Vision 6: Retina

Question 1

Mechanism of horizontal cells

Answer 1

Lateral Inhibition:
* They are inhibitory cells
* They inhibit rods and cons thar are laterally to the stimulated ones + bipolar cells
* Release inhibitory neurotransmitter GABA

Question 2

Mechanism of Amacrine cells

Answer 2

Excitatory cells
* Stimulated by Bipolar cells
* they Excite ganglion cells
* Responsible for indication of Sudden changes of light intensity and mving objects

Question 3

site of Macula lutea and fovea centralis in retina

Answer 3

3mm temporally (laterally) from Optic disc

Question 4

Site of Optic Disc in retina

Answer 4

3mm Nasally (medially) from Macula lutea

Question 5

Photoreceptors distrtibution in and around fovea centralis

Answer 5

• In the fovea centralis, only cones exist
• Surrounding the fovea, rods gradually appear and cones disappear

Question 6

Optic disc is the…….., therefore formes….

Answer 6

• Exit for optic Nerve, and doesn’t precieve light
• Physiological blind spot

Question 7

Explain why fovea centralis has high visual acuity

Answer 7

1. Absence of Convergence: 1 receptor gives 1 bipolar cell, which give to 1 ganglion cell
2. Highly developed pigmented epithelium: suppresses light reflection
3. All other layers of the retina but the cones is displaced to the side, thinning out the retina in the fovea
4. Cones in the fovea are not covered by vessels

Question 8

Explain why retina detachement is Damaging specifically to the photoreceptors

Answer 8

As blood supply of photoreceptors is from Capillar plexus of Chorid

Question 9

Clinical importance of Ophalmoscope

Answer 9

Superficial layer of the retina is the only place in the body where Arterioles can be seen
* Which can value diagnosis of Vascular disorders such as DM or Hypertension

Question 10

Compare between Number of rods and cones

Answer 10

• Rods=120million
• Cones= 6 million

Question 11

Compare between Photopigments of rods and cones

Answer 11

• Rods: 1 Photopigment =Rhodopsin
• Cones= 3 photopigments

Question 12

Compare between Light sensitivity of rods and cones

Answer 12

• Rods are more sensitve to Light than cones, due to Lower threshold than cones

Question 13

Explain why Rods are more sensitive (have a lower threshold) than cones

Answer 13

1. higher amount of Photopigments in their outer sigment, so greater response for each photon
2. Rods have longer duration receptor potential, therefore can summate more easily

Question 14

Compare between types of vision rods and cones are responsible for

Answer 14

• Rods: Scotopic Vision (dim night vision)
• Cones: Photopic Vision (bright day vision)

Question 15

Compare between Acuity, Detailing & color perseption of Rods and cons

Answer 15

• Cones Have higher visual Acuity than rods, due to cones having No converegence
• Cones precieve higher details, rods cannot precive details of object
• Cones precive colour, rods don’t

Question 16

Desribe Purkinje shift phenomenon

Answer 16

It’s the shift between maximal Scotopic Spectral sensitivty (505nm) to maximal Photopic Spectral Sensitivity (550nm)
* In Scotopic vision: 505nm wavelength is obtained at green blue zone, which will appear more luminous
* In Photopic Vision: 550nm wavelength is obtained at Yellow zone, which will appear most luminous