Abstract
Purpose: :
To investigate the effect of altering the scan-depth setting [S, M, L and XL axial lengths] on measurements of the retinal thickness in central fovea of eyes with medium axial length obtained with the Heidelberg SpectralisTM spectral domain OCT (SD-OCT).
Methods: :
Fifteen normal young volunteers with ametropia < ± 6 D and < 1 DC, logMAR acuity > 0.0, and ocular axial length (AL) 24.0 ± 2.5 mm (measured with IOLMaster, Carl Zeiss, Germany), were included. Repeated SD-OCT scans (15 deg scan-width along 0 and 90 deg, 1536 A-scans/B-scan, 9 frames) were obtained from the fovea of each subject’s right eye for all four scan-depth settings for eyes with short (S < 22.5 mm), medium (M: 24.0 ± 2.5 mm = default), long (L: 26.5-29.0 mm) and extra long (XL > 29.0 mm) axial lengths. Five scans were obtained for each setting in the mentioned order and with image alignment (TruTrackTM) activated. Accommodation was suspended and pupils dilated with Cyclopentolate 1 %. All scans were performed on the same day by one experienced operator. Pointwise measurements of central foveal thickness (FT) defined as the distance between the reflexes of the inner limiting membrane and the retinal pigment epithelium/Bruch’s membrane, were obtained from sections with best centering using the built in analysis software (Heyex v.4.0). In addition, analyses of longitudinal reflectivity profile were carried out post-hoc. Average FT was compared for each scan depth setting by repeated measure analysis of variance (ANOVA).
Results: :
Mean AL for eyes analyzed so far (n = 11) was 23.52 mm ± 0.74 (range 22.48-24.62 mm), while mean FT were 221.1 ± 4.9, 221.1 ± 4.8, 220.7 ± 4.7, and 220.5 ± 4.5 µm for scan-depth settings S, M, L and XL, respectively. Repeated ANOVA indicated no significant effect of the scan-depth setting on FT analyzed with Heyex (p = 0,603).
Conclusions: :
Results indicate that different scan-depth settings with Heidelberg Spectralis SD-OCT have no effect on measured central foveal thickness in eyes with AL’s that are within the range of the default setting (M).
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • macula/fovea