The aim of this study was to further define and model the influence of cataract on spectral domain optical coherence tomography (SDOCT) image quality and retinal nerve fibre layer (RNFL) thickness measurements. OCT quality is influenced by opacities in the optical path and cataracts in the elderly can potentially affect OCT images. The more advanced the cataract the thinner the recorded RNFL thickness. In this study, SDOCT images were taken with two different devices (3DOCT-1000 and Cirrus HD-OCT) before and after cataract surgery and compared against normal participants using artificial filters simulating a cataract effect. Forty eyes with cataract were included and OCT image quality improved significantly postoperatively as well as RNFL thickness. The measurements using the artificial filters showed a linear relation in filter induced optical density and change in RNFL thickness. The findings may have clinical implications in diagnosing glaucoma patients with known cataract using the OCT.