Abstract
Purpose: :
To determine factors affecting signal strength (SS) with spectral-domain optical coherence tomography (SD-OCT).
Methods: :
Eighty-three eyes of 47 subjects from the UCLA OCT Imaging Study were included. Open-angle glaucoma patients, glaucoma suspects or normal subjects meeting the following criteria were prospectively enrolled: reliable fields with MD >-15.0 dB, spherical refractive error <8 D and astigmatism <3 D, and no prior glaucoma surgery. Eligible patients underwent a full eye exam including biometry with IOLMaster, and disc and retinal nerve fiber layer (RNFL) OCT imaging (Optic disc Cube 200x200, Cirrus OCT) by a single technician. Linear regression analyses correcting for the correlation of the two eyes of the same subject were performed to determine factors influencing SS on OCT images.
Results: :
Average (± SD) mean deviation was -2.7 ± 3.4 dB. Signal strength ranged from 6 to 10 (mean ± SD: 8.1 ± 0.81). On univariate analyses, older age (p <0.001), longer axial length (p=0.006), thinner central corneal thickness (CCT; p=0.063), higher intraocular pressure (p=0.064), and steeper average keratometry (p=0.072) were predictive of a lower SS. Only age (p<0.001), axial length (p=0.005), and average keratometry (p=0.032) were associated with a lower SS on multivariate analyses. Severity of glaucoma as determined by mean deviation was not a predictive factor for a poorer SS on univariate or multivariate analyses (p= 0.517 and 0.634, respectively).The effect of age did not change after reanalyzing data from eyes with visual acuity better than or equal to 20/25 (46 eyes; p=0.009 for age).
Conclusions: :
Older age, longer axial length and, to a lesser extent, steeper corneal curvature are the major determinants for lower image quality with SD-OCT. The age influence seems to be only partially related to media opacity. This finding has clinical implications since lower SS has been associated with thinner RNFL measurements.
Keywords: imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)