Ocular hypertension

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Ocular hypertension
Classification and external resources
ICD-10 H40.0
ICD-9 365.04
DiseasesDB 5226
eMedicine oph/578
MeSH D009798

Ocular hypertension (OHT) is intraocular pressure higher than normal in the absence of optic nerve damage or visual field loss.[1][2]

Current consensus in ophthalmology defines normal introcular pressure (IOP) as that between 10 mmHg and 21 mmHg.[3][4] Elevated IOP is the most important risk factor for glaucoma, so those with ocular hypertension are frequently considered to have a greater chance of developing the condition.

Intraocular pressure can increase when a patient lies down. There is evidence that some glaucoma patients (e.g., normal tension glaucoma patients) with normal IOP while sitting or standing may have intraocular pressure that is elevated enough to cause problems when they are lying down.

Pathophysiology[edit]

Intraocular pressure is mainly maintained by the liquid aqueous humor, which is produced by the ciliary body of the eye. Aqueous humor normally does not go into the posterior segment of the eye; it is kept out of this area by the lens and the Zonule of Zinn. Instead, it stays only in the anterior segment, which is divided into the anterior and posterior chambers. While the anterior and posterior chambers are very similarly named to the anterior and posterior segments, they are not synonymous. The anterior and posterior chambers are both parts of the anterior segment, which is an important distinction to make in the understanding of the two main mechanisms of ocular hypertension.

When the ciliary bodies produce the aqueous humor, it first flows into the posterior chamber (bounded by the lens and the iris). It then flows through the pupil of the iris into the anterior chamber (bounded by the iris and the cornea). From here, it flows through a structure known as the trabecular meshwork to enter the normal body circulation. Thus, the two main mechanisms of ocular hypertension are an increased production of aqueous humor, and a decreased outflow of aqueous humor.

Treatment[edit]

Medication[edit]

Ocular hypertension is mostly treated with pilocarpine, timolol, acetazolamide and clonidine.[5] There are also other, less commonly used, alternatives, such as medicinal cannabis. Eye drops may initially be started either in one or in both eyes.[6]

Comparison table of ocular antihypertensives
Medication Mechanism Dosage form[7] Adverse effects[7]
pilocarpine muscarinic agonist eye drops
timolol β-receptor antagonist eye drops
acetazolamide carbonic anhydrase inhibitor systemic administration
clonidine α2-receptor agonist eye drops
ecothiopate cholinesterase inhibitor eye drops
carteolol β-receptor antagonist eye drops
dorzolamide carbonic anhydrase inhibitor eye drops
  • bitter taste
  • burning sensation
apraclonidine α-2 agonist eye drops
latanoprost prostaglandin analogue eye drops
bimatoprost prostaglandin analogue eye drops

References[edit]

  1. ^ American Academy of Ophthalmology[dead link]
  2. ^ American Optometric Association - Ocular Hypertension
  3. ^ webMD - Tonometry
  4. ^ eMedicine - Glaucoma Overview
  5. ^ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4.  Page 146
  6. ^ Leffler CT, Amini L (October 2007). "Interpretation of uniocular and binocular trials of glaucoma medications: an observational case series". BMC Ophthalmology 7: 17. doi:10.1186/1471-2415-7-17. PMC 2093925. PMID 17916260. 
  7. ^ a b Unless else specified in boxes, then ref is: Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4.  Page 146

External links[edit]