Observing progressive anatomical changes of the optic nerve head is essential in the detection of progression in glaucoma. Imaging devices continue to evolve and are useful in detecting change in established glaucoma, although probably less useful in an initial diagnosis. Optic nerve head parameters, such as cup area and volume, rim area and volume and cup / disc ratio, as well as retinal nerve fibre layer (RNFL) thickness, depend on accurate delineation of the optic disc margin. Any displacement of the disc margin may indirectly affect the RNFL thickness. This paper from Bascom Palmer examines the impact of manual versus automated disc margin delineation on optic nerve head (ONH) and RNFL using spectral domain optical coherence tomography (OCT). This prospective, cohort study analysed 99 eyes, of 50 subjects, with established glaucoma, glaucoma suspects and normal individuals. The RNFL thickness measurements were not clinically significantly different between the two methods of demarcation, except in one quadrant (inferonasal). For the ONH measurements, the C/D ratio and rim area showed significant differences between the two methods. The authors conclude, however, that there is high agreement between manual and automated determination for RNFL parameters but greater variation in ONH parameters. RNFL parameters are therefore more robust than ONH parameters for consistent follow-up of glaucoma patients. This study shows that in general, the automated software can reliably delineate the disc margin, compared with manual delineation, especially when assessing RNFL parameters.