This is the name given to a group of conditions in which the optic nerve sustains damage where it leaves the eye to connect to the brain. The eye constantly produces aqueous, the clear fluid that fills the anterior chamber and nourishes the eye. The aqueous, filters out of the anterior chamber, through a complex drainage system. The delicate balance between the production and drainage of aqueous determines the eyes’ intra ocular pressure. Most people’s IOP fall between 10 and 21mmHg. However, some eyes can tolerate higher pressures than others. That’s why it may be normal for one person to have a higher pressure than another.
Common types of glaucoma
Open angle: (also called chronic open angle or primary open angle) is the most common type of glaucoma. With this type, even though the anterior structures of the eye appear normal, aqueous fluids builds up within the anterior chamber causing the IOP to become elevated. Left untreated, this may result in permanent damage of the optic nerve and retina. Eye drops are generally prescribed to lower the eye pressure. In some cases surgery is performed if the IOP cannot be adequately controlled with medical therapy.
Acute angle closure:
Only about 10% of the population with glaucoma has this type. Acute angle closure occurs because of an abnormality of the structure in the front eye. In most cases the sapce between the iris an d cornea is more narrow than normal, leaving a smaller channel for the aqueous to pass through. if the flow of aqueous becomes completely blocked, the IOP rises sharply, causing a sudden angle closure attack.
While patients with open angle glaucoma don’t typically have symptoms, those with angle closure glaucoma may experience severe eye pain accompanied by nausea, blurred vision, rainbows and lights, and a red eye. This problem is an emergency and should be treated by an ophthalmologist immediately. If left untreated, severe and permanent loss of vision will occur.
This type occurs as a result of another disease or problem within the eye such as: inflammation, trauma, cataract, previous surgery, diabetes, tumor and certain medications. For this type, both the glaucoma and the underlying problem must be treated.
This is a rare type of glaucoma that is generally seen in infants. In most cases, surgery is required.
Signs and Symptoms
The disease rarely causes symptoms in the early stages. Detection and prevention are only possible with routine eye examinations and central visual field assessment.
The symptoms include: smoky and foggy vision, blurring of distant and near vision, frequent change of glasses, bumping into objects. By the time these symptoms set in, about 50% of optic nerve fibers sub serving vision has been destroyed. When the intraocular pressures are above 40-45mmHg, pain, redness, watering, discomfort, nausea become prominent symptoms especially in certain types such as angle closure glaucomas.
Detection and Diagnosis: Glaucoma evaluation has several components. In addition to measuring the intraocular pressure, the doctor will also evaluate the health of the optic nerve (ophthalmoscopy), test the peripheral vision (visual field test), and examine the structures in the front of the eye with a special lens(gonioscopy) before making a diagnosis. The doctor evaluates the optic nerve and grades its health by noting the cup of the disc ratio. This is simply a comparison of the cup (the depressed area in the center of the nerve) to the entire diameter of the optic nerve. As glaucoma progresses, the area of cupping, or depression increase. Therefore a patient with a higher ratio has more damage.
The progression of glaucoma is monitored with a visual field test. This test maps the central 30o and peripheral vision, allowing the doctor to determine the extent of vision loss from glaucoma and a measure of the effectiveness of the treatment. The visual field test is periodically repeated to verify that the intraocular pressure is being adequately controlled.
The structures in the front of the eye are normally difficult to see without the help of a special gonioscopy lens. This special mirrored contact lens allows the doctor to examine the anterior chamber and the eye drainage system.
Those who are 40years or older should have an annual examination including a measurement of intra ocular pressure. Those who are glaucoma suspects may need additional testing. The progression of glaucoma is monitored with a visual field test
Treatment: Three types of treatment are possible namely
Medical treatment with eye drops and tablets all aimed at lowering the intraocular pressures within the normal range of 10-21mmHg.
Laser treatment: this involves amplification of light to produce heat energy to burn holes in the drainage angle of the eye to improve the drainage of aqueous from the eye. While this may be curative in a few cases, it usually done while waiting for the ultimate surgical treatment.
Surgical treatment. This creates a permanent drainage of the aqueous of the eye thereby lowering the intraocular pressures. Sometimes even this drainage may get blocked by fibrous tissue growth in the eye requiring a repeat of the surgery. In highly recalcitrant cases, a drainage tube is implanted in the eye.