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| DiseaseID |
HGD10 |
| Genetic
Disorder |
Glaucoma
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| Gene
Name |
MYOC gene |
| Description |
"Glaucoma" is a term used for a group of diseases that can lead to damage to the eye's optic nerve and result in blindness. The most common form of the disease is open-angle glaucoma, which affects about 3 million Americans, half of whom don't know they have it. Glaucoma has no symptoms at first but over the years can steal its victims' sight, with side vision being affected first.
It is estimated that nearly 100,000 individuals in the US suffer from glaucoma due to a mutation in the GLC1A gene, found on chromosome 1. There has been some speculation as to the role of the gene product in the eye. As it is found in the structures of the eye involved in pressure regulation, it may cause increased pressure in the eye by obstructing the aqueous outflow.
With early treatment, serious loss of vision and blindness can be prevented. The cloning of the GLCA1 gene is the first step toward an understanding of the pathology of glaucoma at the molecular level and may help in the development of tests for the early detection of the disease, as well as providing a basis for research into effective therapies.
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| Symptoms |
Blurred vision
? Halos around lights
? Reddening of the eye
? Severe eye pain
? Nausea and vomiting
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| Causes |
Glaucoma is the second most common cause of blindness in the US. There are four major types of glaucoma:
Angle-closure (acute) glaucoma Congenital glaucoma Open-angle (chronic) glaucoma Secondary glaucoma All four types of glaucoma are characterized by increased pressure within the eyeball, and therefore all can cause progressive damage to the optic nerve. Open-angle (chronic) glaucoma is by far the most common type of glaucoma.
The front part of the eye is filled with a clear fluid called the aqueous humor. This fluid is constantly made in the back of the eye. It leaves the eye through channels in the front (anterior) chamber of the eye, and eventually drains into the bloodstream. The channels that drain the aqueous humor are in an area called the anterior chamber angle, or simply the angle.
Angle-closure (acute) glaucoma is caused by a shift in the position of the iris of the eye that suddenly blocks the exit of the aqueous humor fluid. This causes a quick, severe, and painful rise in the pressure within the eye (intraocular pressure). Angle-closure glaucoma is an emergency. This is very different from open-angle glaucoma, which painlessly and slowly damages vision.
If you have had acute glaucoma in one eye, you are at risk for an attack in the second eye, and your doctor is likely to recommend preventive treatment.
Dilating eye drops and certain systemic medications may trigger an acute glaucoma attack if you are at risk.
Congenital glaucoma often runs in families (hereditary). It is present at birth, and is the result of the abnormal development of the fluid outflow channels in the eye.
In open-angle glaucoma, the cause is essentially unknown. An increase in eye pressure pushes on the junction of the optic nerve and the retina at the back of the eye, reducing the blood supply to the optic nerve.
Open-angle glaucoma tends to run in families. Your risk is higher if you have a parent or grandparent with open-angle glaucoma. People of African descent are at particularly high risk for this disease.
Secondary glaucoma is caused by:
Drugs such as corticosteroids Eye diseases such as uveitis Systemic diseases |
| Diagnosis |
If your doctor suspects that you have glaucoma, he or she may perform a series of tests to detect any signs of damage. Tests include:
? Tonometry. Tonometry is a simple, painless procedure that measures your intraocular pressure. It is usually the initial screening test for glaucoma.
Two common techniques are air-puff tonometry and applanation tonometry. Air-puff tonometry uses a puff of air to measure the amount of force needed to indent your cornea. An applanation tonometer is a sophisticated device that's usually fitted to a slit lamp. Slit lamps use an intense line of light — a slit — providing illumination of the cornea, iris, lens and anterior chamber, and allowing your doctor a good view of these structures.
With tonometry, your doctor numbs your eyes with drops and has you sit behind the slit lamp, where a small flat-tipped cone pushes lightly against your eyeball. The force required to flatten (applanate) a small area of your cornea translates into a measure of your intraocular pressure .
Average normal eye pressures range from 10 to 21 or 22 millimeters of mercury (mm Hg), though most pressures are within 14 to 16 mm Hg. Doctors consider anyone with eye pressure greater than 22 mm Hg to be at risk of developing glaucoma and in need of careful monitoring for early signs of glaucoma.
Tonometry readings vary somewhat depending on a variety of factors including the thickness of your corneas and whether you've had laser surgery on your eyes. For these reasons, newer technologies are being investigated to improve the standard applanation instrument and obtain more accurate intraocular eye pressure measurements.
? Test for optic nerve damage. To check the fibers in your optic nerve, your eye doctor uses an instrument called an ophthalmoscope or biomicroscope, which enables him or her to look directly through the pupil to the back of your eye. Your doctor may also use laser light and computers to create a three-dimensional image of your optic nerve. This can reveal slight changes that may indicate the beginnings of glaucoma. Your doctor may also make a detailed drawing of your optic nerves and take photographs of the optic nerves in order to monitor any changes that might occur at future visits.
? Visual field test. To check how your visual field has been affected by glaucoma, your doctor uses a perimetry test. One method, known as tangent screen perimetry, requires you to look at a screen with a target in the center. Your eye doctor or a technician manipulates a small object on a wand at different locations in your visual field. You indicate whenever you see the object come into view. By repeating this process over and over again, your entire visual field can be mapped.
? Pachymetry. Your eyes are numbed for this test, which uses an ultrasonic-wave instrument to gauge the thickness of each cornea. The thickness of your corneas is an important factor for accurately diagnosing glaucoma. If you have thick corneas, your eye pressure reading may seem high even though you don't have glaucoma. Conversely, people with thin corneas can have low pressure readings, but have glaucoma.
? Other tests. To distinguish between open-angle glaucoma and angle-closure glaucoma, your eye doctor may use a technique called gonioscopy (go-ne-OS-kuh-pe), in which a special lens with an angled mirror is placed on your eye to inspect the drainage angle. Another test, tonography, can measure how fast fluid drains through the trabecular meshwork.
To establish a diagnosis of glaucoma, several factors must be present:
? Elevated intraocular pressure
? Areas of vision loss
? Damage to your optic nerve
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| Treatment |
The treatment of glaucoma is aimed at reducing intraocular pressure by improving aqueous outflow, reducing the production of aqueous, or both. Doctors accomplish these treatment goals with eyedrops, systemic medications, laser treatment, surgery, or a combination of treatments. |
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