From the Research
The ice pack test is considered positive when there is an improvement of at least 2 millimeters in ptosis after applying an ice pack to the affected eye for 2-5 minutes. This test is used to diagnose myasthenia gravis, a neuromuscular disorder characterized by muscle weakness. The cold temperature from the ice pack temporarily improves neuromuscular transmission by slowing the breakdown of acetylcholine at the neuromuscular junction, which allows for better muscle contraction. To perform the test, measure the palpebral fissure (the distance between the upper and lower eyelids) before and after ice application. If the eyelid elevation improves by 2mm or more, this suggests myasthenia gravis as the cause of the ptosis.
Some key points to consider when performing the ice pack test include:
- The test is a useful screening tool, but it should be followed by more definitive diagnostic tests such as acetylcholine receptor antibody testing or electromyography for confirmation 1.
- The sensitivity of the ice test in patients with complete ptosis decreases considerably 1.
- The ice pack test demonstrated high specificity and an acceptable sensitivity in the differential diagnosis of myasthenic diplopia 2.
- A partial rather than a complete response to the ice pack test may be expected for myasthenic diplopia 2.
It's worth noting that the provided studies 3, 4, 5 do not directly address the question of the millimeter threshold for a positive ice pack test, but study 1 provides evidence that an improvement of at least 2 millimeters in ptosis is considered a positive result. Therefore, the recommended millimeter threshold for a positive ice pack test is 2 millimeters, based on the study by 1.