Measurement of the scleral canal using optical coherence tomography in patients with optic nerve drusen

The etiology of optic nerve drusen (OND) is unknown. A leading hypothesis is that eyes with OND have a small scleral canal. The small scleral canal presumably leads to optic nerve fiber compression, ganglion cell degeneration, extrusion of axonal mitochondria, and calcification of the extruded mitochondria. To determine if subjects with OND have scleral canals that are smaller than subjects without OND, we used optical coherence tomography (OCT) to measure the scleral canal in subjects with and without OND.

Prospective, observational case control study.

The study was conducted with subjects recruited from the clinics of the John A. Moran Eye Center, University of Utah Department of Ophthalmology and Visual Sciences. The study population included 25 subjects with OND, 13 unaffected first-degree relatives of OND subjects, and 17 control subjects. All subjects underwent measurement of the scleral canal with OCT. The main outcome measure was the scleral canal area calculated by OCT.

The average areas of the scleral canals were as follows: control eyes: 1.832 mm(2), unaffected eyes of subjects with unilateral OND: 1.836 mm(2), eyes of unaffected first-degree relatives: 2.067 mm(2), and eyes with OND: 2.520 mm(2). The scleral canal area of unaffected eyes of subjects with unilateral drusen was not significantly different from the control. The eyes of first-degree relatives and eyes with OND both had scleral canal areas significantly larger than the control.

Scleral canal size is probably not an etiologic factor in the pathogenesis of OND.