You really need to do a visual stress assessment. This can be
Simple and efficient for sorting out the best overlay (if your intending to use overlays). If your students are considering lenses the colour may be different. Look up good optician/ophthalmologist in your area.
Also look at the University of Essex Research by Professor Arnold Wilkins
There’s also a You Tube interview with him.
He was involved in the research in the 1990s, when I was teaching just down the road. Knocks spots (or even coloured overlays) off a certain expensive imported alternative.