Abstract
Purpose: :
To measure in vivo changes in retinal structure at different ages in two lines of mice deficient in the beta subunit of phosphodiesterase
Methods: :
Spectral-Domain Optical Coherence Tomography (sdOCT) images were obtained using the Bioptigen sdOCT device with the reference arm placed at 1186mm. Wildtype, rd1 and rd10 mice ranging in age from P14 to P131 were sedated with either 1% isoflurane or ketamine/xylazine. Horizontal and vertical linear scans (1.5mm width,1500 a-scans/b-scan x 60 frames/bscan) were obtained centered on the optic nerve. A rectangular volume scan (1.3 mm x 1.3 mm, 1000 a-scans/b-scan x 100 b-scans, 3 frames/bscan) centered on the nerve was obtained as well as annular scans at 0.3, 0.5, 0.8, 1.0, and 1.2 mm from the center of the nerve (1500 a-scans/b-scan, 100 frames/b-scan). Images were exported as AVI files into imageJ where they were registered using the Stackreg plug-in and averaged. Segmentation was performed using a custom written program in Igor Pro.
Results: :
At all ages tested, the following layers were visible in the wildtype mice: ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), external limiting membrane (ELM), inner segment/outer segment junction (IS/OS), and two outer layers, which likely represent the interdigitation of the photoreceptor tips and the RPE. At P14, the earliest time point tested, rd1 mice already demonstrated loss of IS/OS, ELM, and almost complete loss of the ONL. By P21, the ONL was no longer visible in rd1 mice and the OPL was decreased in thickness. The rd10 mice demonstrated a slower degeneration. At P18, there was loss of the IS/OS, but the ELM and ONL were intact. At P131, rd10 mice had complete degeneration of the ONL and exhibited shallow separation of the retina from the RPE.
Conclusions: :
Spectral Domain OCT imaging is useful for evaluating retinal degeneration in rd1 and rd10 mice. Longitudinal images from rd10 mice also reveal widespread but shallow retinal separation from the RPE. While such separations have been observed histologically, these in vivo images demonstrate that retinal separation is not solely the result of tissue processing.
Keywords: retinal degenerations: hereditary • imaging/image analysis: non-clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)