Alteration of the optic radiations using diffusion-tensor MRI in patients with retinitis pigmentosa

Tractometry of Human Visual White Matter Pathways in Health and Disease

Diffusion-weighted MRI (dMRI) provides a unique non-invasive view of human brain tissue properties. The present review article focuses on tractometry analysis methods that use dMRI to assess the properties of brain tissue within the long-range connections comprising brain networks. We focus specifically on the major white matter tracts that convey visual information. These connections are particularly important because vision provides rich information from the environment that supports a large range of daily life activities. Many of the diseases of the visual system are associated with advanced aging, and tractometry of the visual system is particularly important in the modern aging society. We provide an overview of the tractometry analysis pipeline, which includes a primer on dMRI data acquisition, voxelwise model fitting, tractography, recognition of white matter tracts, and calculation of tract tissue property profiles. We then review dMRI-based methods for analyzing visual white matter tracts: the optic nerve, optic tract, optic radiation, forceps major, and vertical occipital fasciculus. For each tract, we review background anatomical knowledge together with recent findings in tractometry studies on these tracts and their properties in relation to visual function and disease. Overall, we find that measurements of the brain's visual white matter are sensitive to a range of disorders and correlate with perceptual abilities. We highlight new and promising analysis methods, as well as some of the current barriers to progress toward integration of these methods into clinical practice. These barriers, such as variability in measurements between protocols and instruments, are targets for future development.

Visual neuroprosthesis: present and possible perspectives

The purpose of this study is to provide an overview of the replacements used in lost vision in the form of the bionic eye, to show their deficiencies and outline other possibilities for non-invasive stimulation of functional areas of the visual cortex. The review highlights the damage not only to the primary altered cellular structures, but also to all other horizontally and vertically localised structures. Based on the results of a large number of functional magnetic resonance imaging and electrophysiological methods, the authors focus on the pathology of the entire visual pathway in pigmentary retinopathy (PR) and age-related macular degeneration (AMD). This study provides a recent overview of the possible systems used to replace lost vision. These range from stimulation with intraocular implants, through stimulation of the optic nerve and lateral geniculate nucleus to the visual cortex. The second part deals with the design of image processing technology and its transformation into the form of transcranial stimulation of undamaged parts of the brain, which is protected by a patent. This is comprehensive overview of the current possibilities of replacement of lost vision and a proposal for a new non-invasive methods of stimulation of functional neurons of the visual cortex.

Optogenetics for visual restoration: From proof of principle to translational challenges

Degenerative retinal disorders are a diverse family of diseases commonly leading to irreversible photoreceptor death, while leaving the inner retina relatively intact. Over recent years, innovative gene replacement therapies aiming to halt the progression of certain inherited retinal disorders have made their way into clinics. By rendering surviving retinal neurons light sensitive optogenetic gene therapy now offers a feasible treatment option that can restore lost vision, even in late disease stages and widely independent of the underlying cause of degeneration. Since proof-of-concept almost fifteen years ago, this field has rapidly evolved and a detailed first report on a treated patient has recently been published. In this article, we provide a review of optogenetic approaches for vision restoration. We discuss the currently available optogenetic tools and their relative advantages and disadvantages. Possible cellular targets will be discussed and we will address the question how retinal remodelling may affect the choice of the target and to what extent it may limit the outcomes of optogenetic vision restoration. Finally, we will analyse the evidence for and against optogenetic tool mediated toxicity and will discuss the challenges associated with clinical translation of this promising therapeutic concept.

Altered White Matter Integrity in Patients with Retinal Vein Occlusion: A Diffusion Tensor Imaging and Tract-Based Spatial Statistics Study

Background

To investigate microstructural alterations of white matter in retinal vein occlusion (RVO) patients by tract-based spatial statistics (TBSS) and diffusion tensor imaging (DTI). Material/Methods. DTI was performed on 14 RVO patients and 14 normal controls (HCs). We measured and recorded fractional anisotropy (FA) and radial diffusivity (RD) of white matter fibers and classified them through the receiver operating characteristic (ROC) curve and correlation analysis, respectively.

Results

The mean FA value of white matter in RVO patients is lower than the HCs, and the mean RD value in RVO patients increased, especially in the bilateral posterior thalamic, bilateral sagittal stratum, body of corpus callosum, cingulum, and fornix. The ROC curve of different brain regions showed high accuracy. Moreover, the mean FA and RD values were significantly correlated with visual and psychological disorders.

Conclusion

TBSS could be regarded as an important method to reveal the alterations of white matter in RVO patients, indicating the underlying neurological mechanism of the RVO.

Multi-Contrast Magnetic Resonance Imaging of Visual White Matter Pathways in Patients With Glaucoma

Purpose

Glaucoma is a disorder that involves visual field loss caused by retinal ganglion cell damage. Previous diffusion magnetic resonance imaging (dMRI) studies have demonstrated that retinal ganglion cell damage affects tissues in the optic tract (OT) and optic radiation (OR). However, because previous studies have used a simple diffusion tensor model to analyze dMRI data, the microstructural interpretation of white matter tissue changes remains uncertain. In this study, we used a multi-contrast MRI approach to further clarify the type of microstructural damage that occurs in patients with glaucoma.

Methods

We collected dMRI data from 17 patients with glaucoma and 30 controls using 3-tesla (3T) MRI. Using the dMRI data, we estimated three types of tissue property metrics: intracellular volume fraction (ICVF), orientation dispersion index (ODI), and isotropic volume fraction (IsoV). Quantitative T1 (qT1) data, which may be relatively specific to myelin, were collected from all subjects.

Results

In the OT, all four metrics showed significant differences between the glaucoma and control groups. In the OR, only the ICVF showed significant between-group differences. ICVF was significantly correlated with qT1 in the OR of the glaucoma group, although qT1 did not show any abnormality at the group level.

Conclusions

Our results suggest that, at the group level, tissue changes in OR caused by glaucoma might be explained by axonal damage, which is reflected in the intracellular diffusion signals, rather than myelin damage. The significant correlation between ICVF and qT1 suggests that myelin damage might also occur in a smaller number of severe cases.

Visual Cortex Engagement in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a family of inherited disorders caused by the progressive degeneration of retinal photoreceptors. There is no cure for RP, but recent research advances have provided promising results from many clinical trials. All these therapeutic strategies are focused on preserving existing photoreceptors or substituting light-responsive elements. Vision recovery, however, strongly relies on the anatomical and functional integrity of the visual system beyond photoreceptors. Although the retinal structure and optic pathway are substantially preserved at least in early stages of RP, studies describing the visual cortex status are missing. Using a well-established mouse model of RP, we analyzed the response of visual cortical circuits to the progressive degeneration of photoreceptors. We demonstrated that the visual cortex goes through a transient and previously undescribed alteration in the local excitation/inhibition balance, with a net shift towards increased intracortical inhibition leading to improved filtering and decoding of corrupted visual inputs. These results suggest a compensatory action of the visual cortex that increases the range of residual visual sensitivity in RP.

NEUROTRANSMISSION IN VISUAL ANALYZER AND BIONIC EYE. A REVIEW

AIMS

The aim of the work is to point out the transmission of electrical voltage changes in the visual analyser and thus the efficiency of the bionic eye.

MATERIAL AND METHODS

The review deals with the question of the transmission of electrical changes in visual path voltage under physiological and pathological conditions. In particular, it points to feedback autoregulatory damage not only of primarily altered cellular structures, but of all other, both horizontally and vertically localized. Based on the results of functional magnetic resonance imaging and electrophysiological methods, it shows the pathology of the entire visual pathway in three eye diseases: retinitis pigmentosa, age-related macular degeneration and glaucoma.

RESULTS

The thesis also provides an overview of possible systems that are used to replace lost vision, from epiretinal, subretinal, suprachoroidal implants, through stimulation of the optic nerve, corpus geniculatum laterale to the visual cortex.

CONCLUSION

Due to the pathology of neurotransmission, bionic eye systems cannot be expected to be restored after stabilization of binocular functions.

Preservation of Visual Cortex Plasticity in Retinitis Pigmentosa

Retinitis Pigmentosa (RP) is a class of inherited disorders caused by the progressive death of photoreceptors in the retina. RP is still orphan of an effective treatment, with increasing optimism deriving from research aimed at arresting neurodegeneration or replacing light-responsive elements. All these therapeutic strategies rely on the functional integrity of the visual system downstream of photoreceptors. Whereas the inner retinal structure and optic radiation are known to be considerably preserved at least in early stages of RP, very little is known about the visual cortex. Remarkably, it remains completely unclear whether visual cortex plasticity is still present in RP. Using a well-established murine model of RP, the rd10 mouse, we report that visual cortical circuits retain high levels of plasticity, preserving their capability of input-dependent remodelling even at a late stage of retinal degeneration.

Neuroplasticity of the visual cortex: in sickness and in health

Brain plasticity refers to the ability of synaptic connections to adapt their function and structure in response to experience, including environmental changes, sensory deprivation and injuries. Plasticity is a distinctive, but not exclusive, property of the developing nervous system. This review introduces the concept of neuroplasticity and describes classic paradigms to illustrate cellular and molecular mechanisms underlying synapse modifiability. Then, we summarize a growing number of studies showing that the adult cerebral cortex retains a significant degree of plasticity highlighting how the identification of strategies to enhance the plastic potential of the adult brain could pave the way for the development of novel therapeutic approaches aimed at treating amblyopia and other neurodevelopmental disorders. Finally, we analyze how the visual system adjusts to neurodegenerative conditions leading to blindness and we discuss the crucial role of spared plasticity in the visual system for sight recovery.

Radiation-Induced Cerebro-Ophthalmic Effects in Humans

Exposure to ionizing radiation (IR) could affect the human brain and eyes leading to both cognitive and visual impairments. The aim of this paper was to review and analyze the current literature, and to comment on the ensuing findings in the light of our personal contributions in this field. The review was carried out according to the PRISMA guidelines by searching PubMed, Scopus, Embase, PsycINFO and Google Scholar English papers published from January 2000 to January 2020. The results showed that prenatally or childhood-exposed individuals are a particular target group with a higher risk for possible radiation effects and neurodegenerative diseases. In adulthood and medical/interventional radiologists, the most frequent IR-induced ophthalmic effects include cataracts, glaucoma, optic neuropathy, retinopathy and angiopathy, sometimes associated with specific neurocognitive deficits. According to available information that eye alterations may induce or may be associated with brain dysfunctions and vice versa, we propose to label this relationship "eye-brain axis", as well as to deepen the diagnosis of eye pathologies as early and easily obtainable markers of possible low dose IR-induced brain damage.

BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT. Part І. THE CONSEQUENCES OF IRRADIATION OF THE PARTICIPANTS OF THE LIQUIDATION OF THE CHORNOBYL ACCIDENT

BACKGROUND

Exposure to ionizing radiation could affect the brain and eyes leading to cognitive and vision impairment, behavior disorders and performance decrement during professional irradiation at medical radiology, includinginterventional radiological procedures, long-term space flights, and radiation accidents.

OBJECTIVE

The objective was to analyze the current experimental, epidemiological, and clinical data on the radiation cerebro-ophthalmic effects.

MATERIALS AND METHODS

In our analytical review peer-reviewed publications via the bibliographic and scientometric bases PubMed / MEDLINE, Scopus, Web of Science, and selected papers from the library catalog of NRCRM - theleading institution in the field of studying the medical effects of ionizing radiation - were used.

RESULTS

The probable radiation-induced cerebro-ophthalmic effects in human adults comprise radiation cataracts,radiation glaucoma, radiation-induced optic neuropathy, retinopathies, angiopathies as well as specific neurocognitive deficit in the various neuropsychiatric pathology including cerebrovascular pathology and neurodegenerativediseases. Specific attention is paid to the likely stochastic nature of many of those effects. Those prenatally and inchildhood exposed are a particular target group with a higher risk for possible radiation effects and neurodegenerative diseases.

CONCLUSIONS

The experimental, clinical, epidemiological, anatomical and pathophysiological rationale for visualsystem and central nervous system (CNS) radiosensitivity is given. The necessity for further international studieswith adequate dosimetric support and the follow-up medical and biophysical monitoring of high radiation riskcohorts is justified. The first part of the study currently being published presents the results of the study of theeffects of irradiation in the participants of emergency works at the Chornobyl Nuclear Power Plant (ChNPP).

Electrically Evoked Potentials Are Reduced Compared to Axon Numbers in Rhodopsin P347L Transgenic Rabbits With Severe Photoreceptor Degeneration

Purpose

To determine the relationship between the amplitudes of the electrically evoked potentials (EEPs) and the number of optic nerve axons at a late stage of retinal degeneration in rhodopsin P347L transgenic (Tg) rabbits, a model of retinitis pigmentosa.

Methods

Six eyes of six wild-type (WT) (43.8 ± 7.5 months of age) and six eyes of six Tg (40.3 ± 2.6 months of age) rabbits were studied. The EEPs were elicited by 1 to 5 mA of transcorneal electrical stimulation. The first positive wave, the P1 component, was analyzed. After euthanasia, the number of axons in the optic nerve was counted.

Results

The threshold current to elicit a P1 was significantly higher in Tg rabbits than WT rabbits. The amplitude of P1 elicited by 5 mA in Tg rabbits was about 24% of that in WT rabbits (P < 0.01). The number of axons in the optic nerve of Tg rabbits was reduced to about 59% of that of WT rabbits (P < 0.01). The correlation between the axon number and the amplitude of the P1 in Tg and WT rabbits was not significant. The mean ratio of the P1 amplitude/axon in Tg rabbits was decreased to 53% of that in WT rabbits (P < 0.05).

Conclusions

The degree of reduction in the EEP in Tg rabbits is more severe than the reduction in the number of optic nerve axons. The use of transcorneal electrical stimulation to determine the suitable candidates for prosthesis at the end-stage of retinitis pigmentosa may underestimate the condition of the optic nerves.

Arterial Spin Labeling Perfusion Magnetic Resonance Imaging Reveals Resting Cerebral Blood Flow Alterations Specific to Retinitis Pigmentosa Patients

Purpose: This study aimed to assess resting cerebral blood flow (CBF) changes in retinitis pigmentosa (RP) patients using a pseudo-continuous arterial spin labeling (pCASL) perfusion method.Methods: Forty-nine RP patients and 51 healthy controls (HCs) underwent T1-weighted structural and pCASL sequence magnetic resonance imaging (MRI) scans at rest. Two-sample t-tests were performed to compare CBF differences between groups. Pearson correlation was used to analyze relationships between CBF values and clinical variables in the RP group.Results: Compared with HCs, RP patients had significantly lower CBF values in the bilateral cuneus/lingual gyrus/precuneus/posterior cingulate/middle occipital gyrus. In the RP group, CBF values in the left middle occipital and inferior occipital gyrus were positively correlated with mean retinal nerve fiber layer thickness; furthermore, CBF values in several regions were correlated with duration of disease and age of onset.Conclusions: Our results highlighted that RP patients exhibited decreased CBF values in the visual cortices and vision-related cortices. The results suggest that altered CBF might contribute to trans-synaptic retrograde degeneration of the visual pathway in RP patients.

Linking neural and clinical measures of glaucoma with diffusion magnetic resonance imaging (dMRI)

Purpose

To link optic nerve (ON) structural properties to clinical markers of glaucoma using advanced, semi-automated diffusion magnetic resonance imaging (dMRI) tractography in human glaucoma patients.

Methods

We characterized optic neuropathy in patients with unilateral advanced-stage glaucoma (n = 6) using probabilistic dMRI tractography and compared their results to those in healthy controls (n = 6).

Results

We successfully identified the ONs of glaucoma patients based on dMRI in all patients and confirmed that dMRI measures of the ONs correlated with clinical markers of glaucoma severity. Specifically, we found reduced fractional anisotropy (FA) in the ONs of eyes with advanced, as compared to mild, glaucoma (F(1,10) = 55.474, p < 0.0001, FDR < 0.0005). Furthermore, by comparing the ratios of ON FA in glaucoma patients to those of healthy controls (n = 6), we determined that this difference was beyond that expected from normal anatomical variation (F(1,9) = 20.276, p < 0. 005). Finally, we linked the dMRI measures of ON FA to standard clinical glaucoma measures. ON vertical cup-to-disc ratio (vCD) predicted ON FA (F(1,10) = 11.061, p < 0.01, R² = 0.66), retinal nerve fiber layer thickness (RNFL) predicted ON FA (F(1,10) = 11.477, p < 0.01, R² = 0.63) and ON FA predicted perceptual deficits (visual field index [VFI]) (F(1,10) = 15.308, p < 0.005, R² = 0.52).

Conclusion

We describe semi-automated methods to detect glaucoma-related structural changes using dMRI and confirm that they correlate with clinical measures of glaucoma.

Abnormal intrinsic brain activity in individuals with peripheral vision loss because of retinitis pigmentosa using amplitude of low-frequency fluctuations

The study aimed to determine alterations in intrinsic brain activity in retinitis pigmentosa (RP) individuals using the amplitude of low-frequency fluctuation (ALFF)/fractional amplitude of low-frequency fluctuation (fALFF) method. Sixteen RP individuals (10 men and six women) and 14 healthy controls (HCs) (six men and eight women) closely matched in age, sex, and education were enrolled in the study. The ALFF/fALFF method was applied to compare different intrinsic brain activities between the RP group and the HC group. The relationship between the mean ALFF/fALFF signal values of different brain regions and the visual measurements in RP group was analyzed by Pearson correlation. Compared with HCs, RP individuals had significantly lower ALFF values in the bilateral lingual gyrus (LIGG)/cerebellum posterior lobe [Brodmann area (BA) 17,18], but lower fALFF values in the bilateral LIGG/cerebellum anterior lobe (BA 17,18). Meanwhile, RP individuals had significantly higher ALFF in the bilateral precuneus cortex/middle cingulate cortex (BA 7,31), as well as higher fALFF values in the left superior/middle frontal gyrus (BA 9,10) and bilateral supplementary motor area (BA 6,8) (voxel-level P<0.01, cluster-level P<0.05). Moreover, the fALFF values of the bilateral LIGG/cerebellum anterior lobe showed positive relationships with the best-corrected visual acuity (BCVA)-oculus dexter (r=0.574, P=0.020) and BCVA-oculus sinister (r=0.570, P=0.021) in RP individuals; our results provide evidence that RP individuals may have impaired intrinsic brain activity in the primary visual area and the visuomotor coordination area that correlates with BCVA. Moreover, our findings indicate that reorganization of the dorsal visual stream and the parietoprefrontal pathway occurs in RP individuals.

Diffusivity and quantitative T1 profile of human visual white matter tracts after retinal ganglion cell damage

In patients with retinal ganglion cell diseases, recent diffusion tensor imaging (DTI) studies have revealed structural abnormalities in visual white matter tracts such as the optic tract, and optic radiation. However, the microstructural origin of these diffusivity changes is unknown as DTI metrics involve multiple biological factors and do not correlate directly with specific microstructural properties. In contrast, recent quantitative T1 (qT1) mapping methods provide tissue property measurements relatively specific to myelin volume fractions in white matter. This study aims to improve our understanding of microstructural changes in visual white matter tracts following retinal ganglion cell damage in Leber's hereditary optic neuropathy (LHON) patients by combining DTI and qT1 measurements. We collected these measurements from seven LHON patients and twenty age-matched control subjects. For all individuals, we identified the optic tract and the optic radiation using probabilistic tractography, and evaluated diffusivity and qT1 profiles along them. Both diffusivity and qT1 measurements in the optic tract differed significantly between LHON patients and controls. In the optic radiation, these changes were observed in diffusivity but were not evident in qT1 measurements. This suggests that myelin loss may not explain trans-synaptic diffusivity changes in the optic radiation as a consequence of retinal ganglion cell disease.

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Retinal ganglion cell damage affects diffusivity and T1 along visual pathways.

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DTI metric identified white matter change in both optic tract and optic radiation.

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T1 measurement in optic radiation did not exhibit abnormality, unlike DTI metric.

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Myelin loss may not be a major cause of diffusivity change along optic radiation.

Altered intra- and inter-regional functional connectivity of the visual cortex in individuals with peripheral vision loss due to retinitis pigmentosa

This study investigated changes in intra- and inter-regional functional connectivity (FC) in individuals with retinitis pigmentosa (RP) by using regional homogeneity (ReHo) and FC methods. Sixteen RP individuals and 14 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging scans (fMRI). A combined ReHo and FC method was conducted to evaluate synchronization of brain activity. Compared with HCs, RP individuals had significantly lower ReHo values in the bilateral lingual gyrus/cerebellum posterior lobe (LGG/CPL). In FC analysis, the RP group showed decreased positive FC relative to the HC group, from bilateral LGG/CPL to bilateral LGG/cuneus (CUN) and to left postcentral gyrus (PosCG). In contrast, the RP group showed increased negative FC relative to the HC group, from bilateral LGG/CPL to bilateral thalamus, and decreased negative FC from bilateral LGG/CPL to right middle frontal gyrus (MFG), and to left inferior parietal lobule (IPL). Moreover, ReHo values of the bilateral LGG/CPL showed negative correlations with the duration of RP. FC values of the bilateral LGG/CPL-left IPL showed negative correlations with best-corrected visual acuity (BCVA) of the right eye and left eye in RP individuals. Our results reveal reduced synchronicity of neural activity changes in the primary visual area in RP individuals. Moreover, RP individuals showed intrinsic visual network disconnection and reorganization of the retino-thalamocortical pathway and dorsal visual stream, suggesting impaired visuospatial and stereoscopic vision.

Age-related macular degeneration affects the optic radiation white matter projecting to locations of retinal damage

We investigated the impact of age-related macular degeneration (AMD) on visual acuity and the visual white matter. We combined an adaptive cortical atlas and diffusion-weighted magnetic resonance imaging (dMRI) and tractography to separate optic radiation (OR) projections to different retinal eccentricities in human primary visual cortex. We exploited the known anatomical organization of the OR and clinically relevant data to segment the OR into three primary components projecting to fovea, mid- and far-periphery. We measured white matter tissue properties-fractional anisotropy, linearity, planarity, sphericity-along the aforementioned three components of the optic radiation to compare AMD patients and controls. We found differences in white matter properties specific to OR white matter fascicles projecting to primary visual cortex locations corresponding to the location of retinal damage (fovea). Additionally, we show that the magnitude of white matter properties in AMD patients' correlates with visual acuity. In sum, we demonstrate a specific relation between visual loss, anatomical location of retinal damage and white matter damage in AMD patients. Importantly, we demonstrate that these changes are so profound that can be detected using magnetic resonance imaging data with clinical resolution. The conserved mapping between retinal and white matter damage suggests that retinal neurodegeneration might be a primary cause of white matter degeneration in AMD patients. The results highlight the impact of eye disease on brain tissue, a process that may become an important target to monitor during the course of treatment.

Structure-function correlations in Retinitis Pigmentosa patients with partially preserved vision: a voxel-based morphometry study

Retinitis Pigmentosa is a group of hereditary retinal dystrophy disorders associated with progressive peripheral visual field loss. The impact of this retinal loss in cortical gray matter volume has not been addressed before in Retinitis Pigmentosa patients with low vision. Voxel-based morphometry was applied to study whole brain gray matter volume changes in 27 Retinitis Pigmentosa patients with partially preserved vision and 38 age- and gender-matched normally sighted controls to determine whether peripheral visual loss can lead to changes in gray matter volume. We found significant reductions in gray matter volume that were restricted to the occipital cortex of patients. The anteromedial pattern of reduced gray matter volume in visual primary and association cortices was significantly correlated with the extent of the peripheral visual field deficit in this cohort. Moreover, this pattern was found to be associated with the extent of visual field loss. In summary, we found specific visual cortical gray matter loss in Retinitis Pigmentosa patients associated with their visual function profile. The spatial pattern of gray matter loss is consistent with disuse-driven neuronal atrophy which may have clinical implications for disease management, including prosthetic restoration strategies.

Reduced Field-of-View Diffusion Tensor Imaging of the Optic Nerve in Retinitis Pigmentosa at 3T

BACKGROUND AND PURPOSE

Diffusion tensor imaging may reflect pathology of the optic nerve; however, the ability of DTI to evaluate alterations of the optic nerve in retinitis pigmentosa has not yet been assessed, to our knowledge. The aim of this study was to investigate the diagnostic potential of reduced FOV-DTI in optic neuropathy of retinitis pigmentosa at 3T.

MATERIALS AND METHODS

Thirty-eight patients and thirty-five healthy controls were enrolled in this study. Measures of visual field and visual acuity of both eyes in all subjects were performed. A reduced FOV-DTI sequence was used to derive fractional anisotropy, apparent diffusion coefficient, principal eigenvalue, and orthogonal eigenvalue of the individual optic nerves. Mean fractional anisotropy, ADC, and eigenvalue maps were obtained for quantitative analysis. Further analyses were performed to determine the correlation of fractional anisotropy, ADC, principal eigenvalue, and orthogonal eigenvalue with optic nerves in patients with mean deviation of the visual field and visual acuity, respectively.

RESULTS

The optic nerves of patients with retinitis pigmentosa compared with control subjects showed significantly higher ADC, principal eigenvalue, and orthogonal eigenvalue and significantly lower fractional anisotropy (P < .01). For patients with retinitis pigmentosa, the mean deviation of the visual field of the optic nerve was significantly correlated with mean fractional anisotropy (r = 0.364, P = .001) and orthogonal eigenvalue (r = -0.254, P = .029), but it was not correlated with mean ADC (P = .154) and principal eigenvalue (P = .337). Moreover, no correlation between any DTI parameter and visual acuity in patients with retinitis pigmentosa was observed (P > .05).

CONCLUSIONS

Reduced FOV-DTI measurement of the optic nerve may serve as a biomarker of axonal and myelin damage in optic neuropathy for patients with retinitis pigmentosa.