Dentosphere : World of Dentistry

 # 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 r...

 # 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.  CLICK HERE TO VIEW ALL MCQs

 # 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).  CLICK HERE FOR MORE MCQs

 # 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.  CLICK HERE FOR MORE MCQs

 # 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 (A...

 # 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.  CLICK HERE FOR ALL MCQs

 # Stapedius muscle has its nerve supply from: A. Trigeminal nerve B. Facial nerve C. Glossopharyngeal nerve D. Stato-acoustic nerve The correct answer is: B. Facial nerve Stapedius muscle along with the tensor tympani are muscles of ossicles of middle ear. Stapedius is supplied by facial nerve, whereas tensor tympani is supplied by mandibular nerve. Stapedius and tensor tympani both act simultaneously to damp down the intensity of high pitched sound waves, thus protecting the internal ear. In paralysis of the muscle even normal sounds appear too loud, which is known as "hyperacusis".  CLICK HERE FOR MORE MCQs