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Shumpei Ogawa, Hiromasa Takemura, Hiroshi Horiguchi, Masahiko Terao, Tomoki Haji, Franco Pestilli, Jason D Yeatman, Hiroshi Tsuneoka, Brian A Wandell, Yoichiro Masuda; Disease in the photoreceptors (JMD) or retinal ganglion cells (LHON) affects optic tract and radiation tissue properties. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5844. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with Leber’s hereditary optic neuropathy (LHON) and juvenile macular degeneration (JMD) both have central vision loss: but, their retinal damage differs substantially. Whereas JMD damages principally the retinal photoreceptor layer, LHON damages the retinal ganglion cell (RGC) layer. We investigated whether these two types of retinal damage have different effects on trans-synaptic degeneration. We used optical coherence tomography (OCT) to measure retinal damage, including photoreceptor loss and peripapillary retinal nerve fiber layer thickness (RNFLT); we used diffusion MRI and fiber tracking to measure trans-synaptic degeneration of the optic tract, optic radiation, and occipital callosal fibers (OCF).
LHON (N=6), adult onset JMD (N=5), and healthy controls (N=8) participated in the study. We identified the optic chiasm, lateral geniculate nucleus (LGN), primary visual cortex (V1) and corpus callosum based on T1-weighted anatomical images. We used probabilistic fiber tractography (Sherbondy et al., 2008) to identify the optic tract, optic radiation, and OCF (connecting the left and right hemisphere V1). We compared OCT measures (RFNLT) and diffusion measures (fractional anisotropy, FA) and white matter tract volumes in each visual pathway between the groups.
Confirming the diagnosis, we found that RNFLT in the LHON group is significantly lower than control subjects as reported in standard atlases on healthy controls (Budenz et al., 2007). We found no statistically significant RNFLT difference between JMD subjects and controls - although 2 of 5 JMD patients were within the 90th percentile of the RNFL atlas. In both LHON and JMD the mean optic tract and -radiation FA values are significantly lower than values in controls. In these two tracts the FA values in LHON are lower than the corresponding values in JMD. There is also a corresponding reduction in optic tract and -radiation volume in both patient groups as compared with controls. We found no differences in FA between patients and controls in the OCF or the LGN. Hence, optic tract and -radiation FA reductions are specific to these visual pathways.
There is substantial trans-synaptic degeneration in the optic tract and radiation following damage to the photoreceptor layer (JMD) or retinal ganglion cell layer (LHON). There was no measurable diffusion difference in the OCF.
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