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From the School of Psychology, University of Western Australia, Crawley, Western Australia, Australia.
| Abstract |
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METHODS. Twenty-two nonheadache control subjects (aged 1845 years) and 22 migraineurs (aged 1845 years: 10 migraine with visual aura, 12 migraine without aura) participated. Standard automated perimetry (SAP) and temporal modulation perimetry (TMP) were measured by perimeter (model M-700; Medmont, Pty Ltd., Camberwell, Victoria, Australia). Control subjects attended two test visits: baseline and retest. Migraineurs attended three times: baseline (
4 days after migraine), the day after the offset of the next migraine, and 7 days later. Groups were compared using the global indices of the perimeter: Average Defect (AD) and Pattern Defect (PD), in addition to point-wise comparisons.
RESULTS. Group migraineur TMP performance was significantly worse the day after a migraine, showing decreased general sensitivity and increased localized loss. Performance measured 7 days later was not significantly different from that measured the day after a migraine. Group migraineur SAP performance was not significantly worse after migraine; however, a subgroup of six eyes from five patients had 10 or more visual field locations with decreases in sensitivity greater than control testretest 95% confidence limits.
CONCLUSIONS. Decreased visual field performance was present after migraine, as well as greater testretest variability in the migraine group compared with control subjects. As migraineurs constitute 10% to 15% of the general population, the presence of this subgroup of patients with periodic prolonged decreased visual field sensitivity after migraine has implications for differential clinical diagnosis, and for clinical research using perimetry.
Migraine is a very common condition affecting between 10% and 15% of the population.14 Previous studies indicate that between 30% and 60% of these individuals have visual field deficits at times between migraines.1 3 5 15 Given that the prevalence of glaucoma is approximately 3% of the population over the age of 50,16 17 and that estimates of the percentage of the glaucoma population with a history of migraine is, at most, 30%,6 it is evident that not all healthy young migraineurs with interictal visual field abnormalities will progress to having glaucoma. Indeed, we do not know whether the presence of visual field deficits between migraines is predictive of future eye disease. It is not known whether migraine events themselves affect visual processing, possibly in a cumulative fashion, or whether there are underlying vascular, metabolic, or neurologic differences in some migraineurs that predispose them to both migraine and to eye disease.
Most previous perimetric studies of migraineurs have measured fields at a single time-point cross-sectionally.1 2 4 5 Drummond and Anderson18 demonstrated peripheral visual field constriction with kinetic targets, in a group of subjects with migraine with aura the day after a migraine, that was largely resolved at 7 to 10 days after migraine, but they did not compare performance to testretest variability in a comparable group of nonheadache control subjects. Their study did not find deficits in individuals who had migraine without visual aura. However, the perimetric task used was not capable of identifying small, localized deficits.18 In contrast, we have followed the perimetric performance of one subject with migraine without aura who had a localized TMP deficit that largely but not completely resolved over a 30-day period after migraine.4 Sullivan-Mee and Bowman19 also documented two case reports of migraineurs with persistent visual field deficits (which they define as present >10 days after migraine) that gradually resolved. The findings of Drummond and Anderson18 suggest that such persistence of visual field deficits is likely to be rare.
Studying the time course of visual field deficits relative to migraine events may provide information essential to understanding their relevance, if any, to eye disease, and for enabling correct differential diagnosis of visual field loss due to treatable cause (such as glaucoma). For example, if visual field deficits are directly related to migraine events, therapy to minimize migraine occurrence may have future benefit in reducing the risk of eye disease in susceptible individuals. Even if migrainous visual field deficits have no long-term cumulative significance, knowing whether duration after migraine is likely to affect visual field performance is essential for accurate perimetric interpretation for the management of other eye disease in migraineurs. Our present study was motivated by a need to more systematically investigate postmigraine visual field performance, with comparison to testretest variability in nonheadache control subjects. Migraineurs were assessed interictally (4 days or more after migraine) then at 1 day and 7 days after the cessation of symptoms of their next migraine. Testing at 1 and 7 days after migraine was chosen to enable comparison with the study of Drummond and Anderson.18 Although it would be of interest to test at longer durations after migraine, we wanted to include a representative sample of typical migraineurs, which includes people whose have migraines as frequently as once a week. Two perimetric tasks were used: SAP and TMP. SAP was included, as it is the most commonly used clinical visual field task, and several studies have demonstrated SAP visual field deficits in people with migraine.1 2 3 TMP was also included, as we have previously demonstrated deficits with TMP that were not measurable using SAP.4
| Methods |
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Perimetric Tests
SAP and TMP were performed with a perimeter (model M700; Medmont Pty Ltd., Camberwell, Victoria, Australia). A detailed description of the perimeter can be found elsewhere.21 The Medmont SAP and TMP tasks have recently been shown to yield results comparable to those returned by the Humphrey Field Analyser (HFA; Carl Zeiss Meditec, Dublin, CA) and Humphrey-Zeiss frequency doubling perimeter.22 In brief, the perimeter uses 0.43° (Goldmann size III) light-emitting diodes (LEDs) as stimuli (
max = 565nm). The bowl luminance is 3.2 cd/m2 (CIE1931 x: 0.53, y: 0.42) and the maximum stimulus luminance is 320 cd/m2. SAP thresholds were assessed using the Central Threshold test, which uses a zippy estimation by sequential testing (ZEST) thresholding procedure.23 Flicker thresholds were determined with the Auto-Flicker test. This test presents luminance pedestal flickering stimuli, with the flickering component of the stimulus modulated around a pedestal luminance, that differs from the background luminance. The temporal frequency of the stimuli is varied with eccentricity to improve the dynamic range of the test (1°3°, 18 Hz; 6°, 16 Hz; 10°15°, 12 Hz; and 22°, 9 Hz). Thresholds are measured with a 6/3-dB staircase, and stimuli are presented for 800 ms.
The test patterns for the SAP and TMP tests differ slightly. Figure 1 provides an example of the visual fields measured in one migraine subject, and demonstrates the test pattern. Test stimuli are arranged in concentric rings. Thresholds are collected from the 3°, 6°, 10°, 15°, 22° and 30° rings for SAP (see Fig. 1a ) and the 1°, 3°, 6°, 10°, 15°, and 22° rings for the flicker test (see Fig. 1c ). There are 99 test locations for SAP and 73 test locations for TMP.
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Visual Field Analysis
Analysis was performed using the global indices returned by the perimeter and on a point-wise basis. The Medmont perimeter returns two global indices: the Average Defect (AD), and the Pattern Defect (PD) index. The AD indicates whether there is a generalized depression or elevation across the visual field, compared with the internal normative database of the perimeter, and this index is calculated in a manner similar to the Total Deviation index of the HFA. The PD index is similar to the Pattern Standard Deviation index of the HFA, where higher PD values indicate local asymmetries in an individuals visual field relative to the remainder of their visual fields.
For all point-wise analyses, the locations immediately above and below the blind-spot were excluded for SAP, as these may encroach on the physiological blind spot. These locations are not included in the TMP test pattern (see Fig. 1c ). Statistical comparisons were performed on computer (SigmaStat, ver. 3.0; SPSS Science, Chicago, IL).
| Results |
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Control Retest Performance
In addition to the baseline distribution of the global indices for the control population, Figure 3 also shows the retest distribution. Paired t-tests demonstrated no significant difference in control group performance for SAP at baseline versus retest visits for either the AD (t(43) = 0.52; P = 0.60) or PD (t(43) < 0.01; P > 0.99) indices. Likewise, there was no significant difference in control group global indices for TMP between baseline and retest visits (AD: t(43) = 0.52; P = 0.60; PD: t(43) = -0.07; P = 0.95). Consequently, there was no evidence of a significant learning effect for the control group on either perimetric task.
Migraineur Performance 1 Day after a Migraine
Subjects were required to keep a headache diary and record their antimigraine medications. These included over-the-counter (OTC) analgesics (aspirin, paracetamol), OTC NSAIDs, and antiemetics. These common medications are not known to cause visual field deficits, but to minimize any possible medication effects, we tested migraine participants 1 day after the cessation of their migraine symptoms to allow for medication washout.
The distribution of global indices for the migraine participants obtained the day after a migraine is shown in the right-hand panels of Figure 3 . For SAP (Figs. 3a 3b) visual inspection of Figure 3a shows a similar distribution of AD at baseline and retest visits (paired t-test, t(43) = 0.19; P = 0.85). The distribution of the PD index for SAP is wider at the after-migraine visit than at baseline, with the worst performing subjects being markedly abnormal (four eyes of three subjects were flagged at P < 0.01 relative to the Medmont normative database and are represented as the outliers in Fig. 3b ); however, there is not a significant group difference (paired t-test, t(43) = -1.2, P = 0.23).
The migraine groups TMP performance, measured 1 day after migraine, was significantly worse than at baseline for both the AD and PD indices. For AD, there was a small but statistically significant decrease in generalized sensitivity across the field (paired t-test: t(43) = 3.2, P < 0.01: mean at baseline = -1.13 dB; mean at 1 day after migraine = -1.55 dB). A significant decrease of almost 3 dB in the median PD indicates an increased presence of local field asymmetries relative to baseline in the migraine group (Wilcoxon Signed Rank Test: P < 0.01; median at baseline = 1.68 dB, median at 1 day after migraine = 4.53 dB).
Inspection of Individual TestRetest Performance as a Function of Deficit Severity
Visual inspection of the right-hand panels of Figure 3 demonstrates that some migraineurs returned markedly abnormal PD indices at the test visit 1 day after migraine. However, it is not clear from Figure 3 whether these are subjects that had milder deficits at baseline or were subjects with completely normal baseline performance. To explore this question, Figures 4 and 5 show scatterplots of the global indices returned at baseline and retest for SAP and TMP. Both eyes of each subject are included. Migraine subjects with baseline postmigraine durations of 1 week or less (five subjects, open circles) were individually numbered consistent with Figure 2 (Fig. 3b 3d) . The four subjects with the longest durations after migraine at baseline are also identified individually as the squares. Symbols appearing in the shaded areas are eyes where retest performance was worse than at baseline. Figures 4a and 4b show that generalized sensitivity for SAP was similar for both baseline and retest for most control and migraine subjects. In the migraine group, two eyes (appearing in the bottom right corner of Fig. 4b ) had a large reduction in AD at retest relative to baseline (3.72 and 5.20 dB). Figures 4c and 4d demonstrate a wider scatter in baselineretest performance for the PD index for both migraine and control groups.
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Inspection of the individually identified subjects in Figures 4 and 5 shows that duration after migraine at baseline did not predict performance in these subgroupsperformance was scattered and overlapped. There was no trend in those subjects with shortest duration after migraine at baseline to show least change after the migraine event.
Number of Visual Field Locations with a Significant Decrease in Sensitivity at Retest for Individual Migraine Subjects
The global perimetric indices shown in the previous figures permit a summary of visual field performance for each individual, but do not provide information regarding which visual field locations or how many visual field locations demonstrated decreased sensitivity. To explore these questions, as well as whether visual field deficits were unilateral or bilateral in individual subjects, individual migraine subject performance was compared on a point-wise basis with that of the control group. The baselineretest difference was determined for control subjects for each individual location in the field, for the two test procedures. From these, we determined two-sided 95% confidence limits of control variability. For each migraine subject, we determined the number of locations with baselineretest scores outside the location-specific confidence interval. These are plotted in Figure 6 , where white bars indicate an improvement in performance and black bars a decrease. If a visual field had more than six locations for SAP or five locations for TMP with a significant decrease (or increase) in sensitivity, it was considered statistically significant at P < 0.05 (derived as described elsewhere,5 and shown by the dotted lines in Fig. 6 ). The subject numbering is consistent with that in Figure 2 , with subjects 1 to 10 being from the migraine-without-aura group. Although were no significant group differences between subjects with and without visual aura on any of the measures in this study, Figure 6 enables visual comparison of individuals in the two subject groups. Figure 6 also enables comparison of individual subject performance across the two perimetric tasks.
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TestRetest Variability as a Function of Sensitivity for Individual Visual Field Locations
Figure 6 shows that many locations had significantly reduced sensitivity the day after a migraine, relative to baseline. Next, we explored whether locations with reduced sensitivity at baseline were associated with larger sensitivity losses after a migraine event. First, we determined the 5th and 95th percentiles of retest sensitivity distribution for each level of baseline sensitivity. For example, for all locations measured as 18 dB at baseline (pooled across eccentricity and subjects), we collated the sensitivity measured at retest and determined the 5th, 50th, and 95th empirical percentiles of this retest distribution. These data are shown in Figure 7a for SAP and 7b for TMP. Percentiles were determined only for baseline sensitivities occurring at least 20 times in the data set. The shaded area shows the range between the 5th and 95th percentiles for control subjects.
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Performance of Migraineurs at 1 Week after Migraine
All migraineurs were tested 1 week after migraine. We were interested in determining whether sensitivity had returned to baseline in those individuals with deficits measured the day after a migraine. Box plots of the global indices measured at 1 week after migraine are shown in Figure 8 , along with those for 1 day after migraine for comparison. Group comparisons revealed no significant improvements in the global indices at 1 week relative to 1 day after migraine for either TMP or SAP (paired t-tests, all P > 0.05). There were, however, several individuals with localized deficits measured with SAP the day after a migraine that were not repeated a week later. For TMP, however, performance at 1 week was remarkably similar to that measured at 1 day after migraine in most subjects. Hence, there was a subgroup of migraineurs who demonstrated localized visual field deficits to flickering stimuli the day after a migraine that were not resolved 1 week later.
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| Discussion |
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It is possible that some of the dysfunction measured the day after a migraine can be explained due to effects of fatigue or poor concentration after migraine, or alternately antimigraine medications. We assessed performance 1 day after the offset, rather than onset, of all symptoms to minimize these effects. Nevertheless, fatigue or medication effects would be expected to result in a generalized sensitivity loss across the field. We found a mild change in AD (approximately -0.5 dB) to the flickering stimuli, which may be explained by fatigue or aversion to the task. However, this deficit was not resolved a week after migraine and hence is not readily explained by these factors. Furthermore, the greatest changes in visual field performance after migraine consisted of localized deficits, which are not readily explicable by fatigue or aversion.
The day after a migraine, a subgroup of the migraineurs demonstrated localized visual field deficits that were either absent, or present in a milder form, at their baseline test visits. Many of these deficits were unilateral and arcuate; indeed, no subject demonstrated a bilateral homonymous deficit. As the symptomatology of migraine is cortical, the appearance of precortical visual field deficits in individuals with migraine may seem counterintuitive. However, such deficits have been consistently reported by us4 5 27 and others1 3 in periods between migraine attacks.
Although the mechanism underlying localized field deficits in our migraine group cannot be ascertained from this study, other studies suggest a localized vascular event, possibly at the level of the optic nerve head, as a plausible explanation. Migraine is considered to be a neurovascular condition, whereby neural events result in the alteration of blood flow causing pain and further nerve activation.28 Despite migraine not being a primary vascular condition, several research groups have found migraineurs to have poor peripheral vascular regulation at times between migraine and have proposed that this may increase the risk of NTG in these individuals.12 29 30 Broadway and Drance31 studied peripheral vascular flow in individuals with glaucoma and found that the presence of vasospasm and migraine was higher in people with focal ischemic type optic discs, than those with other types of glaucomatous cupping. There is also evidence that patients with glaucoma32 and also those with migraine may have altered regulation of the potent vasoconstrictor endothelin.33 34 These studies suggest altered perfusion, possibly at the optic nerve head, as a plausible explanation for the localized functional deficits measured in our study.
Greater changes in visual field performance after migraine were identified with TMP than with SAP. Identifying different degrees of loss with TMP than SAP is consistent with our previous work.4 27 Visual-functionspecific perimetry (such as TMP and FDP, which preferentially assess the magnocellular visual pathway, and SWAP, which assesses the koniocellular visual pathway) have also been found to detect functional loss earlier than SAP in glaucoma.35 36 37 38 39 It has been proposed that the larger, sparser neurons of the magnocellular and koniocellular pathways are either more susceptible to damage possibly due to the large axons having a metabolic disadvantage in adverse conditions,40 41 or alternately that the absence of neural redundancy in these pathways makes early functional loss easier to detect.42 As we have previously identified deficits consistent with both M and P pathway loss in people with migraine27 and some of migraine subjects in our present study demonstrated SAP deficits, it seems unlikely that the TMP deficits measured in the current study were due to selective magnocellular pathway involvement.
In addition to a decrease in visual field performance after migraine, we found greater testretest variability in our migraine group relative to control subjects. This more variable visual field performance, related in part to duration after migraine, should warrant exclusion of migraineurs from normative perimetric databases. Such exclusion, predicted from population estimates of migraine prevalence to be approximately 10% to 15% of the normative database,14 may result in a tightening of the normative confidence limits of testretest variability. As these limits are used in statistical analysis to classify visual field progression, it is possible that exclusion of the migraine group may enhance the ability to track visual field progression in other disorders.
In this study, we tested young people with migraine who definitely did not have glaucoma. The longer-term significance, if any, of these visual field deficits is currently unknown, and longitudinal data would be needed to clarify this issue. We assume from our previous case study of a subject with migraine without aura that these deficits eventually resolve.4 However for an interim period after migraine, there is a subgroup of clinical patients with repeatable visual field deficits, that in some instances masquerade as glaucomatous. The presence of a subgroup of clinical patients with greater than usual testretest variability and periodic prolonged decreased sensitivity after migraine has implications for both differential diagnosis in a clinical setting, and clinical research studies using perimetry.
| Footnotes |
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Submitted for publication June 30, 2003; revised November 10, 2003; accepted November 13, 2003.
Disclosure: A.M. McKendrick, None; D.R. Badcock, None
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C.
1734 solely to indicate this fact.
Corresponding author: Allison M. McKendrick, School of Psychology, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia; allisonm{at}psy.uwa.edu.au.
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