What is this Ice Test?
In a case us ptosis suspected to be due to Myasthenia Gravis an Ice Pack need to applied over the suspect eye with closed lids for 2 to 5 minutes.
When is this test considered positive?
If the ptosis improves by 2 mm or more after the application of ice pack
What is the physiological basis of this test?
The lowering of tissue temperature by the ice leads to decrease in the activity of the enzyme acetylcholinesterase found in the neuromuscular junctions and also in the chemical synapses of the cholinergic types. This leads to decrease in the breakdown of acetylcholine and therefore increase in its concentration the neuromuscular junction. This leads to increase in the contraction of the levator muscle.
How sensitive is this Ice Test?
Reportedly 90%
What are the precautions to be followed while carrying out this test?
Ensure that ice pack is not kept for too long as that may lead to cooling of muscle fibers and thereby decreasing their contractibility