Lecture 17 4/10/25

Question 1

What is encompassed by the retina?

Answer 1

-neurosensory retina (everything except RPE)
-retina pigmented epithelial cells

Question 2

What is encompassed by the fundus?

Answer 2

everything seen in the back of the eye, including:
-choroid/tapetum
-retina
-optic nerve
-vessels

Question 3

What are the most important cell types in the retina?

Answer 3

-retinal pigmented epithelium
-photoreceptors (cones and rods)
-bipolar cells
-ganglion cells

Question 4

What is the pathway for neural transmission?

Answer 4

-starts in the photoreceptor
-proceeds to the bipolar cells
-goes from bipolar cells to ganglion cells

Question 5

What is the role of the PRE?

Answer 5

phagocytose the photoreceptor discs

Question 6

What is the role of photopigments?

Answer 6

absorb light to hyperpolarize the cell

Question 7

Which vitamin is essential for photopigment function?

Answer 7

vitamin A

Question 8

Where is the retina attached within the eye?

Answer 8

-optic nerve
-ora serata

Question 9

How is the neurosensory retina “attached” to the RPE?

Answer 9

loosely through the fluid being constantly resorbed by the RPE

Question 10

What happens when a retina “detaches”?

Answer 10

the neurosensory retina detaches from the RPE

Question 11

What are the characteristics of the choroid?

Answer 11

-uveal tissue between the retina and sclera
-contains the tapetum
-heavily pigmented in most individuals
-part of the uveal tract and therefore highly vascular
-provides nutrition to the retina

Question 12

What are the three layers of vessels in the choroid?

Answer 12

-a large vessel layer posteriorly
-a layer of somewhat smaller vessels anterior to the large vessel layer
-a capillary layer anterior to the smaller vessel layer

Question 13

What are the characteristics of the tapetum?

Answer 13

-reflective layer that reflects light back onto the retina that was not already absorbed by the photopigments
-gives a “second chance” to pick up light
-scatters the reflected light, which decreases acuity

Question 14

What are the characteristics of the sclera?

Answer 14

-exterior to the choroid
-relatively acellular, avascular, and essentially non-pigmented
-mostly composed of collagen

Question 15

What are the characteristics of rod cells?

Answer 15

-rhodopsin is the photopigment
-responds best to 495 nm light; conserved across species
-responds in dim light
-bleached out in bright light
-sensitive to movement

Question 16

What are the characteristics of cone cells?

Answer 16

-iodopsin is the photopigment
-responds to certain wavelengths; each cell has a preference that varies by species
-responds in bright light
-provides color vision

Question 17

What is the correlation between a tapetal fundus and RPE?

Answer 17

-animals with a tapetal fundus have a non-pigmented RPE
-animals without a tapetal fundus have a “pigmented” RPE
-“pigmented” RPE absorbs photons and leaves no method for a second chance at the light

Question 18

What are the general characteristics of the fundus?

Answer 18

-everything is layered on top of each other
-retina is “attached” at ora serata and optic nerve
-neurosensory retina is not truly attached to RPE

Question 19

What are the characteristics of direct ophthalmoscopy?

Answer 19

-very magnified
-image is right side up

Question 20

What are the characteristics of indirect ophthalmoscopy?

Answer 20

-image is upside down and backwards
-the larger the lens number, the less magnified the image

Question 21

What are the characteristics of panophthalmoscopy?

Answer 21

-magnification in between direct and indirect
-image right side up
-can be difficult to view if there is any opacity to the cornea, lens, or vitreous

Question 22

What should be evaluated with regards to the optic disc when performing ophthalmoscopy?

Answer 22

-size and shape
-color
-depression
-elevation
-loss of physiologic pit

Question 23

What are the characteristics of normal optic disc size and shape?

Answer 23

-highly variable shape in dogs; triangular to round
-round in cats
-edges should be crisp and well demarcated

Question 24

What is the normal optic disc color?

Answer 24

-whitish to salmon pink in dogs
-light pink to grey in cats

Question 25

Why is the optic disc often elevated around the edges in dogs but flat in cats?

Answer 25

dogs have enough myelin in the optic nerve to cause the slight elevation

Question 26

What is the physiologic pit?

Answer 26

a small central depression in the optic disc in dogs that represents the caudal course of the ganglion cell axons as they head caudally towards the brain

Question 27

What are the characteristics of retinal vessels?

Answer 27

-different species have different vascular patterns -generally a triad or tetrad of major vein-artery pairs with a number of smaller arterioles and venules between them -veins usually extend to center of disc while arterioles do not in dogs -vessels stop at edge of optic nerve head in cats -veins have a larger diameter than arteries -branching should look like a tree

Question 28

What are the characteristics of the tapetal region?

Answer 28

-choroidal structure -homogeneity of the tapetum is the normal finding -hyperreflectivity indicates retinal scarring -absence of a tapetum can occur, most often in color dilute individuals

Question 29

What are the characteristics of the non-tapetal region?

Answer 29

-typically going to be dark brown pigmented -most of what you see is in the choroid, not the retina -RPE is also pigmented in this region and adds to dark brown color -homogeneity is normal -depigmented areas can indicate retinal scarring

Question 30

How is an animal's retina evaluated if they are atapetal and submelanotic?

Answer 30

based of vasculature health and optic nerve health

Question 31

What are the diagnostics done for vision?

Answer 31

-menace reflex -dazzle reflex -pupillary light reflexes (direct and consensual) -cotton ball tracking -maze testing -electroretinogram (ERG) -visual evoked potential (VEP) -MRI -molecular genetic testing

Question 32

What are the characteristics of ERG?

Answer 32

-measures electrical activity in retina via response to a flash of light -combinations of dark adaptation and light intensities can separate rod and cone contribution to the ERG -only the photoreceptors and bipolar cells contribute

Question 33

What are the characteristics of VEP?

Answer 33

-measures electrical activity in visual cortex in response to flash of light -photoreceptors, bipolar cells, ganglion cells, optic nerve, and visual cortex must ALL be intact to have a normal VEP -not commonly done; MRI more common

Question 34

What are the characteristics of an MRI for vision assessment?

Answer 34

-indicated in blind animals with a normal optic nerve head and ERG -used to look for dz caudal to the retina -can show abnormalities in the optic nerve or brain

Question 35

What are the characteristics of molecular genetic tests?

Answer 35

-many canine retinal disorders are genetic and can be diagnosed via DNA testing -allows for retinal dz to be predicted long before phenotypical manifestation -allows for carrier animals to be ID'd