There seems to be little or no information about the morphology of the fetal eye check ligament. The authors examined longitudinal and cross-histologic sections from the large collection of human fetuses at Universidad Complutense, Madrid. In longitudinal sections from 20 fetuses (four at each of 12, 15, 20, 25, and 30 weeks of gestation), a distinct connective tissue band was found connecting the medial and lateral recti and the limbus of the conjunctiva (sites at and around the lateral and medial angles of the conjunctival space). Silver impregnation revealed that the muscle endomysium (type 4 collagen dominant) was connected with composite fibers of the band (type 1 collagen). The cross-sections from three fetuses (20 weeks) exhibited a site-dependent difference in the rectus sheaths: the orbital-sided sheath suddenly increased in thickness when it tightly attached to the muscle bundles. The attaching orbital-sided muscle bundles reached 14% to 15% (or 18%-20%) in the cross-sectional area of the MR (or the LR). Taken together, the distinct connective tissue band extending to the conjunctiva was "originated from" the MR and LR rather than from a part of the muscles inserting into the connective tissue band. This band was most likely a primitive form of the check ligament. The authors hypothesize that the primitive check ligament conducts muscle tension to the conjunctiva to coordinate growth patterns between the anterior and posterior sides of the eyeball. This hypothesis may support en bloc recession for infantile esotropia.
