since I have never heard of Pinguecula... I first googled it and then once again googled "natural cure for pinguecula".
One of the websites = http://www.steadyhealth.com
= had an entry from someone who had been cured... here it is
"After spending a lot of money on eye drops and going to many doctors which obviously did not know much, I cured myself by STOP using visine since I used it quite frequenly. I now Use daily WheatGrass and Must importantly blinking a lot since this is the only way to maintain eyes wet naturally. I wash my eyes about 6- 10 times a day. and whenever i start feeling my eyes dry I blink. Blink, blink is the cure and Daily praying in the morning and at night.

This is how i have managed to cure myself from pinguecula in both of my eyes."

Another person also spoke of vitamins... you will need to look in that website yourself...
Another possibility would be homeopathy:
http://www.abchomeopathy.com

Hoping this may help.