Blood supply and surrounding anatomy make the anterior and posterior portions of the optic nerve susceptible to different ischemic pressures.The posterior optic nerve receives blood primarily from the pial branches of the ophthalmic artery. The optic canal, a boney tunnel leading to the brain, surrounds the most posterior part of this optic nerve segment.The anterior optic nerve receives blood primarily from the posterior ciliary arteries. The anterior optic nerve, a.k.a. the optic nerve head, is surrounded by the scleral canal, and is vulnerable to crowding of nerve fibers. The portion of the optic nerve head that is visible by looking into the eye with an ophthalmoscope is called the optic disc. PION versus AION
At the onset of symptoms, ophthalmoscope examination can differentiate AION from PION. If optic nerve head involvement is observed, it is AION. PION does not produce optic atrophy that is observable via ophthalmoscope until four to eight weeks after onset. In addition, AION often shows a characteristic altitudinal defect on a Humphrey Visual Field test. GCA
The American College of Rheumatology has defined a combination of physical symptoms and inflammatory changes to diagnose giant cell arteritis. Prevention
Individuals with a history of high blood pressure, diabetes, and smoking are most susceptible to PION as they have a compromised system of blood vessel autoregulation. Hence, extra efforts may need to be taken for them in the form of careful or staged surgery or the controlling the anemia from blood loss (by administration of blood transfusions), and the careful maintenance of their blood pressure.
Pharmacology
Mechanism of action
It is a synthetic prostaglandin analog (or more specifically, an analog of prostaglandin F2α) that works by increasing the outflow of aqueous fluid from the eyes.Like other analogs of prostaglandin F2α such as tafluprost and latanoprost, travoprost is an ester prodrug of the free acid, which acts as an agonist at the prostaglandin F receptor, increasing outflow of aqueous fluid from the eye and thus lowering intraocular pressure. Pharmacokinetics
Travoprost is absorbed through the cornea, where it is hydrolysed to the free travoprost acid. Highest concentrations of the acid in the eye are reached one to two hours after application, and its half-life in the aqueous fluid is 1.5 hours. Once it reaches the bloodstream, it is quickly metabolised, so that concentrations in the system do not exceed 25 pg/ml (compared to 20 ng/ml in the eye, which is higher by nearly a factor of 1000).Metabolites are formed by beta oxidation of the acidic chain (compare Tafluprost#Pharmacokinetics), oxidation of the OH-group in the other side chain, and reduction of the double bond next to this OH-group. Travoprost acid and its metabolites are mainly excreted via the kidney with a terminal half-life of 45 minutes. References
External links
"Travoprost". Drug Information Portal. U.S. National Library of Medicine.