How to Find Your Blind Spot - Clinical Skills - 4K

Good afternoon all. So yesterday at the medical school we were teaching the cranial nerve exam and whilst there is going to be a clinical examination video for how to perform the cranial nerve examinations, that will be coming hopefully next week or so, one of the things that we did find during teaching was an area that the students seemed to struggle with quite significantly that being identifying a patient's blind spot or for that matter their own. So I thought this would be worthwhile just producing a little video to try and help people find their own blind spot because if you can't find your own blind spot then you won't be able to explain to a patient what it is that you're asking of them. So what is the blind spot? I think that's worthwhile discussing initially because I think that people have seen so far with the other how-to examination videos I'm relatively garrulous. So the blind spot that we'll be looking for today is a good example of a scotoma, that is any area where there is an obscuration of the visual field. In terms of what we're discussing here we're trying to find the physiological blind spot, sometimes if you have that latin bent referred to as the punctum sacum. This is essentially where the optic nerve, cranial nerve 2, is going into the retina. So one way of thinking about it is it's a wiring point for the eye and as a result of this wiring you can't actually see over that spot. Now what you have to remember is as humans, people, creatures, however you want to look at it, we don't actually see. We are brains living in a black box isolated in all ways from the outside world. We sense and interact with the outside world via electrical stimuli coming in through our nerves etc. Like any system the quality of our output, i.e. vision, is only as good as the input which is applied to the system, i.e. the electrical stimuli coming from our eyes. As a result those inputs, those electrical stimuli, can be fooled into changing how the brain perceives what is going into the eye. Think about magic eye pictures for example, or from a medical perspective, things called Ishihara charts, which is how we determine what a patient is able to see with regard to colour blindness. So here's an image of one of those Ishihara chart plates. Because I'm colour blind, let me ask you, what picture, what number do you see looking at this plate? Me? I'm red green colour blind. As a result I'm missing more the red and green cones in my eye compared to other people who have what we term normal vision. So I am unable to see the numbers which are written here. My brain is unable to create a recognisable pattern, i.e. a number, from the input that it is receiving. I can still see the plate and I can see all the coloured dots, but there isn't a recognisable shape there. Now, how does this relate to your blind spot? Well, we have this patch on the retina that is insensitive to light. So rather than walking round with two small black spots on our vision forever and a day, our brain doesn't recognise this lack of data input there. Or perhaps in another way, our brain papers over this absence of vision like some kind of biological version of Photoshop. So we've all got this patch and none of us can see through it, so we should all technically be equal. Why is it something we have to examine? Well, different conditions can affect the size of this blind spot. So optic neuritis, an inflammation or swelling of that optic nerve for one, and a condition called papilledema, where you have optic disc swelling due to raised intracranial pressure, as another. Simply because this area of blindness on the retina is increasing in these conditions, when we assess for the blind spot, we'd find that patient's area of visual defect, their scotoma, would be larger than our own. Now at this point, I go back to yesterday's tutorials. Because the students were having difficulty finding their blind spots, they were also having difficulty finding each other's blind spots. So I'd like to try and give you a simple method for finding your own blind spot at home, which then in turn will hopefully improve your clinical skills, which is the entire purpose of these videos. First, let's review the brief description from the cloud clinical examination as to how we should formally test the blind spot. To test the blind spot, place a red tip target equidistant between the patient and yourself at the visual fixation point. Move the target temporarily until it disappears. Then move the target slowly up and down, as well as from side to side until it reappears. This will allow you to compare the patient's blind spot with yours. Now, being truly honest, finding a blind spot is very difficult if you've never done it before. So I'm going to put up a small diagram here of a cross and a dot. I know, please try not to get too excited. This is clearly cutting edge clinical education. Hopefully you're watching this on an iPad or a screen that you're actually able to move. So let's try and find your blind spot. Take the iPad and hold it at arm's length. Close your right eye. Now look at the plus symbol with your left eye. Slowly bring the screen towards you until the dot disappears. Once it's disappeared, you've found your blind spot. At this point, you need to carefully move the screen left and then right to find where the dot reappears. Then return to where you think the middle was. And then from that point, move the screen upwards and then downwards until the screen reappears in both orientations. With this, you have mapped out your blind spot. I think it's really, really crucial that you do try this because unless you have found your blind spot and seen what a bizarre thing it is to find this evidence of a visual hallucination where your brain is filling in an absence of sight, then it's very difficult to explain and be able to effectively assess for a patient's blind spot. If you're watching this on a desktop computer, then it might be worthwhile taking a screenshot of the dot and the cross, printing it out and having a go with a piece of paper. But I would thoroughly encourage you to do so. Well, I hope that that little overview has been a benefit to some of you out there. And if you found this useful, I'd be really grateful if you could give it a like and hopefully subscribe to the channel as we'll try and put out some more clinical advice like this and also give it a bit of a share perhaps. I'd hope that it's phrased in such a way that anybody with an interest in science or just how our own biology works would be interested in giving this a go. OK, with that, I'll say cheerio and see you all later.