What is Glaucoma?
Glaucoma is a term used to describe a group of diseases of the eye characterized by progressive and irreversible damage to the optic nerve (nerve of the eye responsible for vision) and which if untreated can lead to blindness. Though raised pressure of the eye (pressure maintained by fluid in the eye) is an important risk factor, a few individuals can develop glaucoma even with normal pressure of the eye.
Types of glaucoma
Glaucoma can be classified into four basic types based on the event initiating damage. They include
The disease burden
Glaucoma is the second leading cause of blindness in the world accounting for upto 8% of total blindness. In India , glaucoma is the leading cause of irreversible blindness with atleast 12 million people affected and nearly 1.2 million people blind from the disease. More than 90 percent of cases of glaucoma remain undiagnosed in the community.
The content of this module has been validated by Dr Tanuj Dada, RP Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi on 17/3/2015.
Primary open angle glaucoma presents as a chronic disease and usually has no symptoms in its early stages and the vision remains normal. As the optic nerve is more damaged, peripheral (side) vision is lost progressively till only the central vision is left resulting in tunnel vision (as if looking through the end of a narrow tunnel).
Primary angle closure glaucoma can present either as a chronic disease as said above or as an acute attack. The symptoms of an acute attack include sudden blurring of vision, pain in the eyes, headache, nausea, vomiting and seeing rainbow like rings around lights.
Secondary glaucoma result from other predisposing conditions of the eye or body and may be asymptomatic or present with the symptoms of predisposing conditions like trauma, uveitis (inflammation of the middle layer of the eye) and so on.
Developmental glaucoma affects children. It can present with large eyes, whitening of the cornea (front part of the eye), excessive tearing, sensitivity to light (closure of eyes on light exposure), jerky movements of the eyes and squinting of the eyes (condition in which one of the eyes turns inwards or outwards as the other eye looks forward).
Glaucoma is of multifactorial etiology and raised pressure of the eye is the most important among them and the only modifiable risk factor. As already mentioned, though raised eye pressure is a risk factor, glaucoma can occur even in individuals with normal pressure. The most common abnormality of the eye leading to raised pressure of the eye is an abnormal drainage angle (angle is a structure of the eye where the fluid produced inside the eye exits). This abnormality of the angle causes obstruction to the flow of the fluid which accumulates inside the eye and causes pressure on the optic nerve leading to progressive damage and loss of vision.
Who is at risk?
Although glaucoma can affect anyone in any age group, some individuals are at higher risk than others. Common risk factors include elevated pressure of the eye, age over 40 years, individuals with a family history of glaucoma, use of steroid-containing medications (eye drops/ pills/inhalers/ skin creams), those with higher refractive error (power) of the eyes , patients with history of blunt eye injury, history of hypertension and diabetes.
The diagnosis of glaucoma is based on a review of history pertaining to the above said symptoms and risk factors, a comprehensive eye examination and several tests to support the diagnosis. Tests which are used in the diagnosis of glaucoma include – measurement of pressure of the eye using an instrument called tonometer, a look at the optic nerve head with an ophthalmoscope or stereoscopic evaluation on the slit lamp with a 90D lens, evaluation of the drainage system – anterior chamber angle of eye using an instrument called the gonioscope, testing of field of vision of each eye using an instrument known as the perimeter, measurement of thickness of cornea with a pachymeter. Specialized tests done for early detection of glaucoma and follow up include photography of the optic nerve , optical coherence tomography, scanning laser polarimetry and confocal laser scanning ophthalmoscope.
Glaucoma management aims at maintaining the vision related quality of life of the patient throughout his/her lifetime with minimal possible medications at a sustainable cost. The treatment helps to control the disease process so that further damage to the optic nerve can be prevented. There is no cure for glaucoma and treatment cannot restore visual loss but only prevent further deterioration. In the current day practice, reduction of pressure of the eye remains the only modifiable risk factor. Hence the management of glaucoma revolves around the effective control of pressure of the eye with three modalities :
Medical therapy with ocular hypotensive medications, laser therapy and glaucoma surgery.
The most important consideration in the management is that once a diagnosis of glaucoma is made, treatment and regular follow-ups are required lifelong.
Medical management remains the first line of treatment in most of the glaucomas. These medications either decrease the secretion of fluid of the eye or increase its exit through the drainage angle. These agents are available as either eye drops or pills. Currently, following medicines are available to control pressure of the eye. They include- prostaglandin analogues, beta adrenergic blockers, alpha adrenergic agonists, carbonic anhydrase inhibitors, parasympathomimetic agents and hyperosmotic agents.
Patients who are prescribed with these eye drops have to observe the following precautions.
The initial management of primary angle closure disease is laser iridotomy (making a small hole in the iris to bypass pupillary block) usually done with a YAG laser. Laser trabeculoplasty can be performed to lower IOP in patients with Primary open angle glaucoma.
Surgical therapy is required in patients who are intolerant to medical therapy or in whom medical therapy is considered ineffective to control pressure of the eye. Surgical therapy like the medical therapy does not improve the lost visual function, but help to prevent further damage to the optic nerve. Some cases may require continuation of eye drops after surgery for better control of pressure of the eye.
Early diagnosis and treatment is the best way to prevent vision loss from glaucoma. Prevention is only possible with regular life long screening for early detection of glaucoma , done by a qualified ophthalmologist.
Measures advocated at individual level include –
With regular treatment and follow up, most patients can preserve a good quality of vision throughout their lifetime.