Saccadic Intrusions Without Normal Intersaccadic Intervals
Two types of eye movement abnormalities lack the intersaccadic interval that normally occurs between sequential saccades: (1) ocular flutter and (2) opsoclonus. Ocular flutter is characterized by bursts of involuntary, small-amplitude, very high-frequency (10–15 Hz) horizontal eye movements (see Fig 9-4D). Opsoclonus (also known as saccadomania), however, consists of involuntary, multidirectional eye movements with a similarly high frequency but often larger amplitude. A patient may have ocular flutter and opsoclonus during the course of a disease. Both conditions can occur with myoclonus and ataxia (dancing eyes and feet syndrome). Ocular flutter and opsoclonus can be diagnosed with reasonable confidence through clinical examination, although a definitive demonstration of the lack of an intersaccadic interval requires eye movement recordings. The pathophysiology is unknown but may relate to cerebellar/brainstem dysfunction that inhibits omnipause neurons (located in the pons) and activates burst neurons (located in the paramedian pontine reticular formation and rostral interstitial nucleus of the medial longitudinal fasciculus), resulting in uncontrolled, involuntary horizontal and vertical saccadic intrusions (see Chapter 8).
Etiologies of ocular flutter and opsoclonus include paraneoplastic syndromes, encephalitis, drug intoxication, MS, environmental toxins, and hyperosmolar coma. Ocular flutter and opsoclonus may also occur in some patients without explanation in the absence of associated systemic abnormalities. Opsoclonus may be a transient finding that resolves by 6 months of age in otherwise-healthy infants.
Diagnostic workup for ocular flutter and opsoclonus includes searching for a tumor and an associated paraneoplastic syndrome. In children, neuroblastoma (or another tumor of neural crest origin) is the primary consideration, whereas in adults, small-cell carcinoma of the lung or cancer of the breast or ovaries is of prime concern. Evaluation consists of a complete physical examination and may include MRI or computed tomography (CT) of the head, chest, and abdomen; a whole-body positron emission tomography (PET) scan; lumbar puncture; and a test of urine catecholamine levels (to detect elevated homovanillic acid and vanillylmandelic acid, associated with neuroblastoma). Abnormal paraneoplastic antibodies may be found in the serum or cerebrospinal fluid of some patients with paraneoplastic syndrome–induced ocular flutter/opsoclonus. A serologic or cerebrospinal fluid assay for the immunoglobulin G anti–neuronal nuclear antibody type 2 (ANNA-2, or anti-Ri) can help confirm the diagnosis in cases that are secondary to cancer of the breast or ovary, whereas anti–neuronal nuclear antibody type 1 (ANNA-1, or anti-Hu) is present in some children with neuroblastoma. However, many patients with paraneoplastic syndromes do not have detectable anti–neuronal nuclear antibodies. Therefore, the absence of these antibodies does not exclude a paraneoplastic syndrome.
Treatment of ocular flutter and opsoclonus is directed at the underlying etiology. Regardless of etiology, immunomodulation with corticosteroids, plasmapharesis, intravenous immunoglobulin, or azathioprine may reduce the saccadic oscillations and associated oscillopsia. Other medications that may reduce symptoms include propranolol, verapamil, gabapentin, and thiamine.
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Hoyt CS, Mousel DK, Weber AA. Transient supranuclear disturbances of gaze in healthy neonates. Am J Ophthalmol. 1980;89(5):708–713.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.