I had to have a field test done fairly regularly as well as other tests while I was on ethambutol. If you follow instructions and make sure you are aware of what the signs are if things are going bad you should be OK. I would stay under the care of an eye specialist that is capable of doing field tests. I accidentally double dosed on ethambutol and my eyes became very sensitive to anything white. It was hard to look at. I was taken off ethambutol immediately and my eyesight repaired. They warn you about losing shades of colours, that if when years are normal you have a flat red and a bright red that the difference will be less discernible if things are going wrong. Listen to both the infectious disease specialist and the ophthalmologist and you should be OK.