A sty is an infection of single eye lash follicle or an abscess on the eyelid.
It normally occur where your eye lashes grow.
Causes
Bacteria (stapphyloccal bacteria)
Source: MedicineNet
Source: DesiMD
Source: YouTube
Source: ePharmapedia
Source: MedicineNet
It can be mistaken for:
Small yellow patches around your eyes? (This shows one may have cholesterol deposits called xanthelasmata and indicate heart disease or a heart attack)
A white ring around your pupils? (Cholesterol deposits are high enough to cause heart disease especially if under 40 years of age)
Blood vessels in the eye that appear of bronze or grey colour? (If appear bronze or grayer and appear looped or sharp bends look out for high blood pressure and diabetes)