Abstract
Purpose: :
Spectral domain optical coherence tomography (SD-OCT) is a non-invasive technique for in vivo imaging of retinal structures. Brn3b knockout (-/-) mice lose a majority of their retinal ganglion cells before birth and are therefore expected to have thinner surface retinal layers compared to wild-type retinas. Three-dimensional (3D) segmentation of SD-OCT images allows quantification and comparison of combined nerve fiber layer (NFL) and inner plexiform layer (IPL) thicknesses in brn3b -/-, heterozygote, and wild-type mice.
Methods: :
A SD-OCT system designed for small animal imaging (Bioptigen, Research Triangle Park, NC) was used for in vivo imaging of mouse retinas. Images were acquired from both eyes of anesthetized knockout brn3b -/- and phenotypically wild-type heterozygote brn3b +/- and wild-type brn3b +/+ mice. Manual 3D segmentation was used for calculation of the NFL and IPL combined thicknesses. NFL cell counts of histological sections were then compared to the calculated layer thicknesses to confirm SD-OCT results.
Results: :
OCT images were obtained from the retinas of three month old brn3b -/-, brn3b +/- and brn3b +/+ mice. Combined NFL and IPL thickness maps calculated by manual segmentation gave an average thickness of 50 +/- 6 µm in brn3b -/- eyes and an average thickness of 65.8 +/- 5.8 µm in phenotypically wild-type eyes (brn3b +/+ and +/-). These differences in average thickness compare well with differences in cell counts of the NFL between knockout and wild type mice retinas.
Conclusions: :
3D segmentation of SD-OCT images provides a suitable method for quantification of retinal layer thickness in vivo. This method demonstrates the reduction in NFL and IPL combined retinal thicknesses in adult brn3b -/- mice compared to phenotypically wild type controls. In vivo imaging capabilities provided by the SD-OCT system will allow researchers to prospectively study changes in retinal ganglion cell death and retinal thickness in knockout brn3b -/- mice.
Keywords: transgenics/knock-outs • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer