Abstract
Abstract: :
Purpose: The Optical Coherence Tomograph (OCT) generates cross sectional tomograms of the retina with ≤ 10 µm axial resolution. OCT software allows to calculate a three dimensional structure of the optic nerve head (ONH). Aim of the study was to evaluate which settings of the ONH analysis are able to differentiate best between normal and glaucoma subjects. Methods: 38 eyes of 24 normals (#1), 39 eyes of 26 patients with moderate (#2) and 21 eyes of 17 patients with advanced POAG (#3) were examined by Stratus OCT (Zeiss, Model 3000, Software Version 2.0). Images were scanned in the "optical disc" mode and analyzed with the "optic nerve head" analysis protocol with two different cup offsets: 0 and 150µm.Composite images (CI) of 6 equally spaced linear scans through a common central axis placed in the center of the optic disc were used to calculate vertical integrated rim area (volume), horizontal integrated rim width (area), disc area, cup area, rim area, cup/disc area ratio, cup/disc horizontal and vertical ratio. For each individual scan (IS) rim area (vertical cross section) and average nerve width @ disc were measured. For statistics a univariate linear regression analysis was conducted. The Sidak correction was used to correct alpha for multiple comparisons. Results:The evaluation of the CI showed statistically significant differences between group #1 and #2 and between #1 and #3 with both cup offsets for all measured parameters (all p <0.001) except disc area (p>0.5). The comparison between #2 and #3 showed only statistically significant differences for horizontal integrated rim width (p=0.0008), rim area (p=0.002), and cup/disc area ratio (0.01) with cup offset 150µm. All other parameters were not statistically significant different. (p>0.05). Using cup offset 0µm the comparison between group #2 and #3 showed statistically significant differences for horizontal integrated rim width (p=0.0008), cup area (p=0.05), rim area (p=0.0003), and cup/disc area ratio (p=0.002). Evaluation of the single scans showed statistically significant differences between group #1 and #2 and between #1 and #3 for both parameters and with each cup offset (all p<0.0001). The comparison between #2 and #3 showed no statistically significant differences for rim area (p>0.05). Average nerve width @ disc was not statistically significant different for the horizontal scan but for all other scans (p<0.03) Conclusion:The analysis of the ONH by OCT is able to differentiate between normals and moderate glaucoma. For the differentiation between moderate and advanced glaucoma the analysis with the 0µm offset seems to be advantageous.
Keywords: clinical (human) or epidemiologic studies: systems/equipment/techniques • laser • optic disc