Development and congenital abnormalities of the nasolacrimal apparatus.

The development of the nasolacrimal apparatus was reassessed based on the examination of serial sections done in 27 (54 orbits) embryos and fetuses ranging in size from 13.6 mm to term. In addition two adult specimens were examined. The entire nasolacrimal apparatus viz. canaliculi, lacrimal sac, and nasolacrimal duct develop contemporaneously. Canalization thereafter occurs throughout its length at the same time. The epithelium which lines the nasolacrimal apparatus abuts against the conjunctival epithelium superiorly in relationship to the puncta and the nasal mucosa at the opening of the nasolacrimal duct. These gossamer-like membranes perforate at term or soon thereafter. With the development of the face, the maxillary process grows medially to abut against, and then to override, the paraxial mesoderm of the nasolacrimal process. The nasooptic fissure is thus formed between these two mesodermal complexes. The surface ectoderm within the fissure thickens in a cord-like fashion and this is the analaga of the nasolacrimal apparatus. There is divergence of opinion as to the subsequent development of tear drainage system. A cord of epithelial cells forms from the nasal cavity and grows cephalad to become continuous with the main cord of buried surface ectoderm (Figure 1). It has been contended by Duke-Elder that the main epithelial cord then sends extensions laterally to form the superior and the inferior canaliculi. The inferior canaliculus extends more laterally than the superior canaliculus. At 3 months' development, canalization of the nasolacrimal apparatus is purported to occur in a segmental manner. These cavities then coalesce in a haphazard manner, finally forming a continuous tube. It is also suggested that the main core of buried epithelium canalizes from cephal caudalwards and that the epithelium arising from the nasal cavity canalizes in a reverse direction. The lacrimal sac then expands: the canaliculi canalize and the final section of the nasolacrimal duct to become patent is the opening into the inferior meatus of the nose below the inferior meatus of the nose below the inferior turbinate.U