The Optic Nerve is the nerve for sight. It is like an electric cable with a million wires that carries electrical impulses from the light sensitive cells of the retina, (at the back of eye) to the brain. Our brain puts them together to form a picture. The earliest change in glaucoma is the damage to the nerve fibers which leads areas of blindness in your field of vision. Unfortunately, people seldom notice these small blind areas until they enlarge which is why glaucoma is often called the silent thief of vision. When the entire nerve is destroyed permanent blindness results. Special tests are the only way to identify these early defects. Early detection and treatment are the keys to prevent optic nerve damage and blindness from Glaucoma (Kala Motia).
A clear fluid called the 'Aqueous Humor' circulates continuously within the eye. This fluid is not a part of the tears on the outer surface of the eye. Produced behind the Iris (The brown part of the eye), it flows forwards through the pupil and drains out of the eye through intricate drainage channels. Normally, fluid production and outflow are balanced. As a result the pressure inside the eye remains stable and within the safe range. If the drainage of this fluid is hampered, the pressure within the eye increases to a level that damages the cells in the optic nerve. This is Glaucoma (Kala Motia).
The drainage portion of the eye, called the "drainage angle" is like a sieve and can be blocked in different ways.
a). It may get blocked suddenly by the iris that closes the drainage angle. Eye pressure increases rapidly, resulting in a sudden loss of vision, severe eye pain and headache, rainbow halos around light accompanied by nausea and vomiting. This is called "Acute Angle Closure Glaucoma" and if not treated as an emergency it leads to permanent blindness.
b). In the second type of Glaucoma, the out flow sieves get blocked by debris. This leads to a slow rise in pressure, known as "Primary Open Angle Glaucoma". Vision is lost so gradually and painlessly that a person is unaware of until the optic nerve is badly damaged. What makes it dangerous is that has no symptoms. This type of Glaucoma is much more common.
c). Glaucoma can also occur after an injury, inflammation of eye, drugs & cataract etc. Glaucoma may rarely be present at birth. The parents may notice their baby's eye enlarging due to the increase in pressure. The cornea becomes cloudy, with watering and increasing sensitivity to light. This needs an urgent eye examination .
The average Intra-Ocular Pressure (IOP; the pressure within the eye like the air pressure in tyre of any vehicles) in adult is 16 mmHg. The actual upper limit of normal pressure, however, is difficult to pinpoint. If the 10P is consistently above 21mmHg, the chances of eye damage are probably around 10%. When the 10P is above 26mmHg, the likelihood increases to about 50%. What constitutes normal 10P is an individual matter for each person. For example, some persons with an 10P of 16mmHg may need surgery while, others with an 10P of 30mmHg may be kept under observation only. The 10P is different and independent of blood pressure. Don't confuse it with the pressures of day to day life!
All types of Glaucoma have three features in common. These form the basis to diagnose Glaucoma, measure the extent of damage, and monitor its progression.
a). Increased 10P: The pressure inside the eye is measured with Goldmann applanation tonometer. A prism with blue lights touches the eye to accurately check 10P. There are however some types of glaucoma where damage may occur even with a normal pressure, called Normal Tension Glaucoma.
b). Cupping and atrophy of the Optic Nerve: It is the drying up of the optic nerve (the nerve of sight) as it suffers damage due to high pressure inside the eye. It is assessed by examination of the fundus of the eye.
c). Retinal Nevre Fibre Layer (RNFL) defects and Visual Field Defects: The slow death of nerve fibers is the earliest change to occur in Glaucoma. This nerve fibre layer damage is picked by a specialized instrument called OCT. Visual Fields defects are missing areas in the field of sight, though the person may be seeing well otherwise. This is measured with an instrument called a perimeter. The modern perimeter is computerized to measure; analyse, compare and report the defects.
Unfortunately there are no symptoms in early stages. A person with Chronic Glaucoma is usually unaware of the disease. Like the hands of a clock, Chronic Glaucoma moves so slowly that its progress is not noticed. It is a silent thief of vision.
On the other hand, Acute Glaucoma, in which the pressure rises rapidly, causes severe symptoms which compel the patient to consult a doctor. Symptoms that suggest the presence of Chronic or Acute Glaucoma include are shown in above table.
Getting an annual eye examination at Patiala Eye Hospital & Lasik Laser Centre is the best way to detect Glaucoma. During a complete work up for Glaucoma, we will be asure your Int ra-Ocular Pres sure (Tonometry), the central corneal thickness (Pachymetry) inspect the drainage angle of the eye (Gonioscopy), evaluate for optic nerve head damage (Ophthalmoscopy), test the visual field of each eye (Perimetry) and measure the thickness of your retinal nerve fibre layer (OCT examination).
All of these tests may not be necessary for every person. But it is very important that these tests be repeated on a regular basis to monitor the progress of disease and to detect glaucoma at the earliest possible stage.
People with high 10P have a higher risk of developing optic nerve damage. Other important risk factors include advancing age, severe myopia (near sighted), and a family history of Glaucoma, presence of Diabetes, past injury to the eye, surgery, or history of severe anaemia or shock.
We will weigh all these factors before deciding whether you need treatment for Glaucoma or not. If your risk of developing Glaucoma is higher than normal but there is no optic nerve damage, you will be monitored periodically as a 'Glaucoma Suspect'.