The anlage of the membranous lacrimal conduit begins as an ectodermal thickening along the naso-optic fissure in the 7‑mm or 32‑day embryo (Figure 1).
This thickened ectoderm lies between the lateral nasal and maxillary processes and arises at about the same time as the olfactory groove.
The olfactory pit is well formed in the 9‑mm or 37‑day embryo and the thickened ectoderm of the lacrimal anlage detaches and becomes buried beneath the surface ectoderm in the 12‑mm or 42‑day embryo.
The solid cord of epithelial cells becomes canalized beginning in the 32–36‑mm or 60‑day embryo, first patent at the ocular end and concluding at the lower nasal end.
Figure 1. (AMA Arch Ophthalmol. 1952;47(2):141–158).
The horizontal portion of the lacrimal system establishes a lumen before the vertical portion and connects with the canaliculi forming at the lid margin.
Distal canalization at the inferior meatus occurs after birth.
- In a 1950 study at the Carnegie Institute of Washington, the nasolacrimal passages of 15 full-term stillborn infants were examined.
- The nasolacrimal duct was found to be in communication with the nose at birth in only 27% of cases.
- 2 infants had 1 duct open and the other closed.
- Only 2 infants had both ducts open to the nose.
- Only a mucosal membrane separated the lacrimal duct from the nasal meatus, and the distal duct was ballooned under the inferior turbinate.