The understanding of lacrimal embryology is very crucial to the understanding of lacrimal anatomy and its subsequent clinical and surgical applications. The lacrimal passages develop along the line of cleft between the maxillary process and the lateral nasal process [1,2,3,4,5]. The development of the lacrimal system begins at Carnegie Stage 16 (CRL, 11 mm), when an epithelial thickening of the lacrimal groove forms the lacrimal lamina [4]. At Carnegie Stage 19 (CRL, 17 mm), the lacrimal lamina separates from the surface ectoderm and forms the lacrimal cord. The lateral extreme of the cord closest to the surface ectoderm bifurcates, thus giving rise to the canaliculi. At Carnegie Stage 20 (CRL, 19–21 mm), the lacrimal cord is arranged lateral to the nasal capsule and finally lateral and inferior to the inferior meatal lamina. At Carnegie Stage 22 (CRL, 26 mm), the cells of the lacrimal cord condense at its periphery but are more loosely organized centrally, toward the future lumen [4].

Fig. 1.1
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Schematic diagram of lacrimal drainage development. The earliest stage is the formation of a line of cleft between the fronto-nasal process and the lateral nasal process (Photo courtesy: Himika Gupta, Mumbai)

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Fig. 1.2
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Schematic diagram of lacrimal drainage development. The diagram shows a clear differentiation of the embryologic processes and the lacrimal placode between them (Photo courtesy: Himika Gupta, Mumbai)

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From the tenth week (CRL, 48–55 mm), various significant changes occur such as canalization of the lacrimal cord and development of the surrounding tissues [4, 5]. Canalization occurs at the same time throughout the nasolacrimal apparatus [5]. The canalicular epithelium comes in contact with the palpebral conjunctival epithelium and both epithelia form a continuous epithelial lamina [4]. The caudal extreme of the lacrimal duct and the inferior meatal lamina makes contact and the latter begins to cavitate [1, 2, 4]. During the 12th week of development, reabsorption of the inferior meatal lamina is clearly visible (CRL, 74 mm).

Fig. 1.3
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Schematic diagram of lacrimal drainage development. Note the out budding of solid canaliculi from the lacrimal placode (Photo courtesy: Himika Gupta, Mumbai)

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Fig. 1.4
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Schematic diagram of lacrimal drainage development. Note the differentiation into canaliculi and the attempt of the distal end to meet the inferior meatal lamina (Photo courtesy: Himika Gupta, Mumbai)

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Fig. 1.5
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Schematic diagram of lacrimal drainage development. The process of canalization happens centrally and extends toward the periphery forming the lumina (Photo courtesy: Himika Gupta, Mumbai)

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Fig. 1.6
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A 22-week-old fetus. Note the development of the eyelids and the nose

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Fig. 1.7
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A 26-week-old fetus. Note the well-developed eyelids and the nose

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Fig. 1.8
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Clinico-embryological correlations: Lacrimal drainage agenesis in a craniofacial syndrome

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Fig. 1.9
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Clinico-embryological correlations: Left eye showing focal ankyloblepharon and proximal lacrimal drainage agenesis

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Fig. 1.10
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Clinico-embryological correlations: Right eye showing focal ankyloblepharon and proximal lacrimal drainage agenesis

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Fig. 1.11
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Clinico-embryological correlations: An ectopic punctum in the left medial canthus

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Fig. 1.12
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Clinico-embryological correlations: A right upper punctal agenesis

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Fig. 1.13
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Clinico-embryological correlations: A right lower eyelid showing supernumerary puncta

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Fig. 1.14
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Clinico-embryological correlations: A left congenital lacrimal fistula being demonstrated by a 3-probe test

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Fig. 1.15
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Clinico-embryological correlations: Lacrimal sac dysgenesis in a case of punctal and canalicular agenesis. Note the thinned-out cystic walls of the lacrimal sac

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Fig. 1.16
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Clinico-embryological correlations: Endoscopic view of the left lacrimal sac with an anterior inferior lacrimal diverticulum

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Fig. 1.17
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Clinico-embryological correlations: The lower most non-canalized segment of the nasolacrimal duct

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Fig. 1.18
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Clinico-embryological correlations: Ectopic lacrimal gland within the lacrimal sac. Clinical photograph of an infant with a large lacrimal sac mass

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Fig. 1.19
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Clinico-embryological correlations: Ectopic lacrimal gland within the lacrimal sac. Clinical photograph of the right eye of the patient in Fig. 1.18 showing punctal and canalicular agenesis

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Fig. 1.20
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Clinico-embryological correlations: Ectopic lacrimal gland within the lacrimal sac. Intraoperative photograph of the intra-sac mass removal

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Fig. 1.21
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Clinico-embryological correlations: Microphotograph confirming the ectopic lacrimal gland within the lacrimal sac

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Although the canalicular lumina become patent by the fourth month after gestation, the lacrimal puncta do not open onto the eyelid margins until the eyelids separate during the seventh month. However, the lower end of the duct is often separated from the inferior meatus at birth by a membrane constituted by the apposed mucosal linings of the lower ductal end and the nasal fossa. Only in 30% is the lowermost end patent at birth [1, 2]. An obstruction at this site balloons out later into the inferior meatus and its opening mostly occur after birth.