Biochem of retina (Heck)

Question 1

Structures of the retina

Answer 1

 Ora serrata- jagged region between the nonsensory and the sensory retina

 Nonsensory retinal pigment epithelium

 Sensory retina
• Macula lutea
• Fovea centralis
• Optic disk

Question 2

Retina cell types (neurons)

Answer 2

Photoreceptor cells (Rods and Cones)

Retinal ganglion cells

Interneurons (integrating neurons)
o Bipolar cells, horizontal cells and amacrine cells

Retinal pigment epithelial cells (RPE)
o Outermost layer separating the retina from the choroid

Neuron support cells
o Mueller cells

Question 3

10 layers in order of signal transduction

Answer 3

	Pigment epithelial cells (RPE)
	Photoreceptor cells
	Outer limiting membrane
	Outer nuclear layer
	Outer plexiform layer
	Inner nuclear layer
	Inner plexiform layer
	Ganglion cell layer
	Optic nerve fibers
	Inner limiting membrane

Question 4

photoreceptors

Answer 4

inner segment (rich in organelles)
outer segment
rods
cones
interphotoreceptor matrix
retinal pigment epithelium (RPE)
bleaching
visual cycle

Question 5

the outer segment of photoreceptors

Answer 5

• Series of flat membranous disks which contain photopigment
• Undergo continuous turnover
o Old are phagocytosed by pigment epithelium

Question 6

rods

Answer 6

• Light of differing intensities
• Periphery
• Contain rhodopsin photopigment

Question 7

cones

Answer 7

• Blue, green or red.
• Fovea
• Contain iodopsin

Question 8

interphotoreceptor matrix

Answer 8

• Connection between photoreceptor and RPE
• Important in recycling (Interstitial Retinoid Binding Protein (IRBP), Transports retinol to the RPE and retinal to the photoreceptor; Shedding of older disks)

Question 9

Retinal Pigment Epithelium (RPE)

Answer 9

• Contain melanin granules

• Phagocytose shed disks
o Degraded in lysosomes
(Released into choriocapillaris)

• Express Retinol re-isomerization enzyme (Enzymatic conversion of 11-cis retinal to retinol)

• Rods (End in rod spherule)
 Dendrites of bipolar cells
 Neurites of horizontal cells

•	Cones
o	End in cone pedicles
	Dendrites of bipolar cells
	Neurites of horizontal cells
o	Photopsins
	The opsins (protein) in cones
	Together with the chromophore (11-cis retinal) are called iodopsins
	When red, green and blue are stimulated together white light is seen

Question 10

Bleaching

Answer 10

• Photopigment absorbs a photon of light and changes confirmation
o Photopigment contains the protein (i.e. rhodopsin) and 11-cis-retinal
o A photon causes a conformational change in 11-cis-retinal
o Photopigment now acts as a GPCR
 Induces GMP from cGMP
 cGMP dependent Na+ channels close
• Hyperpolarization causes to cell to stop releasing neurotransmitter
• The photopigment is disassembled and 11-cis-retinol converted by pigment epithelium

Question 11

Visual cycle

Answer 11

•	Bleaching and cycling between retinoids
o	Retinoic Acid (Vitamin A)
o	All-trans-retinol
o	11-cis retinal
o	All-trans retinal

Question 12

Leber congenital amaurosis type 2

Answer 12

RPE65
- Isomerohydrolase
• Conversion of all-trans retinol to 11-cis retinal

Autosomal recessive

Adenoviral Delivery Vector

Question 13

Retina Conducting neurons: bipolar cells

Answer 13

Receive impulse form photoreceptor cell

Rod and cone varieties

• Diffuse Cone Bipolar cells and Rod Bipolar Cells receive input from multiple photoreceptors
• Midget Cone Bipolar Cells receive input from one photoreceptor and communicate with one ganglion cell

Question 14

Retina Association Neurons

Answer 14

Integrate signaling

• Amacrine Cells: Neurites ending on axon terminals of bipolar cells and ganglion cell dendrites and bodies
• Horizontal Cells: Neurites ending on cone pedicles and rod spherules

Question 15

Structures of the retina: fovea

Answer 15

Visual axis of the cornea: Depression in the retina
 Flattening of the inner layers to let more light in

o Greatest visual discretion
 The most neuronal interconnections for the most representation in the visual cortex

o Almost exclusively cones
 Poor in low light

Question 16

structures of the retina: optic nerve

Answer 16

Convergence of the axons of retinal ganglion cells
o Unmyelinated afferent fibers
o Myelination begins at optic disc

Absence of photoreceptor
o Blind spot

Question 17

Retinal blood supply

Answer 17

Choroid
o Maintenance of the outer retina

Central retinal artery
o Rises from the optic nerve head
o Maintenance of inner retina
 Has branches that supply three layers of capillary networks
 Branches run posterior to the inner limiting membrane, within the nerve fiber layer (Capillaries can be found running through the retina but generally no deeper than the outer plexiform or nuclear layer)

Question 18

Retinal detachment

Answer 18

Detachment of the photoreceptor cell layer from the pigment epithelial layer can result in blindness

RPE needed to maintain support of visual function

Choroid needed to nourish and maintain cells

Question 19

Deiabetic Retinopathy prevalence

Answer 19

o 60-80% of all diabetics develop some sort of retinopathy
o 15-20 years after diagnosis
o Nearly all type 1 diabetics after 20 years
o 50% of which will have proliferative

Question 20

Diabetic Retinopathy histopathology

Answer 20

Microaneurysms (Small outpouchings from retinal capillaries)

Cotton-wool spots (Regional failure of retinal microvascular circulation resulting in ischemia)

Retinal veins (Dilated and tortuous)

Retinal arteries (White and non-perfused, Eventually absent of endothelial cells, Solely basement membrane)

Selective loss of pericytes (From retinal capillaries; Pericytes contain smooth muscle actin and help regulate capillary blood flow)

Apoptosis of capillary endothelial cells

Question 21

Categories of diabetic retinopathy

Answer 21

preproliferative (nonproliferative) and proliferative

Question 22

Preproliferative diabetic retinopathy

Answer 22

 Increased size and number of intraretinal hemorrhages
 Most vision loss occurs from macular edema
 Would not treat unless clinically significant

Question 23

proliferative diabetic retinopathy

Answer 23

 Includes the formation of new blood vessels
 Neovascularization
 Can protrude into vitreous
 Hemorrhage here and cloud vision
 Detach retina
 Can eventually extend into and grow from other structures in the eye
 Causing secondary forms of blindness

Question 24

detection of diabetic retinopathy: fundoscopy

Answer 24

o	Fundoscopy (Opthalmoscopy)
	Requires dilation of the pupil
	Direct
	Indirect
	Lens is held in hand
	Binocular so give 3D results
	Fundus Photography
	Same basic principles of opthalmoscope

Question 25

detection of diabetic retinopathy: fluorescein angiography

Answer 25

 Sodium fluorescein dye is injected into a vein in the patient’s arm
 Retinal photography captures green fluorescence in the retina
 Can visualize hemorrhages and neovascularization that are difficult to see with human eye

Question 26

detection of diabetic retinopathy: optical coherence tomography (OCT)

Answer 26

 Uses the interference pattern of infrared beams to create a cross section of the retina
 Retinal thickness increases in DR and ME