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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Medial squint may be the result of a lesion involving:

 # Medial squint may be the result of a lesion involving:

A. III cranial nerve

B. IV cranial nerve

C. VI cranial nerve

D. Optic nerve

The correct answer is. C. VI cranial nerve.

Medial squint is the result of palsy of lateral rectus of eye. All the extraocular muscles are supplied by the third cranial nerve (Oculomotor nerve) EXCEPT Lateral rectus which is supplied by sixth cranial nerve (Abducent nerve) and Superior Obique which is supplied by fourth cranial nerve (Trochlear nerve). 

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Superior rectus helps in:

 # Superior rectus helps in all of the following movements EXCEPT:

A. Upward rotation

B. Lateral rotation

C. Intorsion

D. Medial rotation

The correct answer is B. Lateral rotation. 

All the rectus muscles are involved in medial rotation of eye except the lateral rectus. Lateral rectus is the only rectus muscle involved in lateral rotation. 

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Muscles is involved in elevation of the eyeball

 # Which of the following group of muscles is involved in elevation of the eyeball?

A. Superior rectus and inferior oblique

B. Inferior rectus and Superior oblique

C. Superior Oblique and superior rectus

D. Inferior oblique and Inferior rectus

The correct answer is : A. Superior rectus and inferior oblique

Action of Individual Muscles:

Levator Palpebrae superioris - Elevation of upper eyelid

Superior rectus - Upward rotation, medial rotation and intorsion

Inferior rectus- Downward rotation, medial rotation and extorsion

Medial rectus- Medial rotation

Lateral rectus- Lateral rotation

Superior oblique- Downward rotation, lateral rotation and intorsion 

Inferior oblique- Upward rotation and extorsion

Single movements of eyeball and muscles involved:

Upward rotation (Elevation)- Superior rectus and inferior oblique

Downward rotation (Depression)- Inferior rectus and Superior oblique

Medial rotation (Adduction)- Medial rectus, Superior rectus and Inferior rectus

Lateral rotation (Abduction)- Lateral rectus, Superior oblique and inferior oblique

Intorsion- Superior rectus and superior oblique

Extorsion- Inferior oblique and Inferior rectus

Nasolacrimal duct is directed:

 # Nasolacrimal duct is directed:

A. Downward, medially, backwards

B. Downward, laterally, backwards

C. Downward, laterally, forward

D. Downward, medially, forward

The correct answer is: B. Downward, laterally, backwards

Nasolacrimal duct: The groove for nasolacrimal duct is located medially near the orbital margin. It is a membranous passage of 18 mm length. It begins at the lower end of the lacrimal sac, runs downwards, backwards and laterally, and opens into the inferior meatus of the nose. A fold of mucous membrane called the valve of Hasner forms an imperfect valve at the lower end of the duct. 

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