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C CLINICAL RESEARCH

For practical purposes, a PSD or GHT that is repeatedly ‘outside normal limits’ can be considered as diagnostic of
glaucomatous VF loss. The word ‘repeatedly’ is critical: in the Ocular Hypertension Treatment Study, an astonish-
ing 86% of patients with one abnormal VF (suggesting conversion of ocular hypertension to manifest glaucoma)
reverted to normal on the next assessment. 275

Clinical Recommendations for AVF assessment in glaucoma:
• Early glaucomatous defects can include arcuate or partial arcuate loss, paracentral scotoma, nasal step,
and/or diffuse visual field depression: be vigilant for an increased mean deviation in the absence of media
opacity. 273
• The importance of a reliable and repeatable baseline visual field assessment cannot be overstated: without
knowing the starting point, it is impossible to accurately identify progression.
Although clinicians have long relied on 24-2 or 30-2 testing strategies, it is now recognized that macular dam-
age may be found as frequently as peripheral defects in early glaucoma, providing that the correct testing
strategy is employed. 260,276 Only four of the 54 points in the relatively coarse 24-2 grid (6 spacing between
°
points) fall in the central 8 to 10 of the macula, versus all 68 points of the finer 10-2 grid (2 spacing). This poor
°
°
sampling is exacerbated by RGC displacement at the fovea. As a result, a small initial paracentral scotoma
277
may be missed by 24-2 but detected by 10-2 analysis, as shown in Figure 13. 253,278 In reviewing the anatomy of
the RNFL, the basis for early macular damage becomes clear: the majority of RGC axons from the superior
macula enter the temporal ONH as the papillomacular bundle, whereas those from the inferior macula project
to the inferior-temporal pole, a region that Hood and colleagues have termed the macular vulnerability zone
(MVZ). 252,259 Loss of RGC in the MVZ leads to a superior arcuate defect that threatens fixation, one of the crite-
ria that defines advanced glaucoma, and has a significant impact on vision-related quality of life. 258,279

38 CANADIAN JOURNAL of OPTOMETRY | REVUE CANADIENNE D’OPTOMÉTRIE VOL. 79 SUPPLEMENT 1, 2017