The correct answer is option 4, which states that the cornea in the human eye is composed of proteins and cells. The cornea is a transparent, dome-shaped tissue that covers the front part of the eye, acting as a protective layer. It is the clear outermost layer of the eye and plays a crucial role in maintaining the shape of the eye and refracting light.

Option 1, which suggests that the cornea is a light sensitive screen, is incorrect. The cornea itself does not have the ability to detect or respond to light. That function is performed by the retina, a layer of cells at the back of the eye.

Option 2, which states that the cornea is a muscular diaphragm, is also incorrect. The cornea does not have any muscles. It is a nonvascular tissue, meaning it does not contain blood vessels, which makes option 3 incorrect.

In conclusion, the cornea is a clear, proteinaceous tissue that covers the front of the eye and is responsible for allowing light to enter the eye and undergo refraction.