External acoustic meatus - Bony or Cartilaginous

 # Which of the following about external acoustic meatus is correct?

A. External acoustic meatus is purely cartilaginous in nature

B. External acoustic meatus is totally bony in nature

C. Medial side is bony in nature, whereas lateral side is cartilaginous in nature

D. Medial side is cartilaginous in nature, whereas lateral side is bony in nature

The correct answer is C. Medial side is bony in nature, whereas lateral side is cartilaginous in nature

External ear consists of auricle and the external acoustic meatus. 

External acoustic meatus is 24 mm long, of which medial two thirds (16 mm) are bony and lateral one third (8 mm) is cartilaginous. It can be examined by pulling the pinna upwards, backwards and outwards. The skin  lining the anterior half of the meatus is supplied by the auriculotemporal nerve and lining the posterior half by the auricular branch of the vagus. External auditory meatus contains modified sebaceous glands. Its floor is longer than its roof. It is narrowest near the tympanic membrane. 

Auricle is made of elastic cartilage. Nerve supply is from facial, vagus and mandibular nerve. Inflammation of the external ear is extremely painful  because its skin is highly vascular and firmly adherent to the underlying tissue. 

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In detachment of retina, the separation is between the:

# In detachment of retina, the separation is between the:

A. Choroid and retina

B. Pigmented layer and layer of rods and cornea

C. Layer of rods and cones and external limiting membrane

D. Layer of nerve fibres and internal limiting membrane

 

The correct answer is B. Pigmented layer and layer of rods and cones.

In detachment of the retina, the outer pigmented layer remains attached to the choroid, but the remaining layers of the retina separate from the pigmented layer and are displaced inwards. 

Most of the eye's interior is filled with vitreous. There are millions of fine fibres intertwined within the vitreous that are attached to the surface of the retina. As we age, the vitreous slowly shrinks or liquifies, and these fibres pull on the retinal surface. Usually the fibres break, allowing the vitreous to separate and shrink from the retina. This is a vitreous detachment which occurs towards inside. 

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Snyder's test tell us the:

 # Snyder's test tell us the: (AIPG-96)

a) Exact nature of microorganisms

b) Combined acidogenic nature of microorganisms

c) Enamel dissolving capacity of saliva

d) All of the above

The correct answer is B. Combined acidogenic nature of microorganisms

Snyder test measures the ability of the salivary microorganisms to form organic acids from a carbohydrate medium. In this test the glucose agar medium contains an indicator dye "Bromocresol green" which changes color from green to yellow in the range of PH 5.4 to 3.8

 

Colour observations in snyder test:- 

24 hrs	48 hrs	72 hrs
If yellow marked caries susceptibility	If yellow  definate caries susceptibility	If yellow  limited caries susceptibility
If green continue to incubate and observe at 48 hrs	If green continue to incubate and observe at 72 hrs	If green caries inactive

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Caries activity in very young children is evaluated by:

 # The valuable test for evaluating caries activity in very young children: (KCET-10)

a) Lactobacillus colony count test

b) Swab test

c) Alban test

d) Colorimetric Snyder test

The correct answer is B. Swab Test.

Swab test was developed by Grainger et al. It has an advantage over the other tests in that no collection of saliva is necessary. So it is valuable in evaluating caries activity in very young children.

 Procedure:

The oral flora is sampled by swabbing the buccal surfacesof the teeth with a cotton applicator, and the sample is subsequently incubated in the medium. The change in pH following a 48-hour incubation period is either read on a pH meter or read by the use of a color indicator.

 Principle:

Same as Snyder test

INTERPRETATION
pH	Caries activity
<= 4.1	Marked caries activity
4.2 to 4.4	Active
4.5 to 4.6	Slightly active
> 4.6	Caries inactive

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The visual sense has maximum acuity at:

 # The visual sense has maximum acuity at :

A. Ora serrata

B. Optic disc

C. Macula lutea

D. Fovea centralis

The correct answer is D. Fovea Centralis.

At the posterior pole of the eye, 3 mm lateral to the optic disc there is another depression of similar size called the macula lutea. It is avascular and yellow in color. The center of the macula is further depressed to form the fovea centralis. This is the thinnest part of the retina. It contains cones only and it is the site of maximum visual acuity. 

The rods and cones are the light receptors of the eye. The rods contain a pigment called visual purple. They can respond to dim light (Scotopic vision). The periphery of the retina contains only rods, but the fovea centralis contains no rods. The cones can only respond to bright light (photopic vision) and are sensitive to color. The fovea centralis has only cones. 

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The aqueous humor is secreted from:

 # The aqueous humor is secreted from:

A. Scleral spur

B. Sinus venosus sclerae

C. Ciliary processes

D. Suprachoroid lamina

The correct answer is C. Ciliary processes.

Aqueous humor is a clear fluid which fills the space between the cornea in front and the lens behind in the anterior segment. This space is divided by the iris into anterior and posterior chambers which communicates freely with each other via pupil. The aqueous humor is secreted into the posterior chamber from the capillaries in the ciliary processes. It passes into the anterior chamber through the pupil. From the anterior chamber it is drained into the anterior ciliary veins through the iridocorneal angle or angle of anterior chamber located between the fibres of the ligamentum pectinatum and the canal of Schlemm. Interference with the drainage of the aqueous humor into the canal of Schlemm results in an increase of intraocular pressure (glaucoma). This produces cupping of the optic disc and pressure atrophy o the retina causing blindness. 

The vitreous humor is clear gel that fills the space between the lens and the retina of the eyeball of humans. It is often referred to as the vitreous body or simply 'the vitreous'. It is produced by certain retinal cells. 

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The cornea is nourished by:

 # The cornea is nourished by:

A. Aqueous humor

B. Lymphatic fluid

C. Lacrimal fluid

D. All of the above

The correct answer is B. Lymphatic fluid.

The cornea is more convex than the sclera, but the curvature diminishes with age. It is separated from the iris by a space called the anterior chamber of the eye. The cornea is avascular and is nourished by lymph which circulates in the numerous corneal spaces. Pain is the only sensation aroused from the cornea. 

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