Understanding Right Eye Position in 3rd Cranial Nerve Palsy
The 3rd cranial nerve, also known as the oculomotor nerve, controls several key muscles responsible for eye movement and eyelid function. These include the medial rectus (moves eye inwards), superior rectus (moves eye upwards), inferior rectus (moves eye downwards), and inferior oblique (moves eye upwards and outwards). It also controls the eyelid.
Mechanism of Eye Deviation
When the right 3rd cranial nerve experiences a palsy (weakness or paralysis), the muscles it controls on the right side are affected. The eye's position is then primarily determined by the muscles NOT controlled by the 3rd nerve:
- Lateral Rectus Muscle: Controlled by the 6th cranial nerve, this muscle moves the eye outwards (abduction). Its unopposed action causes the eye to drift outwards.
- Superior Oblique Muscle: Controlled by the 4th cranial nerve, this muscle primarily moves the eye downwards and outwards. Its unopposed action contributes to the downward and outward deviation.
Resulting Eye Position
The combined unopposed action of the lateral rectus and the superior oblique muscles causes the affected right eye to rest in a position that is:
- Downwards: Due to the unopposed action of the superior oblique muscle.
- Outwards: Due to the unopposed action of the lateral rectus muscle.
Therefore, the primary resting position of the right eye in a right 3rd cranial nerve palsy is downwards and outwards.
Important Questions from Neuropathies
Consider the following clinical features :
1. Hypomimia
2. Dysphonia
3. Festination gait
4. Cogwheel rigidity
Which of the features given above are generally present in Parkinsonism?
- Circuits between the basal ganglia and the motor cortex constitute the extra pyramidal system which controls muscle tone, body posture and the initiation of movement. Lesions of the extra pyramidal system present clinically with :
Consider the following statements regarding Transient Global Amnesia (TGA):
1. TGA mainly affects middle aged persons who present with abrupt, discrete loss of anterograde memory lasting for few hours.
2. During the episode, the patients are unable to record new memories resulting in repetitive questioning.
3. Consciousness is impaired during the episode and the patient is unable to perform even simple motor functions.
4. After 4-6 hours, memory function and behaviour return to normal but the patient has complete and persistent amnesia for the duration of the episode.
Which of the statements given above are correct?
- Which one of the following distinguishes axonal degeneration from segmental demyelination on electrophysiological studies?
- Which of the following are correct with regard to Levodopa ?
1. It is most effective for relieving tremors
2. Only a small portion of total drug reaches the brain
3. Nausea may be offset by domperidone
4. It may trigger hallucinations
Select the correct answer using the code given below :
