WHAT IS MIGRAINE: VISUAL SYMPTOMS

It is very common during a migraine headache to find light troublesome and disturbing (photophobia) whilst darkness is soothing.

Blurred vision is also frequent but the most characteristic visual symptom is an inability to see out of part of the visual field. The visual abnormalities can take different forms and be very dramatic. The whole visual field may be fragmented and interrupted by shiny lines, arranged like constellations, a phenomenon known as fortification spectra, because of its resemblance to a castellated fort. (Some mystics have interpreted these as visions of 'the eternal city'.) There may also be small multicolored areas of flashing lights, zigzag patterns, or 'Catherine wheels', and there is usually generalized blurring of vision, as if looking through steam or water. Another common visual feature is loss of the vision either in a roughly circular area, or in half of a visual field, i.e. the area seen to one side. (Just as one side of the body is controlled by the opposite half of the brain, the area of space perceived on one side is a function of the opposite side of the brain; this means that damage of the visual area of the left half of the brain produces a loss in vision of the right half of the visual fields of both eyes. Such a blacking-out during a migraine attack implies that one hemisphere of the brain is affected.)

Less common disturbances of perception are changes in the size and the shape of objects, the appearance that objects are tilted or far away or that colors have faded. (These changes are due to alteration in blood flow to the parietal lobes of the brain, which deal with orientation in space and time.)

Migrainous patients sometimes complain that they feel taller, or are 'about one foot high'. At one time it was thought that Lewis Carroll, a migraine sufferer, was drawing on his own experience of such sensations in Alice in Wonderland, but this intriguing explanation was somewhat discredited by the later suggestion that he wrote this book before he developed migrainous symptoms.

The visual disturbances (aura) usually herald the onset of headache but occasionally occur later in the attack. Rarely the headache itself plays only a small part in the attack, as in the following case.

Patient CD., a 42-year-old physician, was driving along Regent Street during the rush-hour to an appointment for which he was late. He suddenly found he could not read the license-plate of the car immediately in front of him. He had never suffered from migrainous symptoms previously. After about 30 seconds the blind spot (scotoma) began to alter, opening up to form an enlarging crescent of shimmering angles which spread to the periphery of the visual field and disappeared. This phenomenon-a typical migrainous aura-lasted precisely 20 minutes and was followed by irritability and lack of appetite lasting a few hours, but no headache was noticed.

There is little doubt that these symptoms were migrainous in origin in spite of the absence of headache, i.e. the cause was a narrowing (spasm) of the blood vessels (vasoconstriction) feeding the brain, so that less blood flowed to it.

Other manifestations of the narrowing of these blood vessels are transient weakness and numbness, or even loss of consciousness. The weakness, which can be as severe as that which occurs in stroke, may continue after the headache has gone; in a very small minority, the diminution in blood flow may be so severe that permanent damage of the brain results in permanent weakness.

Other people report changes in auditory perception, for instance speech may sound as though it is being played at too fast a speed. Sounds may seem overwhelmingly loud, or continue to reverberate after they have ceased.

Rarely, a sufferer may feel there is another person looking on-the doppelganger.

Migraine sufferers often do not mention such odd sensations and perceptions for fear of being thought 'insane' but all these phenomena are consistent with a migrainous aura due to vasoconstriction.