Visual part 2

Question 1

Describe the blood supplies associated with the retina: choroid and central artery of the retina.

Answer 1

Central artery of retina radiates out and surrounds the macular region (Branch of the internal carotid)
FOVEA IS AVASCULAR – reduces vascular interference with high acuity
choroid veins

Question 2

Describe the fovea, macula and optic disc

Answer 2

Fovea centralis: central point of retina with only cones and no rods, imparting high levels of visual
acuity
Macula lutea: yellow area surrounding fovea
Optic disc: (“blind spot”) contains axons of “ganglion cells”, but no receptor cells

Question 3

What is the blind spot?

Answer 3

contains axons of “ganglion cells”, but no receptor cells. where optic nerve emerges

Question 4

Describe the layers of the retina and what the different cells do.

Answer 4

outer–>inner (inverted retina)

1. Retinal pigmented epithelium
2. Photoreceptors (rods and cones) absorb visible light
3. Neural cells integrate light information: bipolar, horizontal and amacrine cells
4. Ganglion cells project visual information to thalamus/sup. colliculus

Question 5

describe the photoreceptrs

Answer 5

outer segment with stacks of discs contain pigments:
iodopsin in cones –> COLOR, acuity
rhodopsin in rods–> light, peripheral
inner segment wit nucleus and synaptic terminal that release glutamate

Question 6

How does light activate rods and cones?

Answer 6

Pigments are forms of opsin, but respond to different parts of the spectrum of visible light (about 450-700 nm)
Respond to light by hyperpolarizing the cells and releasing less transmitter (glut)

Question 7

Describe the fovea in terms of receptor cells and retinal organization.

Answer 7

center of the visual field–> cones for acuity
Cones are more exposed to incoming light by the outward
dispersal of ganglion and other integrative cells.
Each cone activates a single ganglion cell increasing the acuity of vision.
AVASCULAR

Question 8

How does the fovea organization differ from the peripheral retina?

Answer 8

Rods are primarily in peripheral part

of retina.

Question 9

Describe the functions of the retinal pigmented epithelium in regards to retinal support.

Answer 9

RPE deep to photoreceptors
Visual acuity: RPE absorbs light passing through retina in order to limit reflection
Antioxidant: many free radicals made by blue light
Maintain photoreceptor excitability (Visual cycle
of retinal). Trans-retinal recycled to 11-cis-retinal
Nutrient transport
Phagocytosis of photoreceptor cell debris

Question 10

What kinds of retinal detachment are there?

Answer 10

The contact between the neural retina and the RPE is mechanically unstable
Macular degeneration due to rupture of blood vessel or build up of cellular waste material can detach the retina
Exudative mac degen

Question 11

Between which layers does retinal detachment occur?

Answer 11

between the neural retina and the pigmented epithelium

Question 12

Describe the optic nerve/tract in terms of neurons, glia, meninges and CSF.

Answer 12

Axons of ganglion cells that transmit visual information to the thalamus
• CNS glia • Central artery & veins of the retina
Oligodendrocytes myelinate the axons. Astrocytes surround cell bodies and dendrites; contact blood vessels

Meninges
• Dura • Subarachnoid space with CSF• Pia mater

Question 13

What is papilledema?

Answer 13

Increased CSF pressure limits venous return from
retina. Causes edema under optic disc. blurred
disc margins and dilated tortuous veins

Question 14

whats the mechanism of photoreceptor hyperpolarization?

Answer 14

Light coverts 11-cis retinal (aldehyde form of vit
A) to trans-retinal. This causes opsin to activate PDE via transducin (a G protein)
PDE reduces the background levels of cGMP
which closes Na+ and Ca++ channels–>hyperpolarizing
LESS GLUT

Question 15

RODS

Answer 15

Scotopic: vision in dim light. High sensitivity (more pigment; night vision)
Low acuity (rods absent in fovea).Sensitive to scattered light. good at MOTION
Achromatic: only rhodopsin
Peripheral

Question 16

CONES

Answer 16

Photopic: vision in bright light. Low sensitivity (less pigment)
High acuity (concentrated in fovea). Sensitive to direct axial light. SPATIAL Resolution.
Chromatic: Color vision: three types of pigmented cells

Question 17

retinitis pigmentosa

Answer 17

deficinent uptake of membrane fragments by RPE leading to waste accumulation separating receptors from choroid.