Possible Clues:

• Vision tiredness
• Fourth letter in chart -- see it any differently? The reason?
• Certainly in English school pupils are involved in such trouble
• Downside of reading in poor light
• It might cause pupils problem, of course, in English school
• Agreed ... within a damaged retina there's a vision problem
• Knackered retina? Yes.
• Discomfort of sightseers right inside Orient Express?
• Problem, indeed, damaged retina's brought about
• Looks at what instructor does which makes it hard to see