Quantification Of Photoreceptor Layer Thickness Using Ultrahigh Resolution Optical Coherence Tomography

Abstract

Abstract: : Purpose: To demonstrate in vivo quantification of the inner and outer photoreceptor layer thickness (PRLT) in the central foveal region by ultrahigh resolution optical coherence tomography (UHR OCT). Methods: A compact UHR OCT system has been developed enabling unprecedented visualization of intraretinal layers, especially the photoreceptor layer with 3 µm axial resolution. Normal subjects as well as selected patients with different macular pathologies were imaged and the inner and outer segment of the photoreceptors have been segmented and quantified. Results: Ultrahigh resolution OCT enables unprecedented in vivo identification of all major intraretinal layers. In normal subjects the central total PRLT was typically about 90 µm with about 45 µm thickness for both the photoreceptor inner and outer segments (IS, OS). At a distance of about 3 mm nasal, temporal, inferior and superior, the total PRLT decreases to about 50 µm with the photoreceptor IS being about 30 µm and the photoreceptor OS decreasing to about 20 µm. This is in accordance with the well–known increase in cone outer segment in the central foveal region. In patients with acute central serous chorioretinopathy, an increase in central total PRLT of typically up to 120 µm could be detected with UHR OCT, especially due to increased thickness of the photoreceptor OS. In patients with adult–onset foveal vitelliform dystrophy, central PRLT was up to 150 µm, whereas in patients with Stargardt dystrophy or retinitis pigmentosa, central PRLT of typically only 30 µm and 50 µm parafoveally were measured by UHR OCT. Conclusions: Enhanced visualization and precise quantification of the photoreceptor OS and photoreceptor IS have the potential for objective diagnosis of macular pathologies. Therefore, ultrahigh resolution ophthalmic OCT has the potential to enhance sensitivity for early ophthalmic diagnosis, as well as to contribute to a better under standing of ocular disease pathogenesis.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • photoreceptors • retina