At the end of ERG and OCT acquisition at 15 weeks after suture application, a subset of OHT animals (n = 7) were euthanized by intracardiac injection of pentobarbital (Lethabarb; Virbac Pty Ltd., Crookwell, NSW, Australia). Eyes were enucleated and the cornea was pierced with a 30-gauge needle to allow penetration of the fixative (10% neutral buffered formalin). Before paraffin embedding and sectioning, tissue was dehydrated in washes of 70%, 95%, and 100% ethanol, then treated with chloroform (Sigma-Aldrich Pty Ltd., Castle Hill, NSW, Australia) and embedded in paraffin blocks. Sections (10-μm thickness) were cut and mounted on glass slides (Superfrost Plus; Thermo Scientific, Waltham, MA, USA). Slides were subsequently dewaxed, rehydrated, and stained with hematoxylin and eosin (H&E). Light microscopy and image capture were performed with an Aperio ScanScope CS instrument (Leica, North Ryde, NSW, Australia) at ×20 magnification and analyzed in Aperio ImageScope software. The number of cells in the ganglion cell layer was counted over an area of 250 (horizontal) × 20 (vertical) μm2, starting at 200 μm lateral to the scleral opening. Cell counts from both sides of the optic nerve were averaged to return an overall value for that retina. For each eye, cell counts were averaged over three consecutive sections.