Glaucoma: The ‘Silent Thief of Vision’
What is Glaucoma
Glaucoma is a disease of the optic nerve, the part of the eye that carries the images to the brain for us to interpret. The optic nerve is made up of many nerve fibers, like an electric cable containing numerous wires. When damage to the optic nerve fibers occurs, blind spots in the vision develop. Typically, these blind spots initially occur in the peripheral vision and may go undetected until significant optic nerve damage occurs, resulting in permanent blindness. This is why glaucoma is known as the “silent thief of vision.”
Clear liquid called the aqueous humor circulates inside the front portion of the eye. This is different from the tears on the external surface of the eye. Normally there is an equilibrium between the fluid secreted into the eye and the amount that flows out through a microscopic drainage system to maintain a healthy level of pressure within the eye. If the drainage area for the aqueous humor, known as the drainage angle, is blocked or not working normally, the excess fluid cannot flow out of the eye and the intraocular pressure increases. This pressure causes damage to the weakest part of the wall of the eye, which happens to be the optic nerve.
Early detection and treatment are the keys to preventing optic nerve damage and blindness from glaucoma.
How Prevalent is Glaucoma?
Glaucoma is one of the leading causes of blindness in the United States. It is estimated that over 4 million Americans have glaucoma. Unfortunately, up to half of them are unaware they have the disease. Worldwide there may be as many as 70 million people that have glaucoma.
What are the Different Types of Glaucoma?
Chronic or primary open-angle glaucoma is the most common form. The drainage angle is open but becomes less efficient over time. This results in a gradual increase in pressure that can damage the optic nerve. In some patients, the optic nerve becomes sensitive even to normal pressure and is at risk for damage- this is known as normal tension glaucoma. In either case, treatment is necessary to prevent further optic nerve damage and vision loss. Typically, open-angle glaucoma has no symptoms in the early stages, and vision remains normal until the optic nerve sustains significant damage.
Closed-angle glaucoma causes a more sudden rise in eye pressure. The drainage angle may become partially or completely blocked when the iris (the colored part of the eye) is pushed over this area. This often occurs in small or farsighted eyes. Since the fluid cannot exit the eye, intraocular pressure builds rapidly and causes an acute closed-angle attack. Symptoms may include: severe eye pain and redness, blurred vision, colored halos, headache, nausea and vomiting. This is a true eye emergency and can cause loss of vision in a 24 hour period. An urgent laser treatment (iridotomy) is required to break the attack. Fortunately, this is much less common than open-angle glaucoma.
Other types of glaucoma may be associated with trauma, medications (especially steroids), inflammation or tumors in the eye.
Who is at risk for Glaucoma?
The most important risk factors include: age (typically > 50 years old), elevated eye pressure, family history of glaucoma, African or Hispanic ancestry, farsightedness or high nearsightedness, past eye injuries, thinner central corneal thickness, systemic health problems including diabetes, migraine headaches and poor circulation, and pre-existing thinning of the optic nerve.
How is Glaucoma Detected?
As mentioned earlier, early detection and treatment of glaucoma is essential to prevent permanent loss of vision. Therefore, complete eye examinations are the only sure way to detect glaucoma. Only checking the pressure of the eye (tonometry) is not sufficient to determine if one has glaucoma- this is only one component of the evaluation. Additional testing includes: inspection of the drainage angle of the eye with a special instrument (gonioscopy), evaluation of the optic nerve through a dilated pupil (ophthalmoscopy), and evaluation of the peripheral vision (visual field testing or perimetry).
Today there are more sophisticated technologies to monitor for optic nerve damage. In our office we use several technologies: 1) Optical coherence tomography (OCT) which is a computerized imaging technique that uses laser light to make a 3D image of the back of the eye, 2) Heidelberg retina tomography (HRT) which is a confocal scanning laser ophthalmoscope that produces an accurate, detailed 3D topographic map of the optic nerve, and 3) Digital photographs which provide stereo pictures of the optic nerves. All these modalities give baseline information of the optic nerve that allows for comparison in the future to detect early progression of damage.
How is Glaucoma Treated?
The treatment of glaucoma involves lowering the intraocular pressure to protect the optic nerve. Traditional treatment for glaucoma involves the use of medications in the form of eye drops or pills to lower the eye pressure. Significant advancements in eye drops in the past decade have enabled patients to control glaucoma with as little as one drop per day. Nevertheless, all medications have the potential for side effects and this needs to be discussed thoroughly with the treating eye doctor.
Laser treatment for glaucoma became popular in the early 1980’s. In our office we offer a more advanced technology known as Selective Laser Trabeculoplasty (SLT). This safe and effective treatment uses laser light to stimulate the body’s own healing response to “clean up” the drainage angle and lower the eye pressure without causing thermal damage like the previous lasers. It has approximately an 80% success rate and may enable patients to get off their eye drops! The treatment takes less than 5 minutes, is essentially painless, and is performed in the office setting.
Laser iridotomy mentioned above for closed-angle glaucoma is a brief procedure that creates a hole in the iris to improve flow of aqueous fluid to the drain. This is performed emergently to prevent sudden blindness during an attack. It is also performed prophylactically if the physician believes the patient is at risk for an attack due to a narrow drainage angle.
Glaucoma surgery is typically the last resort for glaucoma patients that cannot be controlled with medications or laser treatment. This involves making a “man-made” drainage opening in the wall of the eye and can be associated with complications. New microinvasive glaucoma surgery (MIGS) is on the horizon which looks very promising.
Although there is no cure for glaucoma, the “silent thief of vision”, early detection and treatment can prevent optic nerve damage and permanent loss of vision. Advanced technologies and treatments have made it easier for the physician to accomplish this goal. Treatment for glaucoma requires teamwork between the patient and the eye doctor. The patient must be responsible to take the recommended medication and follow up with the eye doctor as recommended.
Anyone with the risk factors mentioned above should have a complete eye exam as soon as possible. The results of that exam will dictate how often the patient should be evaluated. Adults without risk factors should get an eye disease screening at age 40. Adults 65 years and older should have an eye exam every one to two years as recommended by the eye doctor.
Neil Zusman, M.D.
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