Possible Clues:

• Eye drop that makes your pupils widen, e.g.
• What produces growth in pupil, slow but incomplete
• Stretching muscle
• Surgical instrument for making a tube or cavity wider
• Surgeon's instrument
• Trainload without an elaborate instrument
• Eye doctor, at times
• Ophthalmologist's solution, maybe
• Eye drops, perhaps
• Drug that makes one live longer, reportedly