Inner most Layer of the
Eye
Retina
Contains light sensitive cells and relays the infortion throught the optic nerve (photoreceptors)
Light enter the eye throught the pupil is fouccused onto the retina by the lens. Information is transmitted by the photoreceptor cells to the brain by the optic nerve ii.
Rods are sensitive to low light levels – bl/wh
Cones sensitive to bright light- colour vision
Dogs have 95% rodes and 5% cones
The extrinsic eye muscles
Movement of the eye controlled by muscles attached to the sclera.
Muscles are supplies by the cranial nerves.
Retractor blubi – retraction of the globe.
Dorsal, ventral, medial& lateral rectus- move the eye up down l & r
Eyelids
Also know as the plaperbra
Firbous layer covered in skin and mucous membrane.
Continues as the conjunctiva
Upper and lower lid meet at the medial and later canthus
Contain Meibomian glands froms part of the tear film
Eyelashes- cilia- lines the palpebral edge.
Third eyelod s the nictitting membrane
Contains cartilage
Covered by ucous membrane & lymphoid tissue
Third eyelid gland- tear production
Prolapse- cherry eye.
Tear film produced by:
Meibomian gland
Third eyelid gland (harderian gland)
Lacrimal gland( main)
Lubricates
Proctects
Maintains corneal transparency
Drains into the lacrimal puncta ( tear ducts) this is then drains into the nasolacrimal duct and into the nasal cavity.
Eyelid – species varation
Rabbits
Third eyelid contains a ot of lymphoid tissue that can swell.
Harderian ( third eyelid gland) in bucks may swell in breeding season.
Naso lacrimal duct disease common with dental malocclusion.
Large punctum lacrimale can be cannulised.
