How to Check Visual Acuity in Low Vision Patients
The First Step of Checking Visual Acuity
[00:00] If your patient cannot see the big E, then you're going to see if they can count fingers. So what you're going to do is you're going to go to the end of the room. You estimate about how far away the end of the room is. Let's say the end of the room is five feet. You're going to hold two fingers up like this because I think it's easier to see. So I put it on the back of my hand towards the patient. So I'll say how many fingers am I holding up? If they can count my fingers, it would be "count fingers" at five feet, if my hand was five feet away from her. If she can't count my fingers from the end of the room, then I'm going to slowly move a little bit closer to her until she can.
Test if the patient Can See Hand Motion
[00:37] Let's say I'm up here and she can tell that there are two fingers. It will be, "Count fingers at..." And then you estimate how far it is. Let's say it's one foot. If I get all the way up to her eye and she still can't count my fingers, then you go to the end of the room and you see if she gets hand motion. So what you do is you say to the patient, "Can you tell if I'm moving my hand up and down or side to side?" If they can tell you which way you're moving your hand, it would be hand motion at however many feet away you are. If you do it at the end of the room and they can't tell which way your hand is moving, then you move a little bit closer and a little bit closer until she can. Can you tell which way my hand is moving? [Demonstrating.]
How to use a Transilluminator to check Visual Acuity
[01:19] Nope. Still can't tell. How about now? Still can't tell. If she can't see my hand moving even from a close distance, then I'm going to get my transilluminator out and I'm going to project it in all four quadrants from about 15 inches away. So I'm going to project it superotemporally, inferotemporally, inferonasally, and superonasally, and we're going to ask her if she sees the light and if she can tell where the light is coming from. So if she can see the light and she can tell me which quadrant it's coming from, that is Light Perception with Projection (LP with P). If she can only tell that there's a light, but she can't tell you what quadrant it's coming from, that's just Light Perception (LP). Now, you have to check and document all four quadrants separately because she might be LP (Light Perception) in one quad and LP with P (Light Perception with Projection) in the other three quads. Now, if I show my light with the transilluminator and she cannot see it, then you get your indirect ophthalmoscope out and you try again. If she can't see the indirect ophthalmoscope, then you call it NLP or Absent Like Perception or No Light Perception, but you don't call them NLP unless and until they cannot see the indirect ophthalmoscope light.