | pages = 683895 | date = 2015 | pmid = 26167293 | pmc = 4475733 | doi = 10.1155/2015/683895 | doi-access = free }}</ref>

==Classification==
Current consensus among [[ophthalmologists]] and [[optometrists]] defines normal intraocular pressure as that between 10 [[mmHg]] and 20 mmHg.<ref>[http://www.webmd.com/hw/lab_tests/hw201323.asp webMD - Tonometry]</ref><ref>[http://www.emedicinehealth.com/articles/14545-1.asp Glaucoma Overview] {{Webarchive|url=https://web.archive.org/web/20080704200634/http://www.emedicinehealth.com/articles/14545-1.asp |date=4 July 2008 }} from eMedicine</ref><ref name="Hashemi-Mohammad2015">{{cite journal |vauthors = Hashemi H, Kashi AH, Fotouhi A, Mohammad K |title = Distribution of intraocular pressure in healthy Iranian individuals: the Tehran Eye Study |journal = Br J Ophthalmol |volume = 89 |issue = 6 |pages = 652–7 |date = June 2005 |pmid = 15923494 |pmc = 1772663 |doi = 10.1136/bjo.2004.058057}}</ref><ref name="Pooranee2015">{{cite web |author=Pooranee |title=Do you know about Intra Ocular Pressure? |website=Health Education Bureau, Information and Communication Technology Agency, Sri Lanka |date=2015-10-09 |url=http://www.healthedu.gov.lk/web/index.php?option=com_content&view=article&id=96%3Ado-you-know-about-intra-ocular-pressure&catid=17%3Aspecial-article&lang=en |access-date=2015-11-04 |archive-date=22 March 2017 |archive-url=https://web.archive.org/web/20170322013535/http://www.healthedu.gov.lk/web/index.php?option=com_content&view=article&id=96%3Ado-you-know-about-intra-ocular-pressure&catid=17%3Aspecial-article&lang=en |url-status=dead }}</ref> The average value of intraocular pressure is 15.5 mmHg with fluctuations of about 2.75 mmHg.<ref name=Janunts>{{Cite web|url=http://www.uniklinikum-saarland.de/de/einrichtungen/kliniken_institute/experimentelle_ophthalmologie/forschung/iop_sensing/|title=Optical remote sensing of intraocular pressure by an implantable nanostructured array|author=Janunts E|work=Medizinische Fakultät der Universität des Saarlandes|url-status=dead|archive-url=https://web.archive.org/web/20120425132825/http://www.uniklinikum-saarland.de/de/einrichtungen/kliniken_institute/experimentelle_ophthalmologie/forschung/iop_sensing/|archive-date=2012-04-25}}</ref>

[[Ocular hypertension]] (OHT) is defined by intraocular pressure being higher than normal, in the absence of [[optic nerve]] damage or [[visual field]] loss.<ref name="Vieira">{{cite journal | vauthors = Vieira GM, Oliveira HB, de Andrade DT, Bottaro M, Ritch R | title = Intraocular pressure variation during weight lifting | journal = Arch. Ophthalmol. | volume = 124 | issue = 9 | pages = 1251–4 | date = September 2006 | pmid = 16966619 | doi = 10.1001/archopht.124.9.1251  | s2cid = 32361659 | doi-access =  }}</ref><ref>[http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/ocular-hypertension?sso=y Ocular Hypertension], [[American Optometric Association]]. Accessed 2015-11-3.</ref>

Ocular hypotension, hypotony, or [[ocular hypotony]], is typically defined as intraocular pressure equal to or less than 5 mmHg.<ref name="MedscapeOcularHypotony">{{cite web | title=Ocular Hypotony: Background, Pathophysiology, Epidemiology | website=Medscape Reference | date=2014-02-05 | url=http://emedicine.medscape.com/article/1207657-overview#showall | access-date = 2015-11-04}}</ref><ref name="Henderer">{{cite journal | vauthors = Henderer JD, Budenz DL, Flynn HW, Schiffman JC, Feuer WJ, Murray TG | title = Elevated intraocular pressure and hypotony following silicone oil retinal tamponade for complex retinal detachment: incidence and risk factors | journal = Arch. Ophthalmol. | volume = 117 | issue = 2 | pages = 189–95 | date = February 1999 | pmid = 10037563 | doi = 10.1001/archopht.117.2.189 | doi-access =  }}</ref> Such low intraocular pressure could indicate fluid leakage and deflation of the eyeball.

==Influencing factors==
=== Daily variation ===
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 may not decrease<ref name="pmid21330554">{{cite journal |vauthors = Liu JH, Weinreb RN |title = Monitoring intraocular pressure for 24 h |journal = Br J Ophthalmol |volume = 95 |issue = 5 |pages = 599–600 |date = May 2011 |pmid = 21330554 |doi = 10.1136/bjo.2010.199737  |s2cid = 42736853 }}</ref> despite the slower production of aqueous humour.<ref>{{cite journal |last=Brubaker RF |title=Flow of aqueous humor in humans |journal=Invest Ophthalmol Vis Sci |year=1991 |volume=32 |issue=13 |pages=3145–3166 |pmid=1748546}}</ref>   [[Glaucoma]] patients' 24-hour IOP profiles may differ from those of healthy individuals.<ref name="pmid12657596">{{cite journal |vauthors = Liu JH, Zhang X, Kripke DF, Weinreb RN |title = Twenty-four-hour intraocular pressure pattern associated with early glaucomatous changes |journal = Invest. Ophthalmol. Vis. Sci. |volume = 44 |issue = 4 |pages = 1586–90 |date = April 2003 |pmid = 12657596 |doi = 10.1167/iovs.02-0666 |issn=1552-5783 |doi-access = }}</ref>

=== Fitness and exercise ===
There is some inconclusive research that indicates that exercise could possibly affect IOP (some positively and some negatively).<ref>Studies have also been conducted on both healthy and sedentary individuals to determine if intraocular pressure could be reduced with other types of exercise. Some forms of exertion have been found to result in a decrease in intraocular pressure. Exercises studied included; walking, jogging, and running. [http://journals.tubitak.gov.tr/medical/issues/sag-00-30-2/sag-30-2-20-9907-19.pdf Acute Dynamic Exercise Reduces Intraocular Pressure] {{Webarchive|url=https://web.archive.org/web/20110928075707/http://journals.tubitak.gov.tr/medical/issues/sag-00-30-2/sag-30-2-20-9907-19.pdf |date=28 September 2011 }}, Departments of Ophthalmology, Physiology, Faculty of Medicine, Atatürk University, Erzurum- Turkey. July 1999.</ref><ref>[http://informahealthcare.com/doi/abs/10.1080/03014469500004202 Qureshi IA. Effects of mild, moderate and severe exercise on intraocular pressure of sedentary subjects. Rawalpindi Medical College, Rawalpindi, Pakistan]</ref><ref name="Vieira" />

=== Musical instruments ===
Playing some musical wind instruments has been linked to increases in intraocular pressure.  A 2011 study focused on brass and woodwind instruments observed "temporary and sometimes dramatic elevations and fluctuations in IOP".<ref name="pmid21234587">{{cite journal | vauthors = Schmidtmann G, Jahnke S, Seidel EJ, Sickenberger W, Grein HJ | title = Intraocular pressure fluctuations in professional brass and woodwind musicians during common playing conditions | journal = Graefes Arch. Clin. Exp. Ophthalmol. | volume = 249 | issue = 6 | pages = 895–901 | date = June 2011 | pmid = 21234587 | doi = 10.1007/s00417-010-1600-x | url = https://pearl.plymouth.ac.uk/bitstream/10026.1/10195/1/Schmidtmann_2011.pdf | hdl = 10026.1/10195 | s2cid = 21452109 | hdl-access = free | access-date = 24 September 2019 | archive-date = 11 January 2022 | archive-url = https://web.archive.org/web/20220111155744/https://pearl.plymouth.ac.uk/bitstream/handle/10026.1/10195/Schmidtmann_2011.pdf;jsessionid=C5A3CBDA079355BE3F54DAFDFC2C8B64?sequence=1 | url-status = dead }}</ref>
Another study found that the magnitude of increase in intraocular pressure correlates with the intraoral resistance associated with the instrument, and linked intermittent elevation of intraocular pressure from playing high-resistance wind instruments to incidence of visual field loss.<ref name="pmid10647731">{{cite journal | vauthors = Schuman JS, Massicotte EC, Connolly S, Hertzmark E, Mukherji B, Kunen MZ | title = Increased intraocular pressure and visual field defects in high resistance wind instrument players | journal = Ophthalmology | volume = 107 | issue = 1 | pages = 127–33 | date = January 2000 | pmid = 10647731 | doi = 10.1016/s0161-6420(99)00015-9 }}</ref>
The range of intraoral pressure involved in various classes of ethnic wind instruments, such as [[Native American flute]]s, has been shown to be generally lower than Western classical wind instruments.<ref name="IOP_Ethnic">
{{cite journal
 | title = Intraoral Pressure in Ethnic Wind Instruments
 | author = Clinton F. Goss
 | date=August 2013
 | url = http://www.Flutopedia.com/refs/Goss_2013_IntraoralPressureInEthnicWindInstruments.pdf
 | journal=Flutopedia
 | access-date = 22 August 2013
 | bibcode = 2013arXiv1308.5214G
 | arxiv=1308.5214
}}
</ref>

=== Drugs ===
Intraocular pressure also varies with a number of other factors such as [[heart]] rate, [[Respiration (physiology)|respiration]], fluid intake, systemic medication and topical drugs. [[Ethanol|Alcohol]] and [[Cannabis (drug)|marijuana]] consumption leads to a transient decrease in intraocular pressure and [[caffeine]] may increase intraocular pressure.<ref>Intraocular pressure measure on normal eyes by Pardianto G et al., in Mimbar Ilmiah Oftalmologi Indonesia.2005;2:78-9.</ref>

Taken orally, [[glycerol]] (often mixed with fruit juice to reduce its sweet taste) can cause a rapid, temporary decrease in intraocular pressure.  This can be a useful initial emergency treatment of severely elevated pressure.<ref name="pmid14184494">{{cite journal | vauthors = Drance SM | title = Effect of Oral Glycerol on Intraocular Pressure in Normal and Glaucomatous Eyes | journal = Arch. Ophthalmol. | volume = 72 | issue = 4| pages = 491–3 | date = October 1964 | pmid = 14184494 | doi = 10.1001/archopht.1964.00970020491009 }}</ref>

The depolarising muscle relaxant [[succinylcholine]], which is used in [[anaesthesia]], transiently increases IOP by around 10&nbsp;mmHg for a few minutes.  This is significant for example if the patient requires anaesthesia for a [[trauma (medicine)|trauma]] and has sustained an eye (globe) perforation.  The mechanism is not clear but it is thought to involve contraction of tonic [[myofibrils]] and transient dilation of [[choroidal]] blood vessels.  [[Ketamine]] also increases IOP.<ref>{{cite book|vauthors = Brunton L, Chabner BA, Knollman B|title=Goodman & Gilman's: The Pharmacological Basis of Therapeutics|chapter=19. General Anesthetics and Therapeutic Gases|publisher=The McGraw-Hill Companies, Inc.|isbn=978-0-07-162442-8|date=2011|edition=12th|location=New York, USA|page=539}}</ref><ref>{{Cite web |title=Ocular Therapeutix Inc (OCUL) |url=https://biotickr.com/biotech-stocks/united-states-of-america/ocul-ocular-therapeutix-inc |access-date=2022-09-13 |website=biotickr |language=en}}</ref>

==Significance==
Ocular hypertension is the most important risk factor for [[glaucoma]].

Intraocular pressure has been measured as an outcome in a systematic review comparing the effect of neuroprotective agents in slowing the progression of open [[Glaucoma|angle glaucoma]].<ref name="Sena">{{cite journal | vauthors = Sena DF, Lindsley K | title = Neuroprotection for treatment of glaucoma in adults | journal = Cochrane Database Syst Rev | volume = 1 | pages = CD006539 | date = January 2017 | issue = 1 | pmid = 28122126 | pmc = 5370094 | doi = 10.1002/14651858.CD006539.pub4 }}</ref>

Differences in pressure between the two eyes are often clinically significant, and potentially associated with certain types of glaucoma, as well as  [[iritis]] or [[retinal detachment]].

Intraocular pressure may become elevated due to anatomical problems, [[inflammation]] of the eye, genetic factors, or as a [[Adverse effect (medicine)|side-effect]] from [[medication]]. Intraocular pressure laws follow fundamentally from physics. Any kinds of intraocular surgery should be done by considering the intraocular pressure fluctuation. Sudden increase of intraocular pressure can lead to intraocular micro barotrauma and cause ischemic effects and mechanical stress to retinal [[nerve fiber layer]]. Sudden intraocular pressure drop can lead to intraocular decompression that generates micro bubbles that potentially cause multiple micro emboli and leading to hypoxia, ischemia and retinal micro structure damage.<ref name="pmid25804599">{{cite journal | vauthors = Pardianto G | title = Recent awareness and consideration of intraocular pressure fluctuation during eye surgery | journal = J Cataract Refract Surg | volume = 41 | issue = 3 | pages = 695 | date = March 2015 | pmid = 25804599 | doi = 10.1016/j.jcrs.2015.01.009 | doi-access = free }}</ref>

==References==
{{reflist}}

==External links==
* [http://www.allaboutvision.com/eye-exam/expect.htm www.allaboutvision.com] What To Expect During a Comprehensive Eye Exam
* [http://www.emedicinehealth.com/ocular_hypertension/article_em.htm www.emedicinehealth.com] Ocular Hypertension
* [http://www.tonometerdiaton.com/ www.tonometerdiaton.com] Transpalpebral Transscleral Tonometry

{{Eye and ear physiology}}

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{{Use dmy dates|date=August 2019}}

{{DEFAULTSORT:Intraocular Pressure}}
[[Category:Ophthalmology]]
[[Category:Eye]]
[[Category:Vision]]