fMRI evidence that precision ophthalmic tints reduce cortical hyperactivation in migraine

Abstract

Background: Certain patterns can induce perceptual illusions/distortions and visual discomfort in most people, headaches in patients with migraine, and seizures in patients with photosensitive epilepsy. Visual stimuli are common triggers for migraine attacks, possibly because of a hyperexcitability of the visual cortex shown in patients with migraine. Precision ophthalmic tints (POTs) are claimed to reduce perceptual distortions and visual discomfort and to prevent migraine headaches in some patients. We report an fMRI visual cortical activation study designed to investigate neurological mechanisms for the beneficial effects of POTs in migraine.

Methods: Eleven migraineurs and 11 age- and sex-matched non-headache controls participated in the study using non-stressful and stressful striped patterns viewed through gray, POT, and control coloured lenses.

Results: For all lenses, controls and migraineurs did not differ in their response to the non-stressful patterns. When the migraineurs wore gray lenses or control coloured lenses, the stressful pattern resulted in activation that was greater than in the controls. There was also an absence of the characteristic low-pass spatial frequency (SF) tuning in extrastriate visual areas. When POTs were worn, however, both cortical activation and SF tuning were normalized. Both when observing the stressful pattern and under more typical viewing conditions, the POTs reduced visual discomfort more than either of the other two lenses.

Conclusion: The normalization of cortical activation and SF tuning in the migraineurs by POTs suggests a neurological basis for the therapeutic effect of these lenses in reducing visual cortical hyperactivation in migraine.

Figures

Figure 1

Illustration of three black-and-white stripes with a low spatial frequency (SF) (top), a medium SF (middle), and a high SF (bottom). When the width of the whole pattern is about 8 cm and the viewing distance is about 36 cm, the corresponding SF values for the three stripes are approximately 0.31, 2.5, and 7.9 cpd, respectively. The experimental patterns were larger than those shown, subtending 10° × 13° (height × width) at the eye.

Figure 2

(A) CIE 1976 UCS diagram (10) showing the colour appearance (chromaticities) of the precision ophthalmic tint (POT) and coloured lenses used by the 11 migraine patients and their control subjects in the fMRI study. The chromaticity of each POT is marked by a solid circular point, and a line connects the point to the chromaticity of its paired coloured lens (cross). (B) The effects of the gray, the POT, and the coloured lenses in reducing visual discomfort relative to that without lenses when viewing the stressful pattern out of doors in direct sunlight. The degree of visual discomfort was self-scored using a 0–10 scale with 0 representing no visual discomfort and 10 representing severe visual discomfort. Overall, the POT lenses had the most significant reduction in visual discomfort followed by the coloured lenses and then the gray lenses. The reduction with the POT lenses was significantly larger than that with the coloured lenses (t-test, p = 0.005). The reduction with the coloured lenses showed no difference compared to that of the gray lenses (p = 0.253). Although the effect was the smallest among the three lens types, the reduction with the gray lenses was significant (p = 0.027) compared to that without lenses. Error bars indicate the standard deviations.

Figure 3

Activation in visual areas V1, V2, V3, V3A, and V4 from the non-stressful striped pattern (SF 0.31 cpd) for the control subjects (A) and the migraine patients (B). Left columns in (A) and (B), averaged cortical activation curves for the three lenses; right columns in (A) and (B), comparison of the peak heights of the cortical activation curves in the left columns. No significant difference in activation was observed in any area. Error bars indicate the standard errors of the means. CCL, control coloured lens; CGL, control gray lens; POT, precision ophthalmic tint.

Figure 4

Normalized activation in visual areas V1, V2, V3, V3A, and V4 from the stressful striped pattern (SF 2.5 cpd) for the control subjects (A) and the migraine patients (B). Left columns in (A) and (B), normalized cortical area activation curves; right columns in (A) and (B), comparison of the peak heights of the normalized cortical area activation curves in the left columns. (Note that, to reduce the filter-induced activation variations, the cortical area response curve to the stressful pattern was normalized by dividing the height of the corresponding cortical area response curve to the non-stressful pattern for each lens.) For the control subjects, cortical area activation showed no difference in any visual area among the three lenses. For the migraine patients, however, the POTs produced significant reductions to cortical activation in V3 and V4. The POTs also reduced the cortical activation in V2 and V3A, though the differences were not statistically significant. Error bars indicate the standard errors of the means. CCL, control coloured lens; CGL, control gray lens; POT, precision ophthalmic tint.

Figure 5

Precision ophthalmic tint-induced cortical activation reduction in the migraine patients relative to the mean cortical activation for the control gray and coloured lenses. Error bars indicate the standard errors of the means.

Figure 6

Comparison of cortical area activation between the control subjects and the migraine patients wearing control gray (G), coloured (C), and precision ophthalmic tint (POT) lenses, shown as a function of the spatial frequency (SF) of the pattern of stripes. The dashed-lines represent the mean peak heights of cortical area activation with the three lenses for the control subjects. The red solid lines represent the mean peak heights of cortical area activation of the G and C lenses for the migraine patients. The blue solid lines represent the peak heights of cortical area activation of the POTs for the migraine patients. Error bars indicate the standard errors of the means.