Journal of Neuro-Ophthalmology, September 2000, Volume 20, Issue 3

Functional Bitemporal Quadrantopia and the Multifocal Visual Evoked Potential

Cases of functional bitemporal hemianopia rarely have been reported. The authors describe the case of a patient with dense bilateral inferotemporal quadrantic field defects on a functional basis that was confirmed by multifocal visual evoked potential. The normality of the multifocal visual evoked potential provides evidence of the functional basis of the field defects.

Journal of Neuro- Ophthalmology 20( 3): 159- 162, 2000. © 2000 Lippincott Williams & Wilkins, Inc., Philadelphia Functional Bitemporal Quadrantopia and the Multifocal Visual Evoked Potential Dianna L. Miele, MD, Jeffrey G. Odel, MD, Myles M. Behrens, MD, Xian Zhang, BA, and Donald C. Hood, PhD Cases of functional bitemporal hemianopia rarely have been reported. The authors describe the case of a patient with dense bilateral inferotemporal quadrantic field defects on a functional basis that was confirmed by multifocal visual evoked potential. The normality of the multifocal visual evoked potential pro­vides evidence of the functional basis of the field defects. Key Words: Functional visual field defect-- Hemianopia- Multifocal visual evoked potential- Quadrantopia. CASE REPORT A 34- year- old woman who was an ophthalmic techni­cian presented for neuro- ophthalmologic evaluation of dense inferior bitemporal quadrantopia. The defects re­spected the horizontal and the vertical meridians and were discovered when she had a visual field performed as a test subject for a new machine ten months previ­ously; the defects were precisely unchanged after a 10- month interval ( Fig. 1). She had been asymptomatic, ex­cept for occasional mild headache and corrected myopia. An MRI scan obtained when the visual field abnormality was found showed a 1- cm pineal cyst with a wall that was slightly thicker than usual, but it was believed to be unrelated to the visual problem. Otherwise, results of the scan were within normal limits, including the appearance of the optic chiasm, which showed no sign of compres­sive or infiltrative defect. On examination, the patient's visual acuity with her glasses was 20/ 25 OD ( 20/ 20 with +. 25 sphere added), and 20/ 25 - 3 OS ( not improved). AO/ Hardy- Rand- Rittler ( HRR) color plates were 6 of 6 OU, and Amsler grid results were negative bilaterally. Her visual fields, tested with Humphrey 24- 2 central threshold Swedish Interactive Thresholding Algorithm ( SITA) standard pe­rimetry, were the same as previously reported by her ophthalmologist, with dense inferotemporal quadrantic Manuscript received November 2, 1999; accepted May 18, 2000. From the College of Physicians and Surgeons ( DLM) and the De­partment of Psychology ( XZ, DCH), Columbia University, New York, New York; and the Department of Ophthalmology ( JGO, MMB), Co­lumbia- Presbyterian Medical Center, New York, New York. Address correspondence and reprint requests to Jeffrey G. Odel, MD, 635 West 165th Street, New York, NY 10032. defect OU. There was no red hemianopic disparity above in either eye, although there was inferior disparity with nasal preference. Pupils were 3 mm and reactive to light, and there was no relative afferent defect. Posterior poles were normal, and optic disc appearance was slightly myopic in configuration, but there was no indication of atrophy. The peripapillary retinal nerve fiber layer ap­peared to be intact, and no retinal abnormality was seen in the superonasal quadrants. Based on the history and examination findings, the cause of the defect was uncer­tain, although it was suspected to be nonorganic in na­ture. An MRI scan was repeated 1 year later, and the results were unchanged. The patient was referred back to her ophthalmologist for follow- up. The patient returned 4 months later for additional neuro- ophthalmologic evaluation to address worsening visual field and visual acuity. At that time, her visual acuity with glasses was 20/ 30 ± 1 OD that improved to 20/ 20 - 1 with +. 75 sphere added. Visual acuity OS was 20/ 40 - 1 , which did not improve with manifest refraction over her glass and improved only to 20/ 40 + 1 by pinhole. AO/ HRR color plates were again 6 of 6 OU, and Amsler grid results again were normal. A small esodeviation was noted, and four diopter prism base- out test results sug­gested microtropia. During the examination, while at­tempting stereo circle testing, the patient mentioned that she never was able to appreciate stereo circles or ani­mals, which suggested microtropia with mild amblyopia OS. She also recalled that visual acuity OS was not fully correctable over the years. Her visual field, as tested with Humphrey perimetry, again showed the dense bitemporal quadrantic defect with some upper extension OS. On tangent screen, her visual fields were again full in all but the inferotemporal quadrants. Both eyes were tested to 30° to 3/ iooo white. Therefore, there was some inconsistency between the tangent screen and the Humphrey field in this regard. Her pupils were 2 mm bilaterally and reacted to light well and equally, without relative afferent defect. The poste­rior poles again appeared to be normal. When tested with regard to the hemifield slide phenomena, the examiner ( MMB) found she was able to see within the anticipated gap beyond the point of fixation inferiorly. 159 160 D. L. MIELE ET AL. 2S • » | ' <• II 21 29 31 32 33 I f 8 It (• < i (• ( i ( i a 31 32 32 ( 1 (• ( 1 II 27 31 32 34 32 31 29 23 it 31 33 >? 34 32 31 27 32 31 31 31 32 32 21 |" 27 27 » , 25 m , » 21 21 " l 32 29 31 31 29 33 31 31 27 31 32 ? 2 34 32 32 31 23 31 33 32 32 32 n 29 31 32 32 32 <• ( I ( 9 31 32 3! ^ < l II II ( 1 31 32 g n ( 1 II 31 \ n 1 < l ( 1 ¥ FIG. 1. Humphrey 24- 2 automated perimetry test showing dense inferior bitemporal quadrantopia. The gray scale is shown. There are 0/ 13 fixation losses OU, 0% false- positive errors OD, 1% false- positive errors OS, and 0% false negative errors OU. One month after the patient's second neuro- ophthal­mologic evaluation, examination findings were found to be unchanged, except for a return to the initial finding of inferior dense bitemporal quadrantic hemianopic defects, as seen with Humphrey perimetry. Her mild amblyopia OS persisted. At that time, multifocal visual evoked po­tential ( mVEP) was performed to confirm that the cause of the defects was not organic. The mVEP, a relatively new technique ( 1), allows the simultaneous recording of 60 responses from a single visual stimulus. The stimulus consists of 60 sectors, each of which is a 16- element checkerboard ( Fig. 2A). The sectors are scaled to ap­proximately match cortical magnification. The insert in Figure 2A shows the central 12 sectors. The spatial re­lation of the 60 sectors to the test locations of the Hum­phrey 24- 2 is shown in Figure 2B. Each sector goes through a random sequence of pattern reversals. After approximately 15 minutes of recording, the VERIS soft­ware ( Electro Diagnostic Imaging, San Mateo, CA) gen­erates 60 responses, one associated with each sector. The mVEP responses obtained from monocular stimulation OU are shown together in Figure 2C ( black = OD; gray = OS). The responses within each quadrant were added together and presented in Figure 2D. ( The superior right quadrant is outlined in Fig. 2D). The responses in the inferotemporal quadrants were within normal limits. More importantly, the mVEP responses OU were nearly identical ( Figs. 2C and 2D). Overall, the responses OS were slightly smaller, probably because of her mild am­blyopia, but there was no indication of the quadrantic defects seen in the original Humphrey automated perim­etry ( Fig. 1). In normal subjects, the monocular mVEP responses obtained after separate stimulation OU are ex­pected to show good agreement, as is discussed below. However, patients with amblyopia often show compara­tively decreased sensitivity in the affected eye. DISCUSSION Cases of functional bitemporal hemianopia rarely have been reported ( 2,3,4). Our patient presented with bilat­eral inferior temporal quadrantic, hemianopic, and alti-tudinal field loss OU. This defect was unusual in its respect of the horizontal meridian. Normally, a bitempo­ral defect is expected to have vertical demarcation, but not to respect the horizontal meridian precisely. This is because there is no anatomic correlate for an inferotem­poral bitemporal quadrantopia that respects the horizon­tal meridian. In addition, the lack of development of optic atrophy and the normality of the chiasm on MRI scans increased the examiner's index of suspicion of a nonorganic basis for the patient's field loss. The lack of postfixation blindness in the patient's sec­ond examination provided additional reason for suspi­cion. During her initial examination, the patient was un­able to see in the field posterior to fixation, which is to be expected with an organic bitemporal field loss ( 5). How­ever, she did not exhibit this sign during her second examination, which increased the suspicion that her dis­ease process was not organic. In addition, her visual field defects, while initially repeatedly unchanged, became somewhat inconsistent between tests, with her field at the time of our second examination showing superior exten­sion OS with further impairment of visual acuity, while our third field reverted to the original defect, which was limited to the inferior portion of the temporal visual field. Therefore, an mVEP was obtained. In their early report of the mVEP, Baseler et al. ( 1) concluded that the variability across subjects because of variations in gross cortical anatomy precluded its imple­mentation in the clinical setting. Although other studies ( 6,7) have reported a qualitative agreement between mVEP responses and the topography of the visual field, as determined by automated perimetry, the normal range includes very small, often nondetectable, responses ( 8). Hood et al. recently demonstrated that the monocular mVEP responses obtained after separate stimulation OU showed good agreement in control subjects ( 8). In addi­tion, abnormalities in patients detected by this interocular comparison of mVEP responses were consistent with au­tomated perimetry findings. The mVEP technique, including the suggested in­terocular comparison, proved useful in our case. The mVEP results did not correspond to the field defects the patient exhibited on automated perimetry, but rather they supported a nonorganic cause of field loss. In particular, the patient had good signals on mVEP where the auto­mated fields showed significant decrease in response sensitivity. Furthermore, the interocular comparison re­vealed similar responses from both eyes for stimulation throughout the lower field. J Neuro- Ophthalmol, Vol. 20, No. 3, 2000 FUNCTIONAL BITEMPORAL QUADRANTOPIA AND mVEP 161 B •; M-< ~" Left Superior Field Right Superior Field yv*^ v^* v Left Inferior Field Right Inferior Field - iA u 100 ms FIG. 2. A: The stimulus. The stimulus array consists of 60 separate sectors, each of which is a 16- element checkerboard. There are 12 sectors in the central 4.3°, as shown in the insert. Each sector goes through a sequence of pattern reversals. The software ( VERIS; Electro Diagnostic Imaging) produces 60 responses, each of which is associated with a particular sector ( see references 1, 6, and 8 for details). B: The locations for the Humphrey 24- 2 visual field superimposed on the multifocal visual evoked potential stimulus. C: The multifocal visual evoked potential: the multifocal visual evoked potential responses for monocular stimulation OD ( black) and OS ( gray). The location of the responses does not correspond with the location of the sectors in panel A; they are positioned for ease of presentation. The calibration bars ( lower right) denote 200 nV and 100 ms. D: Summed multifocal visual evoked potential responses: the responses OD ( black) and OS ( gray) were added for each of the four quadrants of the field. The responses of the right superior field are outlined in panel C. ( Panels A and B are modified from Fig. 1 in reference 8). Hesterberg and Tredici ( 9) reported that coexistence of organic and nonorganic disease frequently occurs, and Weller and Wiedemann ( 10) reported that previously ex­isting eye disease predisposes the eye to become the vehicle through which functional disturbances may be manifested later in life. Therefore, it is plausible that this patient's amblyopia ( and her status as an ophthalmic technician) may have been the nidus for the onset of functional visual field disturbance. In summary, it has been suggested that one potential clinical application for the mVEP is the evaluation of functional visual field defects. We find that the mVEP, which is objective and easy for the patient, is effective in the assessment of functional visual field defects, espe­cially when an interocular comparison of responses is made. However, it is important to note that clinical skill remains the best method for diagnosing nonorganic dis­ease. REFERENCES Baseler HA, Sutter EE, Klein SA et al. The topography of visual evoked response properties across the visual field. Electroencepha-logr Clin Neurophysiol 1994; 90: 65- 81. Keane JR. Patterns of hysterical hemianopia. Neurology 1998,51: 1230- 1. Keane JR. Neuro- ophthalmic signs and symptoms of hysteria. 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