retina

Question 1

retinal location

Answer 1

A delicate complex structure which contains the light sensitive receptors of the eye, extends from the ora serrata to the optic nerve head or disc

Question 2

function of retina

Answer 2

• Convert electromagnetic energy in the retinal image into neural signals
• Neural signals are then gathered to be transmitted out of the eye through the optic nerve

Question 3

retinal layers (choroid to vitreous)

Answer 3

1. retinal pigment epithelium (RPE)
2. photoreceptor layer (PR)
3. external limiting membrane (ELM)
4. outer nuclear layer (ONL)
5. outer plexiform layer (OPL)
6. inner nuclear layer (INL)
7. inner plexiform layer (IPL)
8. ganglion cell layer (GCL)
9. nerve fibre layer (NFL)
10. inner limiting membrane (ILM)

Question 4

what is RPE layer?

Answer 4

• Single layer of cuboidal cells extending from the ora serrata to optic nerve head
• Anteriorly continuous with the pigmented epithelium of the ciliary body
• AttachedtotheBruch’smembraneofthechoroid

Question 5

function of RPE layer

Answer 5

• Protects the photoreceptors from excessive light
• Supports the receptors
  > Provide receptors with a pathway of nourishment and oxygen from the choriocapillaries
  > Performs phagocytosis (engulfing) of discs and removing waste products shed by rods and cones from the photoreceptors
• ‘Blood retina’ barrier
  > Forms a barrier against liquids and substances moving between the choroid and the neural retina
• Reisomerization of all-trans-retinal into 11-cis-retinal

Question 6

description of photoreceptors

Answer 6

rods

• shape: cylindrical
• photopigments: rhodopsin
• synaptic end: spherule(narrower)
• responsible for: night vision(colourless vision)

cones

• shape: conical
• photopigments: iodopsins (3 types and reacts to blue, green and red)
• synaptic end: pedicle(wider)
• responsible for: day & colour vision

Question 7

photoreceptor distribution

Answer 7

• Total rods ~ 120 million vs total cones ~ 6 million
• Central of fovea (foveola) there are no rods at all
• High concentration of cones at the foveola
• At ora serrata, there is decreased in number of receptors

Question 8

macula

Answer 8

• 3-4mm temporal to optic disc
• can be divided into
  > fovea
  > parafovea
  > periofovea
• no vessels in macula area
• but sometimes cilio-retinal artery (from circle of Haller-Zinn) may be present
• RPE & choroid capillary bed are increased at the macula
  > this will supply the macula area

Question 9

retinal blood supply

Answer 9

• Outer retina: photoreceptors & RPE etc receive their supply from the choriocapillaries
• Inner retina: supplied by central retinal artery a branch from Ophthalmic artery
• Veins are mostly in correspondence with the artery
  > will eventually drain into the cavernous sinus at the back of the eye