Test 38   (ocular physiology)

1. The following are true about the tear film:

a. the normal volume is about 20 ul

b. its main protein content is made up of immunoglobulins

c. the lysozyme concentration is the greatest

d. the concentration of Ig A is greater than that of Ig G

e. the mucous layer is deficient in vitamin A deficiency

Answera.F   b.F   c.T   d.T   d.F   e.T
The normal volume is 5-10ul.
Albumin is the main protein constituent.
Although Ig A plays an important in mucous membrane defence system., the concentration of Ig A equals that of Ig G in the tear film.
 

2. With regard to the vitreous:

a. its water content is about 90%

b. its volume is about 5ml in each eye

c. its viscosity increases with age

d. its viscosity is contributed by the presence of sodium hyaluronate

e. it is the main source of glucose for the retina

Answera.F   b.F   c.F   d.T   e.F
Its volume is about 4 ml in each eye.
Its water content is about 99%.
Its viscosity decreases with age.
The retina obtains its nutrients from the retinal artery.
 

3. True statements about saccadic eye movements include:

a. only occur when the patient is awake

b. the velocity is under voluntary control

c. the maximum velocity is 700 degrees / second

d. it has a latency of 250msec

e. the posterior commissure control the vertical saccade

Answera.F   b.F   c.T   d.T   e.T
Rapid eye movement in sleep is a type of saccadic eye movement.
Saccadic movement is not under voluntary control.
 

4. The following are true about electroretinogram:

a. the a-wave is produced by the photoreceptors

b. the b-wave is produced by the ganglion cells

c. c-wave is produced by the retinal pigment epithelium

d. different light frequencies can be used to separate rod and cone response

e. it is useful for detecting early Best's disease

Answera.T   b.F   c.T   d.T   e.F
b-wave is thought to be produced by Mueller cells. 
Best's disease is best detected with electro-oculogram.

5. The following are true:

a. the ratio of rod to cone is about 20:1

b. there are more ganglion cells in the retina than photoreceptors

c. the rod density is the highest nasal to the optic disc

d. the retinal artery is the main supply of nutrients to the photoreceptors

e. papilloedema does not occur in optic atrophy

Answera.T   b.F   c.F   d.F   e.T
There are about 1 million ganglion cells whereas the photoreceptors number 126 millions.
The rod density is highest at 6 mm from the fovea
The photoreceptors receive their nutrients mainly from the choroidal circulation.