Lecture 21 Histology of the Eye Flashcards by Whitney Jennings

Name the three tunics of the eyeball

Fibrous Tunic
Vascular Tunic
Inner Tunic

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Fibrous Tunic

Sclera (tunica fibrosa)

Cornea

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Vascular Tunic

Choroid
Ciliary Body
Iris

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Inner Tunic

Retina

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Sclera Layers

Episcleral Layer
Sclera Proper
Lamina Cribrosa

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Episcleral layer

Outer layer
Loosely arranged collagen and elastic fibers
Highly vascular
Attaches the lining of the eyelid (conjunctiva) to the sclera

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Sclera Proper

Made up of interlacing collagen fibers
Attachment site for tendons or extrinsic eye muscles
Collagen bundles are always parallel to outer surface of sclera

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Lamina Cribrosa

Perforated disc of sclera

Pass through for optic nerve fibers

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What is the name of the junction between the sclera and the cornea? What is its characteristic?

The Limbus

It is highly vascularized

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Name the layers of the cornea

Corneal epithelium 
Bowman's membrane 
Corneal stroma 
Descemet's membrane 
Corneal Endothelium

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Corneal Epithelium

Stratified, nonkeratinized squamous epithelium (5-6 layers)

High mitotic activity in the basal layer (Turnover = 1 week)

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Bowman’s membrane

Acellular layer separated epithelium from stroma

Randomly arranged collagen fibers

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Corneal Stroma

Thin layers of ordered arrays of collagen fibers

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Descement’s membrane

Acellular layer of collagen bundles

Separates stroma from endothelium

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Corneal endothelium

Single layer of large squamous cells

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Choroid (Part of the Vascular Tunic)

Extends anterior to ora serrata of the retina
Highly vascularized with loose CT
Bruch’s (glassy) membrane

Describe the highly vascularized loose connective tissue of the choroid

Forms choriocapillary network - contains small BVs that supply cells of the retina
Provides nutrients to outer layers of the retina
Consists of medium & large arteries & veins as well as a wide-bore capillary network
Contains melanocytes

Describe Bruch’s (glassy) membrane of the choroid

Acellular fused basal laminae of choriocapillaries and pigmented retinal epithelium

Ciliary body (Part of the Vascular Tunic)

Wedge-shaped expansion of choroid peripheral to the lens
Covered by a double layer of cells
Suspensory ligaments (of Zinn) extend to just behind lens equator and anchor the lens in place
Ciliary muscles

Describe the double layer of cells in the ciliary body

Innermost layer is continuous with the pigmented layer of the retina
Surface layer is from the sensory layer of the retina
Produces aqueous humor

Describe the ciliary muscles of the ciliary body

Smooth muscle mass that changes the shape of the lens

Innervated by parasympathetic neurons

Ciliary muscles and accommodation:

One group of muscles is responsible for flattening the lens

A second group of muscles is responsible for allowing the lens to become thicker

Describe the nonpigmented surface layer of cells of the ciliary body

Produce aqueous humor
Basal infoldings
Secrete aqueous humor into posterior chamber

Aqueous humor

Percolates through trabecular mashwork

Flows into canal of Schlemm

Iris (Part of the Vascular Tunic)

Located anterior to the lens and separates the anterior and posterior chambers Angle Surround Pupil Double layer of epithelium Melanocytes - the more melanocytes, the darker

Describe the Angle of the Iris

Formed at lateral borders of the anterior chamber Loos CT Part of the passageway of aqueous humor

Describe the double layer of epithelium of the Iris

Inner layer = pigmented epithelial cells Outer layer of radially oriented myofilaments - dilator pupillae muscle, sympathetic innervation, dilate pupil Concentric layer of myofilaments - constricts pupil, parasympathetic innervation

What are the two subdivisions of the retina?

Photosensitive region that lies posterior to the ora serrata | Non-photosensitive region that lies anterior to the ora serrata

Describe the photosensitive region of the retina

Optic Disc | Fovea Centralis

Optic disc of photosensitive region of retina

Region on posterior aspect of eye where optic nerve exits | Has no photosensitive retina & constitutes the blind spot

Fovea centralis of photosensitive region of retina

About 2.5 mm lateral to optic disc Contains yellow pigment = macula lutea Contains only cone-type photoreceptors Area of most acute vision

Describe the non-photosensitive region of the retina

Consists of two cell layers covering iris, ciliary body, and ciliary processes

What are the chambers of the eye?

Anterior chamber Posterior chamber Vitreal chamber

Anterior chamber

Posterior to cornea and anterior to iris

Posterior Chamber

Posterior to iris and anterior to lens

Vitreal Chamber

Posterior to lens Contains vitreous body Gelatinous mass made up of 99% water, hyaluronic acid, and vitrein Hyaloid canal is the site of fetal artery

Glaucoma

Increased intraocular pressure due to compromised drainage of aqueous humor from anterior chamber