The Retina Flashcards
Ten Layers of the Retina
The retina extends over what portion of the globe?
posterior 2/3 of the globe
The retina is internally bound by?
the vitreous body
The retina is externally connected to?
Bruch’s membrane
When does the retna lose the reddish color and turn gray/opacify?
~ 1 hour after death
What detects light and movement in the retina?
Rods
What provides color and form vision in the retina?
Cones
What is the internal background of the eye?
Fundus Oculi
What color is the fundus oculi?
Orange-red color derived from the choroidal blood vessels and the retinal pigment epithelium
In fair subjects is the fundus oculi lighter or darker? Darker subjects?
Fair - Lighter fundi
Darker - Darker, grayish fundi
When looking at the fundus oculi in albinos what is seen?
White scleral tissue is exposed, one sees choroidal vessels through the retina
Where does the optic nerve leave the eye?
At the optic disc or papilla
located 3mm medially to and slightly above the posterior globe
What is the optic disc completely devoid of causing the blind spot?
Photoreceptors
Where is the fovea centralis located and how big is it?
Temporal to and below the posterior pole
1 - 2 mm in diameter
At the fovea centralis retinal (thinning/thickening) produces a _____ _____ in the surface where the nerve elements are heaped to formed _____ ____
Thinning
Shallow Depression
Henle’s Layer
How big is the foveola?
0.35 mm in diameter, within the fovea
Where are the cones contained?
In the foveola
Where is the macula lutea found?
Around the fovea centralis
(yellow spot - yellowish pigment xanthophyll)
The ora serrata separates what?
Separates the neural part of the retinal periphery from the ciliary body
Where does the ora serrata lie?
8.5 mm behind the limbus
6 mm in front of the equator
What are thinner and lighter in the retina (veins/ arteries)?
Arteries
Are anastomoses found in the retina?
No
Does the fovea contain any vessels?
The fovea is free of obstruction from blood vessels
What are the four subdivisions in the retina?
- Pigment Epithelial Layer
- Photorecepter Layer
- The Intermediate Layer
- The Ganglion Cell Layer
What does the the pigment epithelial layer (RPE) form?
Forms a single stratum of epithelial cells attached to Bruch’s membrane
(There are about 5 million in each eye)
Pigmented projections intrude where in the pigment epithelial layer? What do they do?
between adjacent rods and cones
Protect receptors from excessive and scattered light
Is mitosis demonstrated in the pigment cells?
No
Each pigment epithelium cell is in contact with an average of up to how many photoreceptors?
45 photoreceptors
What are the functions of the pigment epithelial layer?
FUNCTIONS:
- Absorption of light and removal of heat
- Restricts stray light; protects receptors from undesirable effects of light
- Provides photoreceptors with nutrients/ O2
- Reservoirs of useful substances (ex. Vit A)
- Provide slow disintegration, a role in phagocytotic activity
Is there a connection between the RPE and receptors? Why?
No anatomical connection exists
Leads to the ease with which two layers can be deteched
What are photoreceptors?
Sensory cells that transform light into electrical energy by chemical processes
What type of arrangement do photoreceptors have?
Palisade arrangment (parallel pickett fence appearance)
Held in position by the external limiting membrane
What is the size of rods?
Long (40-60 um)
Slender (2 um)
Where is the photosensitive part of the rods?
The outer segment
What is contained in the outer segment?
Rhodopsin (photopigment)
600 - 1000 loosely stacked disc units (lamellae)
Lamellae are formed at what rate?
1-5 per hour at the bottom of the segment
When do rods slough?
In the morning or in the light after long dark periods
(in a group of 30 from top of segment)
How long does it take for rod lamellae to be completely renewed?
1-2 weeks
