Possible Clues:

• Tension on the visual organ
• Reading problem tutor had after English, certainly
• This writer said Labour is in trouble with the Observer
• Like 21 across on coach, low wattage might be responsible for this
• What could trouble retina? Yes!
• Difficulty in sight? English agreed to prepare
• Possible effect of too much reading
• Headache source
• Reading problem
• Disturbed serenity, receiving a tired look