New insights into lacrimal gland anatomy using 7T MRI and electron microscopy: Relevance for lacrimal gland targeted therapies and bioengineering.

ABSTRACT

PURPOSE: To study the tissue architecture, isthmus (connection between two lobes) of the lacrimal gland using preclinical 7T MRI in combination with histology and electron microscopy. METHODS: Ten lacrimal glands from Caucasian body donors (mean age 78.7 years) were studied using 7T-MRI (N = 5; scanned at 75-µm intervals), histology, and electron microscopy (N = 5) and 3D cinematic rendering (CR) techniques. RESULTS: 3D CR images showed uniform-sized lobules (widest lobule diameter, 1.68 ± 0.19 mm in orbital lobe, 1.68 ± 0.17 mm in palpebral lobe) in both lobes, separated by septae (size, 0.29 ± 0.09 mm). The internal framework of the gland resembled a honeycoomb pattern. In CR and histology, the isthmus contained glandular acini, large blood vessels, nerves, and no more than two ducts having a tortuous course towards the conjunctival surface. On assigning a color display to the rendered lacrimal gland, all glands showed a blood vessel originating from the main lacrimal artery just 5 mm beyond the hilum and making it course to the palpebral lobe via isthmus. The distance between the conjunctiva and the central substance of the orbital and palpebral lobe was 9.4 ± 0.2 mm and 2.8 ± 0.7 mm, respectively. Electron microscopy of the palpebral lobe revealed compact subepithelial layer in the overlying conjunctiva, followed by loosely scattered collagen bundles that contained the gland lobules. CONCLUSION: 3D-CR can be used to study the lacrimal gland microstructure, help fabricate a 3D scaffold for lacrimal gland bioprinting, and serve as guide for transconjunctival lacrimal gland targeted therapies i.e., 2.9 & 9 mm long needle to reach the orbital and palpebral lobe center, respectively in normal-size glands.