Glaucoma is a disease affecting the visual acuity i.e the ability to see. It is the second leading cause of blindness (after cataract) and the most significant cause of irreversible blindness globally. At present, 8 million people are bilaterally blind due to glaucoma. As per the estimate suggested by the International Agency for the Prevention of blindness, 80 million people will suffer from glaucoma by the year 2020.
It is necessary to understand the basic human eye anatomy in order to comprehend the pathophysiology involved in the disease. The human eye is a specialized visual organ which consists of a complex of structures. Iris is the colored part of the eye. Cornea is the dome covering the iris. Pupil is the black circular opening in the iris that lets the light in. Just behind the iris and the pupil lies the lens which helps focus light on the back of the eye. The inner lining of the eye contains special light-sensing cells known as retinal cells. When we see an object, the light passes through the pupil and lens to the back of the eye where retinal cells convert light into electrical impulses. These impulses are carried to the brain by the optic nerve. This is how the object is visualized and interpreted by the human eye. Glaucoma is characterized by the degeneration of the optic nerve, hence, causing impaired visual perception.
But what damages the optic nerve? The answer to this question lies in the concept of aqueous humor and Intraocular pressure (IOP). Aqueous humor is a clear fluid present in the front part of the eye which nourishes the structures within the eye. This fluid is constantly produced by the ciliary body, which surrounds the lens of the eye. The aqueous humor then passes through the pupil and leaves the eye through tiny drainage channels, scientifically termed as trabecular meshwork. These channels are located at something called as drainage angle of the eye (the angle where cornea attaches to the base of the iris). The adequate production and effective drainage of the aqueous humor is necessary to maintain the normal pressure within the eye, medically known as IOP. In glaucoma, there is elevated IOP which causes irreversible degeneration of optic nerve, hence, leading to visual impairment, which if left untreated can lead to blindness.
Based on the underlying mechanism and patency of the drainage angle of the eye, glaucoma can be of several types.
Glaucoma is often termed as “the sneak thief of sight” as it is usually indiscernible in the initial stages and is almost invariably diagnosed in late stages when it has progressed substantially to cause irreversible damage.
The patients with glaucoma are unable to see the objects within their particular field of vision or the visibility is limited. A point of significance is that initially there is loss of peripheral vision which is usually left unnoticed by the patient, thus making the disease progress to its final stage which is marked by loss of central vision too. There are appearances of blind spots which makes it difficult for an individual to lead a normal life. Activities such as driving become cumbersome as the individual is able to visualize the street ahead but finds it difficult to visualize the people walking on the sidewalks. People also complain of difficulty in adjusting to changes in light such as entering a dark room immediately after outdoors. People with glaucoma also finds it difficult to perceive obstacles such as steps, etc.
Evident clinical findings such as red eye are rare and can be seen in cases of secondary glaucoma caused by recent trauma to the eye. Occasionally, there may be a sudden rise in IOP leading to symptoms such as headache, pain in the eye and presence of halos around the eyes.
Although everyone is at risk of developing glaucoma, there are certain risk factors that predispose an individual to it. The significant risk factors are:
Certain eye conditions such as nearsightedness and farsightedness also increase the risk of developing glaucoma.
If you are experiencing blurring of vision, have a recent history of trauma to the eye, can see blind spots in your field of vision or are unable to see peripheral objects, these along with a positive family history raises a strong suspicion of glaucoma and you must visit your eye doctor soon.
As described earlier, the most important cause of glaucoma is raised IOP which can be due to an abnormality in production or drainage of aqueous humor, or both. It may be impossible to prevent glaucoma, but steps can be taken to detect glaucoma at an early stage and hence, prevent its debilitating consequences.
An eye specialist called as Ophthalmologist must be sought if suspecting visual disturbances.
An ophthalmologist can diagnose glaucoma even before it has shown its first symptom. The various diagnostic modalities used by an ophthalmologist are listed below.
Once the diagnostic workup is done, the ophthalmologist offers appropriate treatment to the individual.
Various drugs have been advocated in the treatment of glaucoma.
Beta-adrenergic antagonists are administered as eye drops. This class of drug reduces the secretion of aqueous humor, thus normalizing the IOP. These include medications such as timolol, levobunolol, carteolol, and metipranolol.
But, due to some major cardiac side effects (reduced heart rate and low blood pressure), beta-adrenergic antagonists have been replaced with another class of drug known as prostaglandin analogue. This group of drug causes effective drainage of aqueous humor, thus relieving the raised IOP. Prostaglandin analogues include latanoprost, travoprost, bimatoprost, and tafluprost.
Another class of drug known as adrenergic agonists helps in glaucoma by both, reduction in production of aqueous humor and facilitating its effective drainage. The most popular adrenergic agonist is brimonidine.
Osmotic agents are another important group of drugs which are used in acute cases of glaucoma but must be used cautiously as they can cause major side effects such as nausea, fluid accumulation in heart and lungs, bleeding in the brain and kidney problems. Examples of osmotic agents include isosorbide (ismotic, administered orally) and mannitol (Osmitrol).
There are various forms of laser therapy useful in the treatment of glaucoma.
Laser iridotomy is done in closed-angle glaucoma. In this procedure, a hole is made in the iris to drain out the excessive aqueous humor.
Laser trabeculoplasty is used as an adjuvant along with the medications. In this procedure, laser is applied through a mirrored contact lens in the corners of the eye causing minor laser burns in them, thus causing the drainage of fluid.
Laser cyclo-ablation is used when all other treatment modalities have failed to produce outcomes. In this procedure, the aqueous humor producing cells known as ciliary body are destroyed by laser application.
In severe cases of glaucoma, surgical intervention might be needed.
Trabeculectomy is the most commonly used surgery and produces the most significant reduction in IOP. It involves removal of a small piece of the clogged trabecular meshwork in order to facilitate fluid drainage. A small collecting bag, medically termed as “filtering bleb” is created in the conjunctiva to collect the drained fluid and pass it on to the blood.
Aqueous shunt devices (glaucoma implants or tubes) involve the use of artificial devices such as a plastic tube inside the eye to drain the excess fluid and a plastic reservoir beneath the conjunctiva to collect the excess fluid.
However, it must be kept in mind that there is no cure for glaucoma as it causes an irreversible damage to the optic nerve. Hence, the goal of therapy is directed at arresting the damage and preventing blindness.
There are various over-the-counter medications available to treat glaucoma. Trade names of the commonly used medications are listed below.
Medicines that reduce the production of aqueous humor
Medicines that facilitate the drainage of fluid
Guide to take glaucoma medications
Although allopathic modalities are the safest methods to combat glaucoma, there is no denying the importance of alternative medicine in the treatment of glaucoma.
Herbal remedies: Various herbal remedies have been used in the treatment of glaucoma.
Good nutrition can play a vital role. Nutrients such as Vitamin E, C and A as well as fatty acids and minerals can help protect the optic nerve.
Lastly, regular exercise and yoga are also beneficial in glaucoma.
At this point, it is important to emphasize that the damage caused by glaucoma cannot be reversed. Hence, the health experts strongly recommend that awareness of glaucoma is necessary on a global level. Every individual must be aware of all the risk factors of glaucoma and must take preventive measures in order to facilitate early detection of glaucoma. People must realize that glaucoma is not just a disorder affecting the physical well-being of the individuals, but it also has major psychological implications associated with blindness, thus violating the independence of leading a normal healthy life.
Academician, Shelly's rich experience as an academic and research professional speaks volume. Her fields of interest are genetics, biotechnology and drug research. Shelly keeps herself abreast with latest scientific researches all around the globe and loves to write about the same.
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