Abstract
Purpose: :
To visualize and assess time-dependent changes in the retinal structures of rabbits with retinal degeneration by using spectral-domain optical coherence tomography (SD-OCT).
Methods: :
Rhodopsin Pro347Leu transgenic (Tg) rabbits1) (n = 6 eyes) and wild type (WT, NZW) rabbits (n = 4 eyes) were investigated at 6 and 8 weeks of age with SD-OCT (Multiline OCT, Heidelberg Engineering, Germany). We measured the total retinal thickness within a 3-mm diameter circle whose center was 3 mm inferior from the lower edge of the optic nerve head. A vertical scan through the optic nerve head was taken to determine the mean ONL thickness at 7 regions (0.5-1.0, 1.0-1.5, 1.5-2.0, 2.0-2.5, 2.5-3.0, 3.0-3.5, and 3.5-4.0 mm below the lower edge of the optic nerve head). Scotopic electroretinograms (ERG) were also recorded at 6 and 8 weeks old in the Tg and WT rabbits.
Results: :
The total retinal thickness in the Tg and WT rabbits at 6 weeks were 178.8 ± 7.4 and 199.7 ± 3.3 µm (mean ± SD), respectively. The total retinal thickness in Tg rabbits was significantly thinner than that in WT rabbits (p = 0.029). The ONL thickness in 6-week-old Tg rabbits was thinner than that in 6-week-old WT rabbits at sections 2.5-3.0, 3.0-3.5, and 3.5-4.0 mm inferior from the lower edge of the optic nerve head. In Tg rabbits, the ONL thickness was thinner at 8 weeks. On the OCT images of 6-week-old Tg rabbits, the parts corresponding to the inner segments (IS) and outer segments (OS) of the photoreceptors were widely hyperreflective and showed granular appearance. The junction between the IS and OS, which has been known to correlate with visual function, was practically undetectable in the 6-week-old Tg rabbits. OCT images of the outer retinal layers in Tg rabbits appeared unchanged at 8 weeks old.On ERG examination, the a-wave amplitudes of the mixed cone and rod response in Tg rabbits was 51.6 ± 18.7 µV at 6 weeks and approximately the same at 8 weeks. These amplitudes were significantly smaller than those in WT rabbits, both at 6 and 8 weeks (p = 0.0081, p = 0.0024).
Conclusions: :
We showed the in vivo time-dependent changes of photoreceptors in a rabbit model of retinal degenerationusing SD-OCT. Photoreceptor damage detected on OCT images correlated well with the visual function measured using ERG. Thus, in vivo imaging of Tg rabbits using SD-OCT will facilitate characterization of disease dynamics and evaluation of therapeutic effects after experimental interventions.1) Kondo M et al. IOVS. 2009
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • photoreceptors • electroretinography: non-clinical