Optic Nerve Head Morphology is Associated with the Initial Location of Structural Progression in Early Open Angle Glaucoma

Precis: Glaucoma eyes with a small cup-to-disk ratio (CDR) tend to show retinal nerve fiber layer progression earlier than ganglion cell-inner plexiform layer progression.Purpose: To investigate the effects of clinical variables on the temporal relationship between macular ganglion cell-inner plexiform layer (mGCIPL) loss and peripapillary retinal nerve fiber layer (pRNFL) loss in glaucoma.Methods: This retrospective observational study used medical records of patients diagnosed with open angle glaucoma. Structural change was determined using guided progression analysis software of Cirrus optical coherence tomography. Based on the time of detection of pRNFL and mGCIPL changes, eyes showing progressive layer loss were categorized into the pRNFL-first and mGCIPL-first groups. The association between sites of layer thinning and clinical variables such as major retinal arterial angles and several optic disk measurements, including disk area, average CDR, and vertical CDR, were analyzed.Results: A total of 282 eyes were included in the study, of which 104 showed structural progression either in the mGCIPL or pRNFL. Out of these, 49 eyes showed the first progression in pRNFL, while 37 eyes showed the first progression in mGCIPL. The minimum mGCIPL thickness, pRNFL thickness, average CDR, vertical CDR, and location of progression were significantly different between the 2 groups (P=0.041, P=0.034, P=0.015, P<0.001, and P<0.001, respectively). In multivariate analysis, average CDR and vertical CDR were significantly associated with the progression site (P=0.033 and P=0.006, respectively). The structural changes in the inferoinferior area and the superior vulnerability zone were significantly associated with RNFL-first progression (P<0.001 for both).Conclusion: The location of layer loss and CDR are related to the layer where loss is first detected (either pRNFL or mGCIPL) in open angle glaucoma.