Optic radiation damage relates to reduced V1 and thalamus volume in cortical/cerebral visual impairment

Abstract

Purpose : Cortical/cerebral impairment (CVI) is the leading cause of pediatric visual impairment in developed countries. It is caused by pre/perinatal brain damage, which impairs the development of vision-related pathways, leading to visual field loss and deficits in higher order visual processing. The extent to which the primary visual pathway is damaged in CVI is unknown. To this end, the current study examined the volume of the thalamus and V1, as well as tractography of the optic radiations in individuals with CVI compared to typically sighted controls (CTL).

Methods : Subjects were scanned on a 3T Philips Achieva MRI system to acquire two structural T1w and a 64-direction high angular resolution diffusion imaging (HARDI) image (N_CVI=6, N_CTL=6). CVI was caused by either periventricular leukomalacia (PVL N=4) or epilepsy (non-PVL N=2). T1 data were processed in FreeSurfer to measure thalamus volume, V1 volume, and V1 cortical thickness. HARDI data were reconstructed in DSIStudio. Optic radiations were quantified for tract number, tract volume, average quantitative anisotropy (QA), and generalized fractional anisotropy (gFA).

Results : CVI was associated with significant reductions in thalamus volume (CVI=4993.8± 1824.1 mm³, CTL=7864.8±709.6 mm³ (mean±SD), p <0.005), V1 volume (CVI=1752.3± 258.7 mm3, CTL=2218.8± 412.2 mm³, p<0.01), V1 thickness (CVI=1.5±0.1 mm², CTL=1.7±0.08 mm², p<0.05), and optic radiations volume (CVI=6059.2± 5745.6 mm³, CTL=19187.1± 8787 mm³, p<0.005). Decreased fiber number was only observed in CVI due to PVL (CVI_PVL=1565.8±2700, CTL=23965±18451, p<0.05; CVI_non-PVL=10846±14174). QA was significantly increased in CVI (CVI=0.23±0.07, CTL=0.16±0.26, p<0.05), while there were no significant differences in gFA. Significant correlations were observed between thalamus volume and QA (r²=-0.59, p<0.005), tract volume (r³=0.52, p<0.05), and number of reconstructed fibers (r²=0.5, p<0.01). Visual inspection of the optic radiations revealed that fewer fibers were reconstructed to the upper banks of the V1 sulcus in individuals with CVI due to PVL.

Conclusions : The results indicate that the optic radiations, thalamus, and V1 are reduced in CVI. This may depend on the aetiology of CVI. For example, the optic radiations representing the lower visual field were decreased only in CVI due to PVL, corresponding to documented visual field loss.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.