Friday, June 02, 2006

Section 4-B: The Glaucoma Suspect

Patients are followed carefully for the development of glaucoma if they are deemed to be glaucoma suspect. There are various physical findings which may label someone as a glaucoma suspect. Physical findings which are suspect for glaucoma are large cup-to-disc ratios (see Chapter 1), asymmetric cupping between two eyes, and high intraocular pressures (IOP). Patients are suspicious for glaucoma based on optic nerve findings, such as large cups or asymmetric cupping –difference in cup size between the right and left eye (figure 4-1).

Figure 4-1. Asymmetry of cupping. The optic nerve cup at left is larger than the optic nerve cup at right. (same as Figures 1-8, 1-9)

Patients are also glaucoma suspect if they have elevated IOP or ocular hypertension. Normal IOP is considered 10 to 21 mmHg. Those with ocular hypertension have IOPs which are greater than 21 mmHg. Accurate IOP measurement depends on the thickness of the cornea (figure 4-2). Thin corneas may underestimate the IOP measurement since it is easier to press against the cornea when checking the IOP. Thus when the cornea is thin, the true IOP is higher than the measured IOP. Conversely, when the cornea is thick, the true IOP is lowered than the measured IOP. Corneal thickness measurements are made with a pachymeter. (figures 4-3 and 4-4) It is similar to the IOP check and performed with an eyedrop (topical) anesthesia. The IOP measurement is, therefore, combined with the corneal thickness measurement to ascertain true level of IOP.

Figure 4-2. Checking intraocular pressure (IOP) using a Goldmann applanation tip at the slit lamp (same as Figure 1-16).

Figure 4-3. A pachymeter tip used to measure corneal thickness

Despite cupping or high IOPs, the visual field test is normal in glaucoma suspects. Progressing to glaucoma requires cupping with corresponding visual field loss. Those most at risk for the development to glaucoma are those with elevated IOPs, thin corneas (less than 555 microns), African descent, older age, enlarged cups, and a family history of glaucoma.

Figure 4-4. A patient undergoes pachymetry to determine his corneal thickness.

Optic nerve photographs are helpful in following glaucoma suspects. Comparison of optic nerves to previous photos allows eye doctors to determine if there is progression of optic nerve cupping. Changes in the optic nerve appearance over time indicate glaucomatous damage. A visual field test which is initially normal and begins to show signs of visual field loss indicates that glaucoma is developing. It is, therefore, important for glaucoma suspects to be carefully monitored with serial eye examinations over time. Since glaucoma often develops without symptoms, the first signs of glaucoma development may first be detected on examination by an eye doctor. Screening should be performed every 1-4 years after the age of 40 (see Chapter 2), depending on a patient’s risk factors. Those with more risk factors are examined more frequently than those without risks.

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