Page 17 - Demo

Talking glaucoma 17brighter a light is, the greater any change in brightness must be to notice the difference. A candle makes a big difference in a dark room but makes no noticeable difference outside on a sunny day. Similarly, the louder a sound, the greater any change in volume must be for us to notice it. A ticking clock can seem loud in a quiet room but unnoticeable against a jet engine. During a visual field test, the machine is comparing the dimmest light someone can detect with the brightest light the machine can produce. We use decibels to measure this comparison. The same unit is used for vision and sound because we%u2019re measuring how we sense things. As the environment becomes louder, or brighter, we need a greater change to be able to detect that change. While it might seem odd that eye pressure is measured in such an old unit of pressure and that visual fields are measured in the same way as sound levels, there are good, practical and pragmatic reasons for it. The important thing is that millimetres of mercury and decibels give eyecare professionals and people with glaucoma the information they need.Talking glaucoma 17%u201cThe important thing is that millimetres of mercury and decibels give eyecare professionals and people with glaucoma the information they need