17 - alexander's law of nystagmus

it refers to the phenomenon in which the spontaneous nystagmus of a patient with a vestibular lesion is more intense when the patient looks in the quick-phase than in the slow-phase direction.

Alexander's law was investigated in normal subjects as well as patients with vestibular lesions.
During sinusoidal rotations of normal subjects, there was no trace of this phenomenon when subjects looked 25 degrees left and right in the dark.

The phenomenon of Alexander's law is therefore created centrally and is not due to any mechanical properties of the orbit.


--During rotation at constant velocity in the dark, normal subjects did weakly demonstrate Alexander's law because of a mild gaze-evoked nystagmus present in normal subjects in the dark.

Gaze-evoked nystagmus from a cerebellar lesion involved a pronounced demonstration of Alexander's law during rotatory nystagmus.

--In patients with a vestibular lesion and a mild spontaneous nystagmus in the dark that obeyed Alexander's law, the nystagmus reversed upon far gaze in the slow-phase direction.

--in patients with a vestibular lesion, the phenomenon of Alexander's law is created by the sum of vestibular nystagmus and an abnormally large gaze-evoked nystagmus that is consequent to the vestibular lesion.

16 - cherry red spot - macula - causes

what are the causes of the cherry red spot in the macula of the eye ?

answer : 

1. Tay sachs disease


2. Sandhoff's disease

3. Gaucher's disease

4. Niemann pick's disease

5. CRAO - central retinal artery occlusion

6. Sialodosis

7. Berlin's edema ( commotio retinae )


8. Gangliosidoses

9. Metachromatic leukodystrophy 

10. Multiple sulfatase deficiency


a number of mcqs have been asked from this question in various entrance tests . so be careful . if u know any other causes please post in the comments .