Optic Nerve Disorders - part 10

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1. 254 D.C. Hood and K. Holopigian records. First, compare the mfERG responses Figure 11.8 illustrates an example in which to the visual field. In this case, her field depres- the effects of a fixation error are subtler. These sion extended at least to 25° (Figure 11.7F) and mfERGs are from a young woman with a very clearly did not agree with the location of the small central defect in her left visual field. Her depression of the mfERG (circle in Figure acuity was good, and her fixation appeared 11.7B). Based on this evidence alone, the hypo- steady. It was initially thought that her problem thetical retinal deficit in this patient should be was retinal because a few of the paracentral considered suspicious. Second, the 3D plot in responses (see responses in rectangle) appeared Figure 11.7D can be examined. Notice that both reduced in amplitude. However, an examina- the foveal peak and the optic disc depression tion of the 3D plot indicated that she was fixat- are displaced compared to the 3D plot from the ing slightly off center; this is easy to see when control subject with normal fixation (see Figure the 3D plot is compared to the plot from her 11.1A, bottom). The patient appears to be fixat- unaffected right eye. ing eccentrically, and all the apparent abnor- In sum, if care is not taken in the recording malities seen in the trace array in Figure 11.7B and interpretation of mfERGs, then depressed are based on poor fixation. The left column of responses caused by fixation errors can be mis- Figure 11.7 illustrates the point. Here an indi- interpreted as a retinal problem. vidual with normal vision was asked to fixate down and to the left 8.5° from the center. Notice Ruling Out Functional or how the pattern of the patient’s mfERG resem- Nonorganic Causes bles that of the results from the control in Figure 11.7A and 11.7C, except that the patient was When diagnosing optic nerve disorders, it is fixating up and to the left of the target. often important to rule out functional or non- OS OD A B mfERG responses. (B) 3D plots for the mfERGs in Figure 11.8. The problem of eccentric fixation. A. The 3D plot for the left eye indicates that the (A) mfERG from the two eyes of a patient. The left patient was fixating slightly off center, which could eye had a small central defect on the visual field and account for the reduced mfERG amplitudes in that the right eye had a normal visual field result. The area. black circle indicates an area of apparently decreased
2. 11. The Use of Multifocal ERGs and VEPs in Diagnosing Optic Nerve Disorders 255 organic causes. The advantage of the mfERG The Multifocal Visual Evoked technique over the conventional ERG is that Potential it provides a topographical representation that can be compared to the patient’s visual The VEP has long been used to diagnosis disor- fields. If the mfERG is abnormal in the same ders of the optic nerve. For example, delayed location as the field defect, then a nonorganic VEP responses in patients with optic neuritis/ cause can be ruled out. If, on the other hand, multiple sclerosis (ON/MS) were reported the mfERG is normal, then further tests almost 25 years ago.31,32 While the conventional (e.g., the mfVEP) are needed to rule out a VEP, elicited by either a pattern-reversal stimu- nonorganic cause. lus or bright flash, is still used to help in the diagnosis of ON/MS or to rule out nonorganic (functional) causes, the conventional VEP has Special Techniques for Detecting its limitations. First, conventional VEPs are Ganglion Cell Damage with dominated by responses from the lower field in the mfERG most individuals.33–35 Therefore, in some cases, large defects in the upper field will be missed The effectiveness of the human mfERG for with the conventional VEP. Second, the conven- detecting local ganglion cell damage is currently tional pattern reversal VEP is recorded to a under debate. Although some contradictory display at least 15° in diameter.36 Thus, local findings can be found in the literature, the evi- defects can easily be missed. In general, the lack dence is relatively clear on the following points. of spatial information can be a problem for the First, there is a component generated at the conventional VEP. optic nerve head that appears to reflect local The multifocal visual evoked potential ganglion cell activity. Sutter and Bearse23 first (mfVEP), developed by Baseler, Sutter, and identified this component in the human mfERG colleagues,37,38 allows the recording of local and called it the optic nerve head component VEP responses from the visual field by combin- (ONHC). Second, a component similar to the ing conventional VEP recording techniques ONHC has been identified in the monkey with multifocal technology. As in the case of the mfERG, and it appears to depend upon gang- mfERG, each region of the display is an inde- lion cell activity.24 Thus far, attempts to detect pendent stimulus and from a single, continuous glaucomatous damage with standard mfERG EEG signal, the software extracts the VEP recordings show relatively poor sensitivity and/ responses generated to each of the independent or specificity.8,25–27 However, the relatively small regions. Typically, local VEP responses are gen- ONHC in humans can be enhanced with speci- erated simultaneously from 60 regions of the alized paradigms of mfERG stimulation28,29 central 20° to 25° (radius) of the visual field to and/or methods of analysis.23 Finally, although create a topographic profile of the visual field. clear evidence of local damage has been reported in a few patients, in general the results Recording the mfVEP published to date have been disappointing.29,30 Thus, it remains unclear whether specialized For recording the mfVEP, the same electrodes mfERG recordings can be used to detect early and amplifiers employed for conventional VEP damage in patients with glaucoma. If the results recordings are used. However, the parameters of future studies are more encouraging, then of the stimulus and display and the analysis of the mfERG technique still needs to be compa- the raw records are different. Although new paradigms are being developed,39 most of the red to other objective tests of ganglion cell fun- ction, such as the pattern ERG (PERG), the published mfVEP data have been recorded photopic negative response (PhNR), and the with pattern reversal stimulation and a display multifocal VEP. For now, the mfERG cannot be similar to the one shown in Figure 11.9. considered a useful clinical tool for studying This display, first introduced by Baseler, Sutter, and colleagues,37,38 contains 60 sectors ganglion cell damage.
3. 256 D.C. Hood and K. Holopigian There is currently no agreement regarding stan- dard placement for the electrodes. However, all mfVEP recordings include at least one midline electrode placement. For example, for our midline channel we use two electrodes. One is placed at the inion plus 4 cm and serves as the “active,” and the other, on the inion, serves as 5.2° the “reference”; a third electrode, the ground, 44.5° is placed on the forehead. It is not uncommon to record from more than one channel at a time.40–42 For example, we use three “active” electrodes, one placed 4 cm above the inion and two placed 1 cm above and 4 cm lateral to the inion on each side of the midline.40,42 Every Figure 11.9. The multifocal VEP stimulus. This active electrode is referenced to the inion. display contains 60 sectors approximately scaled to account for cortical magnification. Each sector con- Presentation and Analysis of the tains 16 checks, 8 black and 8 white. mfVEP Responses Figure 11.10 shows software-derived mean approximately scaled to account for cortical mfVEP responses from 30 control subjects. The magnification. Each sector contains 16 checks, black traces are the responses for monocular 8 black and 8 white. stimulation of the right eye and the gray traces The mfVEP is recorded monocularly with are the responses from the left eye. As in the electrodes placed over the occipital region. case of the mfERG, each of the individual OD: black OS: gray 200 nV 100 ms Figure 11.10. The software-derived mean mfVEP right eye (OD) and the gray traces are the responses from the left eye (OS). (Reprinted from Hood,10 with responses from 30 control subjects. The black traces are the responses for monocular stimulation of the permission from Elsevier.)
4. 11. The Use of Multifocal ERGs and VEPs in Diagnosing Optic Nerve Disorders 257 mfVEP waveforms in the array is not, techni- is changing rapidly, and the analyses shown cally speaking, a “response.” Rather, each here, based upon our software, soon should be waveform is derived via a correlation between generally available in commercial software.To the stimulation and the continuously recorded illustrate these analyses, consider the patient signal. It is important to note that when the whose visual field (probability plot) is shown mfVEPs are displayed in an array, as in Figure in Figure 11.11A. This patient had unilateral 11.10, the responses are positioned arbitrarily glaucomatous damage in the left eye; the visual so they do not overlap. The spatial scale for field from his right eye was normal. The defects this array is not linear, which can be seen in the left eye are circled in gray and black. The in a comparison of the iso-degree circles in mfVEP responses obtained from the patient’s Figure 11.10 to the display in Figure 11.9. For left eye (red) and right eye (blue) are shown more details about the mfVEP technique, see in Figure 11.11B. Iso-degree contours repre- recent reviews.42,43 senting the same areas of visual space are shown for both the visual field and the mfVEP responses. Nearly Identical mfVEP Responses To determine which of the responses from the left eye (red records in Figure 11.11B) are from the Two Eyes abnormal, mfVEP probability plots analogous There is considerable intersubject variability to the visual field probability plot in Figure in the amplitudes and the waveforms of the 11.11A were developed. Monocular mfVEP mfVEP responses. This variability is caused probability plots (left two panels in Figure by individual differences in the location and 11.11C) were obtained by comparing the folding of the visual cortex.21,42 However, the patient’s monocular mfVEPs to the averaged responses of the two eyes from any individual mfVEPs from the left and right eyes of a group with normal vision are nearly identical, as can of control subjects (see Figure 11.10). For each be seen in the mean responses of Figure 11.10. sector, the amplitude of the patient’s mfVEP These mean responses from the two eyes are was determined and compared to the results nearly identical. The reason for this is that they from a control group.40,42,44,45 Each square is are generated in the same general cortical plotted at the physical center of one of the regions. The responses from the two eyes do sectors of the mfVEP display (see Figure deviate in relatively minor ways. First, there is 11.9A). A colored square indicates that the a small amplitude asymmetry along the hori- mfVEP was statistically significantly different zontal meridian. Second, there is a small inter- from the control data at either the 5% (desatu- ocular latency difference (of 4 or 5 ms) across rated color) or 1% (saturated color) level, and the midline. These small differences can be the color indicates whether it was the left (red) seen in the insets in Figure 11.10. The responses or right (blue) eye that was significantly smaller from the left eye are smaller, but are slightly than normal. faster, than the responses from the right eye Because the visual field (Figure 11.11A) and in the left visual field, and the reverse is mfVEP (Figure 11.11C) probability plots are true in the right visual field. (See Hood and shown on the same linear scale, a direct compa- Greenstein42 for a discussion of the reasons for rison can be made. To aid in this comparison, these differences.) the black and gray ellipses from Figure 11.11A were overlaid onto Figure 11.11C. Notice that the mfVEP results confirm the visual field Topographical Representation defect within the black ellipse but not the defect of the mfVEP within the gray ellipse. To detect local damage to the ganglion cells/ In some patients, especially those with unila- optic nerve requires specialized software, and teral damage, an interocular comparison of the the current analyses available with commerical mfVEP results is a more sensitive indicator of equipment are limited. However, this situation damage than is the monocular comparison to
5. 258 D.C. Hood and K. Holopigian B A OD/OS ratio N.S. OD/OS ratio >4.5 S.D. C Monocular Interocular OS OD Figure 11.11. Results from a patient with glaucoma. (C) Monocular and interocular mfVEP probability (A) The 24–2 HVF (probability plot) for the patient’s plots. Each symbol is in the center of a sector of the left eye with the defects circled in gray and black. mfVEP display. A black square indicates that there (B) The mfVEP responses from the patient’s left eye is no significant difference between the two eyes. The (red) and right eye (blue). The inset shows the results colored squares indicate that there is a significant of comparing the RMS ratios of two pairs of difference at greater than the 5% (desaturated) or responses to those from a group of control subjects. 1% (saturated) level. The color denotes whether the N.S., the ratio of amplitudes is not significantly dif- right (blue) or left (red) eye had the smaller response. ferent from normal. Iso-degree contours represen- A gray square indicates that the responses from ting the same areas of visual space are shown for both eyes were too small to allow for a comparison. (Modified from Fig. 12 in Hood et al.11) both the visual field and the mfVEP responses. the control group.42,46 To obtain the interocular within the gray ellipse is still not apparent, but an arcuate defect is detected in the lower field mfVEP plot in Figure 11.11C (right-hand that was not present in the visual field. panel), the ratio of the mfVEP amplitudes of Subsequent tests confirmed that this defect was the two eyes is measured for each sector of the real. (Hood and Greenstein42 provide a review display and compared to the ratios from the group of controls.21,40,42,47,48 The result is coded of the derivation and use of both monocular and interocular probability plots.) as in the case of the monocular fields. The defect
6. 11. The Use of Multifocal ERGs and VEPs in Diagnosing Optic Nerve Disorders 259 right eye) as well as one that was 34.2 ms slower Measuring Latency as on the monocular comparison (i.e., relative to Well as Amplitude the control group). It is now possible to objectively measure the latency of individual mfVEP waves.49,50 Figure The Origins of the mfVEP 11.12A shows the visual field probability plot There are two lines of evidence that the mfVEP from the left eye of a patient; her right eye had is generated largely in V1. First, as originally a normal visual field. Figure 11.12B shows the pointed out by Baseler et al.,37 the mfVEP mfVEPs from the right and left eyes. Figure waveforms reverse polarity as one crosses the 11.13A shows the amplitude probability plots horizontal meridian (see the reversal of the of her mfVEPs are normal on the monocular waveforms in Figure 11.10).42,51 The mfVEP plots but that the interocular plot shows a rela- from the upper visual field is reversed in polar- tive loss in amplitude for the left eye. Figure ity as compared to the lower, whereas the con- 11.13B shows the results of the latency analysis ventional VEP recorded with the same plotted in an analagous fashion to the ampli- electrodes positions and on the same subjects tude plots. In particular, a colored circle indica- may show the same polarity for upper and tes that the mfVEP latency was significantly lower field stimulation.35 Only potentials gener- longer at either the 5% (desaturated color) or ated from inside the calcarine fissure should 1% (saturated color) level, whereas the color behave this way. Second, a mathematical analy- indicates whether it was the left (red) or sis of the multifocal VEP sources suggests that right (blue) eye that was significantly longer most of the signal is generated in V1.52 Third, than normal. In this example, the latency of the using an application of principal-component left eye was, on average, 7.8 ms slower than analysis, Zhang and Hood53 provided evidence the right, as compared to the normal control that the first principal component of the mfVEP subjects. An individual point is shown that was was generated within the calcarine fissure and 15 ms slower on the interocular comparison thus within V1. The clinical implication is that (i.e., her left eye was delayed relative to her A B Figure 11.12. Results from a patient with vision loss was normal. (B) The mfVEPs from the right (blue) in the left eye. (A) The visual field probability plot and left (red) eyes of the patient. from the affected left eye of a patient; the right eye
7. 260 D.C. Hood and K. Holopigian A Amplitude Probability Plots Interocular Plot Monocular Plots B Latency Probability Plots 15 ms 34.2 ms Figure 11.13. Monocular and interocular probabi- cantly smaller than normal. (B) Latency results. A lity plots derived from the VEP results shown in Fig. colored circle indicates that the mfVEP latency was 11.12. (A) Amplitude results. A colored square indi- significantly longer at either the 5% (desaturated cates that the mfVEP amplitude was significantly color) or 1% (saturated color) level; the color indi- smaller at either the 5% (desaturated color) or 1% cates whether it was the left (red) or right (blue) eye (saturated color) level; the color indicates whether it that was significantly longer than normal. was the left (red) or right (blue) eye that was signifi- However, before summarizing the uses of the damage beyond V1 does not necessarily produce mfVEP, it is important to understand the effects abnormal mfVEPs. of local ganglion cell/optic nerve damage on the mfVEP. Hood et al.46 showed that the signal in The mfVEP and the Diagnosis of the mfVEP response was linearly related to the Optic Nerve Disorders loss in visual field sensitivity. To take a simple example, this means that a loss of 10 dB in visual For a number of years we have recorded field sensitivity will reduce the amplitude of the mfVEPs from the patients of two neuro- signal in the mfVEP response by a factor of 10; ophthalmologists (Drs. M. Behrens and J. Odel) this will result in an mfVEP response indistin- and two glaucoma experts (Drs. R. Ritch and guishable from noise. Therefore, relatively small J. Liebmann). In this section, we summarize the visual field sensitivity losses (6 dB or so) caused most common uses of the mfVEP in diagnosing by optic nerve damage produce profound losses optic nerve disorders. Other examples can be found in recent reviews.42,43 in mfVEP amplitude.
8. 11. The Use of Multifocal ERGs and VEPs in Diagnosing Optic Nerve Disorders 261 this region there are areas with delayed mfVEP The Diagnosis and Follow-Up of Optic responses (asterisks) and regions with reasona- Neuritis/Multiple Sclerosis bly normal mfVEP responses (plus signs). In During the acute phase of ON/MS, mfVEP fact, regions with delays can border regions that amplitudes are depressed in all regions where have responses with normal amplitude and the visual field sensitivity is decreased.54 Typi- latency. Thus, the mfVEP is able to detect local demyelinizaton.54 cally, optic neuritis shows partial or complete recovery within 3 months and so does the Therefore, for diagnosing patients with ON/ mfVEP. In fact, those patients with normal MS, the mfVEP is superior to SAP and the visual fields after recovery have normal or near- conventional VEP. We have seen a number of normal mfVEP amplitudes, although the latency cases of ON/MS in which the mfVEP was in some regions will be markedly delayed.54,55 abnormal but the conventional VEP was These regions with the delayed mfVEP presu- normal. In these patients, whether the conven- mably correspond to the portions of the optic tional VEP is normal depends upon the relative nerve that were demyelinated. The mfVEP contributions of the normal and abnormal records in Figure 11.14B show the range of regions of the visual field. The conventional findings that can be observed in a patient who VEP is most likely to miss local delays if the had an attack of optic neuritis in the left eye.54,55 delays involve very small areas or occur in the In this case, the visual field probability plot upper field, which typically contributes less to (Figure 11.14A) shows a paracentral defect and the overall VEP signal than does the lower field.35 Figure 11.15 shows the SAP probability the amplitude of the mfVEP is depressed in this region (ellipse in Figure 11.14B). However, the plot (panel A) and mfVEP responses (panel B) mfVEP (Figure 11.14B) shows that outside of of a 45-year-old man who complained of blurred A B 24-2 HVF (OS) black: OD gray: OS Figure 11.14. Results from a patient with optic neu- on the visual field (ellipse). However, outside this ritis in the left eye. (A) The visual field probability region there are areas with delayed mfVEP respon- plot from the left eye shows shows a paracentral ses (asterisks) as well as regions with reasonably defect. (B) The mfVEPs from the left eye show normal mfVEP responses (plus signs). (Reprinted from Hood,10 with permission from Elsevier.) depressed amplitudes in the area that was affected
9. 262 D.C. Hood and K. Holopigian A OS OD B OD: black, OS: gray Figure 11.15. Results from a patient with blurred (gray) and right (black) eyes. The insets show the vision in the superior field of the left eye. (A) The mfVEPs summed within each quadrant, indicating visual fields for the left and right eyes were essen- delayed mfVEPs in the upper field for stimulation of the left eye. (Modified from Fig. 14 in Hood et al.11) tially normal. (B) mfVEP response arrays for the left vision in the superior field of his left eye. The visual fields, a small percentage of the patients diagnosis of MS was confirmed from magnetic with ON can present with swollen discs but resonance imaging (MRI) studies, which showed without pain. In these cases, it is important lesions in the left optic nerve. His conventional to distinguish between ON, ischemic optic pattern VEP, as well as his SAP fields (panel A), neuropathy (ION), or a compressive lesion. were normal. The insets in panel B show the We have found the mfVEP useful in these cases.43 mfVEPs summed within each quadrant. The mfVEPs are clearly delayed in the upper field Finally, the mfVEP is particularly useful for the left eye. This change was missed on for following patients with ON/MS, especially the conventional VEP, presumably because the in cases in which the visual field is normal. upper field contributed relatively little to the We have recently documented recovery of conventional VEP. local mfVEP latencies in some patients Although the diagnosis of ON can usually whose visual field thresholds are normal and stable.56 be made based upon the patient’s history and
10. 11. The Use of Multifocal ERGs and VEPs in Diagnosing Optic Nerve Disorders 263 whose complaint of a localized visual loss was Ruling Out Functional or thought to be nonorganic in nature. His fields Nonorganic Causes were unreliable, and he was under emotional The conventional VEP has been used to rule stress at home and work. However, his mfVEP out functional or nonorganic causes for visual confirmed a local deficit in the same general defects. Because multiple, local responses are region as his complaint. The local change in the obtained, the mfVEP is more effective than the mfVEP can be seen in the records of panel A conventional VEP for this purpose. For example, and the interocular probability plot of panel B. a local defect can be identified on the mfVEP The mfVEPs and the corresponding SAP points and can be missed on the conventional VEP if illustrate the local loss. Subsequent tests revea- the defect involves a small part of the total field led a diagnosis of Leber’s optic atrophy. In pati- stimulated. In these cases, the (incorrect) dia- ents such as this one with localized deficits, the gnosis of a functional cause can be avoided. conventional VEP is often normal. Figure 11.16 provides an example of a patient Conversely, when faced with normal mfVEP responses in regions of the field where the visual field shows a profound defect,57 the oph- thalmologist will be comfortable making a dia- A gnosis of a nonorganic cause. In fact, the mfVEP, with its topographical measures, provides more information and a greater degree of certainty than does the conventional VEP. Finally, it is also possible to assess the patient with “functional overlay.” That is, it is not uncommon to have a patient with clear indica- tions of organic disease, but whose visual fields are too bad to be explained by what appears to be the organic cause. A careful quantitative comparison of the mfVEP amplitudes can help to parcel out the nonorganic contributions from the organic ones. Questionable Fields or Fields That Need Confirmation B A related category of patients are those whose visual fields are questionable to the ophthalmologist even though the reliability indices are within the normal ranges. That is, the visual fields do not appear to reflect the other clinical findings. For example, some patients produce visual fields on SAP that are repro- ducible and of good quality (e.g., false positives, false negatives, and fixation errors are low), but which are nonetheless not a veridical indicator of what the patient actually sees. In such cases, the ophthalmologist often has insufficient or contradictory evidence, making it difficult to Figure 11.16. Results from a patient with a localized diagnose the cause of a defect seen on the SAP. vision loss. (A) The mfVEP plots for the left (red) Figure 11.17 shows an example of a 74-year-old and right (blue) eyes. (B) The mfVEP interocular woman with abnormal visual fields. These fields probability plot reveals local losses (red circle).
11. 264 D.C. Hood and K. Holopigian A B OS OD –15 –9 –25 –10 –27 –23 –25 –24 –28 –24 –24 –15 –20 –25 –9 –9 –11 –10 –17 –4 –9 –3 –6 –3 –5 –3 –4 –10 –28 –30–12 –15 –11–12 –20 –26 –7 –4 0 –2 –3 –2 –8 –14 –27 –25 –12–11 –10 –4 –5 –25 –3 –2 –7 –2 –1 –4 –2 –13 –13 –26 –21 –6 –6 –4 –5 –7 –26 –14 –12 –7 –5 –4 –4 –5 –17 –20 –16 –13 –6 –4 –4 –3 –5 –3 –23–18 –24 –13 –21 –28 –7 –13 –8 –7 –10 –21 –29–25 –30–26 –8 –12 –11 –23 Figure 11.17. Results from a patient with abnormal ation plots for this patient reveal large losses in sen- visual fields. (A) mfVEP plots for the left (red) and sitivity that do not agree with the mfVEP findings right (blue) eyes. (B) The Humphrey 24–2 total devi- shown in A. would not be classified as unreliable based upon work is beyond the scope of this chapter. For- standard statistics. Notice in Figure 11.17B (24– tunately, reviews on the use of the mfVEP in 2 Humphrey total deviation plots) that both detecting and following glaucoma are availa- ble.42,58 Our own view is that the mfVEP can be eyes had regions of sensitivity loss that exceeded 15 dB. Her ophthalmologist questioned the very useful to the glaucoma expert. It can be fields because her cup-to-disc ratios [0.6 (OD) used to test unreliable field takers and patients and 0.5 (OS)] were relatively good whereas her with questionable fields or fields that need fields were very poor. The mfVEPs were confirmation. However, we do not believe obtained, and they were inconsistent with her that in its current form it will replace SAP. visual fields. The mfVEP responses from both Although there are conditions under which the mfVEP can detect damage missed on SAP,42,48,59,60 eyes (Figure 11.17A) were quite robust, which did not agree with the large visual field sensitiv- there are conditions under which the reverse is true.42,60 ity losses. Remember that optic nerve damage produces profound decreases in the mfVEP (see foregoing discussion; also Hood et al.46). The Problem of Fixation Errors Other examples of the use of the mfVEP to confirm qustionable fields can be found in pub- Unsteady fixation can cause diminished lished reviews.42 responses in the center of the field.42,60 Inaccu- rate or unsteady fixation will affect the mfVEP results.42,60 Monitoring the eye will assure that Unreliable Visual Field Test Takers fixation is steady, but it will not guarantee that Many patients cannot or will not reliably the fixation is accurate. Some patients with perform SAP. For most of these patients, the central visual problems can have eccentric fixa- mfVEP provides an alternative. tion. Figure 11.18 shows the effects of a 3° fixa- tion error. A control subject was instructed to maintain a steady fixation that was down and Detecting Glaucomatous Damage to the left by 3° for the right eye while the left Most of the work with the mfVEP has focused eye was tested with central fixation. Compared on glaucoma. A detailed description of this to the control condition (Figure 11.18A,B), the
12. 11. The Use of Multifocal ERGs and VEPs in Diagnosing Optic Nerve Disorders 265 fixation OD down & left by 3° fixation in center OU A C B D subject instructed to fixate down and to the left by Figure 11.18. The consequences of eccentric fixa- 3° when testing OD and fixating in the center when tion. Eccentric fixation can give the appearance of an testing OS. (D) The 60 mfVEP responses corre- abnormality in an otherwise normal eye. (A) Interoc- sponding to the probability plot in C. Responses in ular mfVEP probability plot for a control subject the inset show clear polarity reversals and amplitude fixating at the center of the stimulus when testing differences between the two eyes. (Reprinted from both eyes. (B) The 60 mfVEP responses correspond- Hood et al.,43 with permission from Lippincott ing to the probability plot in A. Responses in the Williams & Wilkins.) inset are of the same polarity and appear normal. (C) Interocular mfVEP probability plot for the same eccentric fixation condition (Figure 11.18C,D) field. Confirmation that these symmetrical showed apparent defects in both eyes on the defects are caused by an eccentric fixation can interocular probability plot. It is relatively easy be obtained by examining the responses from to tell that these “defects” are caused by eccen- near the midline. Notice that some of these tric fixation. The probability plot shows a tell- responses (see inset in Figure 11.18D) show a tale sign. In particular, there are smaller polarity reversal between the two eyes. Thus, it responses in diagonally opposite parts of the is important to monitor eye position to avoid
13. 266 D.C. Hood and K. Holopigian false positives from unsteady fixation. In addi- 2. The mfERG and mfVEP are not useful tion, the mfVEP plot and responses (see Figure for problems in the far periphery. In general, 11.18) should be examined to avoid false posi- these tests assess performance on the central tives resulting from eccentric fixation. 20° to 30° from fixation (see Figures 11.1A and 11.9).61 3. These tests do not assess rod system func- Poor mfVEP Test Takers tion. These techniques test the cone system: the cone receptors and cone bipolars are assessed Just as there are patients who are unreliable when recording the mfERG, and the cone path- SAP takers, there are also patients who have ways up to V1 are assessed when recording the great difficulty being tested on the mfVEP. In a mfVEP. This is another reason for using the few cases, these can be the same individuals. ISCEV standard full-field ERG, which tests rod Patients who refuse to cooperate or who go to and cone system function, if panretinal damage sleep may be difficult to test on either SAP or is expected.61 the mfVEP. In our experience, however, the 4. These tests are not appropriate if the overwhelming majority of the patients who are patient cannot maintain fixation or has nystag- poor SAP takers are able to perform the mfVEP mus. Under these conditions, the mfERG and test. On the other hand, there are a small per- mfVEP can be a challenge to interpret, whereas centage of patients who are good SAP takers the standard ERG and VEP are more immune but who do not produce usable mfVEP record- to eye movements and fixation problems.61 ings. In these cases, the responses are difficult 5. If you are going to perform a multifocal to discern because of a high noise level second- test, always attempt to obtain a reliable visual ary to either a large alpha-wave contribution or field using SAP. We repeat that the power of the poor signal-to-noise ratios in general. multifocal technique is that it provides topo- graphical information. This advantage is poorly When Is the Multifocal used without a comparison of the deficits seen on the multifocal test with those seen on Electroretinogram and/or SAP.61 Multifocal Visual Evoked To conclude, when faced with localized Potential Test Needed? damage of the visual fields in patients with steady fixation, the mfERG and mfVEP are The mfERG and mfVEP are not necessarily powerful tools for diagnosing and studying dis- the best electrophysiological tests for every orders of the optic nerve. patient. In deciding whether an mfERG or mfVEP is the appropriate test, the following References points should be kept in mind: 1. If there is no advantage to performing a 1. Holopigian K, Hood DC. Electrophysiology. multifocal test over a full-field test, then the Ophthalmol Clin N Am 2003;16(2):237–51. 2. Sutter EE, Tran D. The field topography of ERG standard full-field ERG or conventional wide- components in man. I. The photopic luminance field VEP should be performed first. In general, response. Vision Res 1992;32(3):433–46. the multifocal tests take more time to adminis- 3. Hood DC. Assessing retinal function with the ter, require more technical expertise to perform multifocal technique. Prog Retin Eye Res and analyze, and are less readily available than 2000;19(5):607–46. the conventional ERG or VEPs.61 For example, 4. Keating D, Parks S, Malloch C, Evans A. A com- if the problem is panretinal (a large area of the parison of CRT and digital stimulus delivery visual field is abnormal), and the ophthalmolo- methods in the multifocal ERG. Doc Ophthal- gist wants to determine if there is retinal mol 2001;102(2):95–114. involvement, then a standard full-field ERG62 is 5. Marmor MF, Hood DC, Keating D, Kondo M, the test of choice. Seeliger MW, Miyake Y. Guidelines for basic
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17. Index A Angiotensin-converting enzyme Anticoagulants ACE. See Angiotensin-converting (ACE), levels of, in for cerebral venous sinus enzyme sarcoidosis, 116 thrombosis, 68–69 Acetazolamide, for IIH, 75, 79 Anterior communicating artery for NAION, 35 Acetylsalicylic acid (ASA), for aneurysm, 101 Anti-MBP. See Anti-myelin basic GCA, 48 Anterior ischemic optic protein Activated protein C (APC), neuropathy (AION), Anti-myelin basic protein (anti- resistance to, NAION and, 42–49 MBP), optic neuritis and, 40 GCA in 7 Acute sphenoid sinusitis, optic diagnosis of, 44–46 Antinuclear antibody (ANA), in neuritis and, 5 incidence of, 42 neuromyelitis optica, Addison’s disease, increased ICP pathophysiology of, 42–44 15–16 and, 72 symptoms and signs of, 42 Antioxidants, for FA, 187–188 Adrenoleukodystrophy, 190–191 treatment of, 46–48 Antiphospholipid antibody Adults, optic neuritis in, 1 visual prognosis of, 48 syndrome, optic neuritis Aicardi syndrome, with congenital OCT for, 240 and, 6 disc pigmentation, 215 optic neuritis v., 3 Anti-phospholipid protein (anti- AIDS other etiologies of, 49 PLP), optic neuritis and, 7 cryptococcosis and, 118–119 Anterior visual pathway gliomas Anti-PLP. See Anti-phospholipid tuberculosis and, 117 benign protein AION. See Anterior ischemic course and prognosis of, APC. See Activated protein C optic neuropathy 107–108 Apoptosis, with traumatic optic Alcohol use histopathology of, 106–107 neuropathy, 137 cavernous hemangioma and, incidence of, 103–104 Aqueductal stenosis, in 225 management of, 108–109 papilledema, 66 optic neuropathy with, 154 neuroimaging of, 106 Arcuate defects Amblyopia, tobacco-alcohol, NF-I association with, 104 in NAION, 31 optic neuropathy with, 154 symptoms and signs of, in suprasellar meningioma, 98 Amiodarone, in optic 104–106 ASA. See Acetylsalicylic acid neuropathy, 157–159 malignant Ascites, with benign anterior Amphotericin B, intravenous, for epidemiology of, 109 visual pathway gliomas, cryptococcosis, 118–119 neuroimaging of, 110 109 ANA. See Antinuclear antibody pathology of, 110 Aspirin, for NAION, 35–36 Anemia prognosis and treatment of, Astigmatism, optic nerve IIH and, 72–73 111 hypoplasia and, 201 increased ICP and, 72 symptoms and signs of, Astrocytic hamartoma NAION with, 38, 40 109–110 diagnostic testing for, 222 PION with, 50–51 Anthrax, optic neuritis with, 4 histopathology of, 222 271
18. 272 Index Cerebral autosomal dominant Bromocriptine, for pituitary Astrocytic hamartoma (cont.) arteriopathy with adenoma, 96 overview of, 221–222 subcortical infarcts and Brucellosis, optic neuritis with, 4 symptoms and signs of, leukoencephalopathy 222–223 (CADASIL), NAION in, C treatment of, 223 41 Cabergoline, for pituitary Atherosclerosis, NAION with, 35 Cerebral venous sinus thrombosis adenoma, 96 ATP deficiency clinical presentation of, 68 CADASIL. See Cerebral in LHON, 152 IIH v., 72 autosomal dominant in optic neuropathy, 153 in papilledema, 67–69 arteriopathy with Autoimmune disease, optic CHAMPS. See Controlled High- subcortical infarcts and neuritis and, 5–6 Risk Subjects Avonex leukoencephalopathy Autosomal dominant progressive Multiple Sclerosis Calpain, optic neuritis with, 7 optic atrophy with Prevention Study Canavan’s syndrome, 192 congenital deafness, 183 Chemotherapy Cantholysis, lateral, for traumatic Autosomal dominant progressive for benign anterior visual optic neuropathy, 139 optic atrophy with pathway gliomas, 109 Canthotomy, lateral, for progressive deafness and for meningeal metastasis, 112 traumatic optic ataxia, 184 for ONSM, 91 neuropathy, 139 Autosomal recessive optic for optic disc tumor, 112–113 Capillary hemangioma atrophy, 181 for paraneoplastic optic cavernous hemangioma v., 225 Azathioprine neuropathy syndromes, 21 histopathology of, 224 for GCA, 47 for suprasellar meningioma, 99 symptoms and signs of, for NMO, 16–17 Children 223–224 for sarcoidosis, 116 IIH in, 79–80 treatment of, 224 neurodegenerative disorders Carbidopa, for NAION, 36 B of, 189–192 Carboplatin, for benign anterior Bacterial infection, optic neuritis optic neuritis in, 1 visual pathway gliomas, and, 5 MS risk factors with, 11–12 109 Bariatric surgery Chlamydia Carotid artery stenosis, NAION for IIH, 78–79 AION and, 44 with, 34 for papilledema, 72 NAION and, 38 Carotid-ophthalmic artery BDGF. See Brain-derived growth Chloramphenicol, in optic aneurysm, 102 factor neuropathy, 159 Caspase inhibitors, for traumatic Behçet’s disease, AION with, 49 Choroidal folds, with elevated optic neuropathy, 140 Behr’s syndrome, 181–182 ICP, 64 Cataract surgery, traumatic optic BENEFIT. See Betaseron in Choroidal melanoma neuropathies after, 142–143 Newly Emerging MS for diagnosis of, 229 Cat scratch disease, optic neuritis Initial Treatment symptoms of, 229 with, 4 Betaseron in Newly Emerging treatment of, 229 Cavernous hemangioma MS for Initial Treatment Chronic inflammatory diagnostic testing for, 225 (BENEFIT), interferon demyelinating histopathology of, 225 beta-1a in, 14 polyneuropathy (CIDP), symptoms and signs of, Blepharoplasty, traumatic optic papilledema and, 67 224–225 neuropathies after, 144 Churg-Strauss angiitis, AION treatment for, 225 Blurry vision, with ocular with, 49 CDMS. See Clinical definite lymphoma, 113 CIDP. See Chronic inflammatory multiple sclerosis Bone marrow transplantation, demyelinating Central retinal artery occlusion for MPS, 190 polyneuropathy (CRAO), with optic disc Bradykinin, with traumatic optic Clinical definite multiple drusen, 212 neuropathy, 137 sclerosis (CDMS) Central retinal vein occlusion Brain-derived growth factor interferon beta-1a and, 13–14 (CRVO), with optic disc (BDGF), for traumatic optic neuritis and, 1 drusen, 212 optic neuropathy, 141 risk of, 8–9 Central scotomas, in NAION, 31 Brimonidine, for NAION, 36
19. Index 273 optic disc dysplasia, 209 Computed tomography (CT) Clomiphene citrate, in optic papillorenal syndrome, 209 of benign anterior visual neuropathy, 161 Congenital disc pigmentation, pathway gliomas, 106 Coagulopathies, NAION with, 214–215 of cerebral venous sinus 40–41 Congenitally anomalous disc thrombosis, 68 Cochrane Database Systematic size of craniopharyngioma, 100 Review, for cerebral congenital tilted disc of fibrous dysplasia, 103 venous sinus thrombosis, syndrome, 204–206 of Grave’s ophthalmopathy, 92 68–69 homonymous hemioptic of idiopathic orbital Coenzyme Q hypoplasia, 203 inflammatory for FA, 187–188 megalopapilla, 203 pseudotumor, 94 for LHON, 177 optic nerve hypoplasia, of IIH, 70, 74 Color Doppler imaging 201–203 of malignant anterior visual for GCA, 45 segmental optic nerve pathway gliomas, 110 for traumatic optic neuropathy, hypoplasia, 203 of ocular lymphoma, 114 136 Congenital tilted disc syndrome of ONSM, 89 Color vision, in optic neuritis, 2 clinical features of, 205 of optic disc tumor, 112 residual deficits with, 11 overview of, 204–205 of papilledema, 65–66 Combined hamartoma of retina symptoms of, 205–206 of pituitary apoplexy, 97 and retinal pigment Continuous positive airway of sphenoid wing meningioma, epithelium pressure (CPAP), for IIH, 99 diagnosis of, 230 73–74 of traumatic optic neuropathy, histopathology of, 230 Contrast sensitivity, in optic 135–136 treatment of, 230 neuritis, 2 Congenital disc anomalies, Complete blood cell count, for residual deficits with, 11 201–215 nutritional optic Controlled High-Risk Subjects congenitally anomalous disc neuropathies, 151 Avonex Multiple Sclerosis size, 201–206 Compressive optic neuropathies Prevention Study congenital tilted disc of anterior visual pathway, (CHAMPS), interferon syndrome, 204–206 88–91 beta-1a in, 13–14 homonymous hemioptic optic nerve sheath Corticosteroids hypoplasia, 203 meningiomas, 88–91 for GCA, 46–47 megalopapilla, 203 of optic nerve, 92–95 for Grave’s ophthalmopathy, optic nerve hypoplasia, Grave’s ophthalmopathy, 93 201–203 92–94 for IIH, 76, 79 segmental optic nerve idiopathic orbital for NAION, 35 hypoplasia, 203 inflammatory for ocular lymphoma, 114 elevated optic disc anomalies, pseudotumor, 94–95 for optic neuritis, 12–13 210–215 sellar and suprasellar for pituitary apoplexy, 97 congenital disc compressive lesions, 95–103 for sarcoidosis, 116 pigmentation, 214–215 anterior communicating for traumatic optic neuropathy, hyaloid system remnants, artery aneurysm, 101 138 213–214 carotid-ophthalmic artery CPAP. See Continuous positive myelinated nerve fibers, aneurysm, 102 airway pressure 214 craniopharyngioma, 99–101 Craniopharyngioma optic disc drusen, 210–213 fibrous dysplasia, 102–103 epidemiology of, 99–100 excavated optic disc anomalies, internal carotid aneurysm, management of, 101 206–209 101 neuroimaging of, 100 morning glory disc anomaly, pituitary adenoma, 95–97 pathology of, 100–101 206–207 pituitary apoplexy, 97 symptoms and signs of, 100 optic disc coloboma, sphenoid sinus mucocele, 102 CRAO. See Central retinal artery 207–208 sphenoid wing meningioma, occlusion optic disc pit, 208–209 99 C-reactive protein (CRP), in peripapillary staphyloma, suprasellar meningioma, GCA, 44–46 208 97–99
20. 274 Index Elevated optic disc anomalies Crohn’s disease Wolfram syndrome with, congenital disc pigmentation, AION with, 49 182–183 214–215 increased ICP and, 74 Diabetes insipidus, diabetes hyaloid system remnants, CRP. See C-reactive protein mellitus, optic atrophy, 213–214 CRVO. See Central retinal vein and sensorineural hearing myelinated nerve fibers, 214 occlusion loss (DIDMOAD). See optic disc drusen, 210–213 Cryotherapy, for capillary Wolfram syndrome Elevated sedimentation rate hemangioma, 224 Diabetic papillopathy, as (ESR), in GCA, 44–46 Cryptococcosis NAION, 37 ENA. See Extractable nuclear diagnostic testing for, 118 DIDMOAD. See Diabetes antigen epidemiology of, 118 insipidus, diabetes Encephalitogenic antibodies, management of, 118–119 mellitus, optic atrophy, optic neuritis and, 6 pathology of, 118 and sensorineural hearing Endoscopic sinus surgery, symptoms and signs of, 118 loss traumatic optic CT. See Computed tomography Digoxin, for optic neuropathy, neuropathies after, 144 Cuban epidemic, of optic 157–159 EOG. See Electro-oculogram neuropathy, 153 Diphenylhydantoin, for NAION, ERG. See Electroretinogram Cup, absent, in NAION, 32 35 ESR. See Elevated sedimentation Cup-to-disc ratio Diplopia, with Grave’s rate in DOA, 178 ophthalmopathy, 93–94 Ethambutol in NAION, 31–34, 37 Direct argon laser for optic neuropathy, 159 in SIAION, 38 photocoagulation, for for tuberculosis, 117–118 Cyanide, optic neuropathy from, capillary hemangioma, 224 Ethylene glycol, in optic 154–155 Disulfiram, in optic neuropathy, neuropathy, 156 Cyanocobalamin 159 Excavated optic disc anomalies for optic neuropathy, 153 Dizocilpine, for traumatic optic morning glory disc anomaly, for vitamin B12 deficiency, 153 neuropathy, 140 206–207 DOA. See Dominant optic Cyclophosphamide optic disc coloboma, 207–208 atrophy for GCA, 47 optic disc pit, 208–209 Dominant optic atrophy (DOA) for idiopathic orbital peripapillary staphyloma, 208 diagnostic testing for, 179 inflammatory Extractable nuclear antigen histopathology of, 179 pseudotumor, 94–95 (ENA), in neuromyelitis incidence of, 177 for sarcoidosis, 116 optica, 15–16 molecular genetics and genetic Cyclosporin A, for GCA, 47 heterogeneity of, 179–180 Cyclosporine F NTG v., 180–181 for idiopathic orbital FA. See Friedreich’s ataxia pathophysiology of, 179 inflammatory Farnsworth-Munsell 100-hue test, symptoms and signs of, pseudotumor, 94–95 for optic neuritis, 2, 11 177–179 for sarcoidosis, 116 Fatal X-linked optic atrophy, treatment of, 180 Cytomegalovirus, infiltration of ataxia, and deafness, 185 Doxycycline, for increased ICP, optic nerve, 119 Fibrous dysplasia 74 epidemiology of, 102 Drugs, in toxic optic D management of, 103 neuropathies, 151 Danazol, for increased ICP, 74 neuroimaging of, 103 Dandy criteria, for IIH, 70, 74 pathology of, 103 E Dapsone, for GCA, 47 symptoms and signs of, 102 Electro-oculogram (EOG), for Demyelination Fluconazole, oral, for congenital tilted disc cell-mediated damage in, 6–7 cryptococcosis, 118–119 syndrome, 205 optic neuritis and, 6–7 Flucytosine, oral, for Electroretinogram (ERG). See Dexamethasone, for tuberculosis, cryptococcosis, 118–119 also Multifocal 118 Fluorescein angiography electroretinogram Diabetes for astrocytic hamartoma, 222 for congenital tilted disc diabetic papillopathy with, 37 for cavernous hemangioma, 225 syndrome, 205 NAION with, 34, 40