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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.

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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.

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Figure 135-1
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Anatomy of the anterior segment of the eye: (1) anterior segment; (2) posterior segment; (3) ciliary body; (4) trabecular meshwork; (5) cornea; (6) iris.

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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.

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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).

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Figure 135-2
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An eye with angle-closure glaucoma and a markedly elevated IOP. ...

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