The Application Of DTI And BOLD-fMRI In Primary Angle-closure Glaucoma

Background and purposeGlaucoma is a group of optic neuropathies with a gradual loss of retinal ganglion cells accompanied by a progressive degeneration of the optic nerve,is the main causes of blindness worldwide. Early diagnosis is important for protecting the visual function of glaucoma.At present, visual field is still the gold standard for diagnosis of glaucoma.Howerve, Much study shows that lots of the retinal ganglion cells has been died and retinal nerve fiber layer (RNFL) thickness has been thinner before visual field defect.And a correlation between RNFL thickness and visual field defect was observed. Optical Coherent Tomography(OCT) is an non-contact, high resolution, non-invasive ophthalmology imaging technique,which could quantitatively estimate retinal nerve fiber thickness and optic disc parameters,it's similar to pathologic examination of living tissue. It provides a useful tool for early diagnosis, detect optic nerve damage and treatment of glaucoma.Conventional MRI can only show the shap of optic nerve, so the value of conventional MRI for glaucoma diagnosis is limitted. Diffusion tensor imaging (DTI) is the only noninvasive way to study shape and structure of white matter fibers in vivo currently.Bood oxygenation level-dependent functional magnetic resonance imaging (Bold-fMRI) is an noninvasive and repetitive imaging techniques to accurately locate action area and intensity of cerebral cortex,it's widely applied to clinical and fundamental research of cranial nerve subject.But the value of DTI and BOLD-fMRI in early diagnosis of glaucoma is needed to discuss.In our study, DTI and BOLD-fMRI were applied to study primary angle-closure glaucoma, the correlation between DTI parameters FA value and RNFL thickness was analyzed to discuss the value of DTI in detect optic nerve degeneration and clinical severity. BOLD-fMRI was applied to obeserve activation of visual cortex and to appreciate the application value of diagnosis and pathogenesis in primary angle-closure glaucoma. Materials and methods25 patients with chronic primary angle-closure glaucoma (patient group, monocular involvement in 4 cases, the rest were binocular involvement,46 eyes) and 20 normal volunteers (control group,40 eyes) were studied. Conventional MRI of brain and optic nerve and diffusion tensor imaging were performed on all subjects using Magnetom Trio 3T MRI. Single-shot spin echo planar imaging (SE-EPI) sequence was used for DTI. Initial data was handled by Siemens superior Syngo MR B15 workstation, and FA, MD,λ//,λ⊥parameters of DTI in optic nerves was obtained.Retinal nerve fiber layer thickness(RNFL) was measured by optical coherent tomography (OCT) of America OPTOVE company in all patients and control subjects respectively.The correlation between optic nerve FA and RNFL thickness was studied. DTI parameters and RNFL thickness was recorded as x±s. SPSS17,0 software was used for statistical annlysis.Paired and independent samples t tests were used for the group analyses as appropriate. Pearson correlation analysis was applied.The level was a= 0.05, statistics significance standard was P<0.05.fMRI data was analysed by SPM2 software on MATLAB platform. It included: (1) Within group analysis was performed on left and right eyes in patients and control subjects respectively, and average activation imaging were obtained. (2) Group analysis of left eye and right eye between the patients group and control group was performed respectively.The activation differences imaging between two groups were obtained.ResultsDTI and OCT Results1. On conventional MRI, optic nerve became thinner and vaginal cavity widened slightly in 8 optic nerves of 6 cases.2. Compared with control group, FA decreased,λ//,λ⊥and MD values increased in patient group. There was a significant difference of FA,λ//,λ⊥and MD values between patient group and control group (p< 0.05).3. There was no significant difference between right optic nerves and left optic nerves in patient group (p> 0.05).4. The FA of optic nerve in diseased group was lower than contronl group (p< 0.05), while the RNFL thickness was obviously thinner than contronl group (p< 0.05).5. A significant correlation between mean FA of the optic nerve and suferior, inferior and mean RNFL thickness was observed (r value was 0.612,0.557,0.607 respectively, all the p value<0.05).fMRI results1. In the control group, right eye activation image showed that the most obvious activation areas of the single eye of control group was primary visual cortex besides the calcarine sulcus, that was striate cortex(Brodmann17 area).In addition, hibateral fusiform gyrus, hibateral inferior frontal gyrus, left inferior occipital gyrus, middle occipital gyrus, superior occipital gyrus,left lingual gyrus, hibateral cuneate lobe, right inferior temporal gyrus showed activation. Besides, hibateral cerebellar hemisphere, vermis, brainstem, hippocampus also showed actived.2. In the control group, left eye activation image showed that the most obvious activation areas of the single eye of control group was primary visual cortex besides the calcarine sulcus, that was striate cortex(Brodmannl7 area).In addition, hibateral fusiform gyrus,left inferior occipital gyrus, middle occipital gyrus, superior occipital gyrus, left lingual gyrus, hibateral inferior frontal gyrus, hibateral middle frontal gyrus, hibateral cuneate lobe,left middle temporal gyrus showed activation. Lateral geniculate activated in 4 patients.Besides, hibateral cerebellar hemisphere, brainstem, hippocampus also showed actived.3. Compared with control group, right eye activation image showed that activation area and intensity of visual cortex decreased significantly, activation area of the right side visual cortex decreased obviously.Right middle temporal gyrus, right inferior parietal gyrus, right anterior precuneus gyrus appeared actived abnormally. The activation area of right inferior frontal gyrus enlarged.4. Compared with control group, left eye activation image showed that activation area and intensity of visual cortex decreased significantly, activation area of the right side visual cortex decreased obviously, left anterior cingulum gyrus, middle anterior cingulum gyrus, posterior cingulum gyrus, right middle temporal gyrus, hibateral angular gyrus appeared actived abnormally. In addition, the activation area of right middle frontal gyrus, left cuneus enlarged, hibateral cerebellar hemisphere enlarged.Conclusion1. DTI could detect abnormality and quantitatively provide information about the diagnosis and pathological process of optic nerve in patients with PACG.2. A significant correlation between mean FA of the optic nerve and RNFL thickness was observed, which suggests that FA may serve as an indicator of disease severity.3. Visual cortex of nomal person isn't symmetrical, the right side visual cortex actived obviously.4. Left and right eye activation image of glaucoma patient showed that activation area and intensity of visual cortex decreased significantly.5. There was abnormal activation area in the visual cortex, it suggested that compensatory adaptability appeared in the visual cortex of glaucoma patients.6. There were abnormality in DTI parameters of optic nerve and activation of primary visual cortex.It demonstrated that anterior visual pathway lession could influnce visual cortex, so glaucom is an entire visual pathway lesion.