The eye problems you are seeing with the fish are being caused by a bacteria and yes can be contagious.
Methylene Blue although an excellent medicine is designed to treat fungus and parasites and would therefore not have much of an effect on curing bacterial related eye problems.
What I recommend be done is start off by changing 25% of the water in the tank making sure to use dechlorinated water that is the same temperature as the water already in the tank.
After the water change begin to treat with a medicine called Tetracycline which is excellent at treating bacterial eye problems in fish. Click on upcoming link for a detailed view of the product which can be found at most major pet stores.
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=16818
Just follow the directions on the product label for dosage instructions.
As you might already be aware the best way to avoid fish disease is by doing weekly 25% partial water changes and quarantining all new additions before adding to the main tank.
Best wishes and good luck!
.
YOUR TROPICAL FISH RESOURCE
OVER 20 YEARS EXPERIENCE W/TROPICAL FISH---BREEDING, MAINTAINING, CURING
Many thanks for your advice, but so far I have been unable to obtain the treatment you recommended here in the UK, despite the two fairly large local retailers selling other API products.
Today I noticed a striking fall in the colour of two of the remaining 4 Harlequins ( hengeli's) and one in particular was very feeble with a couple of pinkish patches on both their bodies. Regrettably I felt it best to euthanse both in an effort to prevent further spread.
The remaining 2, are the more common Harlequins and includes the one which had the spots in the center of the eyes. In fact one eye is now almost clear, so I took a chance and gave him a repeat bathe in the Meth/Blue. Other than that these two are both clean and very fit.
All being well, tomorrow I hope to get along to a very large aquatics centre and if they don't sell what you suggested I will try another manufacturer's anti-bacterial remedy. Also possibly purchase a product to deal with skin flukes as in my search for a cause that's about all I can come-up with.
Thanks again and apologies if I have been remiss in responding.
Hi again and sorry to hear that you've encountered difficulty in obtaining the medicine.
Listed below are two links to medicines, the first link is to an anti-bacterial medicine that is comparable to the one I recommended earlier and is available in the UK.
As you're concerned about skin flukes the second link will show you a flukes medicine easily found in the UK.
Best wishes.
http://www.shoppingbank.com/sb/880/pia/d/bacteria+control+no7+100ml/pid/9882848
http://www.shoppingbank.com/sb/880/pia/d/nt+labs+bds+fluke+treatment+500ml/pid/10467589