Detecting early glaucoma by visual field parameters

Purpose: To evaluate the sensitivity (Sn) and specificity (Sp) of different perimetric techniques in discriminating normal from glaucomatous eyes and to calculate the ability of visual field parameters in detecting the presence of RNFL defects. Methods: Twenty-three eyes of 23 patients with focal wedge-shaped RNFL defects, as shown with Scanning Laser Ophthalmoscope (SLO, Rodenstock), and with normal standard automated perimetry (SAP) indices (MD and CPSD) were assessed for the presence of glaucoma according to optic disc appearance; glaucoma was diagnosed if there was agreement between two masked evaluators. All patients underwent SAP (full threshold 30-II), blue-yellow (B-Y) perimetry (full threshold 30-II) and frequency doubling technology (FDT) perimetry (full threshold N-30). The last of 3 consecutive tests was considered in the analysis to avoid any "learning effect". Results: According to optic nerve head appearance, 10/23 eyes (43.4%) were diagnosed as having glaucoma. The best perimetric parameters in detecting glaucoma were: cluster of at least 2 contiguous points in the pattern deviation (p<5%) with FDT: Sn=80%, Sp=62%; cluster of at least 2 contiguous points in the pattern deviation (p<5%) of the FDT superior hemifield: Sn=70%, Sp=77%; cluster of at least 2 contiguous points in the pattern deviation (p<5%) of the FDT inferior hemifield: Sn=60%, Sp=92%; cluster of at least 3 contiguous points in the pattern deviation (p<5%) of the B-Y superior hemifield: Sn=60%, Sp=54%. Both B-Y total deviation map (p<5%) and FDT pattern deviation map (p<5%) could detect 56.5% of the RNFL defects. Conclusions: In a very selected population of subjects with wedge shaped RNFL defects and normal SAP indices, FDT seems to be more sensitive and specific than B-Y for the detection of early glaucoma. In 17.4% of eyes neither optic disc examination nor any perimetric parameter could detect the presence of RNFL defects