Hi
I had a go at viewing your photo, not terribly clear picture but I would say relates to the third eyelid. Its always advisable to get an eye problem checked by a vet. As I say to clients, eyes are very delicate structures and there's only 2 of them.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]