Modern glaucoma diagnostics

Closer scrutiny of structural and functional changes can reveal macular damage

Default banner image for Modern glaucoma diagnostics
Photo of Roibeard O’hEineachain

Modern diagnostic techniques including 10-2 visual field perimetric testing and optical coherence tomography (OCT) can detect visually important damage to the macula in eyes with glaucoma better than older techniques, reported Don Hood MD at the 13th European Glaucoma Society Congress in Florence, Italy. “Nearly every glaucoma patient who has undergone the 24-2 or 30-2 testing should undergo the 10-2 test. The 24-2 test can underestimate macular damage, which is very common even in the early stages of glaucoma,” said Dr Hood, Columbia University, New York, New York, USA. He noted that the macula, which he defined as the area within an 8-degree radius from the point of fixation, has less than 2% of the retina’s total area, but contains more than 30% of its retinal ganglion cells. It is vital for reading, driving and facial recognition. He pointed out that a 24-2 test screen has only four points within the macula and its points are spaced by six degrees, starting at +3 degrees from fixation. By comparison, the points in the 10-2 test are spaced by 2 degrees, starting at +1 degree from fixation. The 24-2 visual field test therefore misses the thickest part of the macula. Dr Hood added that in eyes with glaucoma the most vulnerable part of the macula is the lower retinal region, called the macular vulnerability zone. His team and others have demonstrated that retinal ganglion cells (RCGs) from this part of the macula send their axons to the most vulnerable part of the optic disc, whereas RGCs from the remaining macula send their axons to less vulnerable parts of the disc. He emphasised that macular damage should be further scrutinised with an OCT scan that includes the macula. An OCT disc scan can miss damage that can be seen on a cube scan of the macula. Macular damage is best seen on RGC deviation maps, which are available with most 
OCT instruments. He further explained that viewing a large image of a circumpapillary scan will allow assessment of scan quality and detail of local damage, thereby enabling the monitoring of structural changes in eyes with advanced glaucoma. Agreement between perimetry and OCT findings can be confirmed by a topographical comparison of abnormal regions of the OCT with abnormal regions of the visual field, and discrepancies between the two can usually be resolved in the same way. Don Hood: 
dch3@columbia.edu