Objective: To determine the pathologic abnormalities of the levator palpebrae superioris in congenital ptosis.
Methods: By means of light and electron microscopy and immunohistochemistry, anterior levator tissue specimen from 15 patients with congenital ptosis excised during routine levator resections were examined.
Results: All specimens showed lack of muscle fibers with endomysial and perimysial fibrosis and thickening of the aponeurosis. In addition, in four of the 15 patients, an abnormal extracellular material was present. By light microscopy this appeared as an unusual amorphous material arranged in clumps and bands, and electron microscopy showed it to consist of parallel coarse bundles of fibrillogranular material. Collagen type III and fibronectin were identified within this material by immunohistochemistry. There was no detectable collagen types I, II, IV, V, VI, or VII or laminin, and the material did not stain for actin, myosin, myoglobin, amyloid P component, or amyloid A.
Conclusions: In four of 15 samples of levator palpebrae superioris from patients with congenital ptosis, we identified an unusual amorphous extracellular material that stained positively for collagen type III and fibronectin on immunohistochemistry. This novel material, which we call "amorphocollagenoid," may represent a product of dysgenesis of the levator tissues. The source and full composition of this material merit further study.