Glaucoma

Glaucoma is an eye disorder that is more prevalent in people older than 40 years of age. It is characterized by increased intraocular pressure and can develop into complete blindness in later stages. Glaucoma is the third most common age-related eye disease and the second leading cause of blindness in adults in the United States. There is no cure for glaucoma, but the disease can be controlled. Once glaucoma occurs, the patient will always have it and must follow a treatment regimen to maintain stable intraocular eye pressures.

  • What is glaucoma?
  • What are the causes of glaucoma?
  • What are the stages of glaucoma development?
  • What are the risk factors of glaucoma?
  • How is glaucoma diagnosed?
  • What are the signs and symptoms of glaucoma?
  • What are the types of glaucoma?
  • What are the treatment options for glaucoma?
  • What medicines are prescribed for glaucoma?
  • What are the surgical procedures for glaucoma?
  • Patient Teachings

Eye with Glaucoma

What is glaucoma?

Glaucoma refers to a group of diseases characterized by abnormal pressure within the eyeball. This pressure is called the intraocular pressure (IOP). An increase in the IOP (normal is  10-21 mm Hg) will cause damage to the cells of the optic nerve, the structure responsible for transmitting visual information from the eye to the brain. Previously, increased intraocular pressure is the main reason for the occurrence of glaucoma. Though the condition will definitely damage the optic nerve, not all cases of glaucoma are linked to increased intraocular pressure. Some of these cases are due to an abnormal or poor regulation of blood flow to the optic nerve and these patients will have a normal intraocular pressure.

What are the causes of glaucoma?

There are two accepted theories regarding how increased IOP damages the optic nerve in glaucoma.

  1. Direct mechanical theory suggests that high IOP damages the retinal layer as it passes through the optic nerve head.
  2. Indirect ischemic theory suggests that high IOP compresses the microcirculation in the optic nerve head, resulting in cell injury and death.

Some glaucomas appear as exclusively mechanical, and some are exclusively ischemic types. Typically, most cases are a combination of both. Regardless of the cause of damage, glaucomatous changes typically evolve through clearly discernible stages.

What are the stages of glaucoma development?

The following chart illustrates the different stages of glaucoma development:

 

Stages of Glaucoma

Stages of Glaucoma

 

What are the risk factors of glaucoma?

  • Family history of glaucoma
  • Thin cornea
  • African American race
  • Older age
  • Diabetes mellitus
  • Cardiovascular disease
  • Migraine syndromes
  • Nearsightedness (myopia)
  • Eye trauma
  • Prolonged use of topical or systemic corticosteroids

How is glaucoma diagnosed?

There are four ways to diagnose glaucoma and each test or procedure will help the physician arrive to a final diagnosis:

  • Tonometry to measure the IOP
    • Applanation tonometry uses a tiny instrument to apply pressure to the anesthetized cornea.
    • Noncontact tonometry is performed with a tonometer mounted on a slit-lamp microscope using a warm puff of air that flattens an anesthetized area of the cornea to obtain a pressure reading.
    • In contact tonometry, the instrument is placed directly on the anesthetized cornea to measure eye pressure.
    • Tonometry is not adequate to detect glaucoma alone
  • Ophthalmoscopy to inspect the optic nerve.
    • The optic nerve is examined with an ophthalmoscope through dilated pupils, visual field examination looks for loss of peripheral vision, and the angle where the iris meets the cornea is checked.
  • Gonioscopy to examine the filtration angle of the anterior chamber.
    • This is an examination of the front part of the eye to check the angle where the iris meets the cornea; it is used to distinguish between open-angle glaucoma and closed-angle glaucoma
  • Perimetry to assess the visual fields.
    • As the optic nerve damage increases, visual perception in the area is lost. The localized areas of visual loss (ie, scotomas) represent loss of retinal sensitivity and nerve fiber damage and are measured and mapped by perimetry.
    • The results are mapped on a graph.
    • In patients with glaucoma, the graph has a distinct pattern that is different from other ocular diseases and is useful in establishing the diagnosis.

What are the signs and symptoms of glaucoma?

Persons suffering from glaucoma may not know that they have already the condition until they have felt some changes in their vision. Some would have severe and throbbing headache, blurred vision or “halos” around lights, difficulty focusing, difficulty adjusting eyes in low lighting, loss of peripheral vision, and aching or discomfort around the eyes.

The signs and symptoms may also differ to the type of glaucoma.

What are the types of glaucoma?

Opthalmologists will classify the type of glaucoma according to types:

  1. Primary glaucoma
    • Open-angle glaucoma
    • Acute angle-closure glaucoma
  2. Secondary glaucoma may be caused by some infections, tumors, or even injuries.
  3. Congenital glaucoma is due to some developmental abnormalities.

Primary Open-Angle Glaucoma (POAG)

In PAOG, optic nerve damage is chronic and progressive. It is characterized with visual field defects, an IOP of >21 mm Hg (or may have fluctuating IOPs). At first, the person may not know that he is already developing the medical condition. There are usually no symptoms but a possible ocular pain, headache, and seeing halos are prevalent.

Angle-Closure (Pupillary Block) Glaucoma (AAOG)

As the name suggests, there is complete or partial closure of the angle at the junction where the iris meets the cornea. This closure can create an obstruction in aqueous humor outflow thus resulting to an increased IOP. This is considered a medical emergency because as sudden as it develops, it can lead to partial or total blindness if not treated.

Clinical manifestations of AAOG will include periocular pain and the conjunctiva appears inflammed (conjunctival hyperemia) or sometimes referred to as “red eye”. The pain can be associated to further symptoms of nausea and vomiting, decreased heart rate, and profuse sweating. The person will also complain of rapidly progressive visual impairment as the IOP increases. When examined, the pupil appears vertically oval and is fixed in a semi-dilated position.

What are treatment options for glaucoma?

At this time, there is no treatment for glaucoma. Treatment focuses on pharmacologic therapy, laser procedures, surgery, or a combination of these approaches, all of which have potential complications and side effects. The object is to achieve the greatest benefit at the least risk, cost, and inconvenience to the patient. Although treatment cannot reverse optic nerve damage, further damage can be controlled. The goal is to maintain an IOP within a range unlikely to cause further damage.

What medicines are prescribed for glaucoma?

Before the patient is given a drug to help in managing problems in glaucoma, the following principles need to be considered:

  • Periodic follow-up examinations are essential to monitor IOP, the appearance of the optic nerve, the visual fields, and side effects of medications.
  • Therapy takes into account the patient’s health and stage of glaucoma. Comfort, affordability, convenience, lifestyle, and personality are factors to consider in the patient’s adherence to the medical regimen.
  • The patient is usually started on the lowest dose of topical medication and then advanced to increased concentrations until the desired IOP level is reached and maintained.
  • One eye is treated first, with the other eye used as a control in determining the efficacy of the medication; once efficacy has been established, treatment of the other eye is started.
  • If the IOP is elevated in both eyes, both are treated.
  • When results are not satisfactory, a new medication is substituted.
  • The main markers of the efficacy of the medication in glaucoma control are lowering of the IOP to the target pressure, appearance of the optic nerve head, and the visual field.

Cholinergics (miotics)

  • Examples: pilocarpine, carbachol
  • Action: Increases aqueous fluid outflow by contracting the ciliary muscle and causing miosis (constriction of the pupil) and opening of trabecular meshwork
  • Side effects: Periorbital pain, blurry vision, difficulty seeing in the dark

Adrenergic agonists

  • Examples: dipivefrin, epinephrine
  • Action: Reduces production of aqueous humor and increases outflow
  • Side effects: Eye redness and burning; can have systemic effects, including palpitations, elevated blood pressure, tremor, headaches, and anxiety

Beta-blockers

  • Examples: betaxolol, timolol
  • Action: Decreases aqueous humor production
  • Side effects: Can have systemic effects, including bradycardia, exacerbation of pulmonary disease, and hypotension

Alpha-adrenergic agonists

  • Examples: apraclonidine, brimonidine
  • Action: Decreases aqueous humor production
  • Side effects: Eye redness, dry mouth and nasal passages

Carbonic anhydrase inhibitors

  • Examples: acetazolamide, methazolamide, dorzolamide
  • Action: Decreases aqueous humor production
  • Side effects: Oral medications (acetazolamide and methazolamide) associated with serious side effects, including anaphylactic reactions, electrolyte loss, depression, lethargy, gastrointestinal upset, impotence, and weight loss; side effects of topical form (dorzolamide) include topical allergy

Prostaglandin analogs

  • Examples: latanoprost, bimatoprost
  • Action: Increases uveoscleral outflow
  • Side effects: Darkening of the iris, conjunctival redness, possible rash

What are the surgical procedures for glaucoma?

Surgery is indicated if medications no longer able to control the flow of aqueous humor. Surgery focuses on creating an area for the aqueous humor to flow freely, thus preventing increased IOP.

For AACG, laser peripheral iridotomy or surgical iridectomy is performed. Laser iridotomy is a noninvasive procedure utilizing a laser to remove a portion of the iris, thus allowing aqueous fluid to flow through the area. Prophylactic iridotomy may be performed on the other eye to prevent AACG. POAG is treated with argon laser trabeculoplasty (noninvasive laser beam creates openings in trabecular meshwork), trabeculectomy (part of iris and trabecular meshwork removed), or cyclocryotherapy (cryoprobe destroys part of ciliary body)

Patient Teachings

Medications and surgical interventions do not treat glaucoma. It is important that the person will have awareness of this condition and learn how to monitor his/her IOP. The following teaching points will help in the continuing care for glaucoma:

  • Know your intraocular pressure (IOP) measurement and the desired range.
  • Be informed about the extent of your vision loss and optic nerve damage.
  • Keep a record of your eye pressure measurements and visual field test results to monitor your own progress.
  • Review all your medications (including over-the-counter and herbal medications) with your ophthalmologist, and mention any side effects each time you visit.
  • Ask about potential side effects and drug interactions of your eye medications.
  • Ask whether generic or less costly forms of your eye medications are available.
  • Review the dosing schedule with your ophthalmologist and inform him or her if you have trouble following the schedule.
  • Participate in the decision-making process. Let your doctor know what dosing schedule works for you and other preferences regarding your eye care.
  • Have the nurse observe you instilling eye medication to determine whether you are administering it properly.
  • Be aware that glaucoma medications can cause adverse effects if used inappropriately.
  • Eye drops are to be administered as prescribed, not when eyes feel irritated.
  • Ask your ophthalmologist to send a report to your doctor after each appointment.
  • Keep all follow-up appointments

References:

gonioscopy. (n.d.) WordNet 3.0, Farlex clipart collection. (2003-2008). Retrieved April 22 2013 from http://www.thefreedictionary.com/gonioscopy

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