Eyelids cover and protect the globe, remove debris by blinking, and spread the tear film, and the eyelid margins contain the meibomian glands.
Eyelids- cover and protect the globe, remove debris by blinking, spread the tear film, eyelid margins contain the meibomian glands
Cilia (eyelashes)
Vibrissae large sensory hairs
Third Eyelid – also protects the globe and helps to spread the tear film and remove debris
Lacrimal glands – two glands in the dog and cat; one in the lateral upper eyelid and one at the base of the third eyelid, secrete the aqueous portion of the tear film
Nasolacrimal ducts – originate at the puncta of the eyelids, then continues via the canaliculi to the duct proper; the duct ends at the nasal puncta
Conjunctiva – protective lining over globe, contains goblet cells that produce mucin as part of the tear film, also part of the immune system of the eye
Palpebral –lines the eyelids
Third eyelid – covers the third eyelid
Bulbar – lines the globe
Tear Film
Lipid – produced by the meibomian glands
Aqueous – produced by the lacrimal glands
Mucin – produced by the goblet cells
Cornea
Epithelium – outer layer of the cornea
Stroma – main portion of the cornea, consists of lamellae in specific orientation to ensure corneal clarity
Descemet's membrane – innermost layer of the cornea; does not retain fluorescein stain
Endothelium – single cell layer of the inner cornea, does not regenerate and functions as the "sump pump" for the cornea
Anterior Chamber – space between the cornea and iris, filled with aqueous humor
Aqueous Humor (AH) and Iridocorneal Angle (ICA)
The AH is produced by the ciliary body and is an ultrafiltrate of blood that travels through the vessels of the ciliary bodythe AH nourishes the cornea and carries waste away from the anterior segment
The AH exits through the ICA and through an alternative pathway called the uveoscleral pathway
The ICA is the meshwork filter at the junction of the cornea and iris; the anatomy of the ICA determines the predisposition of the eye to glaucoma
Uvea – contains most of the blood vessels in the eye
Iris the central opening forms the pupil and controls the amount of light that reaches the retina
The color of the iris is determined by the number of pigmented cells in the iris
Ciliary body – produces the aqueous humor and removes waste from the eye
Choroid – consists of blood vessels and support tissues for the retina
Main source of nutrition for adjacent retina consists of 4 layers:
1. Suprachoroidea
2. Large-vessel layer
3. Medium-size vessel and tapetum layer
4. Choriocapillaris
Lens
Lens capsule – thin, transparent envelope around the lens, necessary to place an artificial lens at cataract surgery
Zonules – fibers that support and control the lens play a role in accommodation disruption may lead to a lens luxation (loose lens) +/- glaucoma
Vitreous
This body takes up the majority of the eye
Role in light transmission and in supporting both the lens and the retina
The clear matrix is made up of 99% water and 1% other (collagen and hyaluronic acid)
Disruption may be associated with lens luxation +/- glaucoma
Retina
Transparent light-absorbing tissue in the back of the eye
Appears membrane-like when detached
Composed of 10 layers that translate light energy into nerve impulses that are then processed by the brain
Optic Nerve
Conduit for electrical impulses from the retina to reach the brain and visual cortex
The optic nerve is usually myelinated in dogs and non-myelinated in cats
Orbit
Bony cavity surrounding the globe with openings (foramina) for blood vessels and nerves to supply the eye
Protects the globe
Open vs. complete
Position of the orbit controls the visual field of the animal
Multiple bones make up the orbit; these bones vary by species
Dog: lacrimal, zygomatic, frontal, sphenoid, palatine, maxillary
Cat: lacrimal, zygomatic, frontal, sphenoid, palatine, maxillary
Vision
Dog: 20/70
Cat: 20/60
Red/green "color-blind"
Visual horizon is very different between breeds of dogs due to size and height of the head; different breeds of cats have fairly similar vision
Proposed midlevel role poses unacceptable risks
October 30th 2024Proposals that would create a new midlevel practitioner (MLP) role raise serious concerns about the future of quality care for veterinary patients. Sometimes referred to as a veterinary professional associate (VPA), their duties would overlap those of a veterinarian and veterinary technician.
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