cornea
It is called a nictating membrane.
The clear curved membrane that covers the front of the eye is called the cornea. It also focuses light onto the retina.
Don't know what you mean by 'serious.' Do you mean 'serous' as in fluid-filled? The membrane that can cover over a frog/toad's eyes (and other amphibian, reptile, even mammal species) is known as a 'nictating' membrane. It is there to protect against fluid and debris from coming into contact with the corneal surface of those eyes.
myothelial tiisue
cornea
The cornea, or clear layer on the front of the eye.
The transparent layer forming the front eye
The nictitating membrane is the transparent layer the covers the outside of a frogs eye. Frogs have a so-called Nictitating membrane, which they can slide over their eyes for protection. They do this while jumping and swimming.
They have a transparent membrane that covers the eye when they submerge.
Cataracts are a clouding of the lens of the eye or of its surrounding transparent membrane that obstructs the passage of light.
The cornea is responsible for focusing the light that enters the eye. It is the transparent portion of the eye that covers the front of the eye
The front clear surface of the eye is called the cornea. It protects the covering of the eye and helps to focus light.