A novel approach is presented to induce chronic dry eye disease in rabbits by surgically removing all orbital lacrimal glands. This method, distinct from those previously reported, produces a stable, reproducible model of aqueous deficient dry eye well suited to study tear physiology and pathophysiology and ocular therapeutics.
Our safe, reproducible method for a complete dacryoadenectomy in rabbits creates a consistent state of aqueous deficient dry eye that is useful for studying disease physiology and the efficacy of therapeutic interventions. Removal of the superior orbital and palpebral lacrimal glands significantly improves the consistency and severity of the induced dry eye, and limits the compensatory changes in tear production to the ocular surface tissues. Lacrimal gland tissues lying within the orbital compartment adjunct to a large vascular structure.
Familiarity with the anatomy will great aid removal and help prevent surgical complications. Removal the lacrimal gland system is a moderately complex technique involving multiple incision locations and surgical planes, which is best demonstrated visually. Begin by bilaterally removing the nictitating membrane.
Use a micropippette to apply 25 microliters of preservative-free 1%Lidocaine to the eye, and insert a lid speculum between the eyelids. Grasp the nictitating membrane at its apex with 0.3 forceps and pull it over the corneal surface. Then, inject approximately 0.3 milliliters of 1%Lidocaine with one to 100, 000 Epinephrine into the subconjuctival space, using a 26 gauge needle.
This will form a modest-sized bleb over the nictitating membrane. Remove the wire speculum and wait approximately five minutes for the Lidocaine and Epinephrine to take effect. Meanwhile, perform the same procedure on the other eye.
When ready, replace the wire speculum, grasp and extend the nictitating membrane over the corneal surface with the forceps, and cut the membrane at it's base with tenotomy scissors. Remove the wire speculum and place topical antibiotic ointment over the corneal surface. To remove the orbital superior lacrimal gland, or OSLG, infiltrate the incision sites with a 50 to 50 mixture of 2%Lidocaine and one to 100, 000 Epinephrine with 0.5%Bupivacaine.
Then, use a Colorado needle connected to an electrosurgical unit to make the skin incisions along the surgical markings. Typical settings are between 10 and 15 units for both cut and coagulation, but can vary, depending on clinical response. Apply opposing tension across the skin incision to separate the tissues and expose the underlying frontoscutularis muscle fibers.
Then, apply medial pressure on the globe to aid visualization of the OSLG, which is seen as bulging tissue located just medial or deep to the frontoscutularis muscle fibers. If necessary, move the muscle fibers to the side to expose the underlying incisure, and use toothed forceps with capsulotomy scissors to gently retract and cut the fibrous capsule over the OSLG. Using forceps, grasp the OSLG gland tissue and gently pull it through the superior incisure using a hand-over-hand technique.
Cut small fibrous bands with the capsulotomy scissors to free the gland from its position in the orbit. When the gland has been removed, use generous cautery with the Colorado needle to create tissue char, truncating the gland within the incisure as deeply as possible. This will later serve as a confirmatory landmark during the removal of the palpebral superior lacrimal gland, or PSLG.
To remove the PSLG, evert the upper eyelid with a cotton-tipped applicator, which will make the bulbous end of the PSLG visible. Engage the PSLG with toothed forceps and retract it from the eyelid surface while using capsulotomy scissors to cut around its base and separate it from the underlying tarsus. Control moderate bleeding with the monopolar cautery.
Apply continuous traction on the separated tissue plane for dissection, which will allow the main excretory duct of the superior lacrimal gland, or SLG, to be removed, as well. To resect the larger inferior lacrimal gland, or ILG, use the Colorado microdissection needle to incise and separate the skin, the depressor muscle of the inferior palpebra, the zygomatic or labial part of the zygomatic muscle, and the orbicularis muscle. Maintain hemostasis with the monopolar cautery.
As the incision is carried deeper through the skin marking, look for the sheen of a fascial plane over the zygomatic bone or superficial part of the masseter muscle. At this point, maintain the tissue plane and carry it superiorly toward the orbital rim. Identify and incise the capsule surrounding the ILG, then identify the tan tissue of the ILG.
Only the anterior portion of the ILG head will be visible, but it can be followed medially as it passes beneath the zygomatic arch and transitions into the tail. Use tenotomy scissors to cut the orbital septum along the inferior rim, exposing the more posterior portion of the ILG tail. Once the tissue plane is identified, extend the dissection posteriorly along the entire incision line.
Use extreme care to not damage the blood supply which the ILG receives from branches of the carotid artery. Once the entire ILG has been exposed, remove it. If the tail terminates under the posterior canthus, see the manuscript for excision directions.
Due to it's large size, it can be preferable to cut the gland in half and remove the head separately from the tail. After the gland has been removed, close the deep connective tissue plane with multiple interrupted 5-0 ethylene teraphthalate sutures. Then, close the superficial muscles and skin with a running 6-0 polyglactim 910 suture using 0.3 tissue forceps and a needle driver.
This surgical approach has successfully been used to induce dry eye disease, which was confirmed with a panel of clinical and laboratory markers. During the eight weeks of observation, the mean tear break-up time was suppressed by more than 75%of preoperative levels. Similarly, the Schirmer's tear test decreased by approximately 50%and the tear osmolarity increased by 10%which is consistent with dry eye disease.
Complete surgical resection is easiest if the superior orbital lacrimal gland is removed first. It is important to expose all lacrimal gland tissue margins completely.
