movement occurs by a process of diffusion across the endothelium. We shall discuss if

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1 Corneal channels Daljit Singh For the cornea to maintain its hydration, transparency and metabolism, it should have a fluid movement throughout the stroma. We have learnt from the text books that the fluid movement occurs by a process of diffusion across the endothelium. We shall discuss if there is any movement in the form of channels? The cornea is transparent for all practical purposes. That makes it difficult to visualize the transparent channels inside the cornea if any. We have been interested in the conjunctival lymphatics for many years. Conjunctival lymphatics could be demonstrated by injecting trypan blue dye in the peripheral cornea, rather than subconconjunctival injection brought out the lymphatics better We also tried to chart lymphatics in the cornea in painful blind eyes undergoing glaucoma surgery.the dye was injected in the mid-peripheral corneal stroma. It created a small ball of the dye, at the edges of which there were small projections towards the center and the periphery. Slit lamp examination of the injected cornea showed a diffuse presence of the dye only.over the next few days, the dye appeared to become faint. It showed no definite movement towards the center, but disappeared completely in a few days, obviously towards the periphery, in to the limbal lymphatics.

Once, studying the pictures of dye injected conjunctival lymphatics, I found that it had also created a thin circular line in the periphery of the cornea. Obviously it was not in Canal of Schlemm.

2 Once, studying the pictures of dye injected conjunctival lymphatics, I found that it had also created a thin circular line in the periphery of the cornea. Obviously it was not in Canal of Schlemm. Fig.1: The dye that was injected in the peripheral cornea, not only demonstrated the conjunctival lymphatics, but also a blue colored arc in the corneal periphery Later, in an eye undergoing enucleation, the dye was injected with great force in the cornea some distance from the limbus. It happened to produce a ring like appearance along the limbus, indicating the presence of a space that could hold the dye.

3 Fig.2: Trypan blue injected in the cornea has assumed a circular form inside the limbus.

4 Any kind of invisible corneal channels if present in the cornea, are expected to be transparent and fashioned on the lines of sinusoids, rather than definitive vessels likes arteries and veins. But suppose there is a corneal pathology that renders the corneal tissue translucent or semi-opaque, it could make the channels visible. This is just like the transparent limbal lymphatics that get visualized by the presence of slight pigment around them. This possibility occured to me when I first saw a 10 years patient of keratoglobus who had an opacity in the center of the cornea. There were prominent network like darkish lines that divided the large nebular corneal opacity in to many geometrical compartments. The lines became fainter and then disappeared towards transparent peripheral cornea. They did not seem to be some kind of pathology, but were visible due to the tissue changes around them. They had a nearly uniform size. On optical section they were seen to be in the stroma. The endothelial side was normal. We have been watching this patient for over 9 years. His corneal condition has remained the same.

5 Fig 3: ECCE and iris claw lens implantation was done in this case of megalocornea strange corneal opacities, 9 years before. The patient was then 10 years old.

6 ! Fig 4:The first picture was kept as a curiosity of congenital corneal condition co-existing with megalocornea. Nine years later, it became an important document. The appearance of the channels remains essentially the same.

7 Fig.5: Optical section of the cornea of the same megalocornea case as above at the age of 19 years. Clearly there are channels that have a three dimensional existence.

8 A case of postoperative striate keratitis throws light on the existence of the corneal channels. There is seen edema of the cornea and some sort of channel network. Optical section shows that the channels are in the corneal stroma. The appearance is not due to changes in the Descemet membrane. How does so much postoperative keratitis/edema disappear in a matter of hours or a couple of days? It probability happens because the channels in the cornea act like flood drains, as they do elsewhere in the body.

9 ! Fig.6: A case of severe striate keratitis showing island formation due to the showing up of a network of corneal channels. The optical section shows that they are located everywhere in the corneal stroma.

10 Soon we learnt that the best place to study corneal channels is the area in and around the arcus senilis. The semi-opacification of all grades is there to highlight the channels. The pattern of the channels is practically the same as in the case of keratoglobus shown above. The channels go right up to the lucid interval of arcus senilis. Many of the network channels end in to the lucid interval. The lucid interval in the arcus senilis is lucid because it seems to have more sinusoidal channels than elsewhere. An optical section of a lucid interval shall show a roughly triangular appearance, the base being towards the periphery with semi-opaque plates of the corneal tissue on both sides.

12 Figs 7a and b: A 82 years old patient showing a profusion of large and small network channels. Optical section shows that the wider channels are situated in the deeper layers and they have connections anteriorly. It is inconceivable that there should exist channels that drain no where. Thus the corneal channels can sometimes be seen to very clearly connected to the peripheral corneal channel, at regular intervals. Around 3 dozen such connections can be easily seen.

13 Fig.8: Network of corneal channels. Notice a periodic merging of the channels in to the channel of the lucid interval. The lucid interval channel also has to drain somewhere. For this we have a profusion of limbal lymphatics.

Fig.9. Optical section through the corneal periphery.the arcus senilis shows a prominent lucid interval.fine channels in the arcus and lymphatics at the edge of the lucid interval are also visible.

14 Fig.9. Optical section through the corneal periphery.the arcus senilis shows a prominent lucid interval.fine channels in the arcus and lymphatics at the edge of the lucid interval are also visible. Are there finer channels still, which escaped notice thus far? Probably. If we examine cases of non-descript keratitis under high magnification. We see very fine feathery appearances. If these are the finest ramifications of the corneal sinusoidal channels, they could establish most intimate contact with every element of the corneal tissue.

15 Fig.10 The finest chinks in the corneal structure get visible in a variety of stromal conditions.

16 Where and how does the fluid go out of the cornea? There is a myriad of lymphatic channels sitting on the limbus. Their corneal ends disappear in to the corneal periphery and their proximal ends merge in to the conjunctival lymphatics. It is not far fetched to say that there is a continuity between the corneal sinusoidal system and the limbal and conjunctival lymphatics. One can liken whole of the eyeball as a sponge, the porosity of the channels varying from one tissue to the other. We have been trained to study the tissues on histopathology. When we do not find a structure, it is supposed not to exist. The corneal channels can be studied at present only in vivo under a slit lamp microscope.

17 Fig.10: Showing numerous lymphatics over the arcus senilis and at the edge of the lucid interval.

18 Fig.11:A picture of the limbus showing intimate relationship between the limbal lymphatics,and channels in lucid interval and arcus senilis Relationship to the intraocular aqueous:

19 When such a dense network exists close to the limbus right on top of canal of Schlemm, it is inconceivable that that connections do not exist between them. Uptil now we do not have a photographic proof of interconnecting channels. But we have a clinical situation that points to the existence of that connection as follows. The cornea becomes edematous in cases of acute glaucoma. The moment the pressure is released by paracentesis, the cornea clears up within seconds. This miraculous change in water logging could not occur without the assumed channels and their connections to the source of raised intraocular pressure. Why is it that many advanced cases of open angle glaucoma, with intraocular pressure as high as 50 or more do not show corneal edema. It is possible that the channels system has been adapting and increasing the flow along the channels, so that the cornea remains transparent, while the optic disc is getting damaged all the while. Another point : What is the function of limbal capillaries? Don t they function the way they function in the rest of the body? We should consider a regular formation of lymph all round the cornea that nourishes the cornea through a network of channels, that we are considering. This line of thinking makes the fluid movement a dynamic activity, making the cornea a living and throbbing entity, rather than a piece of transparent tissue. A clinical proof of a peripheral channel:

20 Over 6 years ago, a 25 years old patient showed an unusual infection, in that the hypopeon level was not horizontal, but oblique. The infection appeared to extend to the level, where a star has been marked. I felt very uneasy about this patient. He was put on maximum local and oral medical both for fungal and bacterial infections. The patient was recalled after 24 hours. It was found that the infection had extended further along a predetermined path, i.e. along the peripheral corneal channel. This was my first clinical encounter with the pathology in the area of the lucid interval. I had to go abroad for a meeting. I referred the patient to PGI Chandigarh as an emergency, giving my impressions of the nature of the infection. The patient never came back to me, so I am not sure where he got further treatment and what was the final result.

21 Fig.12: A strange obliquely placed collection of exudates in the corneal periphery. The central side has a sharp edge. The opacity shows less opacification towards the center. Small satellite opacities are seen towards 3 O clock. The end of the process is marked with a star.

22 Fig.13: Within 24 hours, the picture has worsened dramatically. The hypopeon has a duplicated form towards 3 O clock.

Fig.14:If we look carefully, the infection has reached to almost 12 O clock in 24 hours time. Considering the speed at which the infection was spreading, I doubt if this eye got saved.

23 Fig.14:If we look carefully, the infection has reached to almost 12 O clock in 24 hours time. Considering the speed at which the infection was spreading, I doubt if this eye got saved. No antibiotic could inside a space, in which the fluid was not showing any movement. Its natural course would have been a ring abscess leading to ring ulcer and its extension towards the center and sloughing of the cornea. Recent experience with similar cases: Forewarned with this kind of infection, it has been possible to save a couple of eyes, by treating the patients in ways different than before. One example is given below.

24 A 40 years old female came with the complaints of pain and redness in the eye of 4 days duration. She had not taken any treatment before.there was no corneal ulcer, but a definite streak of infection could be seen in the peripheral corneal channel. The exudates were broken in between, but a connection between them was there for sure. Going by the previous experience of a failed treatment, a more form of treatment was planned.conjunctival smear no kind of infection. It is possible that the source of infection was systemic, or the corneal route had closed. The lucid interval channel was injected at 12 O clock towards 3 O clock with 1 % voriconazole once.the lower infected crescent was opened with a hockey stick knife and the material removed was tested.it showed fungus. An intensive treatment with local voriconzole and supportive antibiotic drops was started, along with oral itraconazole 150 mg twice a day. The condition was considered as healed after a treatment of 30 days. Her visual acuity was saved at 6/6.

25 !

26 Fig.15: The infected peripheral corneal circular space, on the day of presentation. The infection has spread widely. Notice that the eye does not show much congestion.

27 Fig 16:The lower part of the peripheral corneal space has been opened and subconjunctival voriconazole and moxifloxacin given. The eye apparently appears in worst shape that before.

28 !

29 Fig.17: The condition of the eye 15 days from the start of the treatment.

30 Fig.18: The eye at the end of one month treatment. It is possible that had we not opened the infected peripheral corneal channel, this eye would have been lost from ring abscess and ulcer leading to rapid sloughing of the cornea.in such cases the central corneal sloughing occurs, since it loses all fluid moving and circulating connections with the limbus. To sum up:

31 The concept of corneal channels, dynamically connected to the anterior chamber through corneal endothelium on one side and connected to general circulation through peripheral circular corneal channel ( call it Singh channel) and limbal and conjunctival channels is based on solid photographically recorded observations. One should not lose sight of them when faced with any kind of corneal pathology. References: Singh, D., et al. The Conjunctival Lymphatic System. Annals of Ophthalmology. 2003;35, 2;

Relationship between limbal incisions. angle. and the structures of the anterior chamber

Brit. _7. Ophthal. (I 973) 57, 722 Relationship between limbal incisions and the structures of the anterior chamber angle MOHAMED I. AYOUB AND AHMED H. SAID Department of Ophthalmology, Faculty of Medicine,