Eye disease - Glaucoma medication and surgery

Eye disease - Glaucoma medication and surgery:

Glaucoma medications (eyedrops)

Beta-adrenergic antagonists act against, or block, adrenalin-like substances. These drops work in the treatment of glaucoma by reducing the production of the aqueous humor. For years, they were the gold standard (to which other agents are compared) for treating glaucoma. A few of these medications are timolol (Timoptic), levobunolol (Betagan), carteolol (Ocupress), and metipranolol (Optipranolol).

Used once or twice daily, these drops are very effective. However, side effects, such as the worsening of asthma oremphysema, bradycardia (slow heart rate), low blood pressure, fatigue, andimpotence prohibit their use in some patients. Betaxolol (Betoptic) is a beta-adrenergic antagonist that is more selective in working just on the eye and, therefore, carries less risk of heart (cardiac) or lung (pulmonary) side effects than other drops of this type.

Prostaglandin analogs are similar in chemical structure to the body's prostaglandins. Prostaglandins are hormone-like substances that are involved in a wide range of functions throughout the body. These drops work in glaucoma by increasing the outflow (drainage) of fluid from the eye.

The prostaglandin analogs have replacedbeta blockers as the most commonly prescribed drops for glaucoma. They can be used just once a day. This class of medications has fewer systemic (involving the rest of the body) side effects than beta blockers, but can change the color of the iris as well as thicken and darken the eyelashes. These drops are also more likely to cause redness of the eyes than some other classes of eyedrops. In some patients, they may also cause inflammation inside the eye. Examples of these medications include latanoprost(Xalatan), travoprost (Travatan), andbimatoprost (Lumigan).

Adrenergic agonists are a type of drops that act like adrenalin. They work in glaucoma by both reducing the production of fluid by the eye and increasing its outflow (drainage). The most popular adrenergic agonist is brimonidine(Alphagan). However, there is at least a 12% risk of significant local (eye) allergicreactions. Other members of this class of drops include epinephrine, dipivefrin (Propine) and apraclonidine (Iopidine).

Carbonic anhydrase inhibitors work in glaucoma by reducing the production of fluid in the eye. Eyedrop forms of this type of medication include dorzolamide(Trusopt) and brinzolamide (Azopt). They are used two or three times daily. Carbonic anhydrase inhibitors may also be used as pills (systemically) to remove fluid from the body, including the eye. Oral forms of these medications used for glaucoma include acetazolamide (Diamox) andmethazolamide (Neptazane). Their use in this condition, however, is limited due to their systemic (throughout the body) side effects, including reduction of body potassium, kidney stones, numbness or tingling sensations in the arms and legs,fatigue, and nausea.

Parasympathomimetic agents, which are also called miotics because they narrow (constrict) the pupils, act by opposing adrenalin-like substances. They work in glaucoma by increasing the aqueous outflow from the eye.

The parasympathomimetics were used for many years to treat glaucoma, but because of the appearance of beta blockers and prostaglandins, they are now used infrequently because they need to be used three to four times a day and produce side effects in the eye. These side effects include a small pupil, blurred vision, an aching brow, and an increased risk of retinal detachment. Currently,pilocarpine is used primarily to keep the pupil small in patients with a particular iris configuration (plateau iris) or in patients with a narrow angle prior to laser iridotomy. (See the section above on angle-closure glaucoma.)

Osmotic agents are an additional class of medications used to treat sudden (acute) forms of glaucoma where the eye pressure remains extremely high despite other treatments. These medications include isosorbide (Ismotic, given by mouth) and mannitol (Osmitrol, given through the veins). These medications must be used cautiously as they have significant side effects, including nausea, fluid accumulation in the heart and/orlungs (congestive heart failure and/orpulmonary edema), bleeding in the brain, and kidney problems. Their use is prohibited in patients with uncontrolleddiabetes, heart, kidney, or liverproblems.

Ophthalmologists often prescribe an eyedrop containing more than one class of drug to patients who require more than one type of drug for control of their glaucoma. This simplifies the taking of drops by the patient. The most common example of this is the combination of timolol and dorzolamide in the same drop (Cosopt).

Several new classes of glaucoma drops are currently under development or awaiting FDA approval. Althoughmarijuana use has been shown to reduce intraocular pressure, eyedrops are available which accomplish the same purpose with greater efficacy and less systemic risk.

Glaucoma surgery or laser

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There are several forms of laser therapy for glaucoma. Laser iridotomy (see the section above on angle-closure glaucoma) involves making a hole in the colored part of the eye (iris) to allow fluid to drain normally in eyes with narrow or closed angles. Laser trabeculoplasty is a laser procedure performed only in eyes with open angles. Laser trabeculoplasty does not cure glaucoma, but may be done instead of increasing the number of different eyedrops, or may be recommended when a patient is already using multiple eyedrops (maximal medical therapy). In some cases, it is used as the initial or primary therapy for open-angle glaucoma. This procedure is a quick, relatively painless, and safe method of lowering the intraocular pressure. With the eye numbed by anesthetic drops, the laser treatment is applied through a mirrored contact lens to the angle of the eye. Microscopic laser burns to the angle allow fluid to better exit the drainage channels.

Laser trabeculoplasty is often done in two sessions, weeks or months apart. Unfortunately, the improved drainage as a result of the treatment may last only about two years, by which time the drainage channels tend to clog again. There are different types of laser trabeculoplasty including argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT). ALT is generally not repeated after the second session due to the formation of scar tissue in the angle. SLT is less likely to produce scarring in the angle, so, theoretically, it can be repeated multiple times. However, the likelihood of success with additional treatments when prior attempts have failed is low. Thus, the options for the patient at that time are to increase the use of eyedrops or proceed to surgery.

Laser cyclo-ablation (also known ciliary body destruction, cyclophotocoagulation or cyclocryopexy) is another form of laser treatment generally reserved for patients with severe forms of glaucoma with poor visual potential. This procedure involves applying laser burns or freezing to the part of the eye that makes the aqueous fluid (ciliary body). This therapy destroys the cells that make the fluid, thereby reducing the eye pressure. This type of laser is typically performed after other more traditional therapies have failed.

Glaucoma surgery

Trabeculectomy is a delicate microsurgical procedure used to treat glaucoma. In this operation, a small piece of the clogged trabecular meshwork is removed to create an opening and a new drainage pathway is made for the fluid to exit the eye. As part of this new drainage system, a tiny collecting bag is created from conjunctival tissue. (Theconjunctiva is the clear covering over the white of the eye.) This bag is called a "filtering bleb" and looks like a cystic raised area that is at the top part of the eye under the upper lid. The new drainage system allows fluid to leave the eye, enter the bag/bleb, and then pass into the capillary blood circulation (thereby lowering the eye pressure). Trabeculectomy is the most commonly performed glaucoma surgery. If successful, it is the most effective means of lowering the eye pressure.

Aqueous shunt devices (glaucoma implants or tubes) are artificial drainage devices used to lower the eye pressure. They are essentially plastic microscopic tubes attached to a plastic reservoir. The reservoir (or plate) is placed beneath the conjunctival tissue. The actual tube (which extends from the reservoir) is placed inside the eye to create a new pathway for fluid to exit the eye. This fluid collects within the reservoir beneath the conjunctiva creating a filtering bleb. This procedure may be performed as an alternative to trabeculectomy in patients with certain types of glaucoma. Mini shunts without a reservoir are also used to improve safety and reduce the post surgery chance of pressures that are too low.

Viscocanalostomy, canaloplasty, and the trabecutome are alternative surgical procedures used to lower eye pressure. These procedures are directed at creating openings in the trabecular meshwork, the drainage ring in the wall of the angle of the eye. These surgeries are less invasive than trabeculectomy and aqueous shunt surgery,but may not lower pressure as much.

The surgeon sometimes creates other types of drainage systems. While glaucoma surgery is often effective, complications, such as infection or bleeding, are possible. Accordingly, surgery is usually reserved for cases that cannot otherwise be controlled.

Can glaucoma be prevented?

Primary open-angle glaucoma cannot be prevented, given our current state of knowledge. However the optic-nerve damage and visual loss resulting from glaucoma can be prevented by earlier diagnosis, effective treatment, and compliance with treatment.

Secondary types of glaucoma can often be prevented by avoidance of trauma to the eye and prompt treatment of eye inflammation and other diseases of the eye or body that may cause secondary forms of glaucoma.

Most cases of visual loss from angle-closure glaucomas can be prevented by the appropriate use of laser iridotomy in eyes at risk for the development of acute or chronic angle-closure glaucoma.

What is in the future for glaucoma?

New eyedrops will continue to become available for the treatment of glaucoma. Some drops will be new classes of agents. Other drops will combine some already existing agents into one bottle to achieve an additive effect and to make it easier and more economical for patients to take their medication.

Although lowering intraocular pressure is still the primary method of treating glaucoma, experts see the disease as more a neurological condition than an eye disorder. Researchers are investigating the therapeutic role of neuroprotection of the optic nerve, especially in patients who seem to be having progressive nerve damage and visual field loss despite relatively normal intraocular pressures. Animal models have shown that certain chemical mediators can reduce injury or death of nerve cells. Proving such a benefit for the human optic nerve, however, is more difficult because, for one thing, biopsy or tissue specimens are not readily available. Nevertheless, if any of these mediators in eyedrops can be shown to protect the human optic nerve from glaucomatous damage, this would be a wonderful advance in preventing blindness.

In other studies, new surgical methods are being evaluated to lower the intraocular pressure more safely without significant risk of damage to the eye or loss of vision.

Finally, increased efforts to enhance public awareness of glaucoma, national free screenings for those individuals at risk, earlier diagnosis and treatment and better compliance with treatment are our best hopes to reduce vision loss from glaucoma.