Abstract
BackgroundTo investigate the influence of scan distance on retinal boundary detection errors (RBDEs) and retinal thickness measurements by spectral domain optical coherence tomography (SD-OCT).Methods10 eyes of healthy subjects, 10 eyes with diabetic macular edema (DME) and 10 eyes with neovascular age-related macular degeneration (AMD) were examined with RTVue SD-OCT. The MM5 protocol was used in two consecutive sessions to scan the macula. For the first session, the device was set 3.5 cm from the eye in order to obtain detectable signal with low fundus image quality (suboptimal setting) while in the second session a distance of 2.5 cm was set with a good quality fundus image. The signal strength (SSI) value was recorded. The score for retinal boundary detection errors (RBDE) was calculated for ten scans of each examination. RBDE scores were recorded for the whole scan and also for the peripheral 1.0 mm region. RBDE scores, regional retinal thickness values and SSI values between the two sessions were compared. The correlation between SSI and the number of RBDEs was also examined.ResultsThe SSI was significantly lower with suboptimal settings compared to optimal settings (63.9±12.0 vs. 68.3±12.2, respectively, p = 0.001) and the number of RBDEs was significantly higher with suboptimal settings in the “all-eyes” group along with the group of healthy subjects and eyes with DME (9.1±6.5 vs. 6.8±6.3, p = 0.007; 4.4±2.6 vs. 2.5±1.6, p = 0.035 and 9.7±3.3 vs. 5.1±3.7, p = 0.008, respectively). For these groups, significant negative correlation was found between the SSI and the number of RBDEs. In the AMD group, the number of RBDEs was markedly higher compared to the other groups and there was no difference in RBDEs between optimal and suboptimal settings with the errors being independent of the SSI. There were significantly less peripheral RBDEs with optimal settings in the “all-eyes” group and the DME subgroup (2.7±2.6 vs. 4.2±2.8, p = 0.001 and 1.4±1.7 vs. 4.1±2.2, p = 0.007, respectively). Retinal thickness in the two settings was significantly different only in the outer-superior region in DME.ConclusionsOptimal distance settings improve SD-OCT SSI with a decrease in RBDEs while retinal thickness measurements are independent of scanning distance.
Highlights
To investigate the influence of scan distance on retinal boundary detection errors (RBDEs) and retinal thickness measurements by spectral domain optical coherence tomography (SD-Optical coherence tomography (OCT))
In the case of the normal group, the number of RBDEs was significantly lower with the optimal scan distance setting only for the entire scan, while in the case of the diabetic macular edema (DME) group the same trend was observed both for the entire scan and the peripheral scan parts (Figure 4 and Table 2)
In our study we found significant differences in the number of boundary detection errors between optimal and suboptimal distance settings in healthy eyes and eyes with DME, while there was a high number of RBDEs regardless of the setting in age-related macular degeneration (AMD) which is in accordance with previous reports
Summary
To investigate the influence of scan distance on retinal boundary detection errors (RBDEs) and retinal thickness measurements by spectral domain optical coherence tomography (SD-OCT). Cross-sectional OCT images of the retina correlate well with retinal histology [2,3,4] and can be used for quantitative analysis of retinal morphology, i.e. measurement of retinal thickness [5]. This quantitative analysis can help the follow-up of several retinal pathologies [6,7] and facilitates important clinical decisions, as in the case of diabetes [8,9,10] or age-related macular degeneration (AMD) [11]. As the RTVue device - to other commercially available OCT devices – provides an automatic optimization process for the OCT settings (including focusing, polarization and Z-offset) that was employed in our study, a possible explanation for the differences was the suboptimal scan distance setting of the SD-OCT device, that is, the possibly longer than optimal scanning distance resulting in poor image quality and leading to measurement artifacts
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