(Continued)
The third eyelid
You may recall that we had mentioned that dogs and cats and other species have a third eyelid (nictitating membrane) – in addition to the upper and lower lids, which cover the eyeball during sleep and blinking. From time to time, this third eyelid slides across the eyeball from the nasal corner of the eye to the other side.
When the cat (or dog) wakes up from a deep sleep, you can see the third eyelid retracting to its original position. Many cat/dog owners, seeing this for the first time, panic and begin calling their veterinarians for advice. Well, they should not worry; it is quite normal. In some cases, however, this membrane remains visible, partially or wholly covering the visible surface of the eyeball. One speaks then of a ‘protrusion’ or a ‘prolapse’ – according to the degree of surface coverage. That may be a precursor of