Use of directional optical coherence tomography and selected landmarks to determine foveal topography and microstructure. A strategy to characterize differences between normal and expremature cases

Purpose To determine the topography of the different layers of the fovea by combining directional and conventional optical coherence tomography (OCT) images and measuring layer thickness at the foveal center (FC) and selected eccentricity positions. Furthermore, to use a normative model of foveal microstructure to characterize signs of immaturity in cases with a history of prematurity. Methods Selected eyes from normals and young adults with a history of prematurity were imaged using a commercial spectral domain OCT (SD‐OCT) system. Centered and displaced SD‐OCT entrance beam positions were used to obtain straight and tilted scans, respectively. Horizontal scans through FC with a distinct light reflex were selected for analysis. Straight and tilted SD‐OCT images were registered and averaged prior to flattening to the retinal pigment epithelial (RPE) layer. Retinal layer thickness was measured manually at FC and four lateral positions along the temporal and nasal hemi‐meridians and corrected for axial length differences. Results The distance between FC and foveal wall maximum (FWM) was reduced to 4/5 of that of normals in expremature cases with incomplete extrusion of inner retinal layers (IRL) and reduced foveal pit depth. The Henle fibre layer (HFL) and the combined outer segment and RPE layer (OS+) showed little or no change whereas the outer nuclear layer (ONL) was thickened centrally with a more steep decline of the ONL bulge outside FC in exprematures. Conclusions Our pilot study in young adults demonstrates that signs of immaturity may still be present in adult life with changes in foveal topography similar to those present at the age of 6.5 years after extremely preterm birth (Rosén et al., 2015). It may be useful to use the FWM as a major landmark in studies of abnormal fovea.