|Year : 1955 | Volume
| Issue : 2 | Page : 29-33
The fourth chamber of the eye
KN Mathur, SP Mathur
Department of Ophthalmology, S. N. Medical College, Agra, India
K N Mathur
Department of Ophthalmology, S. N. Medical College, Agra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Mathur K N, Mathur S P. The fourth chamber of the eye. Indian J Ophthalmol 1955;3:29-33
What we see through an ophthalmoscope as a physiological cup in, the centre of the optic nerve head is not a simple empty cup which is filled by protrusion of vitreous, but is a definite space bounded anteriorly by a membrane and posteriorly by the nerve fibres and the lamina cribrosa. It contains a small amount of fluid which is drained through it.
We have arrived at this conclusion as a result of our experiments performed on the animal and human eyes.
| Materials and Methods|| |
From human cadavers we enucleated the eyes with a stump of optic nerve, about 3 cm. long attached to it. A fine needle was introduced at the cut end upto 1 cm. and secured by a thread tied all round the optic nerve over it. About 0.5 c.c. of Indian ink or Prussian blue was injected with a syringe under moderate pressure. The eye was sectioned after freezing. It was observed that the ink collected over the optic nerve head [Figure - 1],[Figure - 2], passed along the retinal blood vessels, and in the hyaloid canal upto the back of the lens. This appearance was more marked in fresh eyes enucleated due to painful absolute glaucoma.
Goats' eyes which also gave a similar appearance showed under microscope that the injected material was present in the interfascicular spaces in the optic nerve, was present over the optic nerve head, and in the perivascular spaces of the retinal artery [Figure - 3]. None of the particles of the injected material could be seen inside the vessel lumen.
| Anatomy of the Fourth Chamber|| |
It may be described as follows,:
It is a funnel-shaped space situated in front of the optic nerve head bounded by the vitreous anteriorly and by the lamina cribrosa posteriorly [Figure - 4],[Figure - 5].
BOUNDARIES:-The anterior wall or the mouth of the funnel is formed by the posterior hyaloid membrane, which is firmly adherent to the nerve fibre layer of the retina at the periphery of the optic nerve head, and thus limits the mouth of the chamber.
The posterior limit of the chamber goes as far back as the lamina cribrosa where the central retinal vessels pierce through it.
The posterior wall is formed by the nerve fibres of the retina as they converge here to pass out into the optic nerve.
SIZE OF THE CHAMBER: -The mouth or the widest portion of the chamber lies facing the vitreous. It is circular measuring about 1.5 mm. in diameter. The visible size of the chamber depends on the shelving and the arrangement of the optic nerve fibres as they converge, in this area to pass out. Normally only a small central portion may be open keeping the rest of the chamber as a potential space.
CONNECTIONS : -
Afferent channels:-(a) Perivascular channels. (b) Hyaloid canal. [Figure - 4],[Figure - 5].
(a) (i) The perivascular channel which runs along the superior retinal vessels, opens at the superior border of this chamber.
(ii) The perivascular channel which runs along the inferior retinal vessels opens at the inferior border.
As stated by Evans these spaces, are responsible for the lymphatic drainage of the retina. They lie between the vascular wall and its glial sheath, go along the vessels upto their finest peripheral branches. The fluid that escapes from the capillaries into the tissue spaces of retina collects round the nerve synapse and nerve fibres in spaces known as perineural spaces. They, in turn, open into the bigger perivascular spaces. The latter discharge their contents in this fourth chamber.
(b) The hyaloid canal which enters the chamber by piercing its mouth, and thus connecting it with the remnants of the retrolental vascular tunic.
Efferent channels:-(a) The contents of this chamber are lymphatic in character. The retinal tissue fluid enters the chamber through the perivascular system. This is drained to the back of the eye along the central retinal vessels into the optic nerve.
(b) According to the anatomy described, the central retinal vessels are also included in the contents of the chamber when they come to lie in the physiological cup.
DEVELOPMENT : -At the 100 mm. stage of human embryo (4 months) we find that a small bulbous swelling appears on the trunk of the hyaloid artery just where it is passing through the disc. Two buds from this form the upper and lower retinal arteries. The bulb-shaped swelling on the hyaloid artery marks the point upto which the main trunk of the hyaloid will eventually atrophy. Before this happens glial cells of Bergmeister's papilla proliferate and grow out into vitreous along the artery. They form a sheath in the form of a cylindrical tube the walls of which are not in intimate contact with that of the artery. This tube is known as the glial sheath which is ectodermal in origin.
During the 7th month the hyaloid artery begins to atrophy, extending in most cases, even below the surfaces of the disc, so that finally a slight excavation, the physiological pit, is produced at the site of the former prominence.
It is, therefore, evident that the hyaloid artery may undergo complete atrophy but the space occupied at the optic nerve head remains as a definite space bounded by the glial tissue. This space we have called as the fourth chamber of the eye.
COMMENTS:-The chamber has not been described only for the sake of description. The fact that it is a definite space bounded on all the sides to make it a chamber has been proved by the experiments described. In the absence of this space, the injected material, should have taken a haphazard distribution along the retinal layers, and into the vitreous. A definite pattern marked out by Indian ink or Prussian-blue showing filling of this chamber and taking a definite course along the retinal blood vessels and the hyaloid canal, goes strongly in favour of the presence of this chamber and its anterior connections.
The ability to fill the fourth chamber by injecting a dye under moderate pressure through a needle introduced into the cut end of the optic nerve, suggests that the fourth chamber drains posteriorly into the perineural and perivascular spaces of the optic nerve which are freely communicating with one another.
The importance of this chamber is that it offers a very tempting explanation for the formation of an optic cup particularly in chronic simple glaucoma where the intra-ocular tension remains at the high-normal level. It may play an important part in the various considerations of glaucoma.
We are indebted to Dr. D. S. Chawdhary, M.S., D.O.M.S., Ph.D. (Edin), Reader in Anatomy, S. N. Medical College, Agra, for the help and personal interest he, took during these investigations.
| Discussion|| |
Dr. Tulsidas (Amritsar):-I have always asked myself the question why should papillcedema be confined to the optic nerve head if it is due to the effect of pressure on the central retinal vein as it courses through the subarachenoid space. In that case the effect should be felt first and most at the terminal capillaries, and that is at the periphery of the retina and not at the nerve head. Can the presence of a chamber in front of the disc communicating with the perivascular spaces within the nerve offer an explanation. It would be interesting to observe the behaviour of the chamber under conditions that stimulate increased intracranial tension and glaucoma.
Dr. Harvery Thorpe (Pittsburg):-Much more information and many more repetitions of the experiment are required before these observations can be taken as correct. There is some degree of posterior drainage along the perivascular spaces, but the presence of a potential chamber in front of the disc capable of playing some part in pathological conditions like glaucoma and others requires clinical, experimental, physiological and histological evidence.
Dr. Talwalkar (Bombay):-If there is such a chamber, can it not be seen and studied with the modern methods of examination with a slit-lamp and biomicroscopy ?
Dr. K. N. Mathur :- I am very thankful to Dr. Tulsi Das for the encouragement he has given by his suggestions for the continuation of this study. Clinical and experimental proofs of this nature will further enhance the importance of this study. I agree with Dr. Thorpe and Dr. Talwalkar that further studies should be made on the lines they have suggested. At the moment I cannot say that an explanation can be offered for the confinement of papilloedema to the optic nerve head, on the theory of the presence of a fourth chamber. However, I feel that it is possible that some of the features of glaucoma can be more satisfactorily explained.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]