Objective — to determine the features of diagnosis of fatty degeneration of the Muller’s muscle of the upper eyelid as a cause of acquired ptosis. Material and methods. The study included 41 patients (43 eyes) with acquired upper eyelid ptosis. Basic parameters were preoperatively analyzed. Survey implied visual examination of the Muller’s muscle projection on inverted upper eyelid, ultrasound biomicroscopy of the upper eyelid structures, transillumination symptom, optical microscopy of the Muller’s muscle specimen under various magnification and three methods of staining. Results. Visual examination confirmed thickening and protrusion of the muscle towards tarsal plate, negative transillumination symptom. Ultrasound biomicroscopy revealed thickened complex of «conjunctiva—Muller’s muscle—aponeurosis of the levator» and a large number of hypoechogenic inclusions in muscle thickness compared with intact eye. Histological examination found partial substituting fatty degeneration of the Muller’s muscle. Conclusion. Comprehensive preoperative diagnosis of ptosis caused by fatty degeneration of the Muller’s muscle is essential for scheduling surgical strategy and obtaining positive clinical result.

Keywords. Muller’s muscle, upper tarsal muscle, ptosis, ultrasound biomicroscopy