Changes in Glaucomatous Optic Disc Cupping or Variability of Computerized Topographic Measurements?

Abstract

To the Editor. —We read the interesting article by Shin et al 1 in the November 1989 issue of theArchiveson the reversal of glaucomatous optic disc cupping. Though their findings are of significance, we feel that an important issue has been overlooked while interpreting the computerized topographic measurements of the optic nerve head. It is essential to distinguish random variability associated with the technique of computerized topographic measurements from actual changes in the optic nerve head over time. Based on repeated measurements on the same eyes, previous studies have reported confidence levels for the variability of optic nerve head topographic measurements with different computerized image analyzers. 2,3 Shin et al 1 used the Rodenstock analyzer. For this instrument, Bishop et al 2 calculated that two measurements on the same glaucomatous eye would have to differ by at least 0.138, 0.273 mm, 2 and 0.189 mm 3 for the