from the PDF attached to Annie's post, above

"...asymmetric ptosis is most often associated with
acquired and autoimmune myasthenia gravis (MG) in
contrast to CMS and other inherited disorders. He and
his coworkers studied the diagnostic value of this
observation by comparing a group of patients with
autoimmune MG or Lambert–Eaton myasthenic syndrome
(LEMS) with a group of patients with hereditary
myopathy. Studying the files of 250 MG or LEMS
D. Beeson et al. / Neuromuscular Disorders 15 (2005) 498–512 505
patients and 83 hereditary myopathy or CMS patients
(dystrophic myotonia, progressive external ophthalmoplegia,
oculopharyngeal muscle dystrophy, CMS) revealed a
similar frequency of ptosis in both groups (76 and 78%,
respectively). Asymmetry was noted in 80% of the MG
or LEMS patients and in 30% of the myopathy or CMS
patients. To verify these findings, a prospective study
was started in which the ptosis was quantified using
digital photography. So far, 52% of 23 MG patients and
none of 20 myopathy/CMS patients were found to have a
significant asymmetric ptosis. The results of these
ongoing studies suggest that asymmetric ptosis points
to an underlying autoimmune disease and less likely
towards a hereditary myopathy or CMS."