While the patient is seated at the slit lamp, you can use tonometry to measure intraocular pressure.

Glaucoma is often called the “sneak thief of sight” because glaucoma can strike without pain or other symptoms. Glaucoma is one of the leading causes of blindness in the U.S. According to National Glaucoma Research, approximately 2.2 million Americans age 40 and older have glaucoma, and as many as 120,000 people per year go blind because of this disease.

Although glaucoma is not curable, it is treatable. Most patients whose condition is caught early do not lose their eyesight.

Progressive Loss

Glaucoma is a condition in which the optic nerve experiences a specific pattern of damage, resulting in a progressive loss of the visual function. It is characterized by increased pressure in the eyeball, caused by the abnormally high production of aqueous humor or decreased drainage of the aqueous. Left untreated, it can lead to permanent damage to the retina and the optic nerve, resulting in reduced vision or possible blindness.

The ciliary body constantly produces aqueous humor, which drains from the anterior chamber through Schlemm’s canal. If this fluid is prevented from draining out of the chamber, an increase in pressure within the eye will result. Intraocular pressure, or IOP, is the fluid pressure within the eye that keeps the cornea and sclera in a state of tension. IOP normally ranges from 8mm Hg to 22mm Hg.

Glaucoma can develop in one or both eyes. Generally, it occurs in both eyes, with one worse than the other.

While anyone can develop glaucoma, some individuals are at higher risk. These include African-Americans, Hispanics, anyone age 60 and older, and individuals with a family history of glaucoma.

The Tests

Glaucoma does not happen overnight. It is usually a slow process. There are no visual symptoms or pain, though individuals with advanced glaucoma may notice a gradual decline in peripheral vision. In other words, objects in front may still be seen clearly, but objects to the side may be missed. The patient may develop “tunnel vision” and can see only straight ahead. Over time, straight ahead vision may decrease until no vision remains.

A comprehensive series of tests help monitor over time if a change in the optic nerve or nerve function has occurred and, if so, determine the level of damage that exists. These tests include:

Tonometry, a simple and painless measurement of IOP. The gold standard is the Goldman applanation tonometer, which is usually attached to a slit lamp and measures IOP by flattening the cornea a small fixed amount. When performing this test, instill one drop of a fluorescein/anesthetic combination solution in each eye. Then, using the slit lamp, bring the head of the tonometer to the center of the cornea. On contact, the limbus will shine a bluish light.

Another applanation tonometer, the non-contact tonometer, uses a puff of air to flatten a circular area of the cornea. The non-contact tonometer measures IOP accurately without anesthesia and without physical contact.

A visual field test. This measures the visual sensitivity of the peripheral, or side, vision. It checks the development of the abnormal blind spot and any visual field defect to detect glaucomatous damage.

Corneal pachymetry. This measures the thickness of the cornea. This is important because individuals who have thicker or thinner corneas may get artificially high or low IOP readings, respectively. Individuals with thinner corneas also have a higher risk of developing glaucoma.

An examination of the optic nerve. Using a high-powered binocular microscope and lenses, the OD looks for subtle signs of optic nerve damage. Areas of thinning may indicate glaucoma. This test helps ensure the accuracy of the intraocular pressure readings. Also, digital optic nerve photography allows the doctor to monitor the optic nerve head changes.

Imaging, such as optical coherence tomography. OCT  determines whether  there is a change in the nerve fiber layer of the optic nerve. This should be done once a year.

Gonioscopy. A magnifying device (a goniolens) used in combination with a strong illumination, lets the doctor examine the angle of the anterior chamber of the eye. This device allows a direct view of the eye’s “drainage” system.

Types of Glaucoma
Primary open angle glaucoma: This most common form of glaucoma develops slowly as the drainage canal of the eye gradually becomes obstructed. There are no early warning signs, so individuals are not aware that they are losing their vision until the advanced stage when tunnel vision occurs.

Acute closure glaucoma: Unlike primary open-angle glaucoma, this type does have symptoms, including severe eye pain that is often associated with nausea and vomiting, blurred vision, halos around lights and/ or reddening of the eye or eyes.

Congenital glaucoma: This rare form occurs in infants and young children and can be inherited. It’s usually the result of incorrect or incomplete development of the eye drainage canals during pregnancy.

Low- or normal-tension glaucoma: Intraocular pressure stays within the normal range, but damage still occurs to the optic nerve and visual fields. A comprehensive medical history is important to identify potential risk factors, such as low blood pressure, that contribute to low-tension glaucoma. The treatment options for low-tension glaucoma are the same as open-angle glaucoma.

Secondary open-angle glaucoma: This form of glaucoma occurs as the result of an eye injury, inflammation or tumor.

Glaucoma Treatments

Glaucoma treatments include the following to lower IOP:

Topical medications. Most patients respond to topical medications, though they may need multiple drops or, in some instances, oral medication.

Laser trabeculoplasty. This procedure, done one eye at a time, helps increase fluid drainage from the eye and may be warranted if drops alone do not control IOP. In many cases, the patient needs to continue using glaucoma medications, and additional laser treatment might be necessary.

Surgery. Conventional surgery to make a new opening for the fluid to leave the eye may become necessary if medication and laser trabeculoplasty fail to control IOP. As with laser procedures, conventional surgery is performed on one eye at a time. Surgery is about 60% to 80% effective at lowering IOP. If the new drainage opening narrows, a second operation may be needed.

While these treatments may save remaining vision, they do not improve sight already lost from glaucoma. That is why early detection and continuous monitoring are very important. The ultimate goal when treating glaucoma, regardless of severity, is to stop further progression of optic nerve damage, visual field loss and loss of visual function. OO

Roberta Beers, CPOT, is an optometric assistant in Erie, PA.



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