Glaucoma often undetected and misunderstood
For years, glaucoma, the leading cause of irreversible blindness was considered when there was elevated pressure within the eye which leads to sudden loss of vision. Glaucoma is still checked by seeing only the pressure of the eye in many cases of routine screening. But experts knew there were glaring gaps in the definition of glaucoma.
Glaucoma is not simply an eye disease, experts now say, but rather a degenerative nerve disorder, not unlike Alzheimer's or Parkinson's disease. Glaucoma is a disease of the major nerve of vision, called the optic nerve. The optic nerve receives light from the retina and transmits impulses to the brain that we perceive as vision.
Glaucoma is characterised by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.
Many people with abnormally high intraocular pressure never develop glaucoma. As many as one in three people who do get the disease have normal or even low pressure. As researchers have tried to resolve those contradictions, a new paradigm for understanding glaucoma has emerged.
Even the official definition of glaucoma, a disease that accounts for more than eight million cases of blindness worldwide, has changed. Today, diagnosis is based on just two features: visible damage to the optic nerve, which leads from the retina at the back of the eye to the brain, and loss of peripheral vision, which can be measured by a simple test in an eye doctor's office.
Researchers still recognise high pressure within the eye as a leading risk factor for glaucoma. And ophthalmologists still use the familiar screening test that measures pressure and screen for the disease. But since about 30 percent of people with the disease have normal or low pressure and there is obviously something else at work.
Intraocular pressure (IOP) in the eye is called another term ocular hypertension which is considered normal with no detectable changes in vision or damage to the structure of your eyes. People suffering from acute near-sightedness are observed to develop this condition and people suffering from diabetes are relatively more prone to develop ocular hypertension.
Elevated IOP can also occur due to inadequate drainage or excessive aqueous fluid production. Steroids and other similar medications can increase the IOP levels. Trauma has also shown tendencies to lead to a lofty IOP level.
"Glaucoma is often called "silent thief of sight" because most types typically cause no pain and produce no symptoms. For this reason, glaucoma often progresses undetected until the optic nerve already has been irreversibly damaged, with varying degrees of permanent vision loss. This is a major hurdle in getting patients who know they have glaucoma to take their medicine before irreversible vision loss occur.
In very few types like acute angle-closure glaucoma, symptoms that occur suddenly can include blurred vision, halos around lights, intense eye pain, nausea and vomiting. "If you have these symptoms, make sure you see an ophthalmologist immediately so that steps can be taken to prevent permanent vision loss", said Dr Khair Ahmed Choudhury, Assistant Professor of Ophthalmology of Sylhet MAG Osmani Medical College.
"Diagnosis should be based on examining the optic nerve, field of vision rather than elevated IOP. Routine screening eye examinations are mandatory since glaucoma usually causes no symptoms in its early stages. Once damage to the optic nerve has occurred, it can not be reversed. Thus, in order to preserve vision, glaucoma must be diagnosed early and followed up regularly.
Individuals of 40-60 years of age should have an eye examination every two to four years and at 65 or over it individuals should have an eye examination every one to two years. People who are at risk should check their eye more frequently at 6 months interval.
For now, the only treatments available for glaucoma work by lowering pressure in the eye, either by decreasing the production of fluid or increasing its outflow. Even in patients with normal intraocular pressure and early signs of the disease, lowering pressure has been shown to significantly slow the progression of nerve damage. Most anti-glaucoma drugs are delivered as eye drops, which may need to be used once or several times a day. When drops are not enough, laser treatments and surgery can be used to allow excess fluid to flow out of the eyes.
Despite effective treatments, many people suffer some preventable loss of peripheral vision. One problem is that the disease too often goes undetected. Maximum people with glaucoma are not aware that their vision is at risk because they have not been tested, surveys suggest.
The longer the disease goes untreated, the greater the chance of loss of vision. Worldwide, an estimated 60 million people have glaucoma, and that number is expected to reach 80 million by 2020. While scientists search for better treatments for glaucoma, the second-leading cause of blindness, people can take action to give themselves the best chance: get a regular glaucoma screening exam, and if glaucoma is diagnosed, take the treatment regimen seriously. Because your sight depends on it.
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