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Lakshmi Rajagopalan, Saumya Nagar, Werhner Orilla, Karl G Csaky, Alexandra Almazan, James A Burke, Michael R Robinson, Susan S Lee; Visualization of conjunctival lymphatic vessels in normotensive rabbits. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1654. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Conjunctival lymphatics may help in drainage of aqueous humor after glaucoma filtration surgery and serve as a site of fluid egress following minimally invasive glaucoma surgery (MIGS) devices that drain into the sub-conjunctival space. However, the location and depth of the draining tube may influence access to the conjunctival lymphatics. The purpose of this study was to evaluate the conjunctival lymphatic vessels at two injection depths, sub-conjunctival (epithelium) and sub-Tenon’s levels in normotensive rabbits to better inform the placement of MIGS devices.
Twelve eyes of six New Zealand white rabbits randomly received 10 μl (0.25 mg/ ml) of Indocyanine green (ICG) either at the sub-conjunctival level (n=7) or at the sub-Tenon’s (n=5) level using a 32g needle. A saline bleb (~5 μl) was raised before the ICG injections to assist with delineating the conjunctival epithelium, Tenon’s fascia, and episclera. The distribution and the appearance of the conjunctival lymphatics were observed over time using the anterior segment module in the spectral domain OCT (Spectralis®, Heidelberg Engineering, Heidelberg, Germany) in the two groups.
There were clear differences in the appearance of lymphatic vessels in the two groups. Lymphatic vessels were more prominent with branching and collector channels seen in the group that received sub-conjunctival injections compared to sub-Tenon’s injections. In 10 out of 12 eyes, lymphatics were found superior to the bleb and in 2 eyes nasal to the bleb. ICG was found to fill the lymphatic channels faster in the sub-conjunctival injection group (2.8 ± 1.3 min) compared to the sub-Tenon’s (15.6 ± 4.8 min) group (p<0.05, one way ANOVA). The conjunctival lymphatics in the rabbit appeared more superficially and none were visualized in the deeper Tenon’s fascia or episcleral regions.
Lymphatic vessels filled faster following sub-conjunctival injections of ICG compared with the slower fill speed observed with the deeper sub-Tenon’s injections of ICG. In this rabbit study, the lymphatics appeared to be more superficial in the conjunctiva. Further study is required to see how these data translate to humans and inform optimal placement of MIGS devices.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure 1: En face image showing the ICG dye filling the lymphatics (arrows)
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