2.5 Diagnostic Procedures/Laboratory Tests.These occur randomly and come in different shapes and sizes. VS patients experience bright flashes or blobs of light in their vision. It is unclear exactly what part of the eye causes this and to what extent healthy people experience it, but it is definitely a distinct symptom of VS. They are particularly noticeable in the first ten minutes or so of exposure to darkness (e.g. Visual Snow Syndrome patients may experience coloured (usually violet or orange) ‘swirls, clouds or waves’ when their eyes are closed. Whilst healthy subjects would only see a handful of these when looking at the blue sky, VS patients may see many more of these leucocytes, even when not looking at a blue sky (such as indoors on a white or cream-coloured wall). This phenomenon is where you can see small white blood cells (called ‘leucocytes’) traveling on a wiggly path within your eyes. In contrast, Visual Snow Syndrome sufferers typically see more floaters and in more lighting conditions (such as indoors), making them potentially very intrusive.īlue-field entoptic phenomenon (BFEP or ‘Scheerer’s phenomenon’) In healthy people, floaters are not usually visible unless looking at the sky, and is often not distracting. Floaters are usually harmless, though it can be a symptom of retinal detachment, a sight-threatening condition. jelly-like substance) inside our eyes shrinks, which causes floaters to form that then cast a shadow on the retina. These are the grey, black and clear cobwebs, clouds, spots and strands that appear in the vision. Sufferers only have to experience one of these excessively to satisfy this aspect of the VS diagnostic criteria. There are four key entoptic phenomena: floaters, blue-field entoptic phenomenon, self-light of the eye and spontaneous photopsia. Healthy subjects experience entoptic phenomena, but Visual Snow Syndrome sufferers experience them to an excessive extent. It is often described as seeing motion as a cinema reel, one frame at a time.Įntoptic phenomena are visual phenomena that arise from the structure of the eye itself. Motion does not seem fluid and instead seems choppy. In some cases, the trailing becomes so severe that the individual becomes unable to perceive motion properly – a condition known as Akinetopsia. For example, the image below shows a hand moving from right to left some people with Visual Snow Syndrome would see a ‘trail’ or some kind of ‘smearing’ behind the hand. Trailing is closely linked to afterimages, and it is where you see a moving object’s motion after it passes your eyes. Additionally, afterimages that healthy people experience are often stronger and last longer in the eyes of a VS patient. The image below illustrates what a patient may experience if they were to look at a computer screen and then look just to the left of it. For instance, a VS patients may look at a black chair briefly and look away, and still see a vague imprint of the chair in their vision even though it was black, not bright. Those with palinopsia experience this to a greater degree – the stimulus does not have to be as intense or prolonged to elicit an afterimage. the sun, as described above), and negative ones if exposure is prolonged (due to cone cells becoming tired). Healthy patients experience both types: positive ones if looking at particularly bright objects (e.g. a red object creates a blue afterimage), last longer and their duration/intensity is related to the length of exposure. Negative ones have inverted colours (e.g. A classic example of a positive afterimage is when you accidentally look at the sun, look away and then see a small blob/imprint. Positive afterimages last for a short duration, are coloured the same as the original image and their intensity is unrelated to the length of exposure to the original image. Patients may experience both or just one of these forms of palinopsia.Īfterimages describe the phenomena of when an imprint of an object continues to be seen in your vision even though you are no longer looking at the object. There are two types of afterimages – positive and negative – and it is useful to differentiate between the two. Palinopsia refers to either excessive ‘after-images’ or ‘trailing’.
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