In Vivo Imaging of the Retina, Choroid, and Optic Nerve Head in Guinea Pigs

<p><i>Purpose:</i> Guinea pigs are increasingly being used as a model of myopia, and may also represent a novel model of glaucoma. Here, optical coherence tomography (OCT) imaging was performed in guinea pigs. <i>In vivo</i> measurements of retinal, choroidal, and optic nerve head parameters were compared with histology, and repeatability and interocular variations were assessed.</p> <p><i>Methods:</i> OCT imaging and histology were performed on adult guinea pigs (<i>n</i> = 9). Using a custom program in MATLAB, total retina, ganglion cell/nerve fiber layer (GC/NFL), outer retina, and choroid thicknesses were determined. Additionally, Bruch’s membrane opening (BMO) area and diameter, and minimum rim width were calculated. Intraobserver, interocular, and intersession coefficients of variation (CV) and intraclass correlation coefficients (ICC) were assessed.</p> <p><i>Results:</i> Retina, GC/NFL, outer retina and choroid thicknesses from <i>in vivo</i> OCT imaging were 147.7 ± 5.8 μm, 59.2 ± 4.5 μm, 72.4 ± 2.4 μm, and 64.8 ± 11.6 μm, respectively. Interocular CV ranged from 1.8% to 11% (paired <i>t</i>-test, <i>p</i> = 0.16 to 0.81), and intersession CV ranged from 1.1% to 5.6% (<i>p</i> = 0.12 to 0.82), with the choroid showing the greatest variability. BMO area was 0.192 ± 0.023 mm², and diameter was 493.79 ± 31.89 μm, with intersession CV of 3.3% and 1.7%, respectively. Hyper reflective retinal layers in OCT correlated with plexiform and RPE layers in histology.</p> <p><i>Conclusion:</i><i>In vivo</i> OCT imaging and quantification of guinea pig retina and optic nerve head parameters were repeatable and similar between eyes of the same animal. <i>In vivo</i> visibility of retinal cell layers correlated well with histological images.</p> <p><b>Abbreviations:</b> optic nerve head (ONH), retinal ganglion cell (RGC), spectral domain optical coherence tomography (SD-OCT), enhanced depth imaging (EDI), minimum rim width (MRW), hematoxylin and eosin (H & E)