Optical coherence tomography (OCT) measurements of the retinal nerve fiber layer (RNFL) are widely used to assess for progressive changes in glaucoma, and there is growing realization of the importance of also detecting progressive macular changes.1 Commercial OCT devices are beginning to offer wide-field imaging capabilities that allow results from RNFL and macular imaging to be combined. In this study, Lee and colleagues examined the ability of wide-field OCT maps, which include circumpapillary RNFL (cpRNFL) and macular ganglion cell-inner plexiform layer (mGCIPL) measurements, to detect progression in early glaucoma.
Ninety-four eyes with an average visual field mean deviation of -1.9 dB were imaged using the Cirrus HD-OCT. Wide-field images were generated from a montage of 200 x 200 pixel optic disc and macular cube scans. Progression on OCT was determined using the Cirrus HD-OCT guided progression analysis (GPA) event analysis and by two masked observers examining serial sets of wide-field OCT thickness and deviation maps. Progression was defined as appearance of a new RNFL defect (or deviated pixels) or an increase in depth or width of an existing defect (or deviated pixels).
Over an average follow-up of almost five years, 50% of eyes progressed on serial stereo disc or red-free fundus photographs. Eyes progressing on photographs had significantly faster rates of change in cpRNFL (-1.65 versus -0.61 µm/year) and mGCIPL (-0.91 versus -0.27 µm/year) and a significantly greater proportion of eyes progressing on photographs were also noted to have progressed on cpRNFL GPA (83.0% versus 15.2%, P < 0.001) and mGCIPL GPA (66% versus 6.4%, P < 0.001). The combined wide-field OCT maps had similar sensitivities and specificities compared to RNFL and mGCIPL GPA (e.g., 83% sensitivity and 95.7% specificity for wide-field OCT deviation map compared to 83% sensitivity and 84.8% specificity for cpRNFL GPA).
Although combined wide-field OCT maps had similar ability to detect progression as GPA software, wide-field images have potential advantages over isolated parapapillary and macular measures. By allowing evaluation of both regions in a single image it is easier to observe the pattern of progressive change; deepening and widening of defects can be seen more easily, and the spatial relationship between RNFL and macular thinning and visual field loss is more apparent. Recent studies have indicated macular measurements may be of particular value in advanced glaucoma and therefore wide-field images may also allow improved detection of progression through a wider spectrum of disease severity.2
Disadvantages of the study included that the wide-field images were obtained by merging two separate scans which led to errors in alignment necessitating almost 5% of paired scans to be excluded. In addition, the reference standard of progressive changes on photographs is likely to be more closely correlated with changes in cpRNFL than mGCIPL and may be less sensitive at detecting change than OCT.