Patient selection: ptosis of an upper eyelid with clinical suspicion of myasthenia
Method:
(1) The degree of ptosis is measured (either as distance from the supraorbital margin or the gap between the eyelids) in mm.
(2) The eyelid is closed and a bag of ice is applied for several (2-3) minutes.
(3) The degree of ptosis is measured again in mm.
change in ptosis in mm =
= (distance between the eyelids after icing) - (distance between the eyelids before icing)
Interpretation:
• If there is no change in the ptosis then myasthenia is less likely and another cause should be considered.
• If the ptosis improves by 2+ mm then myasthenia is more likely.
Theories:
(1) Application of cold improves levator muscle contraction in myasthenics.
(2) Movaghar et al (2000) noted that application of heat as well as cold was effective in reducing the degree of ptosis. They hypothesized that resting the eyelid muscles may be as beneficial as the change in temperature. It is to be noted that application of heat or cold was 15 minutes rather than 2-3 minutes given above.
Performance:
• The test is reported to have a good sensitivity and specificity, but careful control of conditions is required for reliable results. A standardized photograph may make the measurements more reproducible.
• The test is dependent on patient cooperation.
• The test is useful as a bedside test that requires no specialized equipment. Both false positive and false negative results occur, so the diagnosis should be confirmed by a more reliable test.
• While of use for evaluating ptosis, Larner and Thomas (2000) indicate that it may not be as useful for the evaluation of diplopia.
