The normal tendon (technically, the levator aponeurosis) of the eyelid's opening muscle (the levator musle) can be seen as a glistening pink-white structure located high inside of the incision. Just below that tendon is an area of darker red color, and just below that is a tiny rim of additional pinkish-white tendon.
The darker red area represents a tear in the tendon and is the cause of the patient's drooping eyelid.
Defective levator aponeurosis
For comparison: Normal appearance
Since the tendon transmits the pull of the opening muscle to the eyelid, the tear prevents the eyelid from opening to a normal height.
Surgical repair consisted of suturing the two intact portions of the healthy tendon back together again, thereby restoring the levator muscle complex to full strength.
In most patients, the tendon defect is much more subtle in appearance and consists of an ill-defined area of thinning rather than an easily-recognizable tear. In such cases, the tendon is reinforced by surgical tucking.