Our study focused on the neuro-ophthalmological presentations in the Emergency Department (ED) of one of the largest tertiary care centers in the country. To our knowledge there is no other study that looked at neuroophthalmological complaints in the ED, but there are studies that looked at general eye complaints among which neuroophthalmological complaints constituted around 30 percent of the consults. This was the highest subspecialty requiring consultation 8. In our study, more than three quarters of the presentations required consults and they were almost equally divided between ophthalmology, neurology, and both. No specific consults were made to the neuroophthalmologist, as the medical center is an academic institute and the first line of consult would be the resident on call.
When it comes to chief complaints, blurry vision was by far the most frequent followed by headaches, while ocular traumas and red eyes were the most common non-neuroophthalmological eye emergencies in other studies 1,9. Around half of the neuroophthalmological presentations to the emergency department were nonemergent such as migraine, ocular migraine and psycho- somatization which constituted around 50% of the diagnoses. This was in accordance to what Chana et al found when assessing all eye related ED visits in The United States but was more than what Kang found in Taiwan (Only 20% had nonemergent eye conditions) 1,10.
We focused in this study on the various neuroimaging modalities used in the emergency department when faced with neuroophthalmological complaint. Although few studies before looked at neuroimaging use in neuroophthalmological diseases, none of them tackled this issue in the ED setting 6,7.
We found that 57.8% of our patients underwent neuroimaging. Brain CT scans were more commonly done (74.65%), compared to Brain MRIs (25.4%). Around three quarters of the images were read as normal or with findings unrelated to the chief complaints. Of all the CT images done, only 14.9% had clinically relevant abnormal findings compared to 56.3% with MRIs. Along the same lines, a study found no increased diagnostic value in Brain CTs done for patients with isolated double vision without other neurologic signs 11. This shows that brain imaging is overused partly because most ED physicians as well as some ophthalmologists and neurologists are uncomfortable and inexperienced in diagnosing neuro-ophthalmological conditions. In this tertiary care center, an MRI would usually require hospital admission to be performed sometimes the following day, hence, the number of MRIs done in the ED was too little to draw conclusions from.
The two symptomatic presentations that were significantly more likely to yield a clinically relevant positive finding on imaging were blurred vision and changes in the visual field. It is important, however, to note that a significant percentage of patients had blurred vision (77%) which might reduce the importance of this symptom in predicting positive findings on neuroimaging. As for the signs, visual field defects, abnormal pupil reactivity, APD and abnormal optic disc exam were predictors of relevant abnormal brain imaging. This was consistent with other similar studies that showed highest diagnostic yield in patients with an abnormal pupil reactivity (with an ARPD) 6,12 or with a visual field defect 13. All those physical exam parameters could be assessed by the ED physician at the bedside.
Abnormal findings on brain imaging that were considered related to the neuro-ophthalmological presentation included hemorrhage or hypodensity suggestive of stroke, acute lacunar infarcts, inflammation, metastatic lesions involving the visual or ocular motor pathways, and demyelinating diseases. A sub-analysis separating the abnormal findings on CT versus MRI was performed. The only association that remained significant was visual field defect on physical exam. This finding predicted an abnormality on CT scan but not on MRI. The lack of significance in the latter is probably attributed to the small sample size of MRI images done in the ED and it paves the way for future studies with a larger population and a higher number of imaging performed (especially MRI) to possibly achieve significance.
While using a CT scan in the ED for its speed and low cost 5 is a quick and sometimes necessary way to rule out certain entities, like bleeding or small orbital fractures 14, it is rarely helpful in diagnosing neuro-ophthalmological conditions. Therefore, one should be careful when ordering CT scans as some pathologies warrant an MRI, the gold standard diagnostic tool for most neuro-ophthalmic conditions 12, while others can be diagnosed using proper history and physical exam without the need for any image.
One example of an unnecessary CT scan is for a patient aged in the 60ies, who is diabetic and with new onset diplopia. Assessment of the patient showed abducens nerve palsy with no other significant findings. This is most likely microvascular and brain imaging initially is not warranted. Another example is for an adolescent patient also presenting with new onset double vision, after a period of headaches, nausea and vomiting. Eye exam is significant for papilledema. Such a patient will need an MRI and MRV of the brain and CT scan alone is not sufficient. Table 1 summarizes the most common neuroophthalmologic conditions and the need for imaging in various scenarios. As front liners, ED physicians and consultants have the responsibility to make such decisions while considering the cost-effectiveness of the resources, and the additional information the image would add to the working diagnosis. The ED physician should be attentive to both the presentation and physical exam to assess urgency, the need for consultation (ophthalmology or neurology) and threat to sight or life (Table 6).
We conclude that risk indicators for abnormal neuroimaging in the setting of neuro-ophthalmological emergencies are blurred vision, or changes in visual field on history taking. While visual field irregularities, abnormal pupil reactivity with or without afferent pupillary defect or abnormal optic discs, are risk factors related to physical testing. Although those factors are important and -if present- should sway the ED physician towards neuroimaging (Table 7) but still individualizing each case is of utmost importance to prevent time-consuming, resource-draining, and sometimes unnecessary workup/imaging.