Overview
The eye (oculus) consists of the eyeball (bulbus oculi) and its accessory organs: eyelids, conjunctiva, lacrimal apparatus and extrinsic muscles. In the dog the orbit is not closed by bone caudolaterally: the orbital ligament completes the ring between the zygomatic process of the frontal bone and the zygomatic arch.
What is visible from outside
- Cornea (cornea): transparent anterior part of the fibrous tunic, through which the iris and pupil are seen.
- Sclera (sclera): white, opaque part of the fibrous tunic; in the dog it barely shows with the eye in its normal position.
- Eyelids (palpebrae): skin folds with tarsus, tarsal glands and eyelashes on the upper lid. The lower lid has few or no lashes.
- Third eyelid (plica semilunaris conjunctivae): a conjunctival fold with a T-shaped cartilage at the medial angle. Its gland supplies a large share of the tear film.
Clinical relevance
- Prolapse of the third eyelid gland ("cherry eye"): a red mass at the medial angle, common in young and brachycephalic dogs.
- Entropion and ectropion: the lid margin rolls in or out; entropion irritates the cornea with hair.
- Keratoconjunctivitis sicca: deficient aqueous tear production, measured with the Schirmer tear test.
- Corneal ulcer: confirmed with fluorescein, which stains exposed stroma.