Dr

Study Guide For Histology of

The Eye

Dr. Coates

The 3 main structural layers of the entire eye and their functions.

Outermost layer (tunica fibrosa)--supports and protects eye

Middle layer (tunica vasculosa)--highly vascular; provide nutrition

Inner layer (tunica interna)--photoreception

The major chambers; contents; functions.

Anterior chamber--aqueous humor like CSF

Posterior chamber--aqueous humor

Vitreous body--vitreous humor (H.A., collagen)

Important structures of eye & functions.

Structure	Function
Cornea	Refraction, protection
Sclera	Protection, insertion of extraocular mm.
Limbus	Transition zone
Pupil	Admits light
Iris	Control pupil size; function in accommodation
Trabecular meshwork	Absorption of aqueous humor
Lens	Lens accommodation for focusing
Zonule (zonule of zinn)	Suspensory ligament of lens
Ciliary body	Accommodation (parasympathetic CN 3)
Ciliary process	Secrete aqueous humor
Ora serrata	Junction between ciliary body and choroid
Choroid	Nutrition for retina (rods & cones)
Retina	Photoreception

The retina: Layers, especially the 3 main layers concerned with detection and transmission of light signals.

Retinal Layer	Functions
1. Pigmented epithelium	-Absorbs scattered light rays; -Stores and releases vit. A to photoreceptors -Hereditary retinal dystrophy--inability of PE to phagocytize worn out disc
2. Layer of Rods	-sensitive to low light intensities -peripheral vision -rhodopsin in membrane of disc -more rods than cones
Cones	-mediate color vision -sensitive to high light intensities (photopic) -responsible for pattern detection and fine details
3. External limiting membrane	-desmosome-like junction between Muller Cells
4. Outer nuclear layer	-cell bodies of rods and cones
5. Outer plexiform layer	-synapses between axons of rods and cones, bipolar neurons and horizontal cell (local processing of visual information in retina)
6. Inner nuclear layer	-Cell bodies of bipolar cells -main secondary ink in transmission of visual information
7. Inner plexiform layer	-synapses between bipolar and ganglion cells and amacrine cells (local processing of visual information in retina)
8. Ganglion cell layer	-synapses between bipolar and ganglion cells (output cells of retina) -ganglion cells are third main link in transmission of visual information -true action potential started here
9. Nerve fiber layer	-unmyelinated axons of retinal ganglion cells -follow curvature of retina; exit at optic disc -become optic nerve (myelinated) outside retina
10. Internal limiting membrane	-expanded ends of modified glial cells of retina (Muller cells) and basement membrane

Main layers/cells concerned with reception and transmission of light signal:

Structure	Functions
Rods & Cones	-Receive and transduce light signal -receptor potential -hyperpolarizing -transmit to bipolar neurons
Inner nuclear layer	-bipolar cells -slow graded potential -transmit to ganglion cells
Ganglion cell layer	-first in visual transmission chain -true action potential starts here -transmit to brain

Optic disk: what, where and function.

Optic papilla==blind spot (on nasal side)

Emergence of axons from retinal ganglion cells through sclera (lamina cribrosa) to become optic nerve

Entry/exit of major retinal blood vessels

White in normal eye

No rods or cones

Macula lutea and fovea centralis: what, where and function.

Macula lutea==yellow spot

Contains fovea centralis (depressed spot in macula)

ONLY CONES

Area of most acute vision

Lateral (temporal) to disc

Clinical correlations.

Corneal disease (can't refract light)

Diabetic retinopathy (most common cause of blindness)

Papilledema (fluid in papilla)

Lens opacity: cataract (cloudiness in vision)

Glaucoma (too much fluid pressure)

Detached retina (trauma to region may dislodge layers 2-10 of retina due to potential space between pigmented epithelium and rest of retina)

Retinal dystrophy (hereditary--inability of PE to phagocytize worn out discs)

Sample Questions

1.The anterior chamber of the eye

a. lies anterior to the cornea and anterior to the lens and contains aqueous humor.

b. lies posterior to the cornea and anterior to the lens and contains aqueous humor.

c. lies posterior to the cornea and anterior to the lens and contains vitreous humor.

d. lies posterior to the cornea and posterior to the lens and contains vitreous humor.

e. lies in the scleral angle and contains aqueous humor.

2. The retina and optic nerve are derived from the brain.

a. True

b. False

3. The area of most acute vision contains

a. ganglion cells

b. rods only

rods and cones

cones only

e. all the above

4. Rods are visual photoreceptors primarily responsible for detecting

a. sensations of color

b. peripheral vision

c. fine detail

d. low intensity light

5. Which of the following contain smooth muscle elements intrinsic to the eye?

a. ciliary body

b. ciliary process

c. iris

d. sclera