 |
  |
||||||||
 |
|||||||||
|
|||||||||
 |
|||||||||
 |
|||||||||
|
|
 |
|
|
Conditions |
|
|
|
Glaucoma |
|
|
|
Links |
|
|
|
|
 |
|||||||
|
|
|
|||||
|
|||||||
| Glaucoma Overview
Glaucoma is a term applied to a group of disorders in which there is characteristic and recognizable damage to the optic nerve. This damage is usually progressive in nature. The optic nerve consists of a bundle of more than 1 million nerve fibers that connect the retina to the brain. When this nerve bundle is damaged, the transmission of visual information to the brain is compromised and impairment of vision results.  The primary mechanism by which this damage occurs is elevated intraocularpressure (IOP). Normal IOP ranges between 11 and 21 mm Hg ( millimeters of mercury). When the pressure from fluid build-up within the eye exceeds this range, damage to the optic nerve may occur. The undamaged optic nerve head, or optic disc, resembles a “doughnut”. The outer ring consists of nerve tissue and the “cup” is the space left after the nerve fibers fan out to the retina. In the glaucoma patient, these nerve fibers are damaged and eroded which, in turn, leaves a larger space or cup. Early glaucoma can sometimes be diagnosed from the appearance of this “cupping” alone. It should be noted that some people with “normal” IOP could also develop optic nerve damage with resultant loss of vision. It is also true that many people have an IOP > 21 mm Hg with no optic nerve damage. This is called ocular hypertension. The amount of pressure that the optic nerve can withstand without damage is highly variable from individual to individual. (Have option to click and make image larger) Diagram of anterior chamber with route of aqueous flow A clear fluid called aqueous humor flows continuously in and out of the anterior chamber of the eye. This fluid is continuously produced by the eye and serves to nourish the nearby tissues. Pressure build-up and subsequent damage to the optic nerve is almost always caused by some type of blockage of the various drainage mechanisms of the eye. The type of glaucoma that is diagnosed by the ophthalmologist can be defined by the type of blockage that has occurred. The glaucoma treatment goal is to lower the IOP to a level at which no further damage to the optic nerve will occur. This goal is called the target pressure. Classifications Primary Open Angle Glaucoma (POAG) 
POAG is the most common form of the disorder, affecting approximately 3 million people. It accounts for 60%-70% of all glaucomacases and has no signs or symptoms other than vision loss as it progresses. There is a gradual loss of vision beginning with the peripheral vision (see image, right) and, as the disease progresses; there is a loss of central vision as well. Some patients will complain of events that could be caused by “blind spots” in their visual field, such as missing stairs, missing portions of words while reading or having difficulty driving. It generally affects both eyes but not necessarily equally.
How glaucomatous damage can affect vision In the normal eye, fluid leaves the anterior chamber through the open angle formed at the juncture where the iris and the cornea meet. When the fluid reaches this spot, it flows through a spongy network of tissues that serve as a “drain”. This is called the trabecular meshwork. This mechanism represents 83%-96% of the total aqueous outflow in a normal eye. In open angle glaucoma, the angle appears to be open and normal when examined, but the “drain” is actually clogged. The outflow of the fluid is too slow in relation to the continuous production of the aqueous humor and pressure builds inside the eye. This can result in the atrophy of the optic nerve, the development of POAG and consequential loss of vision Angle Closure Glaucoma Angle closure glaucoma accounts for approximately 10% of glaucoma cases. In this case, the angle formed by the meeting of the cornea and the iris is completely blocked rather than clogged. It is generally caused by the angle becoming obstructed by a part of the iris and is more common in farsighted eyes. During the process of normal aging, the lens of the eye thickens and may interfere with the flow of fluid within the eye. This can cause the iris to swell and the angle may become partially or intermittently blocked. Most people who are predisposed to the chronic or intermittent type of angle-closure glaucoma show no signs or symptoms. Some patients, however, may have very subtle symptoms such as redness in the eye, pain, blurred vision or headaches. These intermittent attacks are sometimes improved by sleep. During periods of sleep, the iris tends to contract naturally which may often be sufficient to relieve the blockage that is causing the symptoms. Acute Angle Closure Glaucoma Acute angle closure glaucoma is accompanied by a sudden increase in eye pressure. Symptoms include severe pain and nausea, redness of the eye, blurred vision and headaches. The patient may also see colored halos. An attack of acute angle closure glaucoma is a medical emergency and treatment must be sought out immediately. Without treatment the eye can become blind in as little as one or two days. The goal of treatment is to improve the flow of fluid and lower IOP. Usually, prompt laser surgery and medication can clear the blockage and protect vision. Normal Tension or Low-Pressure Glaucoma Normal tension glaucoma can occur in approximately 1/6 of patients diagnosed with glaucoma. In this particular type, the IOP is within the normal range but the patients exhibit the nerve damage and visual loss typical of glaucoma. Therefore the pressure within these individual’s eyes is too high for their optic nerve to sustain and treatment is directed toward lowering the IOP. Another cause of this type of glaucoma could be an insufficient blood supply to the optic nerve. It is interesting to note that people with this type of glaucoma have a higher incidence of migraine headaches than the general population, which can suggest some sort of vasospasm as a possible cause. Secondary Glaucoma Secondary glaucoma can be caused by some other diseases of the eye such as uveitis, from surgery, by trauma or by the use of drugs such as corticosteroids. Congenital glaucoma Congenital glaucoma is present at birth and is the direct result of the defective development of the outflow channels of the eye. As we have seen, if the outflow of aqueous humor is slowed or blocked, IOP builds and damage to the optic nerve occurs. This condition is often hereditary and surgery is necessary to correct it. Risk Factors Some risk factors for the development of Primary Open Angle Glaucoma (POAG) may include:
Risk factors for the development of Acute Angle-Closure Glaucoma include:
www.lighthouse.org http://www.nei.nih.gov/health/glaucoma/glaucoma_facts.asp |
|||||||
|
|||||||
| © 2009 ISTA Pharmaceuticals. All Rights Reserved. Disclaimer | Privacy Policy |