AACG causes irreversible damage to the optic nerve by increasing intraocular pressure, numerous studies have shown that glaucoma not only causes visual nerve damage, but also affects visual pathways, including the optic tract, optic chiasma, lateral geniculate body, visual radiation, and visual cortex (V1) [14, 15, 16]. However, conventional MRI is of limited value in the diagnosis of optic nerve and can only show changes in optic nerve morphology [17]. fMR technology based on BOLD effect has been widely used in the study of human brain function[18]. In terms of AACG,little has been published regarding its effect on the whole brain.
Right lobule crus2 of cerebellar hemisphere, is located in the cerebellar inferior lobe,the cerebellum is often considered as a link to involve in the regulation of body movement and balance function[19]. Meanwhile,the cerebellum is also involved in cognitive and emotional processing[20], study has reported that even subtle abnormalities in cerebellar volume may have functional impact on cognition[21]. Sang et al. found that there was a functional connection between the cerebellar hemisphic crus2 and the fronto-parietal network, which is very important for visual memory, language, cognition and other aspects [22]. In this study, decreased ALFF values in right lobule crus2 of cerebellar hemisphere may be a result of reduced visual signals from the primary and higher visual cortex to the cerebellum, which may be related to increased intraocular pressure and decreased vision in AACG patients. This may be related to the functional connection between the cerebellar hemispheric crus2 and the fronto-parietal network. Of course, this also suggests that AACG patients have dysfunction in emotional cognition and pain regulation, which provides a pathological basis for the occurrence of negative emotions and pain in PACG patients .
( V1) BA17 is defined as primary visual cortex (primary visual cortex,PVC), which receives visual input from the retina. Glaucoma retinal injury results in decreased visual stimulation received by PVA, resulting in neurodegeneration of visual cortex in glaucoma patients [23]. In the present study, The increase of spontaneous neural activity in BA17 indicated that the function of primary visual cortex was impaired.
The precuneus is involved in the visuospatial imagery, episodic memory retrieval, self-processing, and consciousness [24, 25]. BA18 and BA19 are defined as higher visual cortices that receive input information from PVC. The PVC receives informations from the lateral geniculate nucleus and then sends it out through two distinct anatomical streams[26]. The former involves the parietal gyrus and responds to spatial information and motional orientation; the latter pathway extends into the temporal lobe and responds to color and shapes[27]. Precuneus ( BA7) is part of parietal lobe, which belongs to the dorsal visual network pathway. Previous studies on functional imaging of glaucoma have also shown that the visual dorsal and ventral pathways of glaucoma patients show dysfunction in both task and resting states [28]. In this study, ALFF value of left precuneus (BA7) decreased. This result can be explained as the primary visual cortex and dorsal visual pathway damage caused by glaucoma, resulting in decreased visual information transmission, and then caused by glaucoma Changes in cortical structure and function occurred in the relevant brain regions.
Cuneus(BA18) belongs to the higher visual cortex, the increase of spontaneous neural activity in BA18 indicated that the function of higher visual cortices were impaired.
The fissura calcarina is the concentrated region of the primary visual contex and is involved in the construction of visual field.The lingual gyrus is located below the fissura calcarina and is the site that receives the fibers of the lateral geniculate body.jiang et al. found that brain regions showed a significant main effect for group included the right inferior occipital gyrus (Brodmann area [BA] 18) and right superior frontal gyrus (BA 10) [29]. Chen et al reported that POAG patients showed significant reduction of gray matter volumes in bilateral visual cortex using an optimized VBM analysis method [30]. Previous study have found that glaucomatous neuropathy from POAG may lead to decreased cortical activity in the visual cortex even in the visual field defined as the normal central area [16]. In this study, the decrease in spontaneous activity in the right lingual gyrus was consistent with previous studies. The pathophysiological change of glaucoma is the apoptosis of retinal ganglion cells, thus ,we speculated that visual information is transmitted backward from the visual pathway, decreased retinal input and synaptic degeneration lead to visual network dysfunction.
The supra marginal gyrus is associated with language perception and processing [31]. The inferior parietal lobule (IPL) is the terminal of the dorsal stream, which plays an important role in the coordination of the visual–motor function and is a core component of the parieto-occipital pathway [29] .It participates in a wide spectrum of highly integrated tasks, such as oculomotor, visuospatial imagery [13]. Therefore, decrease spontaneous activity in the right supra marginal gyrus and the inferior parietal gyrus could reflect impaired visual function in the AACG group.
The frontal lobe area ,known as the “frontal eye area”. The frontal lobe is involved in optical positioning, eye rotation adjustment, fixing point determination and spatial information processing. It is an important area for eye movement tracking. The superior frontal gyrus is associated with language perception and processing, and with self-awareness [32]. A study found that the gray matter volume of the superior frontal gyrus was decreased in POAG patients [33]. Chen et al. found a significant decrease in the bilateral gray matter volume in the superior frontal gyrus, postcentral gyrus, Rolandic operculum, and inferior frontal gyrus, which may indicate abnormalities in the CNS other than the visual cortex In this study [30].The decrease of ALFF in the right medial superior frontal gyrus and the left Medial frontal gyrus in AACG group was consistent with previous studies, thus, our results suggest that AACG may cause dysfunction in the frontal network. In addition, abnormal frontal lobe function is one of the important characteristics of the development of depression [34]. George et al. [35] believed that the frontal lobe was closely related to emotional and memory processes, and some scholars believed [36] that various emotional disorders such as depression were related to frontal lobe dysfunction, changes in frontal lobe function may be related to depression in patients with acute angle-closure glaucoma. This abnormal activation of the frontal lobe may lead to an increased risk of depression in patients with acute angle-closure glaucoma.
In conclusion, this study found that patients with acute angle-closure glaucoma had abnormal ALFF in brain areas such as vision, sensorimotor and emotion. It provides a new idea for further research on the neuropathological mechanism and treatment of AACG.