Basics of Glaucoma

Basics of Glaucoma

INFECTION CONTROL IN CLINICAL TONOMETRY

Many infectious agents, including the viruses responsible for acquired

immunodeficiency syndrome, hepatitis, and epidemic keratoconjunctivitis,

are detectable in tears. To prevent transfer of such agents, tonometers must

be cleaned after each use. Use the following processes:

•

The prism head of both Goldmann-type tonometers and the Perkins

tonometer should be cleaned between every exam. The prisms

should be soaked in either a 1:10 sodium hypochlorite (household

bleach) solution, 3 percent hydrogen peroxide, or 70 percent

isopropyl alcohol for 5 minutes, or be wiped thoroughly with an

alcohol sponge. If a soaking solution is used, the prism should be

rinsed and dried before reuse. If alcohol is employed, it should be

allowed to evaporate, or the prism head should be dried before

reuse to prevent damage to the patient’s epithelium.

•

The tonometer tip should be cleaned in the presence of the patient prior to use. It is important to

allow sufficient time for the prism tip to dry to keep from damaging the cornea.

•

The front surface of the air-puff tonometer should be wiped with alcohol between patients

because tears from the patient may contaminate the instrument.

•

Portable electronic applanation devices employ a disposable cover, which should be replaced

immediately after each use.

•

When the tip of the Tonopen has dirt and contaminants in the airspace between the sensor and

the housing, the sensor cannot move freely, resulting in erratic readings and a “bad” calibration

indicator. Cleaning the tip in such situations is necessary. Use canned air, rather than any

chemicals or solutions, to rid the instrument of dust and other contaminants.

•

The Schiotz tonometer requires disassembly to clean both the plunger and the footplate. Unless

the plunger is clean (as opposed to sterile), the measurements may be falsely elevated because

of increased friction between the plunger and the footplate. Use a pipe cleaner to clean inside of

the footplate of tears and any tear film debris. The same solutions for cleaning prism heads then

may be employed to sterilize the instrument.

Evaluation of the Optic Nerve Head

Although elevation of IOP is often the sign that leads to the detection of glaucoma, the appearance of the

optic nerve head is equally important. The characteristic change that occurs in the disc in glaucoma is an

abnormal amount of depression of tissue known as pathologic cupping. The optic nerve head, or optic

disc, is usually round or slightly oval in shape and contains a central cup. This cup is the central

depression of the disc that is seen in most normal individuals. The size of this depression is often

described in relation to the diameter of the disc as the cup-to-disc ratio: The numerator is the diameter of

the cup divided by the diameter of the entire disc taken as 1.00. The average cup-to-disc ratio is 0.4 to

1.00, or 0.4. As glaucomatous damage advances, progressive enlargement of the cup occurs at the

expense of the surrounding rim of nerve tissue.

The tissue between the cup and the disc margin is called the neural rim or neuroretinal rim. The rim in

normal patients has a relatively uniform width and a color that ranges from orange to pink. The size of the

physiologic cup is developmentally determined and is related to the size of the disc. For a given number

of nerve fibers, the larger the overall disc area, the larger the cup.

Cupping in small nerves should be held with high suspicion. The cup-to-disc ratio may increase slightly

with age. Additionally, people with myopia have larger eyes, discs, and cups than do those with normal

vision or those with hyperopia.