Pathogenesis Of Chronic Glaucoma: A Two-Stage Disease

The most pathognomonic feature of chronic glaucoma is the orderly, peripheral-to-central loss of nerve fibers (NF).  Nerve fiber loss never occurs randomly in glaucoma.  The purpose of this study was to determine what could logically explain the orderly loss of NF in glaucoma.

Research study was carried out in a medical office setting.

Direct observation of 20 glaucomatous discs (GD) and 20 non-glaucomatous atrophic discs (NGAD) were analyzed with fundus photography (Topcon NW 6S, Japan). Measuring parameters included the course of blood vessels at the disc margin and disc excavation. The end-stage morphological features of both groups were then compared and deductive reasoning was applied.

Sloping and kinking of blood vessels at the disc margin was present only in GD subjects. Furthermore, morphology of end-stage GD subjects revealed excavation, whereas that of NGAD subject revealed non-excavated discs.  This suggests that the lamina cribrosa (LC) may be sinking, resulting in stretching and severance (axotomy) of NF at the scleral edge. This severance begins with the most peripheral NF (being closest to scleral edge), and ending with the most central NF in an orderly sequence. 

Elevated intraocular pressure (IOP) is the established cause of glaucoma, however elevated IOP can't cause orderly loss of NF by its direct action. Glaucoma may be a two-stage disease. First stage: the degeneration of border tissue of Elschnig.  Second stage: sinking of the LC and initiation of the orderly severance of NF.  The severance of nerve fibers can explain the orderly loss in glaucoma.  Glaucoma may not be an optic disc neuropathy, but an optic disc axotomy.