In 1882, Dr. Galezowski first described ophthalmic megrim, during which patients had a headache with an irreversible monocular visual loss. It affects one in 200 patients who are diagnosed with a migraine. A retinal, ocular, or anterior visual pathway migraine all refer to the same condition. The term "ocular migraine" permits differentiation between the binocular homonymous visual disturbance in a migraine with visual aura and the monocular deficits in an ocular migraine during which one eye is involved possibly due to the affected retina, choroid, or even the optic nerve. Persistent monocular visual loss and abnormal ophthalmological findings have been reported. The pathophysiology of those persistent deficits is not clear. Patients with persistent symptoms have findings of chronicity, for example, pale atrophic disk and optic nerve atrophy that indicate sequelae left in previous attacks.
Based on theories and pathophysiology of a retinal migraine, precipitating factors for a retinal migraine are same for a migraine, with and without aura. Factors include, but are not limited to, emotional stress, high blood pressure, and hormonal contraceptive pills, as well as exercise, being at a higher altitude, dehydration, smoking, low blood sugar, and hyperthermia. Co-morbidity with lupus, atherosclerosis, and sickle cell disease increase the risk of having a retinal migraine.
A retinal migraine is a rare disorder, but the prevalence is not known. Data specific to retinal migraines do not exist, but migraines, in general, have a prevalence of 18.2% in females and 6.5% in male patients, with a higher prevalence in whites followed by blacks followed by Asians. Retinal migraine can start as early as 7 years of age, but most cases start in the second decade and peak in the fourth decade of life. Based on a study by Pradhan et al., it was found that 50% of retinal migraine patients said the vision loss was complete in one eye, up to 20% said it was just blurring, 12% reported an incomplete loss, 7% dimming, and 13% scotoma. More than 75% of patients had a headache on the same side as the vision disturbance within an hour.
Twenty-nine percent of retinal migraine patients have a history of migraine headache, and 50% have a family history of migraine headache.
The pathophysiology of a migraine remains controversial. One theory of ocular migraine is that it is due to vasospasm within the retinal or ciliary vasculature while others think it is a spreading depression of the neuron in the retina that is similar to the spreading depression of the cerebral cortex. The spreading depression of the cerebral cortex is usually seen in the visual aura of a classic migraine; it has been observed in patients having an episode of a retinal migraine, vasoconstriction of both veins, and arteries that could be diffuse or segmental. It also can be noticed by ocular hypoperfusion on fundoscopy. Fluorescein angiography can confirm the diagnosis. The fluorescein angiogram shows delayed filling or occlusion of the central retinal artery and its branches with either a normal ciliary circulation or patchy choroidal defects and capillary dropout. Retinal migraine attacks are precipitated by similar factors as a migraine with aurae such as stress, smoking, hypertension, hormonal contraceptive pills, exercise, bending over, high altitude, dehydration, hypoglycemia, or excessive heat. Strong family history in these patients suggests that a retinal migraine has a genetic predisposition but no clear pattern of inheritance has been described. The vasospasm theory is controversial due to the complexity of the retinal vascular supply. Retina has dual circulation, central retinal artery supplies, inner retinal layers, lacks adrenergic innervation, maintains sensory nerves, and is auto-regulated while the choroidal circulation supplies the posterior retina including the photoreceptors it carries adrenergic fibers without autoregulation.
The patient will present with a wide range of symptoms. Many patients describe positive symptoms such as flashing lights and scintillating scotomas. The negative symptoms are black, shaded, white areas of different sizes of scotomata. Attacks happen a few times per day and can last from 5 to 20 minutes. A retinal migraine shares many properties with a migraine with an aura and acephalgic migraine. Many times, these are difficult to differentiate. However, it is less common to have monocular vision disturbance in an acephalgic migraine or a migraine with aura classic migraine. The visual symptoms during a retinal migraine usually do not last as long as with a visual aura of migraine. Physical examination will show monocular visual acuity loss and/or loss of the visual field, all other cranial nerves and the rest of the neurological examination will be normal.
The attacks must fulfill criteria for a migraine with aura. The aura must be fully reversible and monocular, that is, positive or negative phenomena confirmed during an attack by visual field examination or patient’s drawing of a field defect and at least 2 of the following:
If the attacks are infrequent, such as one per month, then treatment is not necessary. When attacks are more frequent, first-line therapy starts with lifestyle changes that include avoiding dietary triggers such as alcohol and caffeine, controlling stressors like high blood pressure, and ceasing to smoke. If that does not help, then the patient must start a diary to help evaluate the success of the therapy and initiate a prophylaxis therapy. It is usually recommended to avoid ergot and beta-blockers in retinal migraine due to the increased incidence of irreversible vision loss. Calcium channel blockers such as nifedipine and verapamil (most effective) are the mainstay of treatment here. Contraindications to calcium blockers include congestive heart failure, hypotension, sick sinus syndrome, cardiac conductive defects, concomitant, and renal or hepatic failure. Other medications such as coumadin and heparin have been used in isolated cases of patients with antiphospholipid antibody syndrome and retinal migraine. Aspirin and antiepileptic drugs have all been shown to reduce the severity of attacks. Abortive therapy is not used in this condition due to the brief duration of episodes; the main focus of treatment would be to reduce the recurrence of attacks.
The most important initial step in evaluating a patient with suspected retinal migraine is to determine if the visual symptoms are monocular or binocular. Once it is confirmed that it is a monocular visual loss, then the healthcare professional has to rule out all other causes of monocular vision loss because a retinal migraine is a diagnosis of exclusion. Other possibilities that must be entertained are amaurosis fugax as in embolic phenomena of carotid or cardiac source, increase intracranial pressure, orbital apex mass, optic neuritis, giant cell arteritis, migraine with visual aura or anterior ischemic optic neuropathy.
Although a retinal migraine is considered a benign condition, there is a direct correlation between permanent symptoms that persist after the acute attacks and advancing age. Subclinical visual defects and permanent attacks of partial or complete monocular visual loss can occur in elderly patients.
There are complications of a retinal migraine such as CRAO central retinal artery occlusion, retinal infarction, central retinal venous occlusion, BRAO branch retinal artery occlusion, retinal hemorrhages that can lead to edema of the retina and disc, ischemia of choroid or optic nerve, and vitreous hemorrhage. Many of those could lead to irreversible vision loss in the patient.
It is critical to educate the patients about the red flags of vision loss. A visual loss that patients describe as darkness require immediate medical attention and an emergency room visit. Patient must understand that this could be a sign of a stroke or an irreversible eye condition. Visual changes that are more consistent with migraine phenomenon are usually positive such as flashing light. Patient must also be taught that those could come without a headache or any pain. Preventive therapy is important to reduce the attacks frequency and severity and must be done on a daily basis.
A retinal migraine a rare phenomenon that usually affects monocular vision transiently. Duration lasts for 5 to 20 minutes, on average. The prognosis for an ocular migraine is good. The frequency and intensity of the headache typically decrease. During prolonged periods of retinal, choroidal, or optic nerve hypoxia, permanent visual loss may occur.