According to the authors of a recently published letter to the New England Journal of Medicine (1), reading your smartphone in bed can result in transient vision loss – at least if you do it monocularly. In their piece, they describe two cases of patients who experienced transient (~15 minute) monocular vision loss. Careful questioning enabled them to determine the (very benign) cause: bedtime smartphone use. The symptoms were “always in the eye contralateral to the one on which the patient was lying.” Yes, while one eye was on the smartphone (and had become light-adapted), the other was kept in darkness by the pillow (and remained dark-adapted).

As this discrepancy lasted several minutes – and reflected the time-course of scotopic recovery after a bleach – their hypothesis was that differential bleaching of photopigment between the light-adapted viewing eye and the dark-adapted blocked eye was the cause of these patients’ transient blindness in the viewing eye. Two of the authors decided to recreate the conditions themselves. After monocularly viewing a smartphone screen in the dark for 10 or 20 minutes, they measured their visual sensitivity, both psychophysiologically (via a stimulus luminescence test) and electrophysiologically (measuring b-wave amplitude). On both measures, visual sensitivity was decreased in the uncovered eye, with a recovery period lasting approximately 20 minutes.

So, what can be learned? Smartphones are near-ubiquitous today, their screens are getting bigger and brighter, and are in almost constant use by many people. The authors suggest that when a patient presents with amaurosis fugax in one eye, don’t automatically think that the likeliest explanation is thromboembolic in origin. Taking a detailed history is always a good way of avoiding unnecessary diagnostic examinations (and patient anxiety), but add to this a little bit of pillow talk – establish whether a smartphone is being used in bed, and viewed monocularly early in the consultation.