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The authors examined the performance of Guided Progression Analysis (GPA) in spectral-domain optical coherence tomography (OCT) for detection of progressive thinning of the ganglion cell inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) in glaucoma. Glaucomatous eyes were classified into mild (mean deviation [MD],> -6 dB) or moderate-to-advanced (MD, <-6 dB) groups by the severity of their VF defects.
The eyes with progressive GCIPL thinning had a higher probability of VF progression than did the eyes without progressive GCIPL thinning, regardless of glaucoma severity. In addition, the rate of change in the average GCIPL thickness was significantly higher in progressors than in non-progressors, regardless of glaucoma severity. The paper has value as the first to demonstrate the usefulness of GCIPL GPA as a new approach to the detection of glaucoma progression.
GCIPL GPA was more useful than RNFL GPA for detection of progression in the moderate- to-advanced stages of glaucoma. This result seems quite reasonable, because about one-half of the total retinal ganglion cells are concentrated in the macular region where GCIPL analysis is performed and where VF change occurs in the advanced stage of glaucoma. By contrast, as the average RNFL thickness reflects the entirety of retinal ganglion cells, it might be less sensitive for detection of VF changes in moderate-to-advanced glaucoma.
In the final part of their discussion, the authors declared that "the significantly higher rate of change in the average GCIPL thickness in progressors may imply that progressive GCIPL thinning beyond the extent of age-related loss could be used as a biomarker for predicting glaucoma progression." However, the term "prediction" should be used very cautiously, because the current study did not demonstrate any GCIPL GPA utility for prediction of future VF progression but rather, and only, better GCIPL GPA performance than RNFL GPA in differentiating VF progression in cases of moderate-to-advanced glaucoma.