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Editor,—Involuntary closure of the eyelid can be due to either a ptosis with dysfunction of the levator muscle, or a form of blepharospasm with exaggerated contraction of the orbicularis muscle. In true ptosis, no lid crease can be observed in the upper eyelid, whereas in (essential) blepharospasm or (secondary) pseudoptosis a lid crease is present.1 We report a case of involuntary intermittent eyelid closure secundary to an exophoria.
A 67 year old man had complained for 3 years that his left eyelid seemed to fall down and close spontaneously several times a day, and with increasing frequency. This happened especially when he was at home quietly watching television or when he was talking to someone, which made him feel embarrassed. He was able to open the eye again voluntarily, if he paid attention. The eyelid closure never occurred when he was driving a car. Also, when he closed his right eye, he could keep the left one open without any problem. When spontaneous eyelid closure did occur, he sometimes had double vision for a very short while. It had also been noted by his wife that his left eye deviated outward sometimes.
The patient had been known to have hypertension for 20 years and had been treated with medication by his family physician; 6 months before his first visit to our department a light form of diabetes mellitus type 2 had been diagnosed.
When the complaints started 3 years earlier, the patient was seen by a neurologist in a peripheral medical centre, who found no other neurological abnormalities than the intermittent ptosis. Blood tests and EMG for myasthenia were negative. Other blood tests were also normal. At the second visit an active contraction of the left eyelid was noticed and a blepharospasm was suspected. The patient was referred to the neurology department of an academic medical centre for treatment of the blepharospasm with botulin injections.2
At his first visit there, a mild blepharospasm of his left eyelid was diagnosed. It was also noted that while the left eyelid closed, the left eye deviated outward and stayed there until the patient blinked several times. Treatment with botulin toxin was started but had no success. A computed tomography scan of the head was normal. Magnetic resonance imaging of the mesencephalon and the brain showed no abnormalities. A ptosis hook on his glasses was subsequently tried but brought no relief.
Then the patient was referred to the blepharospasm group of the neurology department of our hospital. There it was noticed that when the lid opening narrowed, the eye always deviated outward. With the alternate cover test a latent divergent squint was found. Therefore the patient was referred to us for neuro-ophthalmological evaluation.
We found a visual acuity of 20/20 in the right eye and 16/20 in the left, with a hypermetropic correction of about +2.50. Anterior segments, lens, and funduscopy were unremarkable. Pupillary light reactions were normal, and confrontational field testing was full. With close observation in the examination room we saw that the involuntary closure of the left eyelid was always preceded by an exodeviation of the left eye. This was later confirmed with the use of a video camera. After closure, a lid crease could still be observed in the upper lid.
Subsequent orthoptic examination showed a large exophoria (30 prism dioptres) which easily decompensated in a manifest divergent angle (30 prism dioptres). The eye movements were unrestricted and concomitant. The voluntary convergence was excellent. When a manifest deviation occurred, there was mostly suppression of the left eye, although the patient sometimes experienced double vision, especially when asked about it. At reading distance (30 cm), there was some binocular and stereoscopic vision (TNO stereotest 240"). With the Bagolini striated glasses there was a good fusion area between 20 prism dioptres base temporal and 14 prism dioptres base nasal.
On the basis of these orthoptic results, a presumptive diagnosis was made of a large exophoria of the left eye with a secondary blepharospastic eyelid closure to prevent diplopia. Eye muscle surgery was proposed, and a recession (5 mm) of the lateral rectus and a resection (5 mm) of the medial rectus muscle of the left eye was performed. Postoperatively, the eyes were straight with normal binocular single vision, and no more involuntary eyelid closure or double vision has occurred after a postoperative follow up of 14 months.
In this patient, the easily decompensating exophoria caused diplopia, and this provoked involuntary eyelid closure. The patient was not aware of the diplopia occurring just before his eyelid fell down; he had experienced diplopia occasionally, but could not indicate when. Monocular eye closure in intermittent exotropia has been described and has been thought to be due to avoidance of diplopia.3However, Wiggins and von Noorden4 point out that bright light also may cause monocular eye closure, especially in intermittent exotropes, even when they do not experience diplopia. The authors demonstrated with video recordings that eyelid closure occurred before exodeviation in most patients with intermittent exotropia. We did not test our patient under bright light. The patient’s history indicated, however, that the eyelid fell down especially in quiet indoor situations. We also observed it under (dim) examination room lighting. Moreover the patient had good convergence and fusion. Therefore it does not seem to us that bright light played a role in the eyelid closure in this case.
Although in our patient the exophoria had in fact been noticed at several neurological examinations, it had not been recognised as such, or as the possible trigger for secondary ptosis. Neuro-ophthalmological examination at an earlier stage could have prevented unnecessary neuroimaging and botulin injections.