Agree with the others, clean water, a pinch or two of salt to help with osmoregulatory stress, and if you increase the temp also increase surface agitation to help increase 02 levels. (which are lowered under warmer temps)
If it turns out to be more serious, as in a bacterial infection, you might want to refer to the chart in the following link.
http://www.fishyfarmacy.com/fish_diseases/eyes.html
And not to single you out Pete, but pH shock is a myth.
If ones TDS shifts too quickly it can cause osmotic shock, which for many years hobbyists confused with pH shock, only because most hobbyists don't own a TDS meter.
Osmoregulation has nothing to do with pH, and everything to do with controlling the balance of water/salt concentrations. pH has nothing to do with regards to if ones water is a hypertonic solution, hypotonic solution, or if it's isotonic. The shock part of the equation comes in when a fish has difficulty reaching equilibrium. The "high to low" shift in TDS values becomes more dangerous as the fish cells can become flooded with water faster than they can reach equilibrium, and burst .... which is where the term "shock" comes in.
These links explain things much better than I can...........
http://www.angelsplus.com/ArticleOsmosis.htm
http://www.shrimpnow.com/content.ph...ce-on-Acclimating-and-Quarantining-New-Shrimp
http://www.mtfb.com/MTFBJUNE/MTFB2 pages/jacobsarticle2.htm
The biggest issue with pH is ammonia toxicity, as at higher pH values free ammonia can be much more lethal, especially when higher temps are involved.
HTH