An FMRI Investigation On The Visual Deficits Mechanisms Of Amblyopia

Amblyopia is a relatively common disease occurring at birth,or in the early life,which affects up to 3%of the general population.It is an optical uncorrectable visual disorder and has no detectable pathological or structural abnormalities.Its cause is still in a state of flux,yet indirect indication suggests that the visual impairment experience in early childhood may be the most possible reason.The functional deficit involves three classical models:spatial scale shift,topographical jitter and spatial undersampling,but no consistent conclusion can be accepted.Investigation into its neural basis could help to sreening and interference in amblyopia and guide the new way to treat the illness,as well as to understand the cortical plasticity and visual information processing.Animal models effectively modell the amblyopia by depriving the vison in cats and monkeys,and find out the neural deficits in early visual cortical areas.It cannot completely represent amblyopia,as the amblyopia is too complex to model.Psychophysical research has numerous indirect evidences about amblyopia,but sometimes its conclusion is so controversial that may need neurophysiological technology to prove it.Functional magnetic resonance imaging(fMRI)is an important non-invasive technique for measuring,mapping and researching brain activity that is safe and has excellent temporal and spatial resolution.Here fMRI studies as retinotopic mapping,multifocal flash project and Resting-state fMRI studies were used to analysis the visual deficits of anisometropia amblyopia as followed:1.Retinotopic mapping:According to the visual field,the fMRI retinotopic mapping could offer detail information about the corresponding visual area in each subject.The visual areas(V1-V4)were fine delineated by using VFS(Visual field sign)method.Retinotopic mapping analysis helped us to deep investigate the retinotopic mapping properties of the visual neural system and provided a way to fine process the different visual area as well as avoided the nonlinear distortion from normalization.2.Multifocal flash project:In order to evaluate the defect of topographical jitter and spatial undersampling,the multifocal checkboards were carried out to value the visual deficits in in anisometropia amblyopia.In general,amblyopes(A)tended to have larger interocular deviation scores than the normal controls(N),especially at small eccentricity and high visual areas.Even some extend of variances were evident at different stimulation positions.The correlation between the deviation score and the severity of amblyopia was caculated(i.e.,the visual acuity of the amblyopic eye)in different visual areas and eccentricities.Pearson correlation(p<0.05,2-tailed)between the deviation scores and the severity of amblyopia showed significant correlation in El and E2,but not in E3.Such phenomena existed in all the visual areas we tested here.According to the interocular deviation score results,topographical disorder was an important factor for the anisometropic amblyopia.Through the analysis of average%BOLD signal change,the cluster size and the peak point T value of ROI,we could find that the spatial undersampling may cause the impairment of spatial vision and information transfer between visual area even without contrast sensitivity and spatially broad-band involve.3.The intrinsic neuronal signaling contains the spontaneous fluctuations in blood signal and shows functionally related cortex regions and synchrony within neuroanatomical.Although the certain neurophysiological mechanisms is not clear,the neuronal signal is important for keeping the normal brain region function.Here the functional connection,regional homogeneity(ReHo)and.amplitude of low frequency fluctuations(ALFF)were conducted to analysis the resting-state fMRI studies.In the functional connection part,Brodmannl7(V1),Brodmann18(V2)and Brodmann19(V3,V4 and V5)were selected as the seed region.Focus on the visual area,we noted that the primary visual area showed a significant reduction of functional connection with V2 and V3 and even higher visual region.It may represent that the primary visual area was an important site of deficits in anisometropia amblyopia and may had certain functional defects to deliver information to the higher visual region.While the V2 had an even higher functional connection with other visual region.The possible reason may be that the amblyopia needed more neural connections to deliver the same information or perhaps the V2 needed to do the functional compensation due to the deficits of primary visual area.According to the analysis of ALFF and ReHo,the cognitive,attention and motor control regions performed lower signal homogeneity than the control group,while the region related to the motion sensitivity and integrate had a better signal homogeneity.In conclusion,the visual deficits mechanisms of amblyopia are diversity,amblyopia may suffer from the topographical and spatial undersampling both.We proposed the interocular deviation scores to evaluate the topographical jitter and average%BOLD signal change,the cluster size and the peak point T value of ROI to analysis the spatial undersampling.According to the resting-state fMRI analysis,the functional connection showed the V1 was the first site of deficits in anisometropic amblyopia and the value of functional connection between the V1 and higher visual area decreased.The ReHo and ALFF revealed that the cognitive,attention and motor control regions performed lower signal homogeneity than the control group and may lead to high cognitive dysfunction.The correlation revealed that the vision deficit may correspond to the spontaneous in certain brain area.