With regard to the glaucoma diagnostic ability of neuroretinal rim as determined by Cirrus HD-OCT, Mwanza et al.
4 reported that the average rim area, vertical rim thickness, and horizontal rim thickness had good diagnostic abilities (AUCs, 0.901–0.963). In another study using Cirrus HD-OCT, Sung et al.
5 reported that the AUCs of average rim area ranged from 0.797 to 0.937. These results are comparable to the AUCs of the present study (0.877–0.980). However, the diagnostic ability of sectorial rim assessment was not evaluated in the aforementioned studies. In our study, quadrant and clock-hour rim assessment had good glaucoma diagnostic abilities in all areas with similar AUCs.
The diagnostic abilities of RNFL showed an uneven distribution in the present study; nasal and temporal RNFL thicknesses had lower AUCs than other areas. Leung et al.
1 reported that average RNFL thickness and superior and inferior quadrants RNFL thicknesses had good diagnostic abilities (AUCs, 0.949–0.962), whereas RNFL thicknesses of nasal quadrant and clock-hour sectors 2 to 4, 8, and 9 had lower AUCs (0.535–0.761). In another study, Park et al.
2 also reported lower AUCs of RNFL thicknesses in nasal and temporal quadrants and clock-hour sectors 2 to 4 and 8 to 10 (0.572–0.763) than other areas (0.826–0.963). These results are in agreement with the present study results.
Lower diagnostic ability of RNFL thickness in nasal and temporal areas than superior and inferior areas may be explained by relatively lower amount of RNFL loss in nasal and temporal areas than in other areas. In superior and inferior areas, the amount of RNFL loss ranged from 48% to 57%, whereas it ranged from 3% to 33% in nasal and temporal areas. Apart from the RNFL thickness, the amount of rim area and thickness loss showed even distribution (40%–59%) in all areas, including nasal and temporal areas (
Fig. 2). These differences in topographic distribution of RNFL and rim loss as determined by Cirrus HD-OCT may be a cause of differences in diagnostic abilities between RNFL thickness and rim area and thickness in nasal and temporal areas.
Jonas et al.
7 reported that glaucomatous rim loss assessed by disc photographs occurred in all sectors with regional preferences depending on the stage of the disease. Strouthidis et al.
20 investigated the spatial pattern of longitudinal rim area decline by using the HRT and reported that the slopes of changes in nasal and temporal areas were less than those in superior and inferior areas. On the other hand, a study utilizing serial disc photographs reported that the main pattern of cup extension in eyes with ocular hypertension was generalized expansion,
6 which agrees with the present results; presently, the relative amount sectorial rim area and thickness loss showed even topographic distribution throughout all areas without spatial preference. This discrepancy may stem from several differences in study design. First, in previous studies,
7,20 eyes with ocular hypertension or glaucoma with high IOP were mainly enrolled, whereas in the present study 80% of the patients with mild glaucoma and 60% of the patients with moderate to advanced glaucoma had pretreatment IOP ≤ 21 mm Hg. Second, in the previous study,
20 the spatial pattern of rim change was assessed longitudinally, whereas RNFL and rim were cross-sectionally evaluated in the present study. Third, the differences in rim detection methodology should also be considered; cup margin and disc margin as determined by Cirrus HD-OCT may differ from those detected by disc photograph or HRT.
21 Further studies regarding the longitudinal topographic pattern of rim loss in eyes with different types of glaucoma and using various imaging devices may be needed.
In the present study, no parameters of RNFL thickness and rim area and thickness showed good diagnostic abilities for the discrimination between mild glaucoma and moderate to advanced glaucoma groups. These results suggest that detection of glaucoma progression with RNFL thickness and rim area and thickness as determined by Cirrus HD-OCT may have limited clinical value; other studies also reported that glaucoma progression detection by RNFL thickness or rim area as measured by Cirrus HD-OCT may be less effective than visual field test or macular thickness measurement, especially in advanced glaucoma.
17,22
When the RNFL thickness and rim area and thickness of mild glaucoma and moderate to advanced glaucoma groups were compared, significant differences were found in RNFL thicknesses of global area and superior, inferior, and temporal quadrants, whereas no significant differences were evident in rim area and thickness in all areas. These results imply that neuroretinal rim may not be changed in accordance with a decrease in RNFL thickness with respect to the stages of glaucomatous damage. Further study regarding the difference of sectorial neuroretinal rim and RNFL thickness change in the glaucoma development and progression is needed.
Given that parameters with wider ranges may generate a greater amount of change, a wider range of change to rim thickness compared with RNFL thickness may be considered a possible cause of the better diagnostic ability in nasal and temporal areas. However, given that rim area (which had a narrow range of change) also had better diagnostic ability in nasal and temporal areas compared with RNFL thickness, we think that it cannot be explained by an artifact associated with the range of values.
Sectorial rim thickness assessment has an advantage of its convenience without additional image-processing procedure. Rim thickness at each point also has diagnostic capability similar to rim area at the corresponding clock-hour sector in our study results. However, measurement of rim thickness at a specific point as was performed in the present study may have a limitation of not representing the entire clock-hour sector. We suggest that Cirrus HD-OCT software providing average rim thicknesses in clock-hour sectors may be useful for the neuroretinal rim assessment.
In conclusion, sectorial neuroretinal rim assessment by Cirrus HD-OCT may enhance the glaucoma diagnostic ability, especially in nasal and temporal areas. Patterns in RNFL and rim changes measured by Cirrus HD-OCT may be different according to the stages of glaucomatous damage.