Scleral Canal Size and Optic Nerve Head Drusen

From projected optic disk photographs we measured the size of the scleral canal in two samples of emmetropic patients: one of patients with unilateral pseudopapilledema and drusen and the other of the general normal population. Measurements on the non-drusen-containing optic disk of patients with unilateral drusen were taken to reflect the scleral canal size of the fellow, affected eye. For both trained ( t = 6.642) and untrained ( t = 4.274) observers, the average diameters of the non-drusen-containing optic disks of patients with unilateral drusen were significantly smaller than those of the optic disks of normal patients (P = .0005, one-tailed independent t -test). The association of a small scleral canal with vascular anomalies, frequently noted in optic disks of patients with drusen, indicates a mesodermal dysgenesis of the optic nerve head.