|Year : 1982 | Volume
| Issue : 5 | Page : 479-483
Significance of alymphatic orbit
A.M.U. Institute of Ophthalmology, J.N. Medical college, Aligarh, India
A.M.U. Institute of Ophthalmology, J.N. Medical College, Aligarh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Nath K. Significance of alymphatic orbit. Indian J Ophthalmol 1982;30:479-83
Sometimes we take into consideratior things which are apparent and visible anc tend to ignore those which are out of sight. Yet frequently they may hold the key to some problems. Orbital diseases are multidisciplinary disorders and some of them appear to have their etiology linked with the absence of lymphatics in the orbit. This closed space has the following peculiaries:
(I) It is a privileged space where there are no lymphatics,
(2) It is a closed box where intra-orbital pressure can be generated even to bursting point.
(3) The main extraocular tissues are muscles and fat.
(4) The extra ocular muscles have the finest voluntary muscle fibres with excessive interstitial tissue, and work all the time during working hours and their efficiency is at the top while reading.
(5) Outside the eye the main blood supply goes to the muscles or leaves the orbital space.
(6) As there are no lymphatics, the nourishment of extraocular muscle has to be carried out in a very special manner i.e. without the formation of the lymph and by the protein free plasma filterate from the blood vessels. Can they may be like the tela choridea of the ventricular ependyma producing cerebrospinal like fluid on a very small scale, the capillaries of which are double walled. Th° other possible arrangement could be a close similarity to the mechanism of ciliary bodies producing aqueous for lens and cornea or choroid producing nourishment for the retina.
This leaves us with the question of similarities between the muscular and retinal nourishment. Apparently there are hardly any. If a modified protein free filterate like aqueous can look after the cornea, and a similar fluid from choroid can look after the outer retina, then why can't it look after the extraocular muscles. Perhaps structures like retina, extraocular muscles and brain need such systems for their efficiency and where quick removal of waste products is a necessity.
These peculiarities seem to have a direct bearing on the following diseases :
1. Orbital infamations
(a) Avirulent type-dealt with by phagocytes easily.
(b) Highly virulent type-cellutitis and panophthalmitis (like acute meningitis).
(c) Moderately virulent type-chronic in flammation leading to lymphoid pseudotumors.
2. Endocrinal manifestations
(a) Ophthalmic Grave's disease.
(b) Malignant exophthalmos.
(a) Benign solitary lymphomas.
In the present submission, the aetiopathogenesis of orbital inflammations, pseudotumors, Grave's disease and malignant exophthalmos are discussed.
Pathogenesis of pseudotumors
The pseudotumors of the orbit do not appear to be any thing except unusually delayed antigen antibody reactions occurring under very special circumstances in the absence of lymphatics. The subject is under investigations and we have some positive evidence in this regard.
In the absence of lymphatics, a bacterial antigen can be divided into highly virulent, avirulentt or moderately virulent types. If a highly virulent bacterial antigen is implanted in the orbit, it soon gives rise to orbital cellulitis, and abscess formation while the defence mechanism of the host is minimum in the absence of any treatment. Some leucocytes will slowly and definitely reach by chance or after vasodilatation and find themselves no match to the antigen before any reasonable defence is built up. The contrast between a slowly progressive extraorbital abscess and fulminant acute orbital inflammation is amply evident.
If the antigen is avirulent, the chance wandering survellient phagocytes along with those which reach as a result of local vascular dilatation would engulf them and the complex would be slowly and gradually resolved without leaving significant scarring or traces.
In the third type where the bacterial antigen is only moderately virulent, the fulminating acute reaction is impossible, the chance wandering lymphocytes stay around the lesion and continue their fight. They can only reach there through local capillary circulation in fat and muscles by diapedesis. In the absence of lymphatics the lymphokines are unable to reach the circulation so that the lymphoid system is unable to respond or it responds in a slow and delayed fashion. Chance lymphocytes, while carrying on their routine survellience would drift towards the site of the lesion but are insufficient to deal with the situation. Since the tissue fluid in the area is not going through any of the lymphatics to lymphnodes directly, the cellular and humoral responses are so inadequate that they are unable to deal with the lesion. Here a strange balance is struck and a fight between organisms and the defence mechanisms of the host goes on for years resulting into a pseudotumor or a chronic granuloma.
Exophthalmos in Grace's Disease
Many hypotheses have been put forward regarding the aetiopathogenesis of Ophthalmic Grave's disease but none is entirely satisfactory. [Table - 1]. The pathogenesis has been considered from various angles but never from the physioanotomical aspect. The fundamental fact of the absence of lymphatics has always been overlooked in its aetiopathogenesis.
Essentially, the aetiopathogenesis of Grave's disease should be in common with the excessive production of thyroxine and its action on extraocular muscles like other muscles of the body. Finally it is related to the generation of bursting intraorbital tension due to absence of lymphatics.
Thyroxine increases the metabolism of all skeletal muscles. There is increased break down of certain muscle proteins into creative and then into creatinine. Thyroxine prevents further break down of creatine into creatinine with the result that creatine level in serum increases. These and other breakdown products are swept away both by the lymphatics and blood vessels. In the orbit, the lymphatics are absent. Therefore a part of creatine and phospholipids etc. are retained in the muscles themselves, They naturally exercise their osmotic pressure and the muscle becomes progressively oedematous. The retention of these products of muscle breakdown and increased basal metabolic rate (B.M.R.), cause irritation at places leading to lymphocytic infiltration and fatty degeneration of the interstitial tissue. Some muscle fibres get strangled and necrosed due to lack of nutrition and finally get fibrosed. The pathogenesis of ocular myesthenia gravis must be somewhat similar.
Thyroxine also acts on involuntary muscles like the myocardium where it produces palpitation and tachycardia. Similarly it acts on the smooth muscles of intestines where it causes diarrhoea, while in hypothyroidism, the patient suffers from constipation. This further adds weight to our argument that thyroxine should also stimulate Muller's muscle leading to its sustained contraction and to subsequent oedema and fibrosis.
That this vestigeal Muller's muscle exists is amply proved, by the effect of superior cervical ganglionectomy and existence of Horner's and claud Bernard syndromes. The argument should not be about the existences of Muller's muscle and lid retraction but how the occurrence of lid retraction becomes a permanent feature.
The answer lies in scattered facts. Thyroxine acts on Mullei s muscles like its action on myocardial and intestinal muscles. Whether it is due to adrenal sensitisation to thyroxine or through synapses is a moot point. Chronic sustained contraction of Muller's muscle doesoccur. If any muscle is under perpetual sustained contraction, its ketobolic products are produced in excess of what the blood circulation can cope with. This results in their accumulation in the muscle itself giving rise to its slowly progressive perpetual oedema. Sooner or later, muscle fibres undergo, cloudy 'swelling, necrosis and consequently fibrosis. After fibrosis, we do not except the restoration of their normal functions and we get a permanent lid retraction.
So this explains the occasional reversal of lid retraction in ophthalmic Grave's disease which is reversible if it is treated early,
A more or less similar phenomenon occurs in other extraocular muscles in which the break-down products of increased metabolism are retained in the muscle itself due to the absence of lymphatics and capillary dilatation. The removal of these colloids and lipids is extremely slow as only blool vessels are available to the extravasted lymph like fluid and break-down products. This results in their oedema, cloudy swelling and variable fibrosis.
This oedema of extraocular muscles is responsible for various eye signs in ophthalmic Grave's disease. The lids themselves are a little oedematous (puffy swelling) as well. We get lid lag, globe lag, difficulty in convergence, and tremors on abduction etc. They are all natural when the extra ocular muscles are oedematous and bulky.
During evolution the extra ocular muscles have become slender, finely textured and light weighted. They have also given up the normal circulatory mechanism wherein there is no lymphatic drainage. All this has been done in the interest of highest type of efficiency they have acquired. The price' paid is collection of lymph in adverse circumstances which affects their finest delicate functions.
Pathogenesis of Thyrotropic Exophthalmos
We know that the mean hydrostatic pressure of arota is about 100 mg. of Hg. while in ophthalmic artery the same is around 80 mm of Hg, because of the narrowing
of the internal carotid artery soon after giving its ophthalmic branch. The pressure in ophthalmic artery and veins has to be above the intraocular pressure so that the intraocular circulation can be sustain _d. There is a sudden drop in the venous pressure when the episcleral veins leave the eyeball. It is of the order of 10 mm Hg. These veins finally empty into orbital veins which must have a pressure lower than 10 mm of mercury. In fact it is less than 8 mm of Hg. which is also the osmotic pressure of interstitial fluids.
In Grave's disease, as the disease progresses the patient gets oedema of the extraocular muscle with lymph.ocytic and fatty infiltration, The ketabolic products of the muscles accumulate in the closed space of orbit. Certain amount of readjustment, to accommo .sub date these oedematous tissues, is possible. Either the disease is treated or it regresses leaving behind a certain amount of fatty infiltration, lymphocytic infiltration and fibrosis. But in some cases the intraorbital pressure may rise so that even after readjustment of tissues the intr-orbital pressure rises to 5 or more mm of Hg, causing thereby gradual progressive embarrassment of the venous drainage from the orbit. All exit veins can be embarrassed while arteries tend to continue prouring blood.
This would gradually cause progressive, oedema of lids, fat and muscles and chemosis and papilloedema. Ultimately all the tissues in the orbit get necrosed and fibrosed and finally start shrinking when a certrin amount of circulation may be restored. Thus, we get the end of malignant phase of self limiting thyrotropic exophthalmos which usally lasts for 3 to 6 months.
The initial cause therefore lies in blocking of the degradation of creatine inte creatinine by thyroxine and accumulation of ketabolic products which are retained due to absence of lymphatics in the orbit.
Whether the patient will get the malignant type of exophthalmos or not, will depend on whether the intra-orbital pressure will rise above 5-8 mm of Hg. or not, under various circumstances of hyper-hypo-or euthyroidism. When it does, malignant disease would take its course.
Whether it is uni-or bilateral will again depend on this pressure gradient as and when it occurs.
Management of Endocrine Exophthalmos
From the treatment point of view we have to reorientate our treatment in this disease and it would be on the following lines.
(a) Nursing in semierect posture (gravity)
(b) Salt free diet
(c) High protein diet
(d) Cold compresses- Locally to reduce exudation
(b) High molecular I.V. fluids
(c) Early and repeated decompression of extra ocular muscles (musculoconjunctival)
1. Anticoagulants-to prevent coagulation of lymph in the orbit.
(a) Fibrinolysin injections
(b) Varidase linguets
2. Guanithidine drops (1-5%) to prevent permanent lid retraction.
3. Propranolol for checking various symptoms of hyperthyroidism.
4. Oral steroids
| Summary|| |
Various anantomical pecularities of the orbit are summarized with special emphasis on the role of absence of lymphatics in the orbit in the estiopathogenesis of various orbital lesions. This concept has so far not been appreciated by the ophthalmologists and offers a challenging field to immunopathologists for further investigations of certain confusing orbital lesions.
[Table - 1]