Application of Hemifield Visual Electrophysiology to Diagnose Functional Vision Loss

Neuro-ophthalmologists frequently see patients who are experiencing vision loss not accounted for by a neuro-ophthalmic disorder. In this article, we describe a case of binasal hemianopia in an otherwise healthy 65-year-old woman who was initially diagnosed with glaucoma but ultimately proved to have functional visual loss. This diagnosis was made by confirming by confirming normal visual pathway function using hemifield visual-evoked potential studies.

Photo Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Peter Quiros, MD Application of Hemifield Visual Electrophysiology to Diagnose Functional Vision Loss Heather E. Moss, MD, PhD, Sayena Jabbehdari, MD FIG. 1. Binasal hemianopia. Goldmann visual fields. Abstract: Neuro-ophthalmologists frequently see patients who are experiencing vision loss not accounted for by a neuro-ophthalmic disorder. In this article, we describe a case of binasal hemianopia in an otherwise healthy 65-year-old woman who was initially diagnosed with glaucoma but ultimately proved to have functional visual loss. This diagnosis was made by confirming by confirming normal visual pathway function using hemifield visual-evoked potential studies. Journal of Neuro-Ophthalmology 2020;40:527–529 doi: 10.1097/WNO.0000000000000882 © 2020 by North American Neuro-Ophthalmology Society A 65-year-old woman was seen for complete binasal visual field loss in both eyes. She initially presented with inferior nasal constriction in the right eye 2 years earlier. This progressed to complete nasal loss respecting the vertical meridian over 6 months, at which time the left eye developed inferior visual field loss that progressed to complete nasal loss Departments of Ophthalmology (HEM), and Neurology and Neurological Sciences (HEM), Stanford University, Palo Alto, California; and Department of Ophthalmology and Visual Sciences (SJ), University of Illinois at Chicago, Chicago, Illinois. NIH P30 EY 026877, Unrestricted grant from Research to prevent Blindness to the Stanford Department of Ophthalmology. The authors report no conflicts of interest. Address correspondence to Heather Moss, MD, PhD, Byers Eye Institute, Stanford University, 2370 Watson Court, MC 5353, Palo Alto, CA 94303; E-mail: [e-mail] Moss and Jabbehdari: J Neuro-Ophthalmol 2020; 40: 527-529 respecting the vertical meridian over 6 months. There were no functional limitations when using both eyes, and she reported no disability. She asked whether the findings could be related to stress as her job was particularly difficult. Multiple ophthalmic examinations were normal, and neither retinal nerve fiber layer (RNFL), ganglion cell, nor optic nerve contour changes were apparent on optical coherence tomography (OCT). Previous Humphrey 24-2 threshold perimetry showed complete nasal loss in both eyes with excellent reliability indices (0 fixation losses, false positive ,2%, false negative ,7%) on multiple tests. Noncontrast head and orbit computed tomography and full-field electroretinography had been within normal limits. She had a history of breast cancer in remission after surgery and chemotherapy, acquired hearing loss treated with cochlear implant with subsequent recovery, hepatitis B, idiopathic pancreatitis, and depression. Visual acuity was 20/25 in the right eye and 20/30 in the left eye with complete binasal visual field loss on confrontation testing in both eyes. Anterior and posterior segment examinations of both eyes were unremarkable. Goldmann perimetry showed complete nasal visual field loss and normal temporal fields in both eyes (Fig. 1). OCT showed normal RNFL thickness, normal macula ganglion cell complex thickness, and no structural abnormalities in the retina or optic nerve. CT of orbits and brain with and without contrast and CTA of the head and neck were unrevealing; these included a normal optic chiasm. An MRI could not be performed due to cochlear implants. 527 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay FIG. 2. Hemifield pattern visual evoked potentials. Stimulus patterns with red marker indicating fixation (top row). Occipital recordings for stimulus of the right eye (middle row) and left eye (bottom row). In each recording, red and green tracings are trials, and pink tracing is averaged recording (offset vertically). P100 latencies are similar for all recordings. P100 magnitudes are greater for temporal than nasal recordings in both eyes. Sum of hemifield P100 magnitudes equals the bilateral hemifield recording in each eye. Pattern visual-evoked potentials (VEPs) were recorded in each eye using checkerboard stimulus patterns (0.8o checks, 100% contrast, 2 Hz reversal rate; Envoy, Diagnosys LLC, Lowell, MA). To isolate the blind and seeing visual fields, waveforms were recorded at the occiput for 3 different stimulus areas for each eye: complete central field, nasal hemifield, and temporal hemifield (Fig. 2). In both eyes, P100 latency for all 3 stimulation patterns was similar, and the amplitude of P100 waves recorded during complete field stimulation was greater than for those recorded during temporal field or nasal field stimulation. The nasal field P100 amplitude was slightly less than the temporal field P100 amplitude in both eyes, and the complete field P100 amplitudes approximately equaled the sum of nasal and temporal field P100 amplitudes (Fig. 2). A diagnosis of functional visual field loss was supported by electrophysiological evidence for intact vision in the nasal fields of both eyes. The patient was counseled regarding this finding. Follow-up HVF perimetry was normal, which confirmed the diagnosis of functional visual field loss (Fig. 3). DISCUSSION Functional visual loss syndrome is the patient experience of visual symptoms despite the afferent visual pathways 528 being structurally and functionally intact. It is estimated that up to 5% of patients in ophthalmology clinic without any sign of ocular problems have functional vision loss (1,2). Diagnosis requires excluding other causes of vision loss and confirming normal visual function (3). This is challenging since afferent visual measurements, like all sensory examinations, are inherently subjective. Visual electrophysiology offers objective assessment of the visual pathway. Full-field and central pattern stimulation paradigms can be applied to confirm normal visual pathway function and diagnose functional vision loss that is asymmetric between the 2 eyes. Multifocal VEP testing has been applied to confirm intact visual pathway function in cases of visual field loss (4,5). However, this test is not widely available and requires specialized equipment. This case demonstrates modification of pattern VEP stimulus area to compare visual pathway function between fields within eyes to support a diagnosis of functional vision loss. Our method is based on pattern VEP equipment and does not require multifocal VEP. Although we manipulated the visual stimulus area using a software approach, this might be similarly accomplished by blocking a portion of the screen with opaque paper. Partial nasal visual field loss that is similar to the pattern demonstrated for our patient is a common presentation of Moss and Jabbehdari: J Neuro-Ophthalmol 2020; 40: 527-529 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay of her disorder, perhaps by providing reassurance that visual pathway function was intact in the blind fields. FIG. 3. Humphrey visual field 30-2 after recovery. Reliability indices were 0/11 fixation losses, 0% false-positive errors, and 0% false-negative errors in the right eye and 3/11 fixation losses, 14% false-positive errors, and 5% false-negative errors with the left eye. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: S. Jabbehdari and H. E. Moss; b. Acquisition of data: H. E. Moss; c. Analysis and interpretation of data: S. Jabbehdari and H. E. Moss. Category 2: a. Drafting the manuscript: S. Jabbehdari and H. E. Moss; b. Revising it for intellectual content: S. Jabbehdari and H. E. Moss. Category 3: a. Final approval of the completed manuscript: S. Jabbehdari and H. E. Moss. ACKNOWLEDGMENT optic neuropathies, including glaucoma. Dense nasal loss respecting the vertical meridian from a visual pathway disorder is rare, yet has been reported due to tumor (6) and outer chiasmal compression (7). In our case, imaging did not reveal either of these patterns, nor did OCT support ganglion cell loss as a contributing factor. Owing to the symmetry of symptoms between the 2 eyes, comparison of full-field ERG and pattern VEP testing was not helpful in supporting the suspected diagnosis of functional visual field loss. The results of the hemifield VEP testing confirmed intact nasal field function in both eyes in contrast to both confrontation visual field testing and formal perimetry. Although many patients with functional neurological conditions have co-occurring mood or anxiety disorders, the association between functional visual loss and other psychiatric disease is not absolute. Many patients respond very well to reassurance and intermittent checkups (8). In our case, the hemifield VEP test was associated with resolution Moss and Jabbehdari: J Neuro-Ophthalmol 2020; 40: 527-529 The authors are grateful to Jeffrey Farmer of Diagnosys LLC for his assistance with programming the hemifield pattern stimuli used in this case. REFERENCES 1. Miller BW. A review of practical tests for ocular malingering and hysteria. Surv Ophthalmol. 1973;17:241–246. 2. Kathol RG, Cox TA, Corbett JJ, et al. Functional visual loss: I. A true psychiatric disorder? Psychol Med. 1983;13:307–314. 3. 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