[Sources of error in planimetry of the optic nerve]

No matter how "sophisticated" they may seem to have become, contemporary methods for bioplanimetry of the optic disc vary in precision; easily overlooked or neglected optical influences must, indeed, be taken into consideration; and, of greatest detriment to the meaningfulness of any and all such results is the fact that even "experts" have difficulty in uniformly and reproducibly indicating where the boundaries of the optic disc and its excavation actually lie.