Anatomy
5 questionsWhat is the distance of the medial rectus from the limbus?
Downward and outward movement of eye is affected in injury of?
Yoke muscle for the right superior rectus is:
Which muscles are responsible for the elevation of the eye?
What is the longest part of the optic nerve?
NEET-PG 2013 - Anatomy NEET-PG Practice Questions and MCQs
Question 831: What is the distance of the medial rectus from the limbus?
- A. 4.5 mm
- B. 5.5 mm (Correct Answer)
- C. 7.0 mm
- D. 10 mm
Explanation: ***5.5 mm*** - The **medial rectus muscle** inserts into the sclera at an average distance of **5.5 mm** from the limbus [1]. - This distance is an important anatomical landmark in **ophthalmic surgery** and ocular motility studies. - The insertion distances follow the **Spiral of Tillaux** pattern. *4.5 mm* - This distance does **not correspond** to any of the standard rectus muscle insertion points. - The closest insertion is the **medial rectus at 5.5 mm**, followed by the **inferior rectus at 6.5 mm** [1]. *7.0 mm* - This distance corresponds to the insertion point of the **lateral rectus muscle** from the limbus [1]. - It is the **second farthest insertion point** among the recti muscles. *10 mm* - This distance is incorrect for any of the **rectus muscle insertions** from the limbus. - The rectus muscles insert at varying distances following the **Spiral of Tillaux**: medial (5.5 mm), inferior (6.5 mm), lateral (7.0 mm), and superior (7.7 mm).
Question 832: Downward and outward movement of eye is affected in injury of?
- A. 3rd nerve (Correct Answer)
- B. 4th nerve
- C. 5th nerve
- D. 6th nerve
Explanation: The 3rd cranial nerve (oculomotor nerve) controls most extraocular muscles including the superior rectus, inferior rectus, medial rectus, and inferior oblique, as well as the levator palpebrae superioris. Injury to the 3rd nerve results in paralysis of these muscles, leaving only the lateral rectus (6th nerve) and superior oblique (4th nerve) functioning. This causes the classic "down and out" position of the eye at rest due to the unopposed action of these two muscles [1]. The eye is pulled downward by the superior oblique and outward by the lateral rectus [1]. Additional features include ptosis (drooping eyelid), dilated pupil, and diplopia (double vision) [1][2]. The patient loses the ability to move the eye upward, downward (via inferior rectus), and medially. Incorrect Option: 4th nerve - The 4th cranial nerve (trochlear nerve) innervates the superior oblique muscle. The superior oblique primarily causes depression (downward), intorsion, and abduction of the eye [1]. However, its action is most effective for downward and INWARD movement when the eye is adducted. - 4th nerve palsy results in vertical diplopia (especially when looking down and inward, like reading or descending stairs), hypertropia (upward deviation), and head tilt to the opposite side. This does NOT produce a "down and out" position. Incorrect Option: 5th nerve - The 5th cranial nerve (trigeminal nerve) provides sensory innervation to the face and motor innervation to the muscles of mastication. It has no role in eye movements. Incorrect Option: 6th nerve - The 6th cranial nerve (abducens nerve) innervates the lateral rectus muscle, responsible for abduction (outward movement) of the eye [1]. 6th nerve palsy causes inability to abduct the eye, resulting in esotropia (inward deviation) and horizontal diplopia.
Question 833: Yoke muscle for the right superior rectus is:
- A. Left Inferior Oblique (Correct Answer)
- B. Left Lateral Rectus
- C. Left Superior rectus
- D. Left Inferior rectus
Explanation: ***Left Inferior Oblique*** - Yoke muscles are pairs of synergistic muscles, one in each eye, that act together to produce conjugate eye movements in the same direction of gaze. - The **right superior rectus** and **left inferior oblique** are yoke muscles that work together during **upward and rightward gaze** (dextro-elevation) [1]. - Right SR elevates the **adducted** right eye, while left IO elevates the **abducted** left eye, producing coordinated upward-right movement [1]. - This follows **Hering's Law of Equal Innervation**, where yoke muscles receive equal and simultaneous innervation. *Left Superior rectus* - The left superior rectus is the **contralateral homologous muscle**, not a yoke muscle for the right superior rectus. - Both superior recti work together for **upward gaze in primary position**, but they are versional muscles, not yoke pairs. - Yoke muscles produce conjugate movements in oblique directions, not straight up. *Left Inferior rectus* - The left inferior rectus depresses the left eye and is an antagonist to elevation. - It would pair with the **right superior oblique** for downward-left gaze (levo-depression), not with the right superior rectus. *Left Lateral Rectus* - The left lateral rectus is responsible for **abduction** of the left eye (leftward gaze). - Its yoke muscle is the **right medial rectus** for leftward horizontal gaze (levoversion), not for upward-right gaze.
Question 834: Which muscles are responsible for the elevation of the eye?
- A. SR and IO (Correct Answer)
- B. IO and SO
- C. IR and SR
- D. SO and IR
Explanation: ***SR and IO*** - The **superior rectus (SR)** muscle primarily elevates the eye, especially when the eye is **abducted** [1]. - The **inferior oblique (IO)** muscle also contributes to elevation, particularly when the eye is **adducted** [1]. *IO and SO* - While the **inferior oblique (IO)** elevates the eye, the **superior oblique (SO)** muscle is responsible for **depression** and **intorsion**, not elevation [1]. - Therefore, this combination does not exclusively perform elevation. *IR and SR* - The **superior rectus (SR)** muscle elevates the eye, but the **inferior rectus (IR)** muscle is responsible for **depression** of the eye, not elevation [1]. - This pair has opposing primary actions in vertical movement. *SO and IR* - Both the **superior oblique (SO)** and **inferior rectus (IR)** muscles are primarily involved in **depression** of the eye [1]. - The superior oblique also causes **intorsion**, and the inferior rectus causes **extorsion** [1].
Question 835: What is the longest part of the optic nerve?
- A. Intracanalicular
- B. Intraorbital (Correct Answer)
- C. Intraocular
- D. Intracranial
Explanation: ***Intraorbital*** - The **intraorbital segment** is the **longest portion** of the optic nerve, measuring approximately **25-30 mm**. - It extends from the posterior pole of the eyeball to the **optic canal** and is characterized by a curved, **S-shaped course** within the orbit. - This excess length (approximately 8 mm more than the distance it spans) allows for **free eye movements** without putting tension on the nerve. *Intracranial* - The **intracranial portion** extends from the **optic canal** to the **optic chiasm**, measuring approximately **10-16 mm**. - While often mistakenly thought to be the longest, it is actually the **second longest segment**. - This segment is crucial for the formation of the **optic chiasm** where partial decussation of fibers occurs. *Intracanalicular* - The **intracanalicular portion** passes through the **optic canal** within the sphenoid bone, measuring approximately **4-10 mm**. - This segment is relatively short and constricted, making it vulnerable to compression in conditions like optic nerve gliomas or meningiomas. *Intraocular* - The **intraocular portion** (optic disc) is the **shortest segment**, measuring only about **1 mm**. - It passes through the **lamina cribrosa** of the sclera and is visible on fundoscopy as the optic disc.
Internal Medicine
2 questionsInterstitial nephritis is common with
What is the primary brain region associated with ocular bobbing?
NEET-PG 2013 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 831: Interstitial nephritis is common with
- A. Black water fever
- B. Rhabdomyolysis
- C. Tumor lysis syndrome
- D. Nonsteroidal anti-inflammatory drugs (NSAIDs) (Correct Answer)
Explanation: ***Nonsteroidal anti-inflammatory drugs (NSAIDs)*** - **NSAIDs** are a known cause of **acute interstitial nephritis** (AIN), an inflammatory condition affecting the tubules and interstitium of the kidney [1]. - This adverse reaction often manifests as **fever**, **rash**, **eosinophilia**, and **acute kidney injury**, typically 7-10 days after drug exposure. *Black water fever* - **Blackwater fever** is a severe complication of **malaria**, characterized by massive hemolysis leading to **hemoglobinuria**, which darkens the urine. - It primarily causes **acute kidney injury** through **acute tubular necrosis** due to hemoglobin precipitation in the renal tubules, not interstitial nephritis. *Rhabdomyolysis* - **Rhabdomyolysis** involves the breakdown of muscle tissue, releasing myoglobin into the bloodstream, which is toxic to the kidneys. [1] - This condition leads to **acute kidney injury** predominantly through **acute tubular necrosis** due to myoglobin casts obstructing tubules and direct toxicity, not interstitial inflammation. *Tumor lysis syndrome* - **Tumor lysis syndrome** occurs when large numbers of cancer cells are rapidly destroyed, releasing intracellular contents like potassium, phosphate, and nucleic acids. - The high concentration of **uric acid** and **phosphate** in the renal tubules leads to crystal formation, causing **acute kidney injury** primarily through **acute uric acid nephropathy** and **phosphate nephropathy**, rather than interstitial nephritis [1].
Question 832: What is the primary brain region associated with ocular bobbing?
- A. Midbrain
- B. Pons (Correct Answer)
- C. Medulla
- D. Cerebral cortex
Explanation: Pons - **Ocular bobbing** is a characteristic eye movement disorder strongly associated with **pontine lesions**, particularly infarctions or hemorrhages affecting the tegmentum. - The pons contains critical connections for vertical gaze control within the **brainstem**, and damage here disrupts these pathways [1]. *Midbrain* - While important for eye movements, particularly **vertical gaze centers**, injuries to the midbrain typically cause disorders like Parinaud syndrome (upgaze palsy), not classic ocular bobbing. - Midbrain lesions might cause other types of nystagmus or gaze palsies but not generally the rapid downward and slow upward movement seen in bobbing. *Medulla* - The medulla primarily controls vital functions like breathing and heart rate, as well as some ocular reflexes, but is less directly involved in the generation of sustained vertical eye movements. - Damage to the medulla is more likely to cause effects like **nystagmus** (e.g., downbeat nystagmus in some cases) or other brainstem signs, rather than ocular bobbing. *Cerebral cortex* - The cerebral cortex is responsible for voluntary eye movements and integration of visual information, but it does not directly generate or control the brainstem reflexes associated with ocular bobbing [1]. - Lesions in the cortex would typically manifest as **gaze preference**, apraxia, or other higher-level visual processing deficits, not involuntary brainstem driven eye movements like bobbing.
Ophthalmology
3 questionsRetinitis pigmentosa is characterized by ?
Foster Kennedy syndrome is
What is the condition characterized by a relative afferent pupillary defect?
NEET-PG 2013 - Ophthalmology NEET-PG Practice Questions and MCQs
Question 831: Retinitis pigmentosa is characterized by ?
- A. Loss of central vision
- B. Visual field constriction
- C. Tubular vision
- D. Loss of peripheral vision (Correct Answer)
Explanation: ***Loss of peripheral vision*** - Retinitis pigmentosa is a group of genetic disorders that cause **progressive degeneration of photoreceptor cells**, primarily rods, which are concentrated in the periphery of the retina. - This degeneration leads to a gradual **loss of peripheral vision**, often beginning with **night blindness** and progressing to tunnel vision. *Loss of central vision* - Loss of central vision is characteristic of conditions affecting the **macula**, such as **age-related macular degeneration** or certain forms of **macular dystrophy**. - While later stages of retinitis pigmentosa can affect central vision, the initial and primary characteristic is loss of peripheral vision. *Tubular vision* - **Tubular vision** is an advanced stage of peripheral vision loss, where the visual field shrinks to a narrow central area, resembling looking through a tube. - While it can be a consequence of retinitis pigmentosa, it is a description of the **extent of visual field constriction** rather than the primary characteristic of the disease itself. *Visual field constriction* - **Visual field constriction** is a general term for any reduction in the extent of the visual field. - While retinitis pigmentosa certainly causes visual field constriction, the term "loss of peripheral vision" is more specific to the initial and dominant pattern of vision loss in this condition.
Question 832: Foster Kennedy syndrome is
- A. I/L Optic atrophy C/L papilloedema (Correct Answer)
- B. I/L Optic atrophy with papilloedema
- C. I/L Papilloedema with C/L optic atrophy
- D. I/L Papilloedema C/L papilitis
Explanation: ***I/L Optic atrophy C/L papilloedema*** - **Foster Kennedy syndrome** is characterized by the combination of **ipsilateral optic atrophy** and **contralateral papilledema**. - This constellation of signs is typically caused by a **frontal lobe mass** (e.g., meningioma or glioma) that directly compresses the ipsilateral optic nerve, leading to atrophy, while also causing increased **intracranial pressure** that manifests as papilledema in the contralateral eye. *I/L Papilloedema with C/L optic atrophy* - This describes the reverse of Foster Kennedy syndrome and is not a recognized clinical entity associated with a specific pathological process. - Papilledema is due to **increased intracranial pressure**, and optic atrophy is due to nerve damage; these would typically manifest in specific patterns related to the location and timing of the insult. *I/L Optic atrophy with papilloedema* - This option describes both conditions occurring in the **same (ipsilateral) eye**, which contradicts the characteristic presentation of Foster Kennedy syndrome. - While an eye can have both optic atrophy and papilledema (e.g., resolving papilledema or an underlying condition), it is not the defining feature of Foster Kennedy syndrome. *UL Papilloedema C/L papilitis* - This option mentions **papilledema** in one eye (unilateral or ipsilateral is implied) and **papillitis** in the other. - **Papillitis** is an inflammatory condition of the optic nerve head, while papilledema is due to increased intracranial pressure. This combination is not characteristic of Foster Kennedy syndrome, which specifically involves atrophy and papilledema due to a mass lesion.
Question 833: What is the condition characterized by a relative afferent pupillary defect?
- A. Efferent pathway defect
- B. Cerebral lesion
- C. Total afferent pupillary defect
- D. Marcus Gunn pupil (Correct Answer)
Explanation: ***Marcus Gunn pupil, a defect in the afferent pathway of the eye*** - A **Marcus Gunn pupil**, also known as a **relative afferent pupillary defect (RAPD)**, occurs due to a lesion or dysfunction in the **afferent (sensory) pathway** of one eye. - This results in an asymmetric response to light, where the pupil of the affected eye appears to dilate paradoxically when light is swung from the unaffected to the affected eye during the **swinging flashlight test**. *Efferent pathway defect* - An **efferent pathway defect** (e.g., in the oculomotor nerve, CN III) would cause a **fixed, dilated pupil** with impaired direct and consensual light reflexes, rather than an RAPD. - Such a defect would typically affect the motor response of the pupil, causing it to be unable to constrict. *Cerebral lesion* - While certain cerebral lesions can affect pupillary responses, a **relative afferent pupillary defect** specifically points to an issue in the direct sensory input from the retina to the brainstem. - Large **cerebral lesions** are more likely to cause other neurological signs or abnormalities in the motor control of the eye. *Total afferent pupillary defect* - A **total afferent pupillary defect**, often seen in **amaurotic pupil** (blind eye without light perception), would result in no direct or consensual light response in the affected eye. - In a RAPD, there is still some, albeit reduced, response to light, making it a **relative** defect rather than a total absence of afferent signaling.