Structural Correlation Between the Nerve Fiber Layer and Retinal Ganglion Cell Loss in Mice with Targeted Disruption of theBrn3bGene

Mice with a targeted disruption of Brn3b (knockout Brn3b(-/-)) undergo the loss of a majority of retinal ganglion cells (RGCs) before birth. Spectral domain optical coherence tomography (SD-OCT) allows for the noninvasive examination of Brn3b(-/-) cellular loss in vivo.The central retinas of Brn3b(-/-) and phenotypically wild-type (Brn3b(+/+) and Brn3b(±)) mice were imaged by SD-OCT. The combined nerve fiber layer (NFL) and inner plexiform layer (IPL) were manually segmented and thickness maps were generated. The results were confirmed by histologic and immunofluorescence cell counts of the RGC layer (RGCL) of the same retinas.The combined NFL and IPL of the Brn3b(-/-) retinas were significantly thinner, and the histologic cell counts significantly lower, than those of the phenotypically wild-type retinas (paired t-test; P0.01 and P0.01, respectively). The combined NFL and IPL thickness and the histologic cell count correlated highly (R(2) = 0.9612). Immunofluorescence staining revealed significant RGC-specific loss in Brn3b(-/-) retinas (paired t-test; P0.01). The distribution of combined central NFL and IPL loss was not localized or sectorial.The strong correlation between the combined layer thickness and histologic cell counts validates manual OCT segmentation as a method of monitoring cell loss in the RGCL. A retinal thickness map assessed if combined NFL and IPL thickness loss in Brn3b(-/-) eyes was topographically specific. Generalized RGC and combined NFL and IPL loss was observed in the Brn3b(-/-) retinas, in contrast to topographically specific RGC loss observed in glaucomatous DBA2/J eyes.