The cornea is the transparent anterior part of the eye. It can be thought of as the windshield of the eye. The cornea and the intraocular lens both focus the incoming light rays onto the retina to form images. A thin layer of tears called the tearfilm covers the cornea and prevents it from drying. Blinking cleans the cornea and distributes a uniform layer of tearfilm on the surface of the cornea.
A variety of conditions can affect the cornea and result in blurry vision. Dry eye occurs when lacrimal glands do not produce enough tears, or when tears evaporate too quickly. A healthy and uniform tearfilm is a critical factor necessary to achieve clear vision. Minor trauma to the cornea can result in an abrasion or a scratch. Minor abrasions can usually heal without a scar, but major trauma to the cornea can result in permanent scars and blurry vision. A variety of dystrophies and degenerations can also result in corneal scarring and blurry vision. Furthermore, corneal infections can leave permanent scarring on the cornea. Infections also known as ulcers typically result from improper contact lens use or trauma. The corneal surface must be uniform to focus light rays on the retina. Conditions such as keratoconus or ectasia result in warpage of the corneal surface and blurry vision.