Cat Third Eyelid Sleeping. It is not uncommon for cats to sleep with their eyes partially open, but with the third eyelid covering the eye. They haven’t known that this is a common condition in cats, due to various causes.
In some cases, however, the third eyelid may also be visible when the cat is relaxed and resting; A protruding third eyelid is not always abnormal. If your cat catches sight of movement, it can quickly react.
This means that in the early stages of illness, often the only thing that a cat owner may notice is that the cat has become quiet and withdrawn.
Another site that will give you quite the shock first time you see it is seeing a cat’s third eyelid closed but not their outer eyelid while they are sleeping. Hi bellel, sometimes cat's showing third eyelid is not necessarily to be sick. Another site that will give you quite the shock first time you see it is seeing a cat’s third eyelid closed but not their outer eyelid while they are sleeping. The purpose of the third eyelid is to extend across the eye to protect the cornea from scratches and wipe away dust and debris.