The correct option is C Cornea
The eyeball has three coats namely sclera, choroid and retina. The white and opaque sclera has a ring shaped scleral venous sinus at its junction with cornea which make option D incorrect. Cornea is the transparent window of eye located within otherwise opaque sclera. It has no blood vessels at all which makes option C correct. Choroid is dark pigmented thin vascular layer and is characterized by presence of many blood vessels; option B incorrect. The third layer retina contains rod and cone cells; the blood vessels coming from optic nerve open in retina which makes option A is incorrect. Correct answer is C.