Eyes, Age related illnesses | April 17, 2015 | Author: The Super Pharmacist
Ocular hypertension is a condition in which the fluid within the eye is higher than normal, but no glaucoma-related changes have occurred. Specifically, the diagnosis of ocular hypertension applies when pressure within the eye is greater than 21 mmHg and there is no evidence of damage to the optic disc nor is the patient experiencing decreased vision in one or more visual fields.
The term “ocular hypertension” is somewhat confusing, since in some forms of glaucoma there is also increased pressure within the eye. Further complicating matters, is that a substantial number of people may have glaucoma-related damage to the eye, but pressure within the eye is normal (i.e. normal tension glaucoma). In fact, different ophthalmologists have different definitions for ocular hypertension and glaucoma.
Many believe that ocular hypertension is considered early glaucoma. As such, ocular hypertension can be thought of as a major risk factor for glaucoma. People who receive treatment for ocular hypertension are less likely to develop glaucoma-related damage such as visual field defects and open angle glaucoma.
Glaucoma screening is more than just intraocular pressure screening. Glaucoma is one of the most common causes of blindness in industrialised countries. Considering that glaucoma rarely causes symptoms until damage is already occurred, it is particularly dangerous. This makes glaucoma silent, but potentially blinding. Glaucoma is one of the main reasons experts recommend routine eye examinations. As the table shows, people can have glaucoma with normal pressure in the eye (i.e. normal tension glaucoma) or elevated pressure without glaucoma related damage (i.e. ocular hypertension). A true screening eye examination includes intraocular pressure testing, visual field testing, and retina examinations.
Intraocular pressure can be tested in several ways, and there is no gold standard. One method involves placing a prism against the cornea to test how much pressure is required to flatten the eye. Another method is known as the “puff test” in which a small puff of air is blown onto the eye and its effect is measured. A third, commonly used test, is to place a pen-like device on the eyelid to measure pressure in the eye. These and other tests may be performed by an ophthalmologist to measure intraocular pressure. Pressure greater than 21 mmHg is considered abnormal and consistent with ocular hypertension.
It is important to determine if elevated intraocular pressure is simply ocular hypertension or glaucoma. In glaucoma, there may be changes on the specialised structure in the back of the eye called the retina. More specifically, the examiner will look at a part of the retina called the optic disc, where the optic nerve leaves the eyeball and travels to the brain.
People with normal vision see a binocular vision of the world that is roughly circular or ovoid. This field of vision is actually comprised of several smaller sections, each carried to the brain by a different set of nerves. In someone with visual field defects, one or more of these regions will not contain visual information. In other words, there will be one or more blind spots. An eye doctor can identify these defects through visual field testing.
Since ocular hypertension is considered a risk factor for glaucoma, the risk factors for glaucoma tend to overlap with those for hypertension. Risk factors for ocular hypertension include:
The risk of developing blindness within 15 years of developing ocular hypertension is less than 10%. On the other hand, the risk of someone with ocular hypertension developing primary open angle glaucoma is 3.5% per year.
Importantly, not everyone with ocular hypertension will go on to develop glaucoma. It has been estimated that 12 people need to be treated for ocular hypertension to prevent one case of primary open angle glaucoma in those who have elevated intraocular pressure.
Since ocular hypertension does not cause symptoms, nor is there any existing damage to the eye or deficit in visual fields, treatment for the condition involves reducing intraocular pressure. The primary means of reducing intraocular pressure is with eye drops. Four main classes of eye drops that can be used to reduce intraocular pressure:
There are also combination drugs available that combine two of the above classes into one eye drop solution. Not everyone responds to each of these medications, so there may be a trial and error process initially. The goal is to find a relatively inexpensive, easy to use, and effective eye drop that lowers intraocular pressure. When a second medication is added (which commonly happens), the additional eye drop is usually chosen from another drug class so they may have a synergistic effect on intraocular pressure.
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