Aim-To evaluate and compare four different mathematical formulas for the early detection of morphometric optic nerve head changes in chronic open angle glaucoma. Methods-The optic nerve heads of 161 patients with perimetrically defined glaucomatous optic nerve damage and of 194 normal subjects were examined by confocal laser scanning tomography. Using four formulas of linear discriminant analysis and the optic cup shape measure as the single optic disc variable, the predictive power of each of these methods was examined to diVerentiate between the normal eyes and the glaucoma eyes. Results-The highest predictive power had an optic disc sector based formula, in particular in eyes with medium and large optic discs. This optic disc sector based formula was the one with the best agreement with the other formulas examined. It achieved a better predictability than any single optic disc variable evaluated. Conclusions-Combining quantitative optic disc variables by discriminant analysis functions, the predictive power of semiautomatic quantitative optic nerve head evaluation can be improved by providing the ophthalmologist with a diagnostic score for the detection of glaucomatous optic nerve damage. Because of the pattern of glaucomatous neuroretinal rim loss, an optic disc sector based discriminant formula may have a higher diagnostic precision than other formulas in detecting early glaucomatous damage. (Br J Ophthalmol 2000;84:464-468) Glaucomatous optic nerve damage leads to a multitude of morphological changes of the optic nerve head and to a great variety of functional deficits. The loss in function can be measured by achromatic or blue on yellow perimetry, flicker perimetry, colour vision testing, and many other psychophysical strategies.
1Most of the morphological alterations of the optic nerve head have been described semiquantitatively or qualitatively using the cup/ disc diameter ratio and qualitative variables such as the occurrence of disc haemorrhages and neuroretinal rim notches.
2Since the introduction of confocal laser scanning tomography, new technology has made possible the semiautomatic quantification of the topography optic nerve head. [3][4][5][6][7][8] Using this technique, a whole array of new quantitative variables has become available to detect early changes of the optic disc. [9][10][11][12][13][14] In an eVort to increase the predictive value of the quantitative variables in diVerentiating normal eyes from eyes with early glaucomatous damage, mathematical equations combining various morphometric variables have been proposed to increase the ability to detect early morphological changes.9 10 12-15The purpose of this investigation was to evaluate and compare four of these mathematical models (which have already been calculated and tested in previous studies on diVerent study populations in other glaucoma centres) on a new group of patients with glaucoma.
Patients and methodsThe study included 161 patients with chronic open angle glaucoma with a mean age of 54.9 (SD 11.7) years (range 2...