Congenital blepharoptosis: a literature review of the histology of levator palpebrae superioris muscle.

Purpose: To identify and summarize the available published literature describing histologic features of congenital blepharoptosis and to consider the evidence for its classification as either a dystrophy or a dysgenesis. A brief overview of etiologic factors is included to highlight the controversy surrounding the cause of the condition.
Methods: Online searches of the current medical literature were performed with the use of search engines provided in British University libraries. Keywords used were ptosis, blepharoptosis, and birth defect, combined with eyelid. Manuscript copies were obtained and translated where necessary.
Results: A summary of data found in more than 35 published papers, including theories of etiology (muscular versus neural, genetic versus sporadic, and environmental factors) and evidence for the classification of congenital blepharoptosis as a dysgenesis and as a dystrophy. Study design and data interpretation are commented on where appropriate.
Conclusions: The scarcity of both affected tissue and normal fetal tissue for histologic examination has limited the understanding of the development and classification of congenital blepharoptosis. Each study analyzed had small specimen numbers, highlighting the need for a review of all available data. The available histologic data appear to support the classification of congenital blepharoptosis as a dysgenesis rather than a dystrophy. It is predicted that a greater understanding of the etiology and histology of this condition may distinguish further subtypes. It is also anticipated that a greater understanding of this condition will allow developments in preventive and therapeutic approaches.