Histochemical staining of orbicularis oculi muscle in ectropion and entropion

A histochemical study of orbicularis oculi was undertaken to test the hypothesis that there is a difference in the percentage and size of muscle fibre types which accounts for the development of involutional ectropion or entropion. Wedge excisions from lower lids of patients undergoing repair of these conditions were frozen-sectioned and stained histochemically to reveal muscle fibre types. Five ectropion and five entropion specimens were obtained, and the percentage of type 1 and type 2 fibres, fibre perimeters and fibre diameters were measured. An abundance of type 2 fibres was found in both ectropion (mean 89.6%) and entropion (mean 82.6%). No significant difference was found with respect to fibre type, perimeter or diameter when ectropion was compared with entropion or when either was compared with normals. Type 2 fibres were larger than type 1 in both ectropion and entropion. We conclude that no significant difference could be identified between orbicularis muscle fibres in ectropion, entropion and normals to account for the development of the eyelid malpositions.