| 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.
Contents |
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, or a decreased outflow of aqueous humor.
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]
| 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 |
|
| apraclonidine | α-2 agonist | eye drops | |
| latanoprost | prostaglandin analogue | eye drops | |
| bimatoprost | prostaglandin analogue | eye drops |