I really don't know enough to comment because this is all so third hand.
I've been a member of Audax UK for 20 years and not heard of unusual eye problems in long-distance cyclists. (Trouble with contact lenses, sleep deprivation and foreign bodies are entirely 'usual' IMO.)
I think, as you do, your friend should see someone who knows about eyes.
A high street optometrist/optician can at least examine eyes thoroughly and check the eyes for high pressure (glaucoma).
Don't mess with eyes!
Some hospitals have an Eye Casualty service, though somme of these require referral from another party.