The IHS code is 1.4 for retinal migraine. A short description from the Headache Classification Committee is the following: repeated attacks of monocular scotoma or blindness lasting less than one hour and associated with headache. Other ocular or structural vascular disorder must be ruled out. Additional terms include: ocular migraine, anterior visual pathway migraine, and ophthalmic migraine. This condition may be broadly defined as a transient or permanent monocular visual disturbance accompanying a migraine attack or occurring in an individual with a strong history of migrainous episodes. One term applicable to all such attacks would be "ocular migraine;" however, to include optic nerve dysfunction as well, a more general phrase, ie, "anterior visual pathway migraine," may be preferable. This last phrase would include reported defects, such as ischemic papillitis, retinal hemorrhage, vitreous hemorrhage, central serous retinopathy, pigmentary changes of the retina, and optic nerve atrophy. Retinal migraine occurs more frequently than ophthalmoplegic migraine. We estimate the frequency of strictly monocular visual phenomena occurring in conjunction with migraine to be one of 200 migraine sufferers. Frequently, however, homonymous visual field phenomena in migraineurs is incorrectly attributed to a single eye. For example, a patient with transient right homonymous hemianopia might think that the right eye is affected, because normally the right temporal hemifield is 30-40 degrees larger than the left nasal hemifield.{100} The exact genetic predisposition to this subtype of migraine headache is unknown. The familial occurrence is similar to that expected in all patients with migraine preceded by visual aura, with an estimated 25% positive familial history. Retinal migraine is expected to be more common in women than men, which is true of migraine headaches in general, but this also has not be documented. One may consider two forms of anterior visual pathway migraine: (1) transient monocular blindness and (2) permanent unilateral visual loss, a much less common occurrence. The transient form has a relatively stereotyped presentation, consistent with retinal or optic nerve hypoperfusion from spasm of the central retinal or ophthalmic artery. For example, 10 of 24 patients reported by Tomsak and Jergens{101} described concentric contraction of vision, and only 5 of their patients had an altitudinal or quadratic visual change consistent with spasm of retinal artery branch. Kline and Kelley{102} studied a patient with a history of cluster headache and documented a reduction in central retinal artery blood flow during an attack of ocular migraine by intravenous fluorescein angiography. They noted no change in choroidal perfusion, also suggesting selective spasm of the central retinal artery. Others have noted retinal artery constriction during episodes of migrainous transient monocular blindness{103,104} or normal arterial caliber.{105} It is of interest to note that in the case reported by Wolter and Burchfield,{105} a review of the fundus photographs depicts venous vasoconstriction as well as retinal opacification during an episode.(Fig. 11): Figure 11. Retinal migraine. A. During amaurotic episode. Note dusky appearance of fundus, increased retinal opacity (edema?), and dark, narrowed veins (arrows). Disc is hyperemic. B. Fundus after episode. Note normal caliber of veins (arrows). (Photographs courtesy of Dr. J. Reimer Wolter) Burger and co-workers{106} reported amaurosis fugax episodes due to documented vascular constriction in the retina. Their patients did not have retinal migraine but show the ability of retinal vascular constriction to produce monocular episodes of amaurosis in the absence of embolic phenomena. Permanent unilateral visual loss from anterior visual path migraine is well documented, but uncommon. In addition to arterial or venous retinal vascular occlusions,{72,104,107,108} central serous retinopathy, vitreous hemorrhage, retinal hemorrhage and ischemic optic neuropathy have been noted.{109,110} Newman et al {111} reported bilateral central retinal artery occlusions, disk drusen, and migraine, and other descriptions of anterior visual path migraine and vascular retinopathy are reported.{112,113} A recent unconfirmed report suggests that up to one third of migraineurs have retinal or optic nerve type visual field defects when tested with automated perimetry.{114} Clinical Features of Retinal Migraine The IHS diagnostic criteria for retinal migraine are as follows: A. At least 2 attacks fulfilling B-C. B. Fully reversible monocular scotoma or blindness lasting less than 60 minutes and confirmed by examination during attack or (after proper instruction) by patient's drawing of monocular field defect during an attack. C. Headache follows visual symptoms with a free interval of less than 60 minutes, but may precede them. D. Normal ophthalmological examination outside of attack. Embolism ruled out by appropriate investigations. A typical history is that of a young adult with a pattern of common or classic migraine, who has recurrent episodes of monocular visual loss or monocular scintillating scatomas. The visual loss is often one-sided, stereotyped in nature, and tends to affect the entire monocular visual field,{101} although any of the visual patterns described in migraine with aura may occur on a monocular basis in "retinal" migraine. Carrol{115} suggested that such transient episodes never have a preceding fortification spectra, that the absence of accompanying headache was invariable, and that the visual disturbance never lasted more than 10 minutes. Permanent visual loss is the exception rather than the rule. Transient anterior visual pathway migraine is not associated with other neurologic symptoms, but may be precipitated by postural change or exercise. Approximately one-third of patients have a prior history of migraine.{101} Ocular migraine as a cause of transient monocular blindness should be a diagnosis of exclusion. This was highlighted by a recent case{116} in which a young medical student had episodes of amaurosis fugax, occasionally accompanied by headache, and was considered to have retinal migraine. He turned out to have a large pituitary tumor! Walsh and Hoyt{43} state that "the eye itself can be involved in the angiospastic circulatory disturbance of a migraine attack" and that subsequent visual disturbance is due to retinal hypoxia. The retinal arterioles have been reported to be constricted during such an episode by some authors{43,103} or to be normal despite an ischemic retina.{105} Ischemic papillopathy in migraine was presented by McDonald and Sanders,{117} with sudden monocular visual loss in a migraine patient who had experienced multiple bouts of transient amaurosis of the same eye. A typical nerve fiber bundle defect was present on visual field testing, and fluorescein angiography showed areas of delayed choroidal filling in the peripapillary region. Typical case histories of "retinal migraine" are presented below: The patient was a 22-year-old college student who complained of decreased vision in the left eye. He had a 7-year history of classic migraine headaches, which had been much less frequent in the previous 3 years. Three years prior to examination he awakened to discover decreased vision in the temporal quadrant of the left eye. One year later he again noticed an abrupt onset of a negative scotoma in the inferior nasal periphery of the same eye. Neuro-ophthalmologic examination was normal except for a slight afferent pupillary defect in the left eye and the visual fields. (Fig 16-12, A): Figure 12. Patient with permanent retinal nerve fiber bundle defect attributed to migraine. A. Visual field. B. Visible attenuation of retinal nerve fiber layer (between arrows) corresponding to field defect. Compare with visible nerve fibers entering inferior aspect of disc. Fundus photography revealed an absence of the nerve fiber bundle layer in the superior portion of the left optic disc corresponding to the inferior visual field defect demonstrated on perimetry. (Fig 12, B) A 24-year-old right-handed carpenter complained of "blackouts" in the right eye occurring over the previous 3 months. The patient stated that he had nine episodes of diminished vision in the right eye unassociated with other neuro-ophthalmologic signs. These episodes began as a "blur" starting in the right temporal field and characterized by distinct "lines and angles," or like "a fish net." There was a subjective appreciation of increased brightness during the phenomenon but no particular color. As the effect intensified, the entire field of the right eye became gray such that the patient "could not see anything," and the vision subsequently diminished to bare perception of light. This sensation lasted 10 to 15 minutes and then slowly cleared in reverse fashion. There was no previous history of migraine, transient neurologic phenomena, or family history of migraine. His neurologic and neuro-ophthalmologic examinations were entirely normal. It was the impression that the patient suffered from the retinal form of migraine. The pathogenesis of such episodes is not well defined. It would appear in most instances that the visual disturbances are due to constriction in either the central retinal artery or the ophthalmic artery, with resultant ischemia of the optic nerve or retina. One argument that vasoconstriction occurs in vessels proximal to the retina itself is the work of Laties,{118} who showed the absence of adrenergic innervation to the intraocular branches of the central retinal artery. Additional clinical descriptions of anterior visual pathway migraine and vascular retinopathy associated with this condition are presented by Corbett{112} and Coppeto et al.{119} In general, the prognosis for retinal migraine is similar to that of migraine headache with typical aura. Recurrent attacks are expected with a variable interval. As the true incidence of retinal migraine is unknown, it is uncertain whether there is a higher incidence of permanent neuroretinal injury. The visual field data presented previously{114} suggests that there is a higher incidence of end arteriolar distribution infarction and a higher incidence of permanent visual field defects in retinal migraine than in clinically manifest cerebral infarctions in migraine with aura. However, there may be a higher incidence than expected of cerebral infarctions in migraineurs with visual aura who are studied by MRI. These would, in effect, be silent strokes revealed by neuroimaging which were clinically unsuspected. An infarction in the retina, however, is usually apparent to the patient. A recent study of transient ischemic attacks in young patients, containing a large proportion of migraineurs, suggests a benign prognosis for stroke and myocardial infarction as long as other cardiovascular risk factors are not present.{120} Another study of retinal strokes in people under 30 found that 8 of 27 had migraine. Only 2 patients, however, had migraine as the only association, the others having other systemic and/or ocular risk factor as well.{121} We believe that all patients with retinal migraine should be placed on prophylactic anti-migrainous therapy such as calcium channel blocking or beta-blocking agents. There is a report of the salutary effects of isoproterenol inhalation on anterior visual pathway migraine and other migrainous visual phenomena,{122} but we have not had personal experience with this treatment. Newman et al{111} reported bilateral central retinal artery occlusions, disk drusen, and migraine.