The effect of cycloplegia on outflow resistance in 64 normal eyes, in 29 eyes with chronic simple glaucoma, and in 90 ostensibly normal eyes of the vervet monkey Cercopithecus ethiops have been compared. The effect in normal human eyes and in monkey eyes were strikingly similar. Cycloplegia increases resistance and magnifies the absolute size of interindividual differences. The larger resistance is, the more it increases. This may also be true in open-angle glaucoma. It is shown how a tolerance ellipse construction can be used to combine the diagnostic information from two partly correlated tests, in this case the tonographies before and after homatropine hydrobromide.
Bárány E, Christensen RE. Cycloplegia and Outflow ResistanceIn Normal Human and Monkey Eyes and in Primary Open-Angle Glaucoma. Arch Ophthalmol. 1967;77(6):757-760. doi:10.1001/archopht.1967.00980020759008