Abstract
Retinal and intra-retinal layer thicknesses are routinely generated from optical coherence tomography (OCT) images, but on-board software capabilities and image scaling assumptions are not consistent across devices. This study evaluates the device-independent Iowa Reference Algorithms (Iowa Institute for Biomedical Imaging) for automated intra-retinal layer segmentation and image scaling for three OCT systems. Healthy participants (n = 25) underwent macular volume scans using a Cirrus HD-OCT (Zeiss), 3D-OCT 1000 (Topcon), and a non-commercial long-wavelength (1040nm) OCT on two occasions. Mean thickness of 10 intra-retinal layers was measured in three ETDRS subfields (fovea, inner ring and outer ring) using the Iowa Reference Algorithms. Where available, total retinal thicknesses were measured using on-board software. Measured axial eye length (AEL)-dependent scaling was used throughout, with a comparison made to the system-specific fixed-AEL scaling. Inter-session repeatability and agreement between OCT systems and segmentation methods was assessed. Inter-session coefficient of repeatability (CoR) for the foveal subfield total retinal thickness was 3.43μm, 4.76μm, and 5.98μm for the Zeiss, Topcon, and long-wavelength images respectively. For the commercial software, CoR was 4.63μm (Zeiss) and 7.63μm (Topcon). The Iowa Reference Algorithms demonstrated higher repeatability than the on-board software and, in addition, reliably segmented all 10 intra-retinal layers. With fixed-AEL scaling, the algorithm produced significantly different thickness values for the three OCT devices (P<0.05), with these discrepancies generally characterized by an overall offset (bias) and correlations with axial eye length for the foveal subfield and outer ring (P<0.05). This correlation was reduced to an insignificant level in all cases when AEL-dependent scaling was used. Overall, the Iowa Reference Algorithms are viable for clinical and research use in healthy eyes imaged with these devices, however ocular biometry is required for accurate quantification of OCT images.
Highlights
Optical coherence tomography (SD-optical coherence tomography (OCT)) is an essential imaging tool for the diagnosis and monitoring of retinal diseases such as age-related macular degeneration (AMD) [1,2] and diabetic macular oedema [3,4]
The on-board software of the two commercial instruments used in this study provide only a single lateral scaling value for all patients regardless of axial eye length (AEL), resulting in an error in the reported size of the image which scales with AEL
The aims of the present study are to evaluate the use of Iowa Reference Algorithms as a means of generating repeatable intra-retinal layer thickness values from images of healthy eyes, captured using two commercial standard deviation (SD)-OCT devices and one non-commercial longwavelength device
Summary
Optical coherence tomography (SD-OCT) is an essential imaging tool for the diagnosis and monitoring of retinal diseases such as age-related macular degeneration (AMD) [1,2] and diabetic macular oedema [3,4]. This non-invasive technique allows clinicians to produce threedimensional (3-D) images of intraocular structures in vivo. Whilst manual caliper tools and hand segmentation (hand tracing of intra-retinal layer boundaries) can be simple to perform, it is time consuming ( when implemented in 3-D scans) and subject to significant inter-observer variation [9] These methods are not feasible for use clinically or in large, multi-center clinical trials
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