The macula and glaucoma

For years glaucoma research and clinical care have been primarily focused on the optic nerve head. However, research and clinical anecdotal evidence have shown that the macula could provide information pertinent to the care of our patients with glaucoma. We can gather this information about the macula by utilizing supplementary visual field testing and newer OCT protocols. 

It was once widely believed that the central visual field is affected by glaucoma only in advanced stages. However, multiple studies have shown the central field can be affected much earlier. The commonly used SAP 24-2 has been shown to miss central defects detectable by a 10-2 strategy. Only four points of the 24-2 test the central 10 degrees due to its six-degree separation pattern. The 10-2 test points are separated by only 2 degrees. The studies have shown that central field changes can be detected by the 10-2 in all stages of the disease, not just late stages. 

Of note, these central defects are typically superior and relatively close to the fixation point. Such defects are to be expected because they correspond well with the macular vulnerability zone (the inferior temporal region of the disc that contains fibers from the inferior portion of the macula and is highly susceptible to glaucomatous damage). A resulting shift seems to be occurring in which both 24-2 and 10-2 tests are being utilized for diagnosis, classification, and monitoring of glaucoma. 

We have known for some time that macular nerve fibers are also affected in glaucoma.

With current OCT capabilities, it is possible to evaluate the macula for glaucomatous damage. These macula scans have been shown to have a high rate of reproducibility and to correlate well with other relevant clinical tests, including visual field testing. Most SD-OCT instruments come with a glaucoma macula protocol. 

The approaches utilized typically differ from instrument to instrument. These approaches include Total Macular Thickness, which measures the total macular thickness; Ganglion Cell Complex (GCC) which measures the thickness of the RNFL, GCL, and IPL combined; and Ganglion Cell Analysis, which measures the GCL and IPL combined. All of these have been shown to be of good complementary value to RNFL scans and perimetry and to correlate well with central visual defects. 

Incorporating 10-2 visual field testing and OCT macula analysis into the glaucoma battery can be beneficial in the diagnosing and monitoring of this potentially blinding disease. In short, do not overlook the macula in glaucoma. 

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