Histochemical staining of levator palpebrae superioris in normals and in congenital dystrophic ptosis

Purpose. To measure levator palpebrae superioris (LPS) muscle fibre size in normals and in patients with congenital dystrophic ptosis and to see whether muscle fibre size is related to levator function. Methods. Eight LPS specimens were obtained, four from normal patients (3 from normal levator divided in a bilateral brow suspension procedure and one from an exenteration specimen) and four from levator resection procedures for treatment of congential ptosis. Specimens were frozen-sectioned and stained histochemically to reveal muscle fibre type. The orthogonal diameters of type 1 and type 2 muscle fibres were measured using a computer generated programme and the two groups compared using the Mann-Whitney U test. Results. In the normal group the orthogonal diameters ranged from 11.8 to 21 microns (mean = 17.48, SD = 4.74) for type 1 fibres and 12.3 to 29 microns (mean = 22.5, SD = 7.21) for type 2 fibres. In the congenital ptosis group the mean orthogonal diameters ranged from 9.9 to 21 microns (mean = 15.5, SD = 4.76) for type 1 fibres and 19.3 to 21.6 microns (mean = 21.75, SD =2.01) for type 2 fibres. There was no statistically significant difference in the diameters of type 1 (p = 0.685) or type 2 fibres (p = 0.486) between the two groups. Conclusion. We have analysed the range, mean and SD of LPS muscle fibre size in normals which has only been reported once before. In patients with congential ptosis the size of individual muscle fibres in LPS does not account for the degree of levator function and on the basis of alterations in muscle fibre size, congenital ptosis cannot be classified as a dystrophy.