This study investigates the role of the inferior lacrimal gland (ILG) in tear fluid secretion and its implications for dry eye disease (DED) in rabbits. The methodology involves creating a DED model through ultrasound-guided injection of concanavalin A to induce inflammation and assess ILG function.
In rabbits, the inferior lacrimal gland or ILG occupies the inferior-posterior aspect of the orbital margin and aids in tear fluid secretion necessary to maintain a healthy ocular surface. Impaired ILG function can compromise the ocular surface to inflammatory damage, causing dry eye disease or DED.
To create a DED model, first, prep an anesthetized rabbit, removing all the fur from its scalp and the area around the orbit for ultrasound localization of anatomical landmarks. Next, locate a bone projection, the 'ILG head', along the lower orbital margin. The ILG head rests over the zygomatic or cheekbone and extends posteriorly to form the 'ILG tail', occupying a more medial position in the orbit. Mark this region of ILG head-to-tail transition.
Sweep an ultrasound probe across the marking to identify a change from a bright hyperechoic signal representative of zygomatic bone to a 'no bone echo' signal, indicating the transition of ILG head to tail. Now, inject concanavalin A, a T-cell mitogen, at this site, inserting the needle deep enough to inoculate the ILG tail.
Post-injection, repeat the ultrasound. A dark hypoechoic space indicating the presence of fluid confirms successful concanavalin A delivery. Inside the ILG, concanavalin A induces T-cell infiltration and activation, triggering a proinflammatory response that disrupts ILG functioning, reducing tear fluid secretion. Eventually, the ocular surface also suffers damage, leading to DED.
For ILG injection, view the animal from the side to locate the prominence of the ILG along the lower anterior portion of the orbit. Use a surgical marking pen to draw a vertical line onto the skin, where the superficial part of the ILG gland transitions from its superficial resting place on the zygomatic bone to its more medial location in the orbit.
Sweep a vertically-held ultrasound probe across the line on the skin to identify the end of the zygomatic bone. The ILG transition occurs where the image of the gland changes from a circumscribed hyperechoic line to one without a recognizable medial border. The relative position of the hand-piece to the line drawn on the skin when this change is observed will be the injection site.
To place ConA into a gland at a point just medial to the zygomatic arch bone, set the desired depth of injection as the depth of the zygomatic bone (hyperechoic signal) plus 1 millimeter, minus the known length of the needle. Insert the needle about 12 millimeters into the gland at the injection site, before slowly withdrawing until the length of the exposed needle outside of the body is equal to the calculated difference.
Then, inject 0.2 milliliters of a 1000-microgram of ConA solution, and confirm the success of the injection by ultrasound. The ILG should exhibit a characteristic hypoechoic space.
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