Quantitative studies of elastin in the optic nerve heads of persons with primary open-angle glaucoma

Purpose. Previous studies disagree as to the type of alterations observed in elastin fibers of glaucomatous optic nerve heads. We performed a masked, quantitative and qualitative evaluation of elastin fibers in normal and primary open-angle glaucoma (POAG). Methods. Ten eyes of 10 persons with POAG (confirmed by history and optic nerve evaluation) were compared to 10 age, race and gender-matched controls. None had exfoliation. Optic nerve heads were processed for transmission electron microscopy (TEM). 25 photographs at 20,000X were taken within beams of the lamina cribrosa (LC) and the insertion zone (IZ) of each optic nerve head in a random fashion. Total area for each photograph and its elastin fibers were measured on a planimeter to calculate elastin density and % area. Summary data for POAG and controls was obtained by averaging individual regional data. Results. Elastin fiber size did not differ significantly from control in POAG samples (LC p = 0.47, IZ p = 0.25). Density was not changed significantly by POAG (LC p = 0.40, IZ p = 0.87). However, in both control and POAG eyes, IZ elastin size was nearly double that of the LC, while elastin density in IZ was nearly half that of LC Thus, % elastin area was the same in both regions of the optic nerve head in control and POAG (8%). Masked qualitative evaluation of elastin fiber appearance found no obvious differences between control and POAG. Our study had a 90% power to detect a difference of 50% in % elastin area. Conclusions. We found no statistically significant difference in the elastin fibers in POAG compared to age-matched controls by TEM.