Optic nerve head topography and quantitative measurements of nerve fibre layer thickness are increasingly used in the detection and management of glaucoma and other optic neuropathies. Each technology—scanning laser polarimetry, optical coherence tomography, confocal laser scanning ophthalmoscopy—has its strengths and limitations. There are increasing reports in the literature on the effect of disease states on measurement variability.1 2 We undertook to measure in a prospective study the effect of panretinal photocoagulation (PRP) for diabetic retinopathy on retinal nerve fibre layer thickness (RNFL) and optic nerve rim area (RA). PRP is thought to have little to no effect on optic nerve cupping as measured by stereo-photographs.3 PRP has been shown in experimental models to induce injury to the RNFL both at and remotely from laser burns.4 The effect of PRP has not been prospectively measured using modern scanning laser imaging instruments. Our hypothesis was that there would be a small degree of retrograde …