Orbits and Vision Angles in Animals

Orbit

• It is a bony fossa separating the eye from the cranial cavity and surrounding areas.
• The size, shape, and positioning link to visual activity and feeding behavior
• The orbit's depth contributes to protection and appearance
• The location of the orbit's governs the visual field

Axis and Vision Angles in Domestic Animals

• Dogs' and cats' rostrolateral axes are 10-20 degrees from midline, providing enhanced binocular vision suitable for predators.
• Horses have laterally placed orbits, set 40 degrees from midline for strong monocular vision, aiding prey animals.
• Ruminants have laterally placed orbits approximately 50 degrees from midline, offering strong monocular vision as prey animals.
• Rabbits have laterally placed orbits up to 85 degrees from the midline, providing broad peripheral vision.

Orbit Type

• Complete orbits are found in horses, pigs, and ruminants, providing full bony enclosure.
• Incomplete orbits are present in cats and dogs, with segments not fully enclosed by bone.

Bones in the Orbit

• Cat orbits have six bones
• Dog orbits have 5/6 bones
• Horse orbits have 5 bones (no maxilla)
• Bovine orbits have 5 bones

Orbital Rim Composition in Cats and Dogs

• Made up of 4 bones: frontal, lacrimal, maxilla, and zygomatic
• Supplemented by the supraorbital ligament between zygomatic and frontal bones
• Cats possess a smaller orbital rim compared dogs

Equine Orbital Rim

• Includes four bones: frontal, lacrimal, zygomatic, and temporal bones
• The temporal bone replaces the supraorbital ligament in other species

Bovine Orbital Rim

• The rim consists of three bones that are frontal, lacrimal, and zygomatic bones
• The bovine rim has a complete bony structure with fused zygomatic and frontal bones, lacking a separate ligament

Other Orbit Bones

• The palatine and sphenoid bones form part of the orbit structure.

Orbital Foramina

• Structures pass from most rostral to caudal
• Ethmoidal (CN 5, Ethmoidal nerve and vessels, Branch of trigeminal)
• Optic canal (CN 2, Optic nerve, Internal ophthalmic artery)
• Orbital fissure (CN 3, 4, 5, 6; Oculomotor, Trochlear, Abducens, Trigeminal nerve)
• Rostral alar foramen (CN 5, Trigeminal nerve, Maxillary branch, lower eyelid, and lacrimal gland. Round foramen → alar canal → rostral alar foramen)
• *The orbital fissure is fused with foramen rotundum foramen orbitorotundum in cattle Occulomotor and trochlear (CN 3, 4, 5, 6, Retinal and internal maxillary arteries)

Cavernous Sinus/Middle Cranial Fossa Contains

• CNIII
• CNIV
• CNV (ophthalmic and maxillary branch)
• CNVI

Orbital Fascia Composition

• It consists of a thin, strong connective tissue liner, surrounding orbital structures including the bony fossa
• Subdivided into three entities:
• Periorbita
• Fascia bulbi
• Tenon’s capsule

Orbital Fascia

• 3 sheets of orbital fascia are divided by adipose tissue creating a cushion for the eye and adjacent muscles
• Birds and reptiles don't have much fat in the orbit
• It's possible orbital fat helps position the globe in manatees due to the absence of the retractor oculi muscle
• In dogs, orbital fat surrounds the optic nerve, creating a cone to separate it from the retractor muscles

Extraocular Muscles (EOMs)

• The eye has four recti, two oblique, and retractor bulbi muscles

Eye Muscles

• Dorsal rectus
• Ventral rectus
• Medial rectus
• Lateral rectus

EOM Origin

• Originate from the orbital apex, specifically the annulus of Zinn

Ventral Oblique Muscle Origin

• Originates from the palatine bone of the medial orbit

Rectus Muscle Insertion

• Insert anterior to the globe's equator

Rectus Muscle Insertion Distances

• Insert approximately 5mm posterior to the limbus medially, 6mm ventrally,7mm dorsally, and 9mm laterally

Oblique Muscle Insertion Point

• Insert posterior to the equator of the globe

Dorsal Oblique

• It passes through the trochlea near the medial canthus, turns acutely, and continues dorsolaterally over the globe
• This causes intorsion that moves the dorsal aspect medially and ventrally

Ventral Oblique

• Passes beneath the eye
• Crosses the ventral rectus tendon
• Action is extorsion resulting in moving the ventral globe medially and dorsally
• Both obliques are located through a pulley sling of connective tissue and smooth muscle

Retractor Oculi (Bulbi)

• Forms a cone around the optic nerve retracting the globe into the orbit
• Function is abduction
• Retractor oculi is absent in birds and snakes

LR6SO4 Mnemonic

• Lateral rectus is controlled by the abducens nerve, and the superior oblique is innervated by the trochlear nerve.

Eyelids

• Closure is achieved through contraction of the orbicularis oculi muscle
• Opening occurs via the relaxation of the orbicularis oculi and contraction of the levator palpebrae superioris

Eyelid Functions

• Protection
• Exclusion of light
• Production of tears
• Spreading the tear film

Eyelid Structure

• The upper and lower eyelids are divided into four parts:
  • Outermost skin layer
  • Orbicularis oculi muscle layer
  • Tarsal plate and stromal layer
  • Palpebral conjunctiva (innermost)
• Large cilia roots link to sebaceous glands(Zeis) and modified sweat glands (Moll)

Meibomian Glands

• Conjunctival surface of both eyelids
• Parallel rows of lobules with openings close to the lid margin
• Ducts are stratified squamous epithelium
• Polar and non-polar lipids are contained

Accessory Lacrimal Glands Exist Including

• Glands of Wolfring that line the posterior of upper and lower lids

Glands of Krause

• Glands exist at conjunctival fold.
• Is a mucus producer.
• Ducts are well developed making it part of CALT

Conjunctiva

• Continuous structure with two portions
  • Palpebral (simple to stratified epithelium)
  • Bulbar(junction between palpebral and bulbar conj)
    • This is contiguous with limbal and corneal epithelia
    • Very thin and clear
    • The epithelium transitions to more complex near the Meibomian glands, changing from columnar to stratified columnar.
• Conjunctival fornix (Pseudostratified columnar to stratified cuboidal very thin, and transparent. Junction between palpebral and bulbar conj)

Goblet Cells

• The number of goblet cells rises
• Distribution of cells is inconsistent within the dog species
  • In the dog species they often have very high density
• Most species lack goblet cells except guinea pigs

Conjunctiva Layers

• Substantia propria has 2 layers
• Superficial adenoid layer, contains lymphatic follicles and glands
• Deep fibrious layer, contains nerves and vessles

Conjunctiva Associated Lymphoid Tissue (CALT)

• CALT arranged across 2 layers
• CD8 positive suppressor/cytotoxic cells prevelany
• Lymphatics drain through eyelids to the commissure

Nictitating Membrane

• This is the third eyelid covered in conjunctiva from the medial canthus
• It rests over the front the globe
• It is made of a cartilage plate, rich in vessels.

Nictitating Cartilage Plate

• T Shaped plate with parallel leading edge.
• Cats very smooth
• Dogs, grooves formed by the surface
• Accessory lacrimal has a high prescreens
  • Serous- horse -Mixed animals- cattle/ cats/ dogs/ exotics
  • mucous only - pig

Eyelid Cartilage Composition

• Elastic cartilage in horses,
• Hyaline cartilage in dogs and cats
• Shape is species dependent
• Cats are reverse S shaped
• Dogs are crescent moon
• Horses hooks

Harderian Gland

• Found in rabbits and pigs
• Immunologic/ Photo Protection
• Thermoregulation.
• Osmoregulation.
• Reproduction and pheromones

Movement

• Is indirect.
• Due to retractor oculi bulbi and contractions of the globe.
• Manatees can move third eyelid via paired scleral muscles and lack retractor oculi
• Birds and non mammals also lack

T.E/ TEL

• T. The loop is moved by the pyramidalis muscle.
  • Passing through quadratus muscles

Lacrimal/ Nasolacrimal System

• Tears are needed for optical integrity, normal function
• Pre corneal film function- removal of outer material provides nutrition and removes matter
• Antimicrobial function has three intermixed layers outer, middle and inner

Pre Corneal Layers

• The outer layer is oily and thin from the glands of Zeis. This reduces aqueous evaporation protecting from flowing over face
• The middle later is aqueous based made up of Krause, 61% lacrimal 35% TEL uptake required for Oxygen and normal health
• The inner layer is Mucin from goblet, cells. Glycocalyx provides the most mucous function

Tear Flow

• Excess travels the inferior Col de sac pumped through the pontic
• The blinking of the eyes, surrounded and works in coordination with the eyelids.
• Prevents excess of the lacrimal fluid.

Tear Flow (Path)

• Vertically leaves margins turns medially passes through the orbita.
• Joining each at the lacrimal sacs of the lacrimal bone empties at the ducts
• Short NLDS passage into nasal cavities opening one Cm from the naris

Glands And Inner Vations

• Glands are dorso-lateral innervated cranial nerve v, sympathetic and parasympathetic.
• Cholinergic and pilocarpine will stimulate antisecretions, and will drop

Components And Layers of The Globe (Eye)

• 3 layers
• Outer, fibrous, tunic -Shape determines form
• Middle (uvea) heavily vessels contain internal lights provide nutrition and remove waste. Retine
• Inner with photoreceptors. Shape is based on variation and 2/3 main, 3/1 topog

Variable Size

• (Posterior, anterior),
• (Horizontal, Transverse)
• Variable by species

Variable Dimensions

• Cow and horse are the same dimensions.
  • Top is equatorial
  • Equator goes the previous line
  • Media is on anterior

Optic Nerve

• Positioned lower and the posterior is coated in ciliary nerves and arteries
• Short length ciliary equal is 12
• 7 outter, 5 vented
• Goes through the vessels and choroidal space
• The long has 2 cilliary Enter the scerla from the optic nerve. Cat arteries and retina Have lots if vassles

Conrea Structure

• Transparent allows refraction function requires contents.
• 41 to 42 percent allows light.

Cornea-Aqueous Humor-Tears

• Nourishes and cleans.
• eyelids are protection.
• Elliptical horizontal and vertical diameter high

Thick

• Central .45/.55 peripherally .57/.65 aging males .8/.6 females .6/45
• Sensory supplies
  • Pain+
  • Myelinated+
• Intervated by long cellary and CNV ophthalmic Trigeminal nerve

Limbus

• Anastomotic is umyelinated becoming a blade pattern.
• Stromal intervals different only the small levels are

Transparency

• Vessels of blood
• Nonkeratinized stays moisturized has cells has nuclei

Dehydrated

• Size and arrangement of corneal and vessels
• Onion = layers= bowman’s endothelium

Inner

• Non keratin surface
• (25/40 un domestic
• 2/3 of this amount in the ungulates.
• Simple has 2/4 layers to the squamous

Cartilage

• Cells organized
• Well basement

Corneal Epithelium Cell Characteristics

• Tall and cylindric —Mitosis close to basal cells stratum cells are more villa and micro and scatter
• It scatter electrons is lighter produces pre taunt
• Corner central has more products attached / and various movements
• Lipbus is in all areas but not

Stroma

• 90% of thickness Transparent sheets with cells has the lenses keratin is the form form in some Transform myo-blast and is is not is to be transported
• 999 in one aea
• 789 in another with leukocytes

The Collagen

• made of 5 even types
  • 1 small even straights
  • 6 form matrix function role
  • and cell reactions is to repair
  • 5 type with 1 25 NM.
• 15/10 Supports structures clear because of dehydration with other tissues Hydro
  • 75/85% water

The Corneal Layers

• Epithelium with hydrophobia The pumps act on the Gags. Pumps remove the volume Changes cause Bowmans anier most. This zone is made up of many cells and fibril This tough and elastin does non animals Acellular 3000/2-3

Descements A-CELLULAR

• Basement, stained w PAS if cut rolls more tension similar to ICA
• The endo has regenerative active is hexa.
• The 1/4 for each shape ibr in eyes
  • zonules
  • loss from the edges comp

Reaging

• the cell mitosis and regin.
• A good effect. — Cell do not to the cells easily in. Heredity can do what Then goes into glaucoma Etc

Scleara Tissue

• The reminded fibrous 3 are layerd
• Epi
• Stroma
• Laum Fusca.
• The top is tigh vascular and bings to the tenons capsule — Collagen in into the
• Thickens and links at the conjuctivas has the cells more arranged hence and transparent
• Fusca runs to cillary

The Tissue Contains

• Stroma changes when its thick
  • the blue color
  • Yello is fat
  • Lamium and brown

Components

• The bulk looks like the his to.
• Vessels is blood and channel
  • Size is different depending on globe. And the near equator — Varies with species
    • 5
    • to EOM.
• In thick aquatic it very think prevents change

Scerala Nerves and Vessels

• Many channel for infection the rear pole
  • reduced can effect nerves, to get glaucoma

Scerla Inner-Vations

• Cillary pass body
• Interacting network with veins and outers or cilliary

Uvea (3 Parts)

• Chorid, cillary body, and Iris
• Vessels attached to the surface Iris cilliary (extends)

The Body

• Diaprahm is a pupil the size is from species too And round
• Herbivores oval with Granual irides and limits The have extensions of pigments Improve effectiveness

Pupllies

• Controls the segments.
• Reduction of the light Reduce the peripheral

Dilaterod

• More light for simulation organization
• Center periphery demonetar
• Hairs

The Eye

• Border is 2 cells
• Lots have cells but no b Breaks frequently The Stroma
• Is arranged the sheath Has spacing for vessels and melanin shaprs are

Sphinc ter = 2

• Constructor are connected parasites in the vessel dilator smooth sympathetic
• Bindes

Main Cillary

Root

The Inner

• The cells NOT fenstrated junctions a and c and have 4/5 is radial

Mucsle Strutcre

• Strumcir circular and located near pil and connects and are para
• Is radial or peri contains pigment
• Well derbep and the horse low has

Functions

• Heavy pigement
• The Nurtruiments — 72/9 processes made uo of fluid some has higher chambers processes have
• Milla pro

Cillary Body

• carnibore Blade like
• ungulate ridge tops
• Part posterior

Lies with the fibers Enables visual Mussels helps get body shape

Herbovi

• Common angle

Has inner and outter layaers can cilliary be cut then leads to the exterm

Canivourious

• 2 layers a slit in the middle

Bird have some type

Vasculartoty

• From vessels is devided in 2 then
• The Bales

Ica from chamber

• 3 regions with the side cell

Cilleary Attachments from the zone

• The cillaries is the process
• and by the cells

Vitreous

• Is larger
• gelatunios

Zone

• It is concave paterlla

Made from Hylolid and tertriaty that first formed with thhe body where the vessels go

The body is 4 zones

• From anertriot
• Posteriori — Central

Space

From optic to vessels

• The the

Structure

• Mostly water collagen and cells.

Connects to the disc and capalreus is The fluid may syn and and after

• Tissue form badns and detachd vascular has no flow. — Then The vision has to to long