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Anthony Corcoran, Gonzalo Muyo, Jano van Hemert, Stephen Pemberton, Andy Harvey; An Anatomically Correct Widefield Phantom for Retinal Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2301.
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Widefield ophthalmic-OCT, between 45°-180° field of view (FOV), will enable clinicians to diagnose pathology that presents initially outside the central macula and allow the quantitative analysis of post-vitreoretinal surgery. Increasing the FOV of OCT devices makes them more susceptible to aberrations; both from the eye and the device, distorted images, excessive range in optical pathlength (OPL) and a non-pathological variation in the signal strength. To understand these challenges, we are presenting the only phantom to our knowledge that can simulate the imaging performance of the eye across 180°.
A widefield phantom eye (WPE) was designed in Zemax® and developed using custom lenses to optically mimic the Escudero-Sanz, Navarro widefield schematic eye. The phantom was designed to match the spot radius, OPL and image height of the schematic eye across its entire FOV. The retinal targets were designed to contain both axial layers and transverse structures of scattering material in a transparent suspension to simulate OCT images of a retina.
A water-filled WPE has been designed with interchangeable retinal targets with and an optical performance that maintains the spot radius, OPL and image height of the schematic eye to a tolerance of within 10% of each criterion, across 180° FOV. To our knowledge this is the closest physical model eye described in literature. Figure 1 shows a cross sectional view of the WPE. The ability of the phantom to measure the central transverse and axial resolution of a device can be seen in Figure 2. Using these targets on an early version of the Optos® OCT/SLO yielded an optical transverse and axial resolution of at least 17.5µm and 13.6µm on-axis, respectively. Early observations in navigated images using current OCT systems are displaying anomalies in peripheral retina. These anomalies further demonstrate the need to validate off-axis measurements using the WPE.
We have deigned and are currently manufacturing a phantom eye that offers the greatest similarity reported to our knowledge, to a human eye. The WPE will enable optimisation of widefield OCT devices based on key criteria of image quality such as axial and transverse resolution, sensitivity and FOV. Furthermore, the phantom will serve as a reference tool to compare black-box OCT systems.
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