Test 201  (Ocular anatomy)

1. The following are true about the photoreceptors:

a. the rods have a longer segment than the cones

b. the synaptic terminals of the photoreceptors are
    located in the inner plexiform layer

c. the outer segment of the photoreceptors are orientated 
    with their long axes towards the pupil

d. the inner segment of the photoreceptors has a diameter 
    that is smaller than the outer segment

e. the photoreceptors received nutrients from the 
    choroidal circulation

 
Answera.T   b.F  c.T   d.F  e.T
The synaptic terminals fo the photoreceptors are located in the outer plexiform layer. The inner segment of the photoreceptors are equal or larger than the outer segment, this arrangement allows the light to be funnelled to the outer segment.

2. Regarding the photoreceptors:

a. pedicle is the synaptic terminal of the rods

b. the synaptic terminal of rod has more invaginations 
    than the cones 

c. ellipsoid is the mitochondrial rich area of the 
    photoreceptors

d. the region containing the nucleus is called the myoid

e. unlike the cones, the distal outer segment of the rods 
   are not in direct communication with the extracellular 
   space.

 

Answera.F  b.F  c.T  d.F  e.T
Pedicle is the synaptic terminal of the cones. The synaptic terminal of the rods is called spherule. The synaptic terminal of the cone has more invaginations than the rods. The mitochondrial rich area of the photoreceptors
is called ellipsoid and the Golgi rich area is the myoid. The myoid connects the nucleus to the ellipsoid.

3. Descemet's membrane:

a. is an acellular layer

b. is absent at birth

c. is produced after birth by the keratocytes of the stroma

d. is 5X thicker in old age than in youth

e. is continuos with the Schwalbe's line at the limbus

 
Answer
a.T   b.F  c.F  d.T e.T
The Descemet's membrane is made up of an anterior 
fibrillar layer and a posterior granular layer. The anterior layer is present at birth and the posterior layer is 
produced by the endothelium and acts as its basement 
membrane. In youth, it is about 2 micrometer thick increasing to about 10 micrometer in old age. It is continuous with the Schwalbe's line at the limbus.

 

. 4. The ciliary body:

a. contains a bilayer cuboidal epithelium

b. contains epithelium which is continuos with 
    the neuroretina

c. becomes more anteriorly located with time

d. shows atrophy with age

e. contracts when the eyes are focused at a distant object

Answer
a.T  b.T  c.T  d.T  e.F
Microscopically, the ciliary body consists of the ciliary epithelium, stroma, and the ciliary muscle. The ciliary epithelium covers the inner surface of the ciliary body and is composed of two layers of cuboidal cells. The inner nonpigmented layer is continuous with the neuroretina and shares the same embryologic origin. The outer pigmented layer is continuous with the retinal pigment epithelium. The ciliary stroma is made up of bundles of highly vascularized connective tissue. Ciliary body anteriorization (become more anteriorly 
placed) is progressive with ageing and is even more pronounced in patients older than 55 years. There is a significant age-related atrophy of the ciliary muscular elements, with a notable loss of nuclei and thinning of the muscles, more pronounced in the longitudinal and reticular regions but not in the circular fibres. 

5. The following are true about the cornea:

a. the peripheral cornea has twice the thickness of 
    the central cornea

b. it has a density of nerve endings which is 300 times
    that of the epidermis

c. it is more curved centrally than peripherally

d. it is more curved in the horizontal than the vertical axis

e. it has a refractive index of 1.36

 
Answer
a.T   b.T  c.T  d.F  e.T
The central cornea is usually about 0.5 mm thick and the periphery 1.0 mm. The cornea has a dense supply of sensory nerve supply. It is more curved centrally and in the vertical axis. 

 

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