Test 194  (Ocular anatomy)

1. The cavernous sinus receives blood directly from::

a. internal jugular vein

b. sigmoid sinus

c. superior ophthalmic vein

d. inferior ophthalmic vein

e. sphenoparietal sinus

 
Answera.F   b.F  c.T   d.T  e.T
The inferior ophthalmic vein usually joins the superior ophthalmic vein before entering the cavernous sinus but it sometimes enters the cavernous sinus directly. Other tributaries that enter the sinus directly include superior and inferior petrosal sinuses and inferior and superficial middle cerebral veins.

2. Structures that are anterior to the meibomian glands include:

a. glands of Zeis

b. glands of Moll

c. Wolfring glands

d. Muscle of Riolan

e. glands of Krause

 

Answera.T  b.T  c.F  d.T  e.F
The glands of Zeis and Moll are located in the anterior lamella of the lid associated with the lash follicles. They discharge their secretions around the cilia shaft. The meibomian glands are located in the posterior lamellae within the tarsal plates. The muscle of Riolan is anterior to the tarsal plate. The accessory lacrimal glands of Wolfring and Krause are found in the conjunctiva and hence posterior to the meibomian glands. 

 
 

3. The fovea:
 

a. is the thickest part of the retina

b. has the same diameter as the optic disc

c. is temporal and slightly inferior to the optic disc

d. has no rods

e. contains cones with a peak density of about 
    200,000/mm²

 
Answer
a.F   b.T  c.T  d.T  e.T
The parafoveal region is the thickest part of the retina due to the thick layer of ganglion cells.

 

. 4. The cilioretinal artery:

a. is found in 30% of the population

b. supplies the papillomacular fibres

c. arises from the long ciliary artery

d. is filled early during fluorescein angiography before 
    the retinal artery

e. accounts for macular sparing in patients with central 
    retinal artery occlusion

Answer
a.T  b.T  c.F  d.T  e.T
It arises from the short ciliary artery.

5. True statements about the photoreceptors include:

a. the nasal retina contains more cones than the temporal 
    retina

b. cones are absent outside the macula

c. the highest density of rods are found in the superior 
    retina at eccentricities of 4 to 6 mm

d. the cones are larger in the fovea than in the peripheral 
    cornea

e. blue-sensitive cones are fewer in number than red or 
    green-sensitive cones

 
Answer
a.T   b.F  c.T  d.F  e.T
Rods are absent from the fovea. Their density peaks
in superior and nasal retina (176,000/mm2 and 145,000/mm2, respectively) at eccentricities 
ranging from 4 to 6 mm. The peak density of cones in the fovea is about 200,000/mm2. One millimeter away from the peak, the density of cones has fallen by a factor of 10. On average, the density of cones is greater 
nasally than temporally. In humans, the blue-sensitive 
cones represent 7 to 10% of the total cones. The relative scarcity of blue cones presumably accounts for the relative insensitivity of primate vision to blue light.

 

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