Eyelid function is important in maintaining the health of the cornea and globe. Eyelids distribute tears over the corneal surface, remove foreign bodies from the surface of the eye, control the amount of light entering the eye and protect the globe from trauma.

The lens is composed of crystalline fibers specifically arranged to allow light rays to transilluminate through the lens to the retina. The lens focuses light rays on the retina.

A thorough fundic evaluation is important in diagnosing retinal disease. At the beginning of the exam the menace response, dazzle reflex and the pupillary light reflexes should be assessed. Abnormalities on the neuro-ophthalmic portion of the exam may augment interpretation of fundic findings.

The "red eye" may present for many different reasons. Periocular trauma, conjunctival hyperemia, corneal vascularization, intraocular hemorrhage, and detached subalbinotic retinas may all lead to the complaint of a "red eye". Examination of the eye should lead to localization of the abnormality and standard ophthalmic testing should be performed, including schirmer tear tests, fluorescein staining, and intraocular pressures.

A thorough and systematic examination is important in ophthalmology as in other areas of veterinary medicine.

Many systemic diseases may affect the eye and often the first sign of a systemic disease occurs in the eye.

A cataract is technically any opacity in the lens; it may be a small focal spot or, at the other end of the spectrum, the whole lens may be involved.

An emergency involves anything that is vision-threatening and/or painful for the patient.

Eyelids cover and protect the globe, remove debris by blinking, and spread the tear film, and the eyelid margins contain the meibomian glands.