Are large optic nerve heads susceptible to glaucomatous damage at normal intraocular pressure? A three-dimensional study by laser scanning tomography.

To evaluate the effects of the presence of glaucomatous visual field defects and of intraocular pressure elevations on optic nerve head topography, we analyzed 148 left optic nerve heads of 148 patients using laser scanning tomography. The optic discs are classified according to computerized static perimetry and documented IOP readings: 101 discs show normal visual fields (36 normal discs, 22 ocular hypertensives, 28 normotensive glaucoma suspects and 15 ocular hypertensive glaucoma suspects), 47 discs (34 high-pressure glaucoma discs, 13 normal-tension glaucoma discs) demonstrate glaucomatous visual field damage. A two-way analysis of variance discloses significant differences (P < 0.01) between the groups of optic discs classified according to perimetry for most topometric parameters evaluated except for disc area. Classification according to documented IOP (cut off at 21 mmHg) results in larger disc areas in normotensive discs compared to hypertensive optic nerve heads in the study population. Results suggest that large discs may be susceptible to glaucomatous visual field damage at statistically normal IOP readings.