Test 79    (Ocular anatomy)

1. The Bruch's membrane:

a. is 10 um in thickness
b. contains the basement membrane of the choriocapillaris
c. increases in thickness with age
d. forms part of the blood-retina barrier
e. is abnormal in Ehler-Danlos' syndrome

Answera.F   b.T  c.T  d.F   e.T
Bruch's membrane is about 2-4 um thick. It is 
freely permeable to macro-molecules from the choriocapillaris.

2. The following are true about the iris:

a. it contains pigmented epithelium on its anterior surface.
b. it contains melanocytes in the stroma that determines 
    the iris colour
c. its colour is determined by sympathetic innervations
d. the dilator muscle is innervated by the sympathetic 
    system
e. the constrictor muscle is innervated by the 
    parasympathetic system

Answera.F   b.T   c.T   d.T   e.T
The iris contains pigmented epithelium only on
its posterior surface.
Sympathetic innervation is important for migration 
of melanocytes in foetal life. Therefore, in Horner's 
syndrome, the affected eye tends to have lighter colour.

3. The sclera:

a. contains 50% of water
b. contains mainly type I and III collagen
c. is thinnest near the limbus
d. is penetrated by four vortex veins at its equator
e. forms the lamina cribrosa in the optic nerve region

 
Answera.F   b.T   c.F   d.F   e.T
The sclera contains 70% of water. It is thinnest behind the insertion of the recti. The vortex veins leave the globe behind the equator.

4. Third nerve palsy with pupil sparing is seen in the following 
    conditions:

a. hypetension
b. diabetes mellitus
c. aneurysm of the posterior communicating artery
d. internal carotid artery aneurysm within the cavernous
    sinus
e. uncal herniation

Answera.T   b.T  c.F   d.F  e.F
The oculomotor nerve contains the motor and the 
parasympathetic component. The fibres of the 
parasympathetic nerve are superficial to that of the 
motor nerve and derive the nutrients from the 
cerebrospinal fluid. In compressive lesion as in c, d and e
both components are affected. However, in hypertension and diabetes mellitus only the small vessels that supply the motor component is involved.

5. The following are true about the optic nerve :

a. it is made up of second order neurone
b. the average length in adult is 25 mm
c. the intraocular part is the thickest
d. the intraorbital part is the longest
e. the Schwann cells provide the myelination

Answera.T    b.F   c.F   d.F  e.F
The average length of an optic nerve in adult
is 40 mm (range from 30 to 55 mm).
The intracranial part is the longest.
Myelination is provided by oligodendrocytes.

 
 

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