This chapter reviews three reliable techniques used to measure
intraocular pressure (IOP). Tonometry is the measurement
of IOP. Tonometers commonly used to measure IOP in the
Emergency Department include the Goldman tonometer, the Tono-Pen,
and the Schiøtz tonometer. The Goldman tonometer is considered
the clinical standard used by Ophthalmologists. However, it is difficult
to use and requires a slit lamp biomicroscope. For these reasons,
many Emergency Departments use the Tono-Pen. The Schiøtz
tonometer is mentioned for completeness and historical significance.
It is useful to become comfortable with one or more of these techniques
as early detection of abnormal IOP can prevent irreversible
vision loss. There are multiple traumatic, pathologic, and post-surgical
causes for elevated IOP. The clinical signs and symptoms of elevated
IOP are similar regardless of the etiology.
Aqueous humor is produced by the ciliary body in the posterior
chamber of the eye, directly behind the iris (Figure 135-1). Most
of the aqueous humor flows forward, through the pupil, into the
anterior chamber. It drains out of the eye through the trabecular
meshwork located at the angle where the cornea and iris meet. Aqueous
humor production equals outflow in a healthy eye at steady state.
IOP reflects the pressure of the ocular contents and by convention
is expressed in millimeters of mercury or mmHg.1 The mean
IOP in the general population is 16 mmHg with a standard deviation
of 3 mmHg.2 Therefore, normal pressure is considered
to range from 10 to 21 mmHg.
Anatomy of the anterior segment of the eye: (1) anterior segment; (2) posterior segment; (3) ciliary body; (4)
trabecular meshwork; (5) cornea; (6) iris.
Aqueous humor production and outflow can be dramatically affected
by disease or injury of the eye. Even small changes in IOP over
long time periods can be vision threatening. However, significant
increases in pressure can cause rapid and irreversible damage to
vision in just a few hours. Nontraumatic conditions that result
in an elevation of IOP include primary angle-closure glaucoma and
secondary angle-closure glaucoma. Traumatic conditions associated
with elevated IOP include retrobulbar hemorrhage, hyphema, and traumatic
iritis. Conditions associated with low IOP that threaten vision
include penetrating trauma and post-surgical complications.
Patients with primary or secondary acute angle-closure glaucoma
often present with ocular pain and decreased vision, usually in
one eye. They may describe a headache in the brow region, with or
without associated nausea and vomiting. External examination frequently
reveals that the conjunctiva is erythematous, the cornea appears
milky or hazy, and the pupil is slightly dilated with a sluggish
response to light (Figure 135-2).
An eye with angle-closure glaucoma and a markedly elevated
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