A thin membrane covering the front part of the eye is
Conjunctiva
Conjunctiva is a thin membrane covering the front part of the eye. It is continuous with the inner lining of the eyelids. It is reduced to a single layer of transparent epithelium over the cornea. Iris is the extension of the choroid partially covering the lens and leaving a small spherical opening in the centre called the pupil. Retina is the innermost layer which is sensitive to light.