What instruments measure eye strain?

Symptom: Eye strain is a symptom. There is no " instrument" that measures this. However, if you're having difficulty with your vision and are squinting a lot or are having fatigue as you use your eyes a lot with neat tasks, you need an eye exam to determine if you require glasses. The most common source of "eye strain" is a refractive error which indicates that you may need glasses. At your age presbyopia.