Test 57  (Ocular physiology)

1. When light fell on the eye, the pupil:

a. does not constrict if the optic nerve is severed

b. does not respond if the sympathetic system is not 
    functioning

c. does not respond if the cholinergic system is blocked

d. does not respond if the pretectal nucleus is damaged

e. does not constrict if the ciliary ganglion is damaged

Answera.T   b.F   c.T   d.T   e.T
If the optic nerve is severed, the afferent arm is damaged and the pupil will not respond to light
The sympathetic system is not responsible for light response.
Damage of parasympathetic system such as the pretectal nucleus and ciliary ganglion will give rise to dilated pupil.

2. Rhodopsin:

a. is a red pigment

b. is least sensitive to red light

c. is regenerated when the eyes are closed

d. is most sensitive to light with a wavelength of 500nm

e. is found in the inner segment of rods

Answera.T   b.T   c.T   d.T   e.F
Rhodopsin is found in the outer segment of rods.
It reflects red light and therefore appears red.
It is most sensitive to blue-green light (500nm) and least sensitive to red light.
 

3. The following are true about dark adaptation:

a. only regeneration of rhodopsin is responsible

b. adaptation usually takes about 20 minutes

c. dilatation of pupil plays a part in dark adaptation

d. it is better with the fovea than the peripheral retina

e. wearing dark glasses before entering a dark room 
    decrease the adaptation time

Answera.F   b.T   c.T    d.F   e.T
Regeneration of cone pigment is also important. 
Peripheral retina is better at dark adaptation than the fovea.

4. True statement about dark adaptation include:

a. the threshold for light intensity falls

b. it is biphasic

c. the initial adaptation is due to rod adaptation

d. the change in the light intensity threshold is usually 
    around 100 folds

e. people who wear red goggle before entering a dark 
    room has a faster dark adaptation

Answera.T   b.T   c.F   c.F   e.T
The initial adaptation is due to cone adaptation.
The change in the light intensity threshold is usually around 10000 folds.
Red goggle reduces the bleaching of rhodopsin.

5. Entoptic imagery may be caused by:

a.. opacities of the cornea

b. cells in the tear film

c. cells in the aqueous

d. vitreous cells

e. red blood cells in the retinal vessels

Answera.F   b.F   c.T   d.T   e.T
Entopic phenomenon refers to visual perception formed by the structures within ones eye which may be normal or pathological.