The nasal nerve fibers (NFs) enter the nasal part of the disc. NFs originating from the nasal macular area proceed directly to the temporal part of the ONH whereas the NFs originating from temporal macular area and temporal horizontal raphe arch above and below the macular fibers to reach the ONH hence called arcuate fibers. The retinal NFs enter the ONH as superficial layer as a straight horizontal continuation.

The superficial NFs make 90 degrees turn in the prelaminar area. In the prelaminar area the loose NFs begin to form bundles and become vertically oriented and macular fibers shift to occupy the central position and enter the pores of LC as such. Therefore, in the LC the NFs are vertically oriented, arcuate NFs get mixed with rest of temporal NFs and lose horizontal raphe.

Glaucomatous field defects such as arcuate scotoma and Ronnie’s nasal step fully correlate with the arrangement of NFs while they are in retina or in the ONH before they make 90 degrees turn in the prelaminar region. But after their 90 degrees turn glaucomatous field defects wouldn’t correlate at all with the arrangement of NFs in the prelaminar region and beyond. This shows that primary site of in glaucoma is before NFs make 90 degrees turn. In nutshell, LC can’t be the primary site of injury due to absence of correlation between glaucomatous field loss and arrangement of NFs in lamina cribrosa.