The key elements in glaucoma diagnosis and follow up are measurement of the intraocular pressure, assessment of the optic disc, and examination of the visual field. In the 1920s, Ransom Pickard wrote about the benefits of drawing the optic disc to outline the disc and cup boundaries, placing emphasis also on the depth of the cup.1 2 In addition, he used a grid to measure the size of the cup relative to the disc, and his results of serial drawings over many years show an increase in cupping with the passage of time.3

Armaly4 popularised the use of the cup:disc ratio in the 1960s, particularly in epidemiology studies, but the term was later adopted by clinicians and to this day is the most commonly used clinical method of describing the glaucomatous optic disc. In a classic paper by Lichter in 1976,5 the poor agreement in cup:disc ratio estimation by a number of leading glaucoma specialists clearly illustrated that it is an “inexact method of recording the status of the disc” and “is probably not reliable in checking for small disc changes”. The level of within observer agreement is considerably greater than the …