Normal-Tension Glaucoma (cont.)
Exams and Tests
During an eye examination, your ophthalmologist performs tests to measure IOP as well as to rule out ocular hypertension (any situation in which the pressure inside the eye is higher than normal) and early POAG (see Ocular Hypertension and Primary Open-Angle Glaucoma). These tests are explained below.
- The front of your eyes, including your cornea, anterior chamber, iris, and lens, are examined using a special microscope called a slit lamp. With a slit lamp examination, the ophthalmologist looks for signs of other causes or risk factors of glaucoma.
- Tonometry is a method used to measure the pressure inside the eye.
- Measurements are taken for both eyes on at least 2-3 occasions. Because IOP varies from hour to hour in any individual, measurements may be taken at different times of day (eg, morning and night).
- If you are suspected of having normal-tension glaucoma with normal IOP but a suspicious looking optic nerve, your IOP may be checked several times during a single day (called a diurnal assessment or diurnal curve).
- Gonioscopy is performed to check the drainage angle of your eye; to do so, a special contact lens is placed on the eye. By definition, people with normal-tension glaucoma have open, normal-appearing angles; therefore, this test is important to determine if your angles are open, narrowed, or closed.
- Each optic nerve is examined for any damage or abnormalities; this may require dilation of the pupils to ensure an adequate examination of the optic nerves.
- Different imaging studies may be conducted to document the status of your optic nerve and to detect changes over time. A Doppler ultrasound may be used to monitor blood flow to the eye, including the optic nerve.
- Fundus photographs, which are pictures of your optic disc (the front surface of your optic nerve), are taken for future reference and comparison. In certain people, ophthalmologists obtain this documentation yearly for detailed comparison.
- The retina is examined for any defects. This may also require dilation of the pupils to ensure an adequate examination of the retina.
- Visual field testing checks your peripheral (or side) vision, typically by using an automated visual field machine. Loss of peripheral vision is associated with normal-tension glaucoma.
- This test is done to rule out any visual field
defects due to glaucoma. However, an absence of visual field defects does
not ensure the absence of glaucoma. Visual field defects may not be apparent
until as much as 50% of the optic nerve fiber layer has been lost.
- If your visual field defects seem to progress in a manner that is uncharacteristic of glaucoma, then your ophthalmologist will perform additional tests to look for other causes of vision loss.
Francisco Talavera, PharmD, PhD
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