How to Measure Intraocular Pressure With a Tonometer

Glaucoma is a group of eye conditions that damage the optic nerve and cause blindness. The most common cause of glaucoma is a pressure buildup inside the eye (intraocular pressure). Vision can be lost so gradually that an individual is not aware of the problem until irreversible damage has occurred. A tonometer is a device used to detect glaucoma by determining the cornea's indentation (resistance to pressure). Tonometry, a simple and routine test, is a screening test for glaucoma. Early detection of glaucoma preserves sight. Applanation tonometry is considered the "gold standard," according to "Community Eye Health Journal."

Things You'll Need

• Tonometer, Goldmann or Perkins
• Slit lamp biomicroscope
• Cobalt blue light filter
• Sterile applanation prism (disinfected with isopropyl alcohol 70% or sodium hypochlorite 1%, rinsed in sterile water, wiped dry with clean swab)
• Local anesthetic eye drops
• Fluorescein drops
• Sterile gauze swabs

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Instructions

• 1

  Align the "0" on the measuring prism with the white mark on the head of the tonometer. Set the calibrated tonometer dial to 10 mmHg.

• 2

  Adjust the patient's chair to the correct height. Instruct the patient to place his chin in the chin cup and his forehead on the headband. If you're using the Perkins tonometer, however, have the patient lie in the chair with his head supported.

• 3

  Adjust the slit lamp biomicroscope magnification to 10x.

• 4

  Administer the anesthetic drops to both eyes following the manufacturer's directions. Administer the fluorescein drops to both eyes following the manufacturer's directions.

• 5

  Shine the slit lamp biomicroscope beam onto the tonometer head from the right side of the patient. Adjust the filters and produce a blue beam with the cobalt blue filter. Make the beam as wide and bright as possible.

• 6

  Instruct the patient to keep both eyes open and stare straight ahead without moving. Carefully lift the right eyelid using your thumb without applying pressure on the eye. Shine the blue light onto the head of the tonometer prism.

• 7

  Guide the tonometer slowly forward, perpendicular to the right eye, until it gently touches the center of the cornea. Turn the calibrated tonometer dial clockwise with your free hand. Read the dial when the inner edges of the two fluorescein semi-circles just meet, forming a horizontal "S." Enter the reading into the patient's notes and remove the tonometer from the patient's cornea.

• 8

  Wipe the tonometer tip with a sterile gauze swab, then repeat steps 4 through 7 for the left eye. Disinfect the prism.