Direct insertion of the medial rectus capsulopalpebral fascia to the tarsus.

Purpose: To clarify the insertion of the medial rectus capsulopalpebral fascia to the tarsus in Asians.

Methods: Specimens from 19 (11 right, 8 left) postmortem medial eyelids and orbits of 11 Asians (aged 45-96 years at death) were used. Samples had been fixed in 10% buffered formalin before their removal and microscopic examination. The tarsi were incised at 2 different heights in the upper and lower eyelids, as it was not disclosed which parts had the insertion of the medial rectus capsulopalpebral fascia. The first and second sections, parallel to the eyelid margin, were obtained, respectively, at 1 mm and 5 mm from the upper eyelid margin, and at 1 mm and 3 mm from the lower eyelid margin. Sections were stained with Masson trichrome.

Results: Both upper and lower eyelids demonstrated similar findings. The first sections, which showed the medial rectus capsulopalpebral fascia and included many smooth muscle fibers, did not insert in the tarsi. However, the deep part of Horner muscle directly inserted, whereas the superficial part went in the dense fibrous tissue closely attaching on the tarsi. Then, some of the muscle branched out in the tarsi. The second sections showed that the medial rectus capsulopalpebral fascia had a direct insertion to the tarsi.

Conclusions: The tarsi are supported medially by the medial rectus capsulopalpebral fascia and Horner muscle. The "medial eyelid retractors, " comprising the medial rectus capsulopalpebral fascia and smooth muscles, were clearly defined, highlighting the relationship of the eyelid to the medial rectus muscle and offering a new pathogenesis and treatment for lateral tarsal shifts and lower medial ectropion.