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Glaucoma
Updated: 07/01/2004
Approximately 2 million people in the United States have had the disconcerting experience of being diagnosed with glaucoma. The loss of any of the special senses, especially eyesight, can be a traumatic event. Statistics justify the concern because glaucoma is the leading cause of blindness, affecting 89,000-120,000 people.
WHAT WENT WRONG?
Generally speaking, glaucoma alludes to elevated pressure within the eye due to either hindered or obstructed outflow of aqueous humor, a clear fluid found in the anterior or front of the eye. The aqueous humor flows into the eye at the usual rate but drains too slowly. Aqueous humor, though villainized in the progression of glaucoma, performs tasks that are absolutely essential to the health of the eye. It assists in maintaining normal pressure within the eye, refracting light (the bending of light rays as they pass from air into some other, more dense substance), and providing nutrients to the inner surface of the eye.
The inability to efficiently extricate the fluid from the eye causes an increase in intraocular pressure (IOP). The tiny, delicate nerve fibers that make up the optic nerve at the back of the eye are slowly destroyed. Because the optic nerve relays visual messages from the eye to the brain, where seeing actually takes place, the health of this nerve is essential to sight. Restricting the free flow of aqueous humor, as seen by narrowing, hardening, or constriction of the exit channels, can be a purveyor of glaucoma.
SIGNS AND SYMPTOMS OF GLAUCOMA
The symptoms of glaucoma differ depending upon the type of glaucoma diagnosed. In the majority of cases, especially in early stages, there are few signs of the impending disease. Some patients are without symptoms; others complain of a loss of side vision, followed by reductions in central vision, an inability to adjust the eye to darkened rooms, difficulty focusing on close work, and a frequent need to change eyeglass prescriptions. (Because glaucoma is sometimes missed in routine eye exams, symptoms should always be reported to the examining ophthalmologist or optometrist.)
Acute or Closed-Angle Glaucoma
Glaucoma may be classified into two types: acute (angle-closure, closed-angle, or narrow-angle) and chronic or primary (open-angle or wide-angle), the former being more severe but, fortunately, less common. About 10% of glaucoma is acute or closed-angle, and 90% is chronic or primary open-angle glaucoma. Closed-angle glaucoma represents a medical emergency. Unless the individual has treatment to improve the flow of fluid, the eye can become blind in as little as 2-5 days.
No discharge from the eye is apparent in acute or narrow-angle glaucoma. Symptoms commonly reported are extreme ocular pain, severe headaches, blurred vision, swollen upper lids, eyeballs that are tender and firm, and nausea and vomiting. Dilated pupils and a shallow anterior chamber are usually evidenced upon examination.
Closed-angle glaucoma can occur if the pupil in an eye with a narrow angle between the iris and the cornea markedly dilates, allowing the iris to assume a folded configuration, capable of blocking the exit of aqueous humor from the anterior chamber. Medicinally inducing a constricted pupil, by way of eye drops, is one treatment for acute (closed-angle) glaucoma. The constricted pupil draws the iris away from the cornea, allowing a larger exit chamber for the aqueous humor.
Osmotic agents, such as urea, mannitol, and glycerol, are used to reduce IOP. Acetazolamide, a carbonic anhydrase inhibitor, can be used to reduce fluid formation. Drugs to relieve pressure, in union with either a surgical iridectomy, a small opening in the periphery of the iris, or laser treatments to produce a filtration pathway, are commonly effective. About 60% of the individuals consenting to surgery consider the procedure successful. Approximately 15% of those having surgery report a decline in the quality of life.
Argon laser surgery is an innovation in glaucoma treatment. The laser, a device that produces a high-energy beam of light, is used to make about 100 small burns in the drainage meshwork at the edge of the iris. Scientists think that the scars from these burns help stretch open the holes in the meshwork, making it easier for fluid to filter out. Usually, individuals who have this surgery continue taking some glaucoma medication afterward, although the dosage may be lowered. The positive effects of the laser treatment may wear off eventually, requiring a second or third treatment session.
For those patients whose eyesight is severely compromised, Johns Hopkins Medical Institutes have developed a high-tech video headset that is helping individuals with significant visual impairment lead more independent lives.
Primary Open-Angle Glaucoma (POAG)
Primary open-angle glaucoma (POAG) is often a bilateral condition of genetic determination that develops slowly as the drainage canals gradually become clogged. In open-angle glaucoma, the angle where the iris meets the cornea is as wide and open as it should be. The intraocular pressure rises because the "ebb and flow" of the fluid has been disrupted and drainage out of the eye is impaired. The obstruction in POAG is thought to be within the canal of Schlemm, a tiny vein at the angle of the anterior chamber of the eye that drains the aqueous humor, funneling it back into the bloodstream. (See illustration on page 544.)
Cupping of the optic disc, a small area insensitive to light on the surface of the retina, is another determinant in glaucoma progression. Pale and cupped optic discs may be observed by ophthalmoscopic examination, even when the IOP has been stabilized.
POAG may be asymptomatic, except for a gradual loss of peripheral vision over a period of years. Symptoms may be mild and intermittent, perhaps only occurring while in a darkened room, watching television or a movie. Rest or sleep may appear to rehabilitate the eye for short periods of time. Headaches, blurred vision, and a dull pain in the eyes may be experienced. Halos around lights and central blindness are late manifestations of the condition.
Pilocarpine, a meiotic substance, can usually control POAG by inducing pupil constriction. It can reduce IOP in less than 15 minutes after application and maintain the lowered pressure for about 24 hours. Pilocarpine is actually derived from jaborandi, a tropical tree that grows in South America. Spanish naturalists accredited jaborandi with the ability to treat eye diseases as early as 1648.
Other conventional treatments for POAG include epinephrine, to increase the outflow of aqueous humor, and beta-adrenergic blocking agents, to decrease aqueous humor production. Beta-blocking eye drops are not without undesirable side effects. They tend to disorganize the ratio of HDL, the beneficial cholesterol, to LDL, a form of cholesterol considered extremely harmful when in excess and oxidized. The strength of the epinephrine drops is not great enough to induce a sympathetic nervous system response, which would be contraindicated in a glaucoma patient.
Symptoms of POAG can usually be controlled with treatment, but the treatment is considered lifetime. Vision is usually not impaired permanently if glaucoma is found early and treated.
STRUCTURES OF THE EYE
To understand glaucoma, it is necessary to comprehend the responsibilities of the various structures of the eye and their placement. Recall that the iris is the colored portion of the eye that contains smooth muscle and regulates the amount of light entering the eye. The pupil is the opening in the iris through which light passes to the lens and the retina. The cornea is the part of the eye that produces the greatest amount of convergence of light and composes one-sixth of the outermost tunic, referred to as the fibrous tunic, of the eye bulb. The retina or nervous tunic is the innermost tunic of the eye. The optic nerve passes through the retina at a point called the blind spot. This is an apt description, for the blind spot contains neither rods (photoreceptors that respond to dim light) nor cones (photoreceptors that respond to bright light and allow color vision). Nerve impulses initiated by the rods and cones are passed to the bipolar cells, which in turn pass them to the ganglionic cells. The fibers of these cells pass in front of the retina forming the optic nerve, which carries the nerve impulses to the brain.
WHO IS PRONE TO GLAUCOMA?
About 1 in every 30 people in America, age 40 or over, has glaucoma. This number includes the one-half who are not aware that they have the eye disease. According to the National Eye Institute, a person with diabetes is almost twice as likely to have glaucoma as other adults. The longer an individual has diabetes, the greater his or her risk of becoming a glaucoma victim. This form of glaucoma is referred to as neovascular glaucoma.
The incidence of glaucoma is four to five times greater among African-Americans compared to Caucasian Americans. In the Caucasian American, an increase in the incidence of glaucoma occurs after the age of 50. Hypertension and a family history of glaucoma place an individual at an increased risk.
The risk of glaucoma appears greater in individuals who suffer extremes of farsightedness or nearsightedness. Farsightedness is associated with a greater risk for closed or narrow-angle glaucoma. The individual displays a shorter eye and a shorter axial length. This condition alters the angle, the spongy meshwork of tissue located at the point where the cornea and iris meet, hampering drainage of the aqueous humor. In some individuals, an anatomical peculiarity of the eye, often inherited, makes the angle unusually narrow and easily closed off.
An extremely nearsighted individual has a greater risk association with POAG. The elongated eyeball, characteristic of nearsightedness, allows a larger optic channel, with the optic nerve fiber becoming more susceptible to pressure and injury.
Glaucoma can be congenital, for example, when the ducts responsible for fluid drainage fail to form completely. Some infants are born with defects in the angle of the eye that slow the normal drainage of aqueous humor, a condition most often correctable with surgery if done early enough.
Individuals who have either Ehlers-Danlos syndrome, a disorder of connective tissue, or Marfan's syndrome, a condition characterized by elongation of the bones, appear to have a higher association with glaucoma and other eye complications.
Secondary glaucoma can manifest as a result of a predisposing event, such as eye surgery, advanced cataracts, eye injuries, eye tumors, or uveitis (eye inflammation). Correction of the primary source may allow rectification of the secondary disease as well.
CAN DRUGS CAUSE GLAUCOMA?
According to Leonard Levine, Ph.D., certain drugs can "impair the biological health of the visual system." For example, the Physicians' Desk Reference lists 94 medications that can cause glaucoma, including antihypertensives, antidepressants, and steroids, such as cortisol, which can destroy vital collagen tissue in the eye. Both herbal ephedrine and pseudoephedrine have central nervous system (CNS) stimulating properties. Ephedrine is the stronger of the two, but both are considered stronger than caffeine. The glaucomatous person should avoid these substances, particularly Ma-huang, licorice, and belladonna.
Note: Antihistamines can increase pressure within the eye. If using drugs for other conditions, always inform your doctor of an existing glaucoma condition to avoid prescribing drugs that might adversely affect the disease. Obviously, it behooves individuals relying upon prescription drugs to thoroughly acquaint themselves with the side effects.
The use of certain medications that inhibit cholinergic response has been linked to a higher incidence of glaucoma. An anticholinergic drug blocks acetylcholine receptors, resulting in the inhibition of parasympathetic nerve impulses. This action would make stronger the sympathetic nervous system, an action that could dilate the pupil and relax the iris sphincter. Dilation of the pupil could make smaller the passage between the iris and cornea, complicating the exit of the aqueous humor.
DO ALLERGIES INFLUENCE GLAUCOMA?
Individuals who suffer either food or environmental allergies appear to be at a higher risk for glaucoma. Both causative and therapeutic factors appear to link allergies and glaucoma. Persons with nonresponsive or refractory glaucoma are occasionally asked to consult an allergist, in an attempt to lessen the endogenous stress load. Greater acceptance of the allergy/glaucoma hypothesis adds another dimension to treatment.
CALCIUM--PROS AND CONS
Calcium excesses can be redistributed in the body to soft tissues, contributing to the risk of glaucoma. The more soluble forms of calcium supplementation are usually well absorbed and utilized, such as calcium citrate, calcium bis-glycinate, or microcrystalline hydroxyapatite. The problem with soft tissue damage due to calcium deposition may be more appropriately seen as a consequence of calcium shortages. When calcium levels are in short supply, the parathyroid hormone participates in a cascade that eventually asks the bones to give up a share of their calcium stores. The host loses on two fronts: (1) too many withdrawals can eventually weaken the skeletal system and (2) the release of calcium from the skeleton is not well regulated. Excesses of calcium can tie up in soft tissues, exacerbating arthritis, arteriosclerosis, kidney stones, and glaucoma. Recall that vitamin K assists in keeping calcium in the bone and not in soft tissue. Considering this, adequate amounts of dietary calcium are absolutely essential to prohibit the activity of the parathyroid gland and the subsequent calcium withdrawal from the skeletal frame.
ODDS AND ENDS
The herb bloodroot (Sanguinaria canadensis) may contribute to glaucoma. Toothpastes occasionally contain bloodroot, because the herb is a strong adjunctive component contributing to gum health. Because toothpastes and mouthwashes are not ingested, the amount of bloodroot entering the system would be minimal, but individuals concerned about glaucoma should be aware of the caveat surrounding bloodroot.
Most vitamins and minerals are nonproblematic for the individual with glaucoma, but patients should restrict their intake of niacin to not more than 200 mg daily. |