References
Development of V-FAST: a vision screening tool for ambulance staff
Abstract
Background:
About two-thirds of stroke survivors experience visual problems and most patients who have a stroke limited to the occipital lobe will have visual impairments only.
Aim:
The V-FAST screening tool, which assesses visual symptoms, eye movements, visual field and visual extinction, and a training package to improve diagnostic accuracy of identifying visual impairment in hyperacute strokes were developed and evaluated.
Methods:
The educational package was developed through focus groups. The pilot study screened patients with suspected strokes in prehospital settings; the V-FAST tool was used with 43 of these patients. Each participant was also assessed in hospital using the National Institutes of Health Stroke Scale (NIHSS) and the score compared to V-FAST screening results to determine sensitivity and specificity.
Results:
The education package includes detailed instructions with video. In the pilot study, V-FAST detected visual impairment in 75.9% of FAST-positive and 80% of FAST-negative strokes. Sensitivity and specificity compared to NIHSS were 85.7% and 42.1% respectively.
Conclusion:
V-FAST has good sensitivity to detect vision impairment when screening for possible strokes. The added education package facilitates greater knowledge and understanding of potential visual problems caused by stroke.
Visual impairment following stroke is common and estimated to affect two-thirds of all stroke survivors (Rowe et al, 2019). However, there is no standardised screening for visual impairment for ambulance services.
A particular issue is posterior circulation stroke, in which visual impairments such as visual field loss, visual inattention and eye movement disorders are common and are often FAST-negative (FAST stands for signs of a stroke, including facial drooping, arm weakness and speech difficulties, as well as time to call emergency services) (Rowe and VIS Writing Group, 2017). No ambulance service screening is provided for all these visual problems so there is the potential for misdiagnosis or missed diagnosis.
Where strokes affect the occipital lobe only, around 90% of patients will have only visual complaints (Isaeff, 1974). It is therefore important to assess specifically for this. Furthermore, although stroke is more likely to be considered as a diagnosis for older people, one in four stroke survivors are of working age (Stroke Association, 2018); they are often easily misdiagnosed where their primary complaint is visual, typically as migraine.
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