Glaucoma is the second largest cause of blindness world wide after cataract and approximately 66 million people are estimated to be affected by this sight threatening disorder by the year 2010. This blindness is unfortunately irreversible. Majority of the cases are detected incidentally and sadly at an advanced stage due to the absence of alarming symptoms.
What is glaucoma?
Glaucoma is a degenerative disease of the nerve of the eye (optic nerve), with characteristic changes in the optic nerve and associated loss of peripheral field of vision/side vision. The pressure inside the eye (intraocular pressure-IOP) may or may not be raised. Of the many risk factors that can contribute to the nerve damage, IOP is the only one that can be modified to either prevent the onset or to stop further damage to the nerve.
Intraocular pressure- what is it? How is it measured? What is normal IOP?
Aqueous humor is a fluid that is constantly produced inside the eye and gets drained out of the eye into the blood circulation. It not only maintains the pressure inside the eye but also is required for the nourishment of the lens and the cornea (the outer transparent shell of the eye). Any obstruction to its outflow will result in raised pressure inside the eye and can damage the nerve if it remains so for a long time. The IOP can be measured with the help of an instrument called tonometer. Of all the tonometers, Goldmann applanation tonometer gives the most accurate reading. Other tonometers can be used depending upon the particular situation. Though an IOP of 10 to 21 mm Hg is considered to be normal (seen in 95% of the population), various factors like the corneal thickness can affect the normal IOP measurement. So normality of IOP is always individualized.
Causes of glaucoma
Any obstruction to the outflow of aqueous humor can result in build up of excessive pressure inside the eye and damage to the optic nerve. Though a variety of factors like trauma, inflammation, steroid intake, lens-induced (e.g. a neglected advanced cataract) can cause glaucoma, in majority of the patients a definitive cause cannot be detected (Primary glaucomas). Primary glaucoma can be further classified as Primary open angle glaucoma (POAG) and Primary angle closure glaucoma (PACG). In POAG, the maximum resistance to the aqueous humor outflow is at the trabecular meshwork (Fig.1). In PACG the resistance is at the level of pupil, resulting in the forward bulging and subsequent narrowing of the angle (fig 2.). in either case the nerve damage leads to loss of peripheral vision and in advanced stages, blindness.
 
Can the optic nerve be normal in spite of high IOP?
Yes. This condition is called ocular hypertension (OHT). Some of them may require treatment to prevent the onset of glaucoma.
Can the IOP be still normal in a patient of glaucoma?
Yes. This condition is called Normal tension glaucoma (NTG).Some of them may require treatment to prevent further progression of the disease.
Can children have glaucoma?
Yes. Majority of them have Primary congenital glaucoma. A small proportion of these children may have glaucoma associated with other eye disorders or systemic diseases.
What are the symptoms of glaucoma?
There are no symptoms in case of POAG unless the disease is progressed to a very advanced stage. Patients with PACG may present with redness, pain, intolerance to light, headache. However majority of PACG patients still do not have significant symptoms in our country. Pediatric glaucoma may present with cloudiness of the cornea, intolerance to light (photophobia) and large corneas. By and large most glaucomas can be detected only on examination by an ophthalmologist.
How is peripheral vision assessed?
Peripheral vision can be assessed by a computerized machine called Automated perimeter. It is not only necessary for the diagnosis but also to detect progression of glaucoma during follow-up visits.
Can the visual field be normal in spite of having glaucoma?
Yes. This is called pre-perimetric glaucoma. Some of them can be detected by special perimetric programs called Short Wave Automated perimetry (SWAP) or the ‘Blue on yellow’ perimetry.
Who are at risk of glaucoma?
Age>40 years, family history of glaucoma, Diabetics, myopes (short sightedness), hypertensives, history of eye injury, steroid intake in any form.
What are the tests that a person suspected to have glaucoma have to undergo?
After taking a thorough history, the ophthalmologist measures the IOP preferably by a applanation tonometer. Then he/she performs Gonioscopy to assess the angle. Then after completing a thorough examination, the doctor might ask for certain investigations like, Automated perimetry, central corneal thickness measurement using an ultrasound pachymeter, photographic documentation of the optic nerve and Nerve fiber layer/optic disc evaluation with optical Coherence tomography (OCT).
How is glaucoma treated?
Many of the open angle glaucoma patients are initiated with medical treatment in the form of eye drops and rarely with tablets/intravenous drugs/oral liquid medications (temporarily). Sometimes multiple medications may be required to control the IOP. Surgery (Trabeculectomy/shunt devices) may be required for certain group of patients who do not have good IOP control with maximum tolerable medications or in persons who are unable to continue the medications for various reasons.
In PACG, a hole is made in the iris with the help of laser energy (laser iridotomy) as an initial step in the management. These patients may require additional eye drops or surgery later.
Congenital glaucoma is usually unresponsive to medical management and so surgery is often indicated.
Tips to patients
The goal of management of glaucoma is to preserve functional vision with minimum adverse impact on the quality if life. It is necessary that patients use the medications regularly and persistently. Many of the medications do have significant ocular and systemic side effects. The doctor will enquire about these during the follow-up. It is important for you to let the treating doctor know about other ailments like hypertension, cardiac problems and the medications you are on. It is necessary for the family members of the affected to get examined to rule out glaucoma. Periodic visual field examination is essential in detecting progression of the disease. People with age>40 years, myopes, diabetics should have annual eye checkups to detect and treat glaucoma at an early stage.
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