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Vision & Cow Eye Dissection

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Lacrimal apparatus:

Secretes tears for lubricating

& antibacterial properties

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Palpebrae (eyelids)

Control the amount of light and debris entering the eye

Spread moisture by blinking

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Demodex mites

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Conjunctiva:

Transparent membrane that secretes mucous for lubrication

Palpebral conjunctiva

(Lines internal surface of Palpebrae )

Ocular conjunctiva

(Lines anterior surface of eyeball)

*conjunctivitis- inflammation of conjunctiva

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Extrinsic eye muscles

Lateral rectus

Superior rectus

Medial rectus

Inferior rectus

Superior oblique

Inferior oblique

Superior oblique muscle: controlled by the trochlear nerve. The superior oblique muscle ends in a tendon that passes through a fibrous loop, the trochlea, located anteriorly on the medial aspect of the orbit. Trochlea means “pulley” in Latin; the fourth nerve is named after this structure. “rolls” your eyes

Inferior oblique muscle: it extorts the eye and moves it upward and outward. Innervated by the oculomotor nerve

These two muscles are used to tell left from right. The muscle body mass of the inferior and the tendon of the superior join on the lateral side of the eye

Lateral rectus muscle: controlled by the abducens nerve and is halfway responsible for looking to the side (abduction hence the name of the nerve).

Medial rectus muscle: controlled by the oculomotor nerve, it adducts the eyeball.

Superior rectus muscle: controlled by the oculomotor nerve, primary function is elevation, although it also contributes to intorsion and adduction

Inferior rectus muscle: controlled by the oculomotor nerve, depresses, adducts, rotates laterally, and extorts the eye.

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Inner Segments and Fluids

(cavity)

Posterior

segment

(cavity)

Lens

The lens separates the anterior segment from the posterior segment

Posterior segment:

contains vitreous humor, which is formed before birth

This gel-like fluid keeps the retina pressed against the wall of the eyeball

The posterior segment (sometimes referred to as the vitreous chamber) is filled with a clear gel called vitreous humor that transmits light, supports the posterior surface of the lens, holds the neural retina firmly against the pigmented layer, and contributes to intraocular pressure. The vitreous humor is stagnant and is formed during ocular development

The posterior and anterior segment are separated by the lens. The lens is held in place via the suspensory ligament which attach to the ciliary processes (these are barely visible on our slides).

The anterior segment is composed of two chambers

Anterior – between the cornea and the iris

Posterior – between the iris and the lens

These chambers are filled with aqueous humor, a plasma-like fluid (actually it is produced by filtering blood so is pretty much plasma) that fills the anterior segment. Aqueous humor drains via the canal of Schlemm, it also supports, nourishes, and removes wastes. It is created by the ciliary processes and is continually replenished

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Anterior Segment

anterior segment:

anterior chamber

(anterior to iris)

posterior chamber (posterior to iris)

The aqueous humor that resides in these chambers is continually formed by the capillaries of the ciliary processes.

Aqueous humor:

Maintains the intraocular pressure of the eye
provides nutrients to the avascular lens and cornea

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Internal eye anatomy

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�Fibrous tunic (1 of 3):�

Forms the outermost coat of the eye and is composed of:

Opaque sclera (posterior)
Clear cornea (anterior)

The sclera:

protects the eye and anchors extrinsic muscles

The cornea:

allows light to enter the eye

sclera

cornea

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Problems of Refraction

Figure 15.18

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Vascular tunic (2 of 3):

The ciliary body:

The ciliary processes secrete aqueous humor
The ciliary muscles control lens shape

The iris:

Pigmented region that allows light to pass through the pupil

Also known as the uvea, forms the middle coat of the eye and is composed of:

Choroid
Ciliary body

-ciliary processes

-ciliary muscles

iris

The Choroid :

prevents light scatter with pigmentation
Supplies the retina with blood

Choroid

Ciliary processes

Ciliary muscles

iris

Vascular Tunic is the middle vascularized layer which includes the iris, ciliary body, and choroid

Choroid region: The choroid contains blood vessels that supply the retinal cells with necessary oxygen and remove the waste products of respiration. The choroid gives the inner eye a dark color, which prevents disruptive reflections within the eye.

Ciliary Body: A thickened ring of tissue surrounding the lens. The ciliary body has three functions: accommodation, aqueous humor production and the production and maintenance of the lens zonules. It is composed of ciliary muscle (smooth muscle bundles) and ciliary processes (produce aqueous humor). Aqueous humor, is responsible for providing most of the nutrients for the lens and the cornea and involved in waste management of these areas. When the ciliary muscle contracts, it flattens the lens, generally improving the focus for farther objects. When it relaxes, the lens becomes more convex, generally improving the focus for closer objects.It anchors the suspensory ligament that holds the lens in place

Iris: The colored part of the eye (iris is greek for rainbow). Iris consists of pigmented fibrovascular tissue. It contains a sphincter muscle that contracts the pupil

Pupil: central opening of the iris. Regulates the amount of light entering the eye. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye.

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Sensory Tunic (3 of 3):

The pigmented layer:

Extends anteriorly to cover the posterior side of the iris
absorbs light to prevent light scatter

The neural layer:

Extends anteriorly only to the ciliary body
Contains photoreceptors (rods & cones)

Also known as the retina, forms the innermost coat of the eye and is composed of:

Pigmented layer (outer)
Neural layer (inner)

-rods

-Cones

-Bipolar cells

-Ganglion cells

retina

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Cells of the retina’s neural layer

rods: interpret light in shades of grey

Cones: interpret light in shades of red, green, and blue

Bipolar cells: stimulate ganglion cells after receiving signals from the rods & cones

Ganglion cells: receive signals from bipolar cells and take them into the brain via the optic nerve (a collection of ganglion cell axons)

Some native americans have been shown to have infrared cones! And a large proportion of Germans have cones sensitive into the ultraviolet range, rhodopsin is sensitive to UV (right below blue) this was found out during WWII when the military was looking into UV goggles for troops to fight at night.

Rods

Sensitive to dim light and best suited for night vision

Absorb all wavelengths of visible light

Perceived input is in gray tones only

Sum of visual input from many rods feeds into a single ganglion cell

Results in fuzzy and indistinct images

Cones

Need bright light for activation (have low sensitivity)

There are three types of cones: blue, green, and red (well at least in humans)

Intermediate colors are perceived by activation of more than one type of cone

Each cone synapses with a single ganglion cell

Vision is detailed and has high resolution

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Histology

1.Pigmented epithelium

2.Outer segments of cones and rods

4. Nuclei of rods and cones

6. Bipolar cell nuclei

8. Ganglion cell nuclei

9. Ganglion axons

optic nerve
retina

4. Posterior segment containing vitreous humor

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Now you see it…Now you don’t

Fovea centralis-

found directly behind the lens
Contains mostly cones
For high visual acuity

Optic disc-

AKA “blind spot”
Where ganglion cell axons form the optic nerve to exit the eye
No photoreceptors found here

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Tapetum Lucidum

Layer found immediately behind retina.
Reflects light within the eyes of animals

who live in low light (not humans).

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Visual Pathways

Figure 15.23

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Terms

Accommodation
Emmetropia: normal vision
Myopia: near-sigthedness
Hyperopia: far-sightedness
Presbyopia: “old vision”
Glaucoma: intraocular pressure imbalance
Cataract: clouding of the lens
Conjunctivitis: inflammation of the conjunctiva