Transient Smartphone Blindness
Transient Smartphone "Blindness" (TSB) is a recent phenomenon characterized by acute, painless, transient vision loss associated with smartphone usage while lying down in the dark . While it is usually monocular, it can rarely present bilaterally . As it can masquerade serious, more well-established pathologies, it is important to rule out ischemic retinal and optic nerve disorders, when evaluating a patient with painless, transient vision loss for TSB.
In 2016, Alim-Marvasti et al. described two cases of several months of painless, unilateral, transient vision loss in young individuals (22 and 40 years old) without a reported history of vasculopathic disease. Visual acuity, pupils, intraocular pressures (IOP), color vision by Ishihara plates, fundoscopy, slit lamp examination, optical coherence tomography (OCT), Humphrey Visual Fields (HVF), Magnetic resonance imaging (MRI), and Vitamin A level were all normal. After careful review of each patient's history, symptoms occurred specifically at night while in recumbent position immediately after turning off a smartphone screen at which they had been looking. In both cases, the affected eye was contralateral to the side on which the patient was lying and resolved within minutes. 
The typical history of TSB includes acute, painless, monocular, transient vision loss in the setting of lateral recumbent smartphone usage with low level of ambient light in which the lower eye is occluded (e.g. by a pillow) and the fellow eye is exposed to the bright screen of the device  .
Occasionally, subjects have been reported to only see vague outlines of objects in the affected eye with normal vision in the fellow eye .
While most frequently reported as monocular, Rondeau et al. have reported a case of a 68-year-old woman who experienced binocular TSB in the context of discovering that the patient's phone was set at its maximum brightness setting .
TSB is believed to be due to temporary discrepancy in bleaching of photopigment and ultimate light adaptation between the fellow retinae. The prevailing hypothesis is that while in the lateral recumbent position, one eye is blocked (such as with a pillow, bed sheets) and subsequently becomes dark-adapted while the other eye exposed to the bright screen of the device becomes light-adapted. After the screen of the device is deactivated and the room is once again with low ambient light, the light-adapted eye is perceived to have poor or no vision. The vision returns to the patient's baseline after several minutes.  
Alim-Marvasti et al. sought to reproduce these findings with objective electroretinogram (ERG) recording, exposing the authors to a smartphone screen in a low-ambient light room while one eye was occluded. Exposure was at arm's length and redemonstrated reduced visual sensitivity in the light-exposed eye after screen was powered off with recovery in several minutes. Specifically, the ERG showed reduced B-wave amplitude in the light-exposed eye. 
Examination and Diagnostic Procedures
Naturally, visual acuity (VA), pupils (i.e. RAPD evaluation), intraocular pressure (IOP), confrontational fields (CFs), extraocular movements (EOMs), and color vision should be evaluated. These parameters would be expected to be normal (i.e. near-normal VA, no RAPD, full CFs, intact and painless EOMs, no color desaturation).
HVF, OCT retina, MRI would all expected to be normal or at least inconsistent with the patient's symptoms.
TSB must be distinguished from other causes of acute, painless, transient vision loss, especially thromboembolic disease (e.g. amaurosis fugax).
While non-arteritic anterior ischemic optic neuropathy (NAION) may cause acute, painless, unilateral vision loss, symptoms would be expected to persist (i.e. not transient). 
Additionally, multiple sclerosis (MS) merits consideration in these patients, although pain with eye movement, color desaturation, and abnormal MRI findings (e.g. periventricular white matter changes, enhancing lesions separated by time and space consistent with demyelinating disease) would be expected .
Management and Prognosis
It has been suggested that patients should only use smartphones in well-lit rooms and to assure that neither eye is occluded . Patients should conversely be advised against smartphone usage in dark settings (e.g. before bedtime or early morning before dawn) in order to prevent recurrence . Incidentally, this would also be expected to improve the patient's sleep hygiene .
Given the transient etiology of this phenomenon, the prognosis has thus far been uniformly promising, with full resolution of symptoms.
Comment Regarding Phone Manufacturers
Recently, mobile phone manufacturers have introduced technology to reduce blue light at certain individuals, such as at night. Hasan et al. have suggested that these manufacturers spread awareness in order to warn their clientele of the side effects of smart phone use in poorly-lit rooms .
Correct diagnosis of TSB is imperative as incorrect diagnosis may put patients at risk. If misdiagnosed as thromboembolic etiology (e.g. amaurosis fugax), patients may be unnecessarily started on anticoagulation (such as aspirin ) which can pose obvious bleeding risk to the patient. If incorrectly treated as MS, the patient may inappropriately be started on disease-modifying therapies (e.g. interferons, monoclonal antibodies), which pose significant side effects as well as expense. In addition to the field of Ophthalmology, recognition of this entity is relevant to other physicians to which patients with these symptoms present (e.g. Family Medicine, Internal Medicine, Emergency Medicine).
Ultimately, this phenomenon emphasizes the importance of thorough history-taking in ophthalmology and the field of medicine.
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