DEMONSTRATION "GLASSES" FOR TRAINING IN MEASUREMENT OF THE VISUAL FIELD AND FOR EXPERIENCING IMPAIRED VISION
The different occluders should be all used on top of your prescription spectacles (if you use spectacles) or on a pair of sunglasses.
1. Half field defect: Use regular kitchen wrap or cling film. Fold it to two layers and place two pieces of paper in the fold as shown in the drawing. PD= your interpupillary distance, the distance between the pupils of your eyes, so that the occluder is properly covering one half of your visual field. With this kind of occluder you can demonstrate both right and left sided field loss, homonymous hemianopia. Note, that you can look past the occluder. To avoid that, look straight ahead and turn your head instead. When reading, move the text while staring straight ahead.
2. Quadrant field defect: This occluder is similar to the occluder #1, except that it covers only one quadrant of the visual field in both eyes. Again, you can use the occluder to demonstrate both right and left sided field defects and to train in the measurement of these field defects.
3. Tubular or tunnel field defects of 10 and 20 degrees: Fold the kitchen wrap in two layers and place two pieces of paper in the fold as shown in the drawing. Experiment with the size of the hole by making small holes in a piece of paper and looking through them at 57cm distance. When the piece of the paper is placed against your glasses and you see through the hole an area of 10cm in diameter at the distance of 57cm, your visual field is equal to appr. 10 degrees. When the area seen is 20 cm wide, then your visual field through the hole is 20 degrees. Make measurements of these fields by using a paper with a cross in the centre at the distance of 57cm and map the tubular field.
4. Central scotoma: This is the most difficult lesion to demonstrate because it is so easy to look past the small central occluder. Place them at your PD and keep looking "through" them while talking with another person and when looking at texts and pictures. Use an oval piece of paper approximately the size of the larger hole in occluder #3 to create a scotoma of 20 degrees in diameter. If you look slightly past the occluder, you will experience the effect of a paracentral scotoma.
Disturbing light phenomenons in the visual field cannot be measured but need to be discussed with the child as soon as the child seems to have some loss of vision in the midperipheral areas. There are two simple animations of these light phenomena in the introductory lecture.