Accepted Manuscript Don’t Get Off the Track Rod Foroozan, MD, Andrew G. Lee, MD PII:
S0039-6257(17)30160-1
DOI:
10.1016/j.survophthal.2017.05.005
Reference:
SOP 6724
To appear in:
Survey of Ophthalmology
Received Date: 12 May 2017 Accepted Date: 15 May 2017
Please cite this article as: Foroozan R, Lee AG, Don’t Get Off the Track, Survey of Ophthalmology (2017), doi: 10.1016/j.survophthal.2017.05.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Clinical Challenges
Don’t Get Off the Track
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Authors: Rod Foroozan, MD1 Andrew G. Lee, MD1,2 1
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Baylor College of Medicine
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Hospital, Houston, Texas
Correspondence: Rod Foroozan, M.D.,
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Department of Ophthalmology, Blanton Eye Institute, Houston Methodist
1977 Butler Blvd Houston, TX 77030
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Baylor College of Medicine
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Email:
[email protected]
Fax: (713) 798-6465;
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Tel: (713) 798-6100
The authors have no financial interests in any portion of the manuscript
(In keeping with the format of a clinical pathologic conference, the abstract and key words appear at the end of the manuscript.)
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Case Report A 43-year-old previously healthy man was referred for evaluation of decreased
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vision. There were no other neurological symptoms. He was operating a forklift when he was struck by an oncoming cargo train. He fell and hit his face and
head with loss of consciousness for an estimated 5 minutes. He had mild soft
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tissue swelling involving both upper and lower eyelids. He was taken to the
emergency room and had computed tomography (CT) of the head which showed
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no fractures, no hemorrhage, and no acute intracranial abnormalities. There was mild soft tissue swelling involving the periorbital area on each side. He was hospitalized for observation and had an MRI of brain without contrast that showed no intracranial abnormalities.
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He complained of a shadow in the vision to the left. He was seen by an ophthalmologist the following day, and no acute funduscopic abnormality was noted. He was discharged the day after the accident and was seen 1 week later.
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Visual acuity was 20/20 in each eye and the pupils were minimally reactive in each eye with no relative afferent pupillary defect (RAPD). He identified 10/10
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Ishihara pseudoisochromatic plates with each eye. Extraocular motility and funduscopy were normal. Optical coherence tomography of the retinal nerve fiber layer and macula were normal in each eye. He said he was unable to work and asked to have disability forms completed. He was told there was no ocular abnormality and no restrictions, including at work.
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Are the ophthalmic findings consistent with head trauma? Is a non-contrast CT and MRI of the brain adequate for this patient?
Comments
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Comments by Andrew G. Lee, MD
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What would you do next?
This 43-year-old man was involved in a serious motorized vehicular
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accident with loss of consciousness at the scene supporting the severity of the injury. Although a cranial CT and MRI scan showed only superficial soft tissue injury, these structural imaging studies may miss intracranial disease--and in particular non-contrast studies may miss lesions that may only be visible after contrast enhancement (e.g., meningeal disease, break down of the blood brain
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barrier). In addition, one critical part of the afferent visual pathway examination, the relative afferent pupillary defect (RAPD), was not present. The differential
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diagnosis for the lack of an RAPD in the setting of unilateral loss of vision includes: “no R, no A, no P, or no D”. Specifically, the RAPD is the ophthalmic
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examination sign that we use to detect the defect in the pupil pathway on the afferent side (i.e., an APD). In my opinion, these terms are not synonymous (i.e., an RAPD is not the same as an APD). If the defect is bilateral and symmetric in the afferent pupillary pathway (e.g., bilateral optic neuropathy or bilateral and symmetric glaucoma) then relative to the fellow eye there might not be a detectable RAPD.
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If the cause of the visual complaint is not afferent (e.g., diplopia, nystagmus), then of course there will also be no RAPD. Alternatively however the defect could still be afferent (i.e., sensory visual pathway), but either anterior
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(e.g., cornea, lens, refractive error, vitreous) to the afferent pupillary pathway
(i.e., retinal ganglion cell to optic nerve, chiasm, optic tract and pre-tectal nuclei in midbrain) or posterior to the afferent pupillary pathway (i.e., retrochiasmal
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afferent pathway, lateral geniculate body, optic radiations, and occipital cortex). There also might not be a detectable RAPD because there is no true defect in
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the afferent pathway (e.g., nonorganic visual loss). Finally, there may not be an RAPD detectable (pupils were non-reactive bilaterally or the patient is monocular). Lastly the RAPD as a finding could have been missed by the observer, especially an untrained or novice examiner.
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In this patient, no RAPD was seen, but the pupils were poorly reactive bilaterally this means that the RAPD could easily have been missed. In addition, patients with head trauma often have post-traumatic pain and headache, and the
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use of some pain medications (e.g., opiates) can cause small and poorly reactive pupils that complicate the pupil examination. The initial slit lamp examination was
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also not provided, and traumatic iris sphincter tears, tonic pupils, traumatic mydriasis/miosis (i.e., “stunned iris”), or traumatic uveitis can cause a poorly reactive pupil(s).
In this patient the OCT of the macula and optic nerves were normal.
Unfortunately, although this is helpful for excluding acute structural change in the macula (e.g., traumatic commotio retinae or macular hole) or anterior optic nerve
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(e.g., optic disk edema from traumatic optic neuropathy), a normal OCT does not mean that the patient is normal. A follow up ophthalmic examination and OCT might show delayed development of nerve fiber layer loss and optic atrophy in
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one or both eyes. Traumatic retrobulbar optic neuropathy will initially present with a normal fundus and only later will the telltale sign of optic atrophy develop.
Macular ganglion cell layer OCT might be useful in this setting to demonstrate
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ganglion cell loss that may precede more obvious optic atrophy clinically.
Although nonorganic overlay should be considered in this case, especially
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in light of the request for completion of “disability forms”, this is a diagnosis of exclusion in a patient with this severity of trauma. In my opinion, the diagnosis of nonorganic overlay requires two criteria: 1) a “normal eye examination” (or an examianation that does not account for the complaint); and 2) objective proof that
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the patient sees better than they claim. The presence of criterion one (the “normal” eye examination) is necessary, but not sufficient, for the diagnosis of nonorganic overlay. In addition, one of the fastest tracks to litigation in my
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experience is telling a patient who has a real problem that they are “faking” (e.g., malingering for secondary gain like disability) or that they need to see a
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psychiatrist (e.g., conversion or somatoform disorder). At this point the main piece of information missing from the ophthalmic
examination is a formal visual field. Automated perimetry might show an organic visual field defect in one (e.g., central scotoma or nerve fiber layer defects) or both eyes (e.g., bitemporal hemianopsia or homonymous hemianopsia). A patient with a traumatic bitemporal (traumatic chiasmopathy) or homonymous 5
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hemianopsia (traumatic retrochiasmal lesion) would be expected to have 20/20 visual acuity, might not have an RAPD, and would have an otherwise normal structural eye examination in the acute setting because the eye is technically
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“normal”. In addition, the traumatic chiasm or optic tract lesion is often difficult to image and a noncontrast CT or MRI of the head could easily miss the subtle
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findings of trauma in these locations.
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Case Report (Continued)
Neuro-ophthalmic examination 2 days later showed similar findings with slightly irregular and minimally reactive pupils to light and near. 1+ white cells was noted in the anterior chamber of each eye and small sphincter tears were noted in the
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iris of each eye. Confrontation visual fields suggested decreased sensitivity in the left hemifield. Funduscopy was normal in each eye.
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Automated perimetry showed a left homonymous hemianopia (Figure 1).
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He said he was unable to work and asked to have disability forms completed.
Could the complaint of decreased vision be nonorganic? What test could be performed to demonstrate an organic deficit? Comments (Continued) Comments by Dr. Lee
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Although nonorganic overlay is in the differential diagnosis for this patient, the presence of the uveitis suggests an organic etiology (presumably traumatic uveitis). Likewise, although a homonymous hemianopsia can be “faked” by a
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sophisticated “faker”, an untrained lay person would be unlikely to easily produce a homonymous hemianopsia as a nonorganic visual field defect. In my
experience the most common nonorganic visual field defect is diffuse/generalized
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depression or a “tunnel” constricted visual field (e.g., 5-10 degree central island in one or both eyes) that does not expand appropriately at 1 and 2 meter testing.
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Although nonorganic homonymous hemianopsia would be unlikely in this setting a hemi-field visual evoked potential (VEP) might be useful to confirm the organic nature of the visual field loss especially considering the patient’s persistent request for “disability” papers.
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I believe that every patient with a homonymous hemianopsia should undergo imaging directed at the contralateral retrochiasmal pathway. In this patient who has already had a CT and MRI scan that were normal the differential
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diagnosis includes post-traumatic optic tract syndrome versus unrecognized occipital lesion (e.g., hemorrhage or infarct). The lack of other systemic or
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neurologic findings makes a temporal or parietal lobe optic radiation lesion unlikely. Seizure however would also be in the differential diagnosis of a homonymous hemianopsia without structural retrochiasmal correlate on MRI.
Case Report (Continued)
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Visual evoked potentials using hemifield stimuli showed normal responses in the right hemifield of each eye and no responses in the left hemifield of either eye
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(Figure 2).
He returned 4 months after the injury and visual acuity was 20/20 in each eye.
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The pupils remained minimally reactive to light and near in each eye. Automated perimetry remained unchanged. Both optic discs were pale and optical
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coherence tomography (OCT) of the retinal nerve fiber layer showed decreased measures, diffusely in each eye, but worse superiorly and inferiorly in the right eye and nasally and temporally in the left eye (Figure 3).
(Figure 4). .
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An MRI of the brain without contrast showed atrophy of the right optic tract
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He said he was unable to work and asked to have disability forms completed.
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Why was the initial MRI of the brain normal and would another neuroimaging technique have demonstrated an abnormality in the right optic tract at that time? Why was there no relative afferent pupillary defect?
What would you do with the disability forms?
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Comments (Continued) Comments by Dr. Lee
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The OCT and fundus examination confirm band atrophy in the eye with the temporal visual field defect corresponding to the nasal fibers running like a band across the optic nerve (i.e., band or bowtie atrophy). The fellow eye with
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the nasal hemianopic visual field loss has a corresponding temporal (superior
and inferior) nerve fiber layer loss. This fundus and OCT finding suggests optic
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tract localization in the setting of the left homonymous hemianopsia. An RAPD can be present in the eye with greater visual field loss in a homonymous hemianopsia due to an optic tract syndrome. Typically, because the temporal visual field is larger than the nasal visual field and because the nasal fibers cross in the chiasm from the contralateral eye then a RAPD may be present in the eye
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contralateral to the optic tract lesion. 9,10
Optic tract lesions (and pretectal pathway lesions) can produce a
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contralateral RAPD, thus a right RAPD may be due to either a right sided (prechiasmal) or a left sided (optic tract or pretectal) lesion. The RAPD may be
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ipsilesional however in an optic tract lesion if the visual field loss happens to be greater in the ipsilateral rather than contralateral eye from differential effects on the optic tract (crossing or uncrossed fibers). Likewise, an RAPD may be absent in an optic tract lesion if the visual field loss is bilateral and symmetric and thus relative to the fellow eye there will be no RAPD detectable. Although MRI is sensitive to detection of lesions producing a homonymous hemianopsia the optic tract is notoriously difficult to image. Diffusion tensor imaging (DTI) on MRI may 9
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be useful in this setting for establishing disruption of the optic tract. DTI can show white matter tracts (i.e., tractography) very well and may be more sensitive especially in cases of trauma where an external compressive lesion, contrast
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enhancement, or perilesional T2 edema are not present.1,4,11
Depending on the patient’s job description and the details of their human resources employment contract the presence of the organic homonymous
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hemianopsia and optic tract atrophy likely would qualify the patient for
consideration for disability. Patients with a homonymous hemianopic visual field
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loss may not be able to drive depending on their own state law. The patient might also benefit from low vision rehabilitation therapy and consideration for hemianopic optical devices (e.g., hemianopic prism) or saccadic training in to the
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blind hemifield.
Discussion
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An optic tract syndrome is characterized by the combination of a homonymous hemianopia and RAPD.9,10 Acutely funduscopy is expected to be normal, and
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optic disk pallor develops over weeks to months, depending on the type of lesion. Decreased retinal thickness, particularly involving the ganglion cell and nerve fiber layers, has been found to be helpful in patients with optic tract lesions. 6
An optic tract lesion accounted for 10% of patients with a traumatic homonymous hemianopia in one series.4 Neuroimaging can help distinguish the cause of an
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optic tract syndrome in most cases5; however, even when MRIs were reviewed by neuroradiologists who suspected a lesion, optic tract pathology, particular when intrinsic to the tract, was overlooked. 8 In some patients with homonymous
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visual field loss typical structural imaging may not reveal a cause, whereas
tractography of the visual pathways (including the optic tract1) using diffusion
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tensor imaging has demonstrated the deficit. 11
Visual evoked potentials have been helpful in detecting post-chiasmal visual loss
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and can help document the degree of the functional deficit. Diminished or absent responses to hemifield stimuli has been helpful in documenting the visual deficits in these patients, including when nonorganic visual loss was considered as a potentially superimposed issue.2,3 The development of multifocal VEPs has also
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enabled testing for hemianopic and quadrantic defects without the need to
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assess each hemifield separately. 7
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Abstract:
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A 43 year-old man noted decreased vision after head trauma, with normal
neuroimaging acutely. He had a left homonymous hemianopia, confirmed with hemifield visual evoked potentials, from trauma to the right optic tract. Four
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months after trauma an MRI of the brain showed atrophy of the right optic tract,
and funduscopy revealed optic disc pallor with decreased retinal nerve fiber layer
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measures consistent with an optic tract syndrome.
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Keywords: Traumatic brain injury
Visual evoked potentials
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Optic tract syndrome
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Optical coherence tomography
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Methods of literature search:
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PubMed was the main resource used for literature search. A search was performed for optic tract syndrome and visual evoked potentials.
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Acknowledgements:
Disclosures:
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None
None of the authors have a proprietary or commercial interest in any product or
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concept discussed in the article.
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Legends:
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Figure 1. Automated perimetry showed a left homonymous hemianopia.
Figure 2. Visual evoked potentials using a stimulus of the right hemifield (A)
produced no responses (B).
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showed normal responses in each eye, while stimulation of the left hemifield
Figure 3. T2-weighted axial (A) and coronal (B) views of an MRI of the brain four
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months after head trauma showed atrophy of the right optic tract (arrows).
Figure 4. Optical coherence tomography of the retinal nerve fiber layer four
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months after head trauma showed decreased measures in each eye, diffusely in each eye, but worse superiorly and inferiorly in the right eye and nasally and
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temporally in the left eye.
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References:
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1. Al-Zubidi N, Ansari W, Fung SH, Lee AG. Diffusion tensor imaging in traumatic optic tract syndrome. J Neuroophthalmol 2014;34:95-8. 2. Beck RW, Schatz NJ, Savino J. Involvement of the optic chiasm, optic tract and geniculo-calcarine visual system in multiple sclerosis. Bull Soc Belge Ophtalmol 1983;208 Pt 1:159-91. 3. Biersdorf WR, Bell RA, Beck RW. Pattern flash visual evoked potentials in patients with homonymous hemianopia. Doc Ophthalmol 1992;80:51-61.
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4. Bruce BB, Zhang X, Kedar S, Newman NJ, Biousse V. Traumatic homonymous hemianopia. J Neurol Neurosurg Psychiatry 2006;77:986-8. 5. Fadzli F, Ramli N, Ramli NM. MRI of optic tract lesions: review and correlation with visual field defects. Clin Radiol 2013;68:e538-51. 6. Kanamori A, Nakamura M, Yamada Y, Negi A. Spectral-domain optical coherence tomography detects optic atrophy due to optic tract syndrome. Graefes Arch Clin Exp Ophthalmol 2013;251:591-5. 7. Klistorner AI, Graham SL, Grigg JR, Billson FA. Multifocal topographic visual evoked potential: improving objective detection of local visual field defects. Invest Ophthalmol Vis Sci 1998;39:937-50. 8. Kowal KM, Rivas Rodriguez FF, Srinivasan A, Trobe JD. Spectrum of Magnetic Resonance Imaging Features in Unilateral Optic Tract Dysfunction. J Neuroophthalmol 2017;37:17-23. 9. Newman SA, Miller NR. Optic tract syndrome. Neuro-ophthalmologic considerations. Arch Ophthalmol 1983;101:1241-50. 10. Savino PJ, Paris M, Schatz NJ, Orr LS, Corbett JJ. Optic tract syndrome. A review of 21 patients. Arch Ophthalmol 1978;96:656-63. 11. Yang TH, Oh SY, Kwak K, Lee JM. Homonymous Visual Field Loss without Structural Lesion on Magnetic Resonance Imaging: Documented with Positron Emission Tomography and Diffusion Tensor Imaging. Neuroophthalmology 2014;38:238-42.
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