Conjunctival Lymphatics
Lymphatics are seen throughout the body, since the leakage of the body fluid from the arterial system can not be fully absorbed by the venous system. How can the eye manage the fluid imbalance without the lymphatics ? Consider the uveo scleral outflow that accounts for more than 50 % of the aqueous outflow. Additionally there is leakage from the aqueous veins. Which system comes in to play when a filtration surgery is performed? Which system is to be blamed, when a filtration operation fails to succeed? What produces large avascular blebs? These and a lot of other questions can be addressed with confidence if the presence and the function of the lymphatics is recognized. We have studied lymphatics in the outpatient setting and in the operation theater.
Out-patient study
The easiest way to study lymphatics is to look at the limbus through the high power magnification of a slit lamp microscope. It is possible to see the transparent lymphatics, though in the beginning, it is less convincing. Once we have seen similar channels, that are more well defined, the doubt disappears. The definition is improved by the presence of pigment at the limbus. The colored people of all shades, frequently show the lymphatics, if examined carefully. The eyes of white population lacks the much pigment in the iris, its absence in the limbal area is to be naturally expected. The physical recognition of the lymphatics is the first step towards considering their role in the transport of aqueous in health and disease.
Raw lymphatics get seen easily and frequently, once we know how they look like. They are fairly large transparent structures, running parallel to the limbus. They give a corrugated appearance to the conjunctiva. This appearance gets enhanced if the corrugation is looked at in the area of slit lamp light reflection.
Fig.1: The raw lymphatics visible as transparent channels running parallel to the limbus
The lymphatics at the limbus are fine channels running prependicular to it. They are best visualized if there is some pigment near the limbus. The pigment being outside the lymphatics, helps in outlining them distinctly. The general pattern is very clear- vertical limbal channels flow in to the the circular anastomosing channel network. The corneal ends of the limbal lymphatics seem to disappear in to merge in to a channel network in the cornea. It might sound heretic, but our studies support this view
Fig 2:A network of lymphatics that has been outlined by the limbal pigment which is outside the transparent vessels. The finer close to limbus channels run perpendicularly. Proximally they join each other and the wider circular channels
Fig.3:An extensive network of lymphatic channels at and around the limbus, reaching towards the fornix.
Fig.4: Rivulets of lymphatics beautifully outlined by the pigment around the limbus. The blood vessels show paling of color, where they are crossed anteriorly by the lymphatics.
Observation of trauma cases:
One frequently finds the presence of blood in the lymphatics as a result of trauma, including a surgical one. The pattern of blood filled lymphatics is at variance to the pattern of arteries and veins that we know too well.
Fig.5 : A surgical injury to a blood vessel at 3 O’ clock starting filling up the lymphatics. In less than a minute, a huge network of lymphatics had been highlighted.
Demonstration of lymphatics in the operation theater:
In the operation theater setting, the lymphatics can be demonstrated, by injecting vital dye trypan blue in the periphery of the cornea. The dye soon spreads to fill up the lymphatic network. The network is extensive in every case. However the extent of the network that can be demonstrated varies from case to case. The radial lymphatic vessels close to the limbus are thinner than the network of circular vessels proximally. One or more channels arise from this system that disappear towards the fornices
In failed glaucoma surgery cases, we have found that the scarred areas do not show up the lymphatics. Whatever kind of surgery has been performed on the globe, be it strabismus, glaucoma or retina surgery, the lymphatics shall get damaged in the area of cutting and bipolar cautery. This is one good reason why the tissues should be handled to the minimum in all kinds of operations. Glaucoma surgery is doomed, if attempts are made to produce a drainage track in a non-virgin (previously handled) area
Fig.6: A network of lymphatic channels has become visible after the injection of trypan blue in the periphery of the cornea.
Relationship between the uveoscleral outflow and the conjunctival lymphatics
The literature is replete with information on uveo-scleral outflow. But it does not mention how and where this out coming fluid is disposed off. In one of our studies with trypan blue in a patient who had extensive scarring around the limbus, we found a startling connection between the sclera and subconjunctiva. The dye was injected in the sclera close to the limbus.It traveled inside the sclera and appeared at multiple points around the limbus as blue blots and knots, showing that the dye had traveled in some kind of channels inside the sclera. It also indicated that further connections of these blots were missing. However, when we looked at the conjunctiva proximal to the damaged area, it was found that the conjunctival lymphatics had received the blue dye. Later, we demonstrated this phenomenon in two more cases. How did an injection in the sclera fill the conjunctival lymphatics at such a distance? The only rational answer is that there is a three dimentional network that connects scleral lymphatics to the conjunctival network. It raises another question. How does the uveo-scleral outlow take place? This sclero-conjunctival connection suggests that it may not be a mere diffusion, but actual transport through normal existing channels. Thus uveo-scleral-conjunctical outflow may be as much a secure closed channel transport system, as the Schlemm canal-aqueous vein is.
To sum up:
All evidence collected from the slit lamp examinations and the vital dye injection studies indicates that an important three dimentional lymphatic channel system exists under the conjunctiva. It is connected to a similar scleral channel system (call it lymphatics or any other name). This lymphatic system is responsible for the drainage of the normal out coming aqueous. It can cope with the excessive fluid that drains after glaucoma filtration operations. Obstruction to free flow through lymphatics results in the formation of blebs. Damage to the lymphatic system acts as a trigger to subconjunctival fibrosis, which may become excessive and thereby jeopardize a successful outcome of a filtering operation. It is felt that the glaucoma patients can be handled better, if the role of the lymphatics in the drainage of the aqueous is taken in to consideration, in the designing of the surgical techniques.
References:
- Kent C. Revealed: the Eye’s Lymphatic System. Ophthalmic Manage. 2002; 6, 5: 114.
- Bethke WC. A New Clue to Lymphatic Drainage? Review of Ophthalmology. 2002; 9, 3: 12
- Singh D. Letters: Conjunctival Lymphatic System. J Cataract Refract Surg. 2003; 29, 4; 632-3.
- Singh D, Singh RSJ, Singh K, Singh SK, Singh IR, Singh R, Fugo RJ. The Conjunctival Lymphatic System. Ann Ophthalmol. 2003;35, 2;99-104.TORIS ET AL: Amer.j.Ophtha12 (April 1999)
