Glaucoma

What is glaucoma

Glaucoma is a disease of the major nerve of vision, called the optic nerve. The optic nerve receives light-generated nerve impulses from the retina and transmits these to the brain, where we recognize those electrical signals as vision. Glaucoma is characterized by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.

Glaucoma is usually, but not always, associated with elevated pressure in the eye (intraocular pressure IOP). Generally, it is this elevated eye pressure that leads to damage of the eye (optic) nerve. In some cases, glaucoma may occur in the presence of normal eye pressure. This form of glaucoma is believed to be caused by poor regulation of blood flow to the optic nerve.

How common is glaucoma                                                                                                                       Worldwide, glaucoma is the leading cause of irreversible blindness. In fact, as many as 6 million individuals are blind in both eyes from this disease. In the United States alone, according to one estimate, over 3 million people have glaucoma. As many as half of the individuals with glaucoma, however, may not know that they have the disease. The reason they are unaware is that glaucoma initially causes no symptoms, and the subsequent loss of side vision (peripheral vision) is usually not recognized.

What causes glaucoma

Elevated pressure in the eye is the main factor leading to glaucomatous damage to the eye (optic) nerve. Glaucoma with normal intraocular pressure is discussed below in the section on the different types of glaucoma. The optic nerve, which is located in back of the eye, is the main visual nerve for the eye. This nerve transmits the images we see back to the brain for interpretation. The eye is firm and round, like a basketball. Its tone and shape are maintained by a pressure within the eye (the intraocular pressure), which normally ranges between 8 mm and 22 mm (millimeters) of mercury. When the pressure is too low, the eye becomes softer, while an elevated pressure causes the eye to become harder. The optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged.

The front of the eye is filled with a clear fluid called the aqueous humor, which provides nourishment to the structures in the front of the eye. This fluid is produced constantly by the ciliary body, which surrounds the lens of the eye. The aqueous humor then flows through the pupil and leaves the eye through tiny channels called the trabecular meshwork. These channels are located at what is called the drainage angle of the eye. This angle is where the clear cornea, which covers the front of the eye, attaches to the base (root or periphery) of the iris, which is the colored part of the eye. The cornea covers the iris and the pupil, which are in front of the lens. The pupil is the small, round, black-appearing opening in the center of the iris. Light passes through the pupil, on through the lens, and to the retina at the back of the eye. Please see the figure, which is a diagram that shows the drainage angle of the eye.

 How often should someone be checked (screened) for glaucoma

Age 20-29: Individuals of African descent or with a family history of glaucoma should have an eye examination every three to five years. Others should have an eye exam at least once during this period.

Age 30-39: Individuals of African descent or with a family history of glaucoma should have an eye examination every two to four years. Others should have an eye exam at least twice during this period.

Age 40-64: Individuals should have an eye examination every two to four years.

Age 65 or older: Individuals should have an eye examination every one to two years

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These routine screening eye examinations are mandatory since glaucoma usually causes no symptoms (asymptomatic) in its early stages. Once damage to the optic nerve has occurred, it cannot be reversed. Thus, in order to preserve vision, glaucoma must be diagnosed early and followed regularly. Patients with glaucoma need to be aware that it is a lifelong disease. Compliance with scheduled visits to the eye doctor and with prescribed medication regimens offers the best chance for maintaining vision.

What is the treatment for glaucoma

General approach

Although nerve damage and visual loss from glaucoma cannot usually be reversed, glaucoma is a disease that can generally be controlled. That is, treatment can make the intraocular pressure normal and, therefore, prevent or retard further nerve damage and visual loss. Treatment may involve the use of eyedrops, pills (rarely), laser ,or surgery.

Eyedrops are usually used first in treating most types of open-angle glaucoma. Other than that, laser or surgery is sometimes the first choice of treatment. One or more types of eyedrops may have to be taken up to several times a day to lower intraocular pressure. These drops work either by reducing the production of the aqueous fluid (shutting the faucet) or by increasing the drainage of the fluid out of the eye. Each type of therapy has its benefits and potential complications.

Drugs that can be used can be classified according few groups:

Systemic Ocular Hypertensive

a)Carbonic anhydrase inhibitors:

-Acetazolamide

-Ethoxzolamide

-Methazolamide

b)Hyper Osmotic Agents:

-Mannitol 20% injection

-Oral glycerine with lemon juice

Local Ocular Hypertensive

a)Parasympathomometics:

-Pilocarpine

b)Beta Blockers:

-Bexatolol

-Timolol

c)Sympathomimetics:

-Epinephrine

d)Topical Carbonic anhydrase inhibitors:

-Dorzolamide HCL

..and this is a rare medicine that not usually used by doctors.This drug only used when all the medicine above failed during glaucoma treatment.The drug is Ecothiophate .Echothiophate (Phospholine) is a parasympathomimetic and a phosphorothioate. It is an acetylcholinesterase inhibitor.It is used as an ocular antihypertensive in the treatment of chronic glaucoma and, in some cases, accommodative esotropia.It is actually a organophosphorus compound which is a poison to human  body.So don't simply take it.Discuss with your doctor first. Echothiophate binds irreversibly to cholinesterase. Because of the very slow rate at which echothiophate is hydrolyzed by cholinesterase, its effects can last a week or more. Adverse effects include muscle spasm and other systemic effects.This drug can be used as the last choice in glaucoma before it causes permanent blindness.  

 What are glaucoma symptoms and signs

Patients with open-angle glaucoma and chronic angle-closure glaucoma in general have no symptoms early in the course of the disease. Visual field loss (side vision loss) is not a symptom until late in the course of the disease. Rarely patients with fluctuating levels of intra-ocular pressure may have haziness of vision and see haloes around lights, especially in the morning.

On the other hand, the symptoms of acute angle-closure are often extremely dramatic with the rapid onset of severe eye  pain,headache,nausea, and vomiting and visual blurring.Occasionally, the nausea and vomiting exceed the ocular symptoms to the extent that an ocular cause is not contemplated.

The eyes of patients with open-angle glaucoma or chronic angle-closure glaucoma may appear normal in the mirror or to family or friends. Some patients get slightly red eyes from the chronic use of eyedrops. The ophthalmologist, on examining the patient, may find elevated intraocular pressure, optic-nerve abnormalities, or visual field loss in addition to other less common signs.

The eyes of patients with acute angle-closure glaucoma will appear red, and the pupil of the eye may be large and nonreactive to light. The cornea may appear cloudy to the naked eye. The ophthalmologist will typically find decreased visual acuity, corneal swelling, highly elevated intraocular pressure, and a closed drainage angle.

How is glaucoma diagnosed

An eye doctor (ophthalmologist) can usually detect those individuals who are at risk for glaucoma (because of, for example, a narrow drainage angle or increased intraocular pressure) before nerve damage occurs. The doctor also can diagnose patients who already have glaucoma by observing their nerve damage or visual field loss. The following tests, all of which are painless, may be part of this evaluation.

·         Tonometry determines the pressure in the eye by measuring the tone or firmness of its surface. Several types of tonometers are available for this test, the most common being the applanation tonometer. After the eye has been numbed with anesthetic eyedrops, the tonometer's sensor is placed against the front surface of the eye. The firmer the tone of the surface of the eye, the higher the pressure reading.

·         Pachymetry is a relatively new test being used for the diagnosis and treatment of glaucoma. Pachymetry determines the thickness of the cornea. After the eye has been numbed with anesthetic eyedrops, the pachymeter tip is touched lightly to the front surface of the eye (cornea). Recent studies have shown that corneal thickness can affect the measurement of intraocular pressure. Thicker corneas may give falsely high eye pressure readings and thinner corneas may give falsely low pressure readings. Furthermore, thin corneas may be an additional risk factor for glaucoma.

·         Gonioscopy is done by numbing the eye with anesthetic drops and placing a special type of contact lens with mirrors inside the eye. The mirrors enable the doctor to view the interior of the eye from different directions. The purpose of this test is to examine the drainage angle and drainage area of the eye. In this procedure, the doctor can determine whether the angle is open or narrow and find any other abnormalities within the angle area. As indicated earlier, individuals with narrow angles have an increased risk for a sudden closure of the angle, which can cause an acute angle-closure glaucomatous attack. Gonioscopy can also determine if anything, such as abnormal blood vessels, might be blocking the drainage of the aqueous fluid out of the eye.

·         Ophthalmoscopy is an examination in which the doctor uses a handheld device to look directly through the pupil (the opening in the colored iris) into the eye. This procedure is done to examine the optic nerve (seen as the optic disc) at the back of the eye. Damage to the optic nerve, called cupping of the disc, can be detected in this way. Cupping, which is an indentation of the optic disc, can be caused by increased intraocular pressure. Additionally, a pale color of the nerve can suggest damage to the nerve from poor blood flow or increased intraocular pressure. Special cameras can be used to take photographs of the optic nerve to compare changes over time.

·         Visual Field testing actually maps the visual fields to detect any early (or late) signs of glaucomatous damage to the optic nerve. This test can be grossly done by having the patient look straight ahead with one eye covered and count the fingers shown by the examiner from the side. More typically, however, visual fields are measured by a computerized assessment. For this procedure, one eye is covered and the patient places his or her chin in a type of bowl. Then, when the patient sees lights of various intensities and at different locations, he or she pushes a button. This process produces a computerized map of the visual field, outlining the areas where the eye can or cannot see.

Other, more sophisticated tests may also be employed. All of these tests need to be repeated at intervals to assess the progress of the disease and the effect of the treatment.

TYPES OF GLAUCOMA

TYPES OF GLAUCOMA
Type	Cause/Effect	Symptoms	Comments
Chronic Open Angle Glaucoma	Gradual blockage of drainage channel Pressure builds slowly	Gradual loss of side vision Affects side vision first	This type of glaucoma progresses very slowly and is a lifelong condition.
Acute Closed Angle Glaucoma	Total blockage of drainage channel Sudden increase in pressure	Nausea Blurred vision Severe pain Halos around lights	This condition constitutes a medical emergency, as permanent blindness occurs rapidly without immediate treatment.
Secondary Glaucoma	Injury, infection, tumors, drugs, or inflammation cause scar tissue which blocks the drainage channel	Gradual loss of side vision Affects side vision first	This form of glaucoma may progress slowly, as in cases of chronic glaucoma.
Congenital Glaucoma	Fluid drainage system abnormal at birth	Enlarged eyes Cloudy cornea Light sensitivity Excessive tearing	This condition must be treated soon after birth if vision is to be saved.