I think I see a pink film over the eye. Can you confirm that? Compare to a normal chick if need be.
This may be a bacterial infection of the eye. Both eyes? I recommend flushing the eyes with saline and using an antibiotic ophthalmic ointment in them such as Neosporin or Terramycin.
If you see swelling and the eyes don't respond to the ointment, then you would best start the chick on Tylan 50 at .25ml twice a day for five days. These can be found at most feed stores.
With the eye looking sunken, it looks like conjunctivitis or pinkeye, that might be caused by mycoplasma gallisepticum (MG.) Is the chick having any gasping, sneezing, or being very lethargic or sleepy? Make sure that it is drinking plenty of water, and you can also add water to a small bowl of chick feed and offer it often. Tylan 50 injectable can be used orally, but you need 3 ml syringes with 18 or 20 gauge needles to withdraw it from the vial. Give 0.25 ml (1/4th ml) orally 3 times daily for 5 days. It may chill and need a little extra warmth as well. Use the antibiotic ointment as well. Tylan 50 and Terramycin eye ointment can be found at most farm stores and TSC.