Application of second harmonic imaging microscopy to assess structural changes in optic nerve head structure ex vivo.

Glaucoma represents the second leading cause of blindness worldwide. While both age and intraocular pressure (IOP) are well-recognized risk factors for this disease, the underlying pathologic process involves the accelerated death of retinal ganglion cells (RGCs) that is associated with progressive loss of vision. The loss of RGCs has been postulated to occur primarily by injury to axons in the optic nerve head (ONH) due to its anatomic features and the mechanical vulnerability of the lamina cribrosa, the specialized ONH zone comprised of collagen beams that define the channels or pores through which axon bundles exit the eye. Recent advances in multiphoton microscopy using femtosecond lasers that generate second harmonic (SH) signals from collagen allows for direct optical imaging of the lamina cribrosa. We assess the application of SH generated microscopy (SHG) to the study of the ONH, and test the general hypothesis that increasing intraocular pressure in the same eye results in the movement of ONH collagen beams leading to distortion of the lamina cribrosa channels and compression of the axon bundles.