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ARTICLE
Year : 1966  |  Volume : 14  |  Issue : 2  |  Page : 55-74

Srinivasan oration- a study of optic atrophy


Grant Medical College and Sir Cowasji Jehangir Ophthalmic Hospital, Bombay, India

Date of Web Publication12-Jan-2008

Correspondence Address:
H D Dastoor
Grant Medical College and Sir Cowasji Jehangir Ophthalmic Hospital, Bombay
India
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Source of Support: None, Conflict of Interest: None


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How to cite this article:
Dastoor H D. Srinivasan oration- a study of optic atrophy. Indian J Ophthalmol 1966;14:55-74

How to cite this URL:
Dastoor H D. Srinivasan oration- a study of optic atrophy. Indian J Ophthalmol [serial online] 1966 [cited 2020 Aug 4];14:55-74. Available from: http://www.ijo.in/text.asp?1966/14/2/55/38566

At the outset I am grateful to our Society in honouring me with the Sri­nivasan Award which I deeply appre­ciate to cherish the memory of my dear departed friend and colleague, late Dr. E. V. Srinivasan whose absence many of us feel on the days of our annual meetings. His one great desire in his later years was to establish this Award and after him and onwards, for the fulfillment of which I was instrumental, little realising then that the same would be awarded to me this day.

The subject of Optic Atrophy that 1 have chosen is the one that afflicts a high proportion in the world of the blind whose teeming millions we have amongst us where therapy is almost helpless in the majority of this condi­tion. Though the therapy is limited, the only effective cure is to treat the causative factor giving rise to the atrophy. From this point of view the present study is based on the varied etiological factors giving rise to optic atrophies as reviewed from a large number of our cases as well as from references to standard books and lite­rature on this subject.

To understand some of the import­ant aspects pertaining to the disease it is necessary to consider the anatomi­cal, physiological and histopathological aspects for the treatise.


  Anatomical and Physiological Considerations of the Optic Nerve Top


The reactions of the optic nerve to injury and disease differ in many res­pects from other sensory nerves owing to its peculiar anatomical and physio­logical features. The optic nerve is part of the second neurone in the vi­sual pathway which consists of gang­lion cells, the retinal nerve fibers, the optic nerve, chiasma and the optic tract upto the geniculate body. It con­sists of a trunk of about a million axons arising from the ganglion cells of the retina. It is not like a peripheral nerve but a link in the chain of fibers which run from the rods and cones to the occipital cortex. The nerve fibers are really a part of a tract of the central nervous system, since the retina has developed from the optic vesicle, which is an outpouching of the original neural tube. The optic nerve fibers are com­posed of the usual axon and a myelin sheath, but entirely lack a neurilem­mal sheath. Instead of being separated from one another by neurilemma as are other sensory nerves, neuroglial cells are scattered between them and sepa­rate them. In this respect the optic nerve fibers again resemble the fiber tracts of the brain and spinal cord, which too are myelinated but are de­void of any neurilemmal sheaths.

Myelination of the optic nerve fibers begins very late, and it is not until about the seventh month of fetal life that this has progressed down the nerve as far as the lamina cribrosa. The deposit of myelin usually stops at this point, but occasionally it extends beyond the lamina, and the nerve fibers in the retina then appear as semio­paque white sheets, in one or more quadrants adjacent to the optic disc. This constitutes the condition of re­tained medullated nerve sheaths.

It is to be expected that the anatomic optic nerve, which is actually a tract in the path of conduction, should suffer from and react to injuries and diseases which commonly affect neurons of the second order of the central nervous system and not sensory nerves.

A further point of peculiarity of the optic nerve, as compared with other sensory nerves in the body, is the fact that it is surrounded by prolongations of the sheaths which encase the brain, i.e. the dura, pia and arachnoid. The presence of these layers, and the spaces between them and the nerve, account for many of the peculiarities in the pathologic reactions of the optic nerve. The sheaths surrounding the optic nerve are supplied with many sensory nerve fibers. This gives rise to pain in inflamatory conditions of the nerve and the orbit, such as occurs in retrobulbar neuritis in the acute stage. The fact that patients with choked disk suffer no pain, although the nerve head it­self is edematous and the fibers pressed upon, proves that the pain in retro­bulbar neuritis arises from the sheaths, and not from the nerve fibers them­selves. Since both the subarachnoid and the subdural spaces are in direct communication with those of the brain, these spaces are found to be distended with fluid in the presence of increased intracranial pressure.


  The Optic Nerve Top


The optic nerve which consists of axons from the ganglion cells of the retina extends to the optic chiasma and it is 40 to 50 mm. in length. These axons course towards the optic papilla in the nerve fiber layer of the retina. The nerve emerges from the eye through a short circular opening in the sclera situated 1 mm. below and 3 mm. nasal to the posterior pole of the eye (macula). The nerve fibers become myelinated upon leaving the eye and are supported by neuroglia, thus in­creasing the diameter from 1.5 mm. within the sclera to 3 mm. within the orbit. It is rounded in section while in the orbit and flattened within the cra­nium. It is anatomically divisible into four parts, intra-ocular (within the coats of the eyeball), intra-orbital, intra-osseous or canalicular and intra­cranial.

The relations of the optic nerve are very important from the clinical point of view.

The intraocular part of the optic nerve head merits a special description. As the nerve fibers converge from the retina they pile up at the margin of the disc to form the optic papilla,-a name given by Briggs in 1688. Since they pile up on the nasal side more than on the temporal, the prominence is more marked nasally. This gives rise to a central depression which is pushed temporally due to massing of nasal fibers.

The fibers which originate in the retina turn at a right-angle abruptly to traverse through the scleral canal (1 mm. in length) to form the nerve trunk.

The intraorbital part of the nerve measures about 25 mm. and proceeds backwards and medially in a sinuous manner to allow play of eye move­ments. Here it lies within the cone of recti muscles and is in close proximity of the superior and medial recti at the apex of the orbit, which is the cause of pain on moving the eyes up and in, in cases of optic neuritis. This part of the nerve is surrounded by the exten­sion of the meningeal coverings, and spaces. A supravaginal lymph space encircles the dura itself except at the optic foramen, where the dura is firmly anchored to the overlying bone. Fine pial septa hearing blood vessels and capillaries pass into the nerve sub­stance, dividing it into polygonal bundles.

Between the dural sheath and the muscle cone lies a variable mass of adipose tissue with many vessels, nerves and the ciliary ganglion em­bedded in the mass. [Figure - 1]

The opthalmic artery at first infero­lateral, crosses under the optic nerve along with the nasociliary nerve and superior ophthalmic vein to gain a position lateral to the nerve after it gives off the central retinal branch which runs along the under surface of the nerve and enters it a cm. behind the sclera. Its passage into the nerve is characterised by two right-angled bends between which the nerve tra­verses the subarachnoid space and it is at this spot that it is subjected to pres­sure in increased intracranial tension.

Case No. 1.

An accident of unusual and tragic nature I had the occasion to see with my colleague Dr. Cooper, which brings out the applied anatomy of this region [Figure - 2], was when a general surgeon tried to inject alcohol into the spheno-­palatine ganglion for spheno-palatine neurelgia. Immediately after the injec­tion there was complete loss of vision with total paralysis of all ocular move­ments, without any relief of the spheno-palatine neurelgia. Evidently, as can be seen from the figure, the needle must have slipped past the maxillary nerve and entered the orbit through the inferior orbital fissure.

The intra osseous or intra canalicular part lies in the optic foramen and is 5 to 9 mm. in length. The ophthal­mic artery lies inferolateral to it. The sphenoidal and posterior ethmoidal sinuses are separated from it medially by only a thin bony lamina. Thus sinus infection is quite prone to affect the nerve bringing about optic neuritis and subsequently optic atrophy, as was seen in two of my cases.

In the cranium (intra cranial) from the optic foraman to the chiasma it is about 10 mm. in length. The optic nerves lie above the cavernous sinus and converge over the diaphragma sellae that overlies the pituitary body to form the chiasma. Superior relations are the anterior perforated substance, the medial root of the olfactory tract and the anterior cerebral artery (which crosses from without inwards). Infero­laterally lies the internal carotid artery where it gives off its ophthalmic branch. It will he seen that the optic nerve here is surrounded all round by important structures. Any space oc­cupying lesion in this area, either a tumour of the pituitary or an aneurysm of the internal carotid, would press over the optic nerve and cause atrophy.

It may be noted that besides the visual fibers, the optic nerve carries afferent pupillary reflex fibers, retino­motor (from brain to retina) and pos­sibly also some inter-retinal and auto­nomic trophic fibers.

The arrangement of nerve fibers in the optic nerve and chiasma are too well-known to bear description here and can be seen in any text-book of ophthalmology.


  Blood Supply of the Optic Nerve and Chiasma Top


The optic nerve and chiasma are nourished by the pial felt-work of ca­pillaries and arterioles which reach down to the deeper layers in the inter­lacing septa as elsewhere in the central nervous system. This constitutes the peripheral system of vessels.

There is also an axial system of ves­sels running through the center of the nerve. Anterior to the entrance of the central retinal artery this function is taken up by the collaterals of the cen­tral artery which run forward towards the eyes, while the central retinal ar­tery itself reserves blood for the retina. As the visual fibers pass backwards the nourishment is provided first by the ophthalmic arteries, then at the chiasma by the anterior cerebral and internal carotids while adjacent bran­ches of the circle of Willis may also contribute.

Francois and Neetens (1955) drew special attention to the central optic nerve artery, distinct from the central retinal artery, both originating from the ophthalmic artery, entering the nerve independent of each other. This central optic nerve artery, after reaching the center of the nerve divides into an an­terior and posterior branch which con­stitutes the major axial supply system of the optic nerve.

Thus, in the optic nerve there are two distinct supply lines, (1) the cen­tral retinal artery serves the visual elements of the inner layers of the retina right upto the periphery, and (2) the central artery of the optic nerve which serves mainly the supporting structure in the optic nerve and the papilla and a mm. or so of the retina beyond the edge of the disc. A cilio­retinal artery from it may reach the macula in some cases and save macular vision in obstruction of the central retinal artery.

At the papilla a rich vascular net­work is formed by vessels derived from (a) the circle of Zinn, (b) pial vessels, (c) short posterior ciliary vessels, (d) anterior division of the central artery of the optic nerve. In this network the central retinal artery appears to contri­bute little blood if at all.

This concept of two independent supplies, one for the elements of the retina and the other for the papilla explains many points of pathological ambiguity. For example, if the effects of increased intracranial tension are due to pressure on the central retinal vein as it courses through the sub­arachmoid space, as is ordinarily sup­posed, why should the oedema and haemorrhages be confined to the disc area only in the initial stages and not to the whole retina as in thrombosis of the central retinal vein if this vein is pressed upon during its passage in the arachnoidal space? If we adopt the concept of two supply lines, if we con­sider the central vein of the optic nerve as independent smaller and at a lower pressure than the central retinal vein, the early inflammatory changes con­fined to the disc can be well under­stood.

Similarly, in primary type of optic atrophy, the central retinal blood­-vessels remain unaffected at least in the early part whereas the vessels on the disc get lost, probably because of secondary changes in the supporting elements of the papilla which is sup­plied by the central vessels of the optic nerve.

One can explain on similar lines a pallor of the disc with a normally functioning optic nerve and vice versa a pink disc in the presence of atrophied nerve fibres. In this connection let me quote two cases from my clinical diary.

Case No. 2.

Boy aged 17, studying in college suddenly developed progressive dim­ness of vision which dropped down to less than 6/60 in both eyes. Fundal examination revealed a typical second­ary optic atrophy which presented an alarming outlook. Clinical investiga­tions revealed focal sepsis in the throat. Under treatment with massive doses of antibiotics, the vision gradually im­proved within a period of two months with 6/6 and J 1 vision in each eye. Even with regaining of normal vision the fundal picture of optic disc remain­ed the same as before and even after a duration of almost 15 years it pre­sents the same picture as before with perfectly normal vision.

Case No. 3.

Patient (male) aged 75 with bi­lateral aphakia having normal vision with glasses for over 7 years since the operation developed gradual dimness of vision in both eyes to below 6/60. Fundal examination revealed a classi­cal picture of secondary optic atrophy. All clinical, neurological and patholo­gical investigations proved negative. With the help of the general physician and neurologist the treatment was given with Iodides, B. Complex Vita­mins and massive doses of antibiotics on emperical lines. There was gradual improvement of vision to 6/9 and J 2 in each eye but the optic atrophy pre­sented the same picture as before. The vision remained good for over a period of 5 years during which he had perio­dic checkups.


  Degeneration and Regeneration Top


The optic nerve fibers, like all other nerves in the body, will degenerate when their connections with the cell bodies which govern their nutrition have been severed. When it comes to regeneration, since the optic nerve fibers lack a neurilemmal sheath and resemble the white matter of the brain, their attempt at regeneration fails. Hence one cannot expect any recovery of function in cases in which the fibers have been severed, or in which the ganglion cells in the retina have been destroyed. Once the fiber has atro­phied, it can never recover. On the other hand, apparent cessation of function may not mean that the nerve has degenerated. Pressure on the nerve from tumors, either in the orbit or in­side the skull, may cause great func­tional embarrassment to the point of total loss of sight, yet when the pressure is removed, recovery may be rapid.

In the optic nerve, the medullary sheath and the axis cylinders may show degenerative changes, but in the ab­sence of the neurilemmal sheath the nerve fibers do not regenerate. Thus optic atrophy is characterized by dis­appearance of axis cylinders and the myelin sheaths and a resultant pro­found shrinkage of the optic nerve. There is always a slight orderly pro­liferation of the astrocytes and an in­crease in the collagenous tissue, con­tained in the pial septum. Such is the case with simple optic atrophy. [Figure - 4] a, b However, in secondary and post­neuritic optic atropy there are pro­nounced reactive alterations in the glial and mesenchymal tissues of the nerve head and hence the essential degenera­tive features may be obscured by the proliferation of astrocytes, fibrous con­nective tissue and blood vessels. [Figure - 4] c.

In animals, however, regeneration of some fibers can be seen after experi­mental sectioning of the nerve, indicat­ing presence of centrifugal fibers from the brain e.g. in the cat. In more pri­mitive animals e.g. the newt, a sec­tioned optic nerve regenerates com­pletely.

It is necessary to emphasise that all non-traumatic types of damage to the optic nerve are vascular in nature. De­privation of the blood-supply primarily depresses only the functioning of the nerve as demonstrated by depression of the visual field (contraction for smaller size test-objects). Such fields and lesions are capable of recovery if the vascular supply is restored. Only when this deprivation is continued over a considerable period that the function is totally lost as shown by contraction of the field for larger targets.


  Diagnosis of Optic Atrophy Top


A survey of the available literature of the diagnosis of optic atrophy brings forth the fimiliar triad of symptoms

(1) Pallor of the disc, (2) Reduced visual acuity, (3) Defects in the visual field.

The reduced vision and the defects in the visual field are dependant upon the stage of the disease as well as on the type of nerve fibers implicated and to the extent to which they have un­dergone atrophy.

In a case of diminished vision diag­nosis of optic atrophy depends on (a) pallor of the disc and (b) other changes in the fundus, which may or may not be present.

For reasons explained under blood-­supply of the optic nerve, pallor alone is not sufficient for the diagnosis of optic atrophy, but pallor associated with loss of vision and/or demonstra­ble changes in the visual fields is suffi­cient evidence for actual or potential optic atrophy.

The line separating an apparent pal­lor and an actual one is thin. Pallor of the disc not associated with optic atrophy may be found in myopia and in infants. The disc is normally paler in advancing years than in youth be­cause of the gradual narrowing of the blood vessels as age advances. Again, patients who have suffered from ence­phalomyelitis or disseminated sclerosis and who have temporarily had a reduc­tion in visual acuity may exhibit discs which appear pale in their entirety or only in the temporal one third, but the visual acuity as well as the fields of such individuals may be normal and hence they cannot be said to suffer from optic atrophy. In such cases, the axis cylinders during the acute epi­sodes have been depressed but not des­troyed. As a converse of this, optic atrophy may be present when the nerve head appears grey red, especially after head injury in which the optic nerve is damaged, when the atrophy can be ophthalmoscopically recognised only a fortnight or 3 weeks after the injury.

Causes of Pallor

The normal colour of the disc is mainly dependent upon its blood ves­sels. The temporal aspects of the nerve is always relatively pale in the normal nerve. However, normally the tempo­ral side has a lustre and an appreciable pink edge which is absent in the atro­phic nerve.

In the central nervous system, loss of function is constantly associated with reduction of blood supply so is the case with the optic nerve which has ceased to function normally. There is loss of normal capillarity of the disc due to closure of the finer vessels. In addition to the reduction of the blood supply there is deposition of fibrin or filial tissue which replaces the nerve fibers as they disappear and which fur­ther accounts for the pallor associated with optic atrophy.

Various workers attribute the pal­lor to different causes. Adler has sum­marized the opinions of numerous observers that pallor of the disc may be due to one or all of the following factors; (a) low haemoglobin content of the blood, (b) diminution in the num­ber of capillaries on the disc, (c) over­growth of filial fibers or deposition of fibrin, and (d) actual loss of nerve fibers.

Of these factors the number of ca­pillaries of the disc facilitates ready and precise ophthalmoscopic evalua­tion. Kestenbaum in 1946 pointed out their possible utility in the diagnosis of primary optic atrophy by what he calls the Kestenbaum Capillary Number Test. In order to set a numerical value on the degree of atrophy, the vessels which pass over the margin of the disc may be counted. One starts at the twelve O'Clock position and counts all the vessels crossing the margin, count­ing separately the arteries, veins and the small vessels. "Small vessels" mean the vessels which cannot be re­cognised as arteries or veins. The num­ber of vessels passing over the margin in normal eyes is fairly constant. Usually 9 large vessels (4 or 5 veins and 4 or 5 arteries) and about 10 small vessels can be seen. Of course, there are many exceptions in normal eyes. Sometimes the arteries and veins branch repeatedly on the disc so that more than 9 large vessels pass over the disc's edge. In discs with irregular or inverse distribution of the vessels, the number test is unreliable. In a large majority of cases however the arrange­ment of the vessels is regular enough to permit the use of this test.

In primary optic atrophy, the num­ber of arteries and veins remain un­changed but the number of small ves­sels is diminished to 6 or even less so that an approximate numerical mea­sure of the degree of pallor is possible. The test may be of value in observation of the development of disease. [Figure - 5]

The different colours which charac­terize various forms of optic atrophy may be caused by the relative pre­ponderance of the two factors viz. loss of capillaries and overgrowth of filial tissue. The chalky white disc of tabe­tic optic atrophy, with exposure of the lamina cribrosa, is due to a marked disappearance of the capillaries on the disc. The dirty white disc of post-papillitic atrophy, with filled-in cup and blurred disc margins is due to loss of capillaries with remaining oedema and deposits of fibrin and cellular debris, [Figure - 6],[Figure - 7] while the waxy disc seen in primary pigmentary degenera­tion of the retina is due to an over­growth of glial tissue.

Hence one must not be hasty in judging the condition of the optic nerve from the appearance of the disc alone; for a pale disc due to loss of capillaries may not necessarily indicate a true atrophy of the optic nerve fibers and one cannot always tell the state of degeneration of the fibers from the colour of the disc. So often we see pa­tients in whom the colour of the disc is extremely pale due to loss of capil­laries, but who retain good vision and fields. This is particularly true in cases of advanced arteriosclerosis and in anemic patients.


  Classification of Optic Atrophies Top


Different authors have tried to classi­fy optic atrophies in various ways. Some try to classify on the ophthal­moscopic findings viz., Clinical Classi­fication, whereas others try to base classification on the eetiological fac­tors. These classifications are not ideal and there is a lot of intermingling of the clinical findings in both of these classifications. There is also a third classification based on pathological changes.

The Classical subdivision of optic atrophy into "Primary" and "Second­ary" categories has no etiologic signi­ficance but they merely refer to the appearance of the disc. Primary optic atrophy is said to result when degene­ration and replacement are orderly so that the glial replacement equals the nerve fiber degeneration. The nerve head slowly loses its normal pink co­lour and turns grey-white or chalk­white, with retention of sharp margins. Secondary optic atrophy results when the degeneration of nerve fibers is very rapid and glial replacement is excessive and disorganised. The nerve head de­velopes indistinct margins and the glial tissue fills the physiologic cup and ex­tends past the disc margins. This terminology in general indicates the location of the lesion which has pro­duced the change in the optic nerve. It does not indicate the type of lesion causing the atrophy but merely points out whether the atrophy occured in a nerve head which was previously nor­mal or one which was previously in­flamed or choked. For example, brain tumours may produce either type of atrophy of the optic nerve. Those tumours that produce internal hydro­cephalus will invariably give rise to papilicedema and the resulting atrophy in these cases will be secondary atro­phy. On the other hand, tumours like pituitary adenomas that cause pressure on the chiasma or the optic nerve, but no internal hydrocephalus, will give rise to a primary atrophy.


  Clinical Classification Top


1. Simple (Primary) Optic Atrophy

it is characterised by a uniformly greyish white disc, which has sharply cut margins and clearly visible lamina cribrosa in an otherwise normal ap­pearing fundus with normal blood ves­sels. It occurs characteristically in tabes dorsalis. [Figure - 5] It also occurs as a result of tumours which exert pressure on the optic nerve or the tracts without causing internal hydro­cephalus. The tumour may be in the optic nerve sheaths or inside the skull, particularly a pituitary tumour or a basal meningioma. Basal arachnoiditis also frequently gives rise to primary atrophy, by causing an encystment which exerts pressure on the nerve or chiasma.

So closely does bilateral atrophy of the optic nerves due to pressure from the pituitary resemble tabetic atrophy that in every case of primary type of optic atrophy an X-Ray of the skull to show the pituitary fossa is an abso­lute necessity.

Case 4

A very illustrative case came my way in which an elderly Muhamedan was elsewhere given 3 courses of anti­-syphilitic line of treatment in spite of a negative Wassermann and was al­lowed to run blind till an X-Ray was taken when it was found that the atrophy was due to a large pituitary tumour, and it was too late to improve vision.

2. Consecutive Atrophy

It is the type associated with lesions of the retina and choroid. [Figure - 6]. The lesions may be inflammatory or dege­nerative. Changes in the surrounding retina are mostly found to account for this atrophy. The disc shows a yellow­ish waxy appearance and there is ex­treme attenuation of retinal vessels in advanced cases. This group includes optic atrophy following chorioretinitis and primary pigmentary degeneration of the retina. However one feels that in the former it is the local toxins that secondarily affect the optic nerve caus­ing its atrophy and therefore could be included under the group having a toxic aetiology; whereas in the latter. where the process is an ill-understood abiotrophy, could be included in the group of unknown aetiology.

3. Postneuritic Atrophy

It is characterised by the deposition of fibrous tissue on the disc. It is also associated with narrowing of the retinal vessels. It follows optic neuritis or papilloedema. [Figure - 7]

4. Temporal (Partial) Atrophy

It is characterized by atrophy (pal­lor) of the temporal side of the disc. It is the result of the involvement of the papillomacular bundle and occurs characteristically in toxic amblyopia due to tobacco and alcohol and also in disseminated sclerosis.

5. Glaucomatous Atrophy

Besides the atrophy, the main fea­tures are deep cupping and displace­ment of the vessels to the nasal side of the disc.

6. Vascular Atrophy

It occurs following embolism or thrombosis of central retinal artery and in so-called "Arteriosclerotic Optic Atrophy". Its essential feature is marked attenuation of the retinal ves­sels with pallor of the disc. There is total absence of any primary retinal pathology. Obstruction of the arterial lumen may occur under the following circumstances.

(a) Local arteriosclerotic lesion ex­tends further into the lumen until it is completely obstructed.

(b) A partial arteriosclerotic narrow­ing of the lumen is completed by a thrombus forming at the site.

(c) Associated with an atherosclerosic plaque extending into the lumen, there is added local vasomotor constriction of the vessel, causing complete obstruc­tion. Thus gradual narrowing of the blood vessels leads to progressive di­minution of blood supply and ultimate­ly atrophy.


  Aetiological Classification Top


1. Circulatory: Occlusion of the cen­tral retinal vein or artery, arteriosclero­tic changes within the optic nerve itself disturbing its normal nutrition, or post-haemorrhagic due to sudden mas­sive blood loss e.g. bleeding peptic ulcer, accident trauma, etc. The fundus, besides the optic atrophy. shows ex­treme degree of attenuation of blood vessels.

2. Degenerative : Consecutive atrophy secondary to retinal disease with des­truction of ganglion cells e.g. in reti­nitis or chorioretinitis, or as part of a systemic degenerative disease e.g. Cerebromacular degeneration.

3. Post - oedematous : Secondary to papiloedema. [Figure - 6]

4. Post-inflammatory: Secondary to inflammatory lesions of the nerve itself e.g. neuritis, perineuritis, tuberculosis, syphilis, etc. and also following retro­bulbar neuritis.

5. Pressure and Traction : Due to pressure on the nerve fibers or due to traction, e.g. from bony pressure at the optic foramen (osteitis deformans), pressure of calcified and sclerosed arteries, aneurysms of the internal caro­tid artery and of the arterial circle of Willis, intraorbital or intra-cranial tumours.

6. Toxic : From endogenous and exo­genous toxemia.

7. Traumatic: Intracranial or intra­orbital injury to the nerve.

8. Glaucomatous optic atrophy. 9. Idiopathic and genetically deter­mined:

(a) Leber's disease: considered to be sex-linked recessive gene.

(b) Behr's hereditary optic atro­phy: rare autosomal recessive dis­ease.

(c) Congenital or infantile heredi­tary optic atrophy. There is a severe autosomal recessive form and a milder autosomal dominant one.


  Pathological Classification Top


Though not commonly used it is based on the usually occurring three varieties of pathological changes that are observed.

1. Where the degeneration of nerve fibers occurs fast with irregular fibrosis thereby leading to lack of any definite pattern (secondary optic atrophy).

2. Where the degeneration of nerve fibers is slow and the replacing fibrous tissue gets arranged in the form of columns thereby giving rise to Colum­nar Gliosis.

3. Where the atrophy of nerve fibers occurs without the replacement of fib­rous tissue thereby giving rise to visible empty spaces and produces the Caver­nous Atrophy or Gliosis.

Optic Atrophy may follow injury or infammation of the optic nerve or rais­ed intracranial tension as in cases of intracranial tumours or raised intra­ocular pressure as in glaucoma or from local pathological lesions of the retina such as chorio-retinitis and primary pigmentary degenerations of the retina. Optic atrophy can be ascending or descending, depending upon the site of the primary lesion which caused the atrophy: e.g. a local lesion such as chorioretinitis or retinal degeneration like primary pigmentary degeneration of the retina or glaucoma would give rise to an ascending optic atrophy; whereas intraorbital or intracranial lesions would give rise to descending optic atrophy. [Figure - 8],[Figure - 9]

One can see from the above discus­sion that the classification of optic atrophies is far from clear and not at all uniform. It is best to realise that there is a confusion here in order to appreciate the confusion so that one can accommodate to the man oppo­site, talking about any kind of classifi­cation he may be using.


  Optic Atrophy Following Injury Top


The nerve may be affected in a se­vere head injury. It may be divided if it is involved in a fracture of the ante­rior cranial fossa passing through the optic canal. More commonly, it is pressed by an accompanying haema­toma of the intervaginal space around the nerve which comes from the ves­sels which cross this space, or there is actually an intraneural hemorrhage. At the site of the injury the changes are (I) an acute necrosis resulting in a complete breakdown of the axis cylnders, (2) fragmentation of the me­dullary sheaths, (3) degeneration of the neuroglia and invasion of the polymor­phonuclear leucocytes. These are later replaced by fatty granular cells and finally there results a glial scar. It is interesting to note, that beginning optic atrophy can be made out with the ophthalmoscope in about fourteen days after the injury and is well marked after six weeks. In a diagnosis of this condition one is often at the mercy of the radiologist.

(Case 5) In a recent case which was referred to me from Junagadh, the patient had suffered a peculiar injury 20 days ago. He was injured by a branch of a tree, the point of which hit him between the lower part of the eye­ball and the inferior orbital margin. According to the history there was a "black-eye", the eyeball had become completely immobile and the vision had diminished considerably.

When we examined him for the first­-time, twenty days after the injury, there were no signs of external injury, no hoematoma and the movements of the eyeball were restricted upwards and downwards. There was just light per­ception. The disc was pale but the margin was slightly hazy. It appeared impossible that the nature of the in­jury as could be gauged from the his­tory and the clinical findings could cause a break in the optic nerve fibers. The X-Ray findings as reported by the radiologist were "nothing abnormal." We were inclined to make a diagnosis of hemorrhage in the optic nerve sheath with damage to the superior and inferior rectus muscles.

On referring the case to the neuro­surgeon for a decompression of the optic nerve from the frontal route, the keen eye of the neurosurgeon detected a break in the optic canal in the X-Ray, and argued that it was a complete break of the nerve with injury to the 3rd and 4th C. Nerves. He expressed the futility of an operation. How such an injury could have caused a damage of this nature is anybody's guess and an exercise in the practice of dynamics.


  Optic Atrophy Following Inflammation Top


Inflammations of the optic nerve are usually classified into four groups. (1) Perineuritis, (2) Periaxial Neuritis, (3) Axial Neuritis, (4) Transverse Neu­ritis.

(1) PERINEURITIS: Here the in­flammatory process first affects the sep­tal system, the nerve fibers being se­condarily attacked. The inflammatory process may be an extension from the primary meningitis of the brain along the meningeal coverings; or it may be a direct extension of the localised inflammation of the paranasal sinuses, bony canal, orbit or the eye itself. The nerve fibers are first intact, but owing to the contracting connective tissue and the resulting diminished blood supply or from the spread of the inflammatory process, they eventually degenerate. The medullary sheath degenerates first, then the axis cylinder breaks down into myelin droplets and is absorb: d. Un­like tabes, the degeneration is irregular, so that some portions will stain with Weigert, while neighbouring parts will not. Later the destruction of nerve fibers is followed by glial prolifera­tion.

(2) PERIAXIAL NEURITIS: Here the meningeal inflammation extends along the pial septa into the paren­chyma of the optic nerve. Hence it is also known as parenchymatous dege­neration. The characteristic example of this group is tabetic optic neuritis and atrophy. The degeneration of the nerve may occur with or without inflamma­tory signs, such as oedema of the nerve fibers and cellular infiltration. Spiroch­etes have been demonstrated, but in very small numbers mostly in the pia. The degeneration passes backwards to the chiasma and the optic tract (Wolff).

Changes in the sheaths and septa are always seen. They are largely secondary to the loss of volume of the nerve resulting from degeneration of the nerve fibers. Without any increase in cells, there is a thickening of the main septal fibers, especially around the vessels. The pia is thickened owing to the diminution of the volume of the whole nerve which causes the elastic fibers in it to contract. In the arach­noid, since they occupy a smaller space, the cells appear to have multiplied. The dura appears to retract less than the pia and tends to lie loosely as the nerve shrinks.

This type of atrophy is definitely becoming rarer with more effective treatment of syphilis in the early stages.

(3) AXIAL NEURITIS: The classi­cal example of this group is multiple sclerosis. The toxic factors on the de­generative processes due to malnutri­tion may cause selective affection of the inner portion of the nerve,-axial neuritis. In multiple sclerosis since the axis cylinders remain intact, secondary degeneration is not usually seen. Hence the nerve fibers of the papilla are largely retained and the ganglion cells of the retina are hardly if at all altered. However, frequent attacks of neuritis may ultimately lead to atrophy.

It is now an established fact that disseminated sclerosis is almost non­existent in India, so also the neuritis associated with it.

(Case 6) 1 remember an experi­ence in my early days of practice at an age when youth is synonymous with rashness, of having seen a case of optic neuritis with a central scotoma first in one eye then in the other. Fresh from Europe I made a hasty diagnosis of optic neuritis gave a se­rious prognosis and was rash enough to suggest that he would develop dis­seminated sclerosis in the course of time. The boy recovered full vision and is now 50 years old and has no neurological signs.

On the other hand in India, what we get frequently is viral optic neu­ritis usually bilateral, mostly during the monsoon and just before it, which recovers completely with broad spec­trum antibiotics and corticosteroids.

(4) TRANSVERSE NEURITIS: Axial and periaxial neuritis together constitute transverse neuritis, which may totally destroy the optic nerve as in Devic's disease also known as neuro­myelitis optica. Here, there is destruc­tion of grey and white matter as well as of the axis cylinders.

OPTIC ATROPHY FOLLOWING INTRACRANIAL TUMOURS: At­rophy of the optic nerve follows mecha­nical pressure on the nerve by tumours, usually anterior to the chiasma or in the neighbourhood of the chiasma. These may produce a secondary atrophy with the same ophthalmosco­pic picture as the primary variety. As aready noted, a brain tumour will pro­duce a primary type of atrophy if it presses upon the chiasma or optic nerve, and it may produce a post­papillooedemic atrophy if it results from papilloedema due to increased in­tracranial pressure. Pituitary tumours belong to the former category. Rarely, pituitary tumours may cause a choked disc which may further give rise to post-papilloedemic type of atrophy- as is the case with other intracranial tu­mours. In this type of atrophy, the capillaries which are first distended, later become occluded and are con­verted into strands. The glial and connective tissue sclerosis causes a shrinking of the tissues which further obliterates the capillaries on the disc. Hence the factors producing the opaque white appearance of the se­condary atrophy are the glial and con­nective tissue sclerosis together with obliteration of the capillaries.


  Optic Atrophy in Glaucoma Top


Owing to increased intraocular ten­sion, the lamina cribrosa begins to yield backwards. The amount of cup­ping and its early or late onset depend on not only the amount of intra-ocular tension, but also on the toughness of the lamina cribrosa. Atrophy of the nerve fibers occurs as a result of pres­sure as well as due to vascular sclerosis causing diminution of blod supply as in arteriosclerotic type of optic atrophy. In case of glaucomatous optic atrophy or that following central retinal artery occlusion, the degeneration is not only of nerve fibers and ganglion cells, but also of inner plexiform and inner nuc­lear layers.

According to Goldmann, the glu­comatous excavation is not due to pressure on the optic disc, but it is due to an atrophy of the nerve and the dis­appearance of the supporting glial tissue. The duration of pressure is the chief factor rather than the height of pressure in causing the cupping.

It is also interesting to note that the ERG in glaucoma remains normal even in a case of absolute glaucoma as pointed out by Dhanda, suggesting that the pressure atrophy is of the nerve fibers of the retina which form the optic nerve and not of the perce­pient elements.


  Optic Atrophy in Primary Pigmentary Degeneration of the Retina Top


There is a progressive degeneration of the neuroepithelium, primarily of the rods, to be followed by gradual atrophy of the whole tissue, associated with filial overgrowth, and obliterative sclerosis of the retinal vessels. There is migration of pigment into the retina


  Optic Atrophy in Chorioretinitis Top


During the final stages of the disease there is complete disappearance of the neural elements and their replacement by fibrous tissue deprived from the vascular elements and the glial sup­portive tissue, thus leading to optic atrophy.


  Schnabel's Cavernous Atrophy Top


Schnabel put forward the theory that the cupping of the disc in glaucoma was not due to tension. This type of atrophy is seen in glaucoma without raised intraocular tension. He stated that minute cavities appeared in the nerve, both in front and behind the lamina cribrosa. Those in front of the lamina, enlarged and coalesced together to form a large cavity. Those behind the lamina collapsed and the lamina cribrosa thus drawn back by contract­ing glial (scar) tissue, formed the glau­comatous cup. In the early stages the nerve fibers degenerate and disappear entirely, leaving empty spaces. How­ever, the glial network and septa re­main unchanged. Later as the process of cavitation advances, larger cavities are formed. Thus there is progressive diminution of bond supply of the nerve bringing about the disappearance of the nerve fibers.

Histologically, it is characterised by the mucoid degeneration of the glia in association with the disappearance of the optic nerve fibers. Neither the glia nor the connective tissue elements ex­hibit any proliferative reaction on this condition.


  Optic Atrophy from Exogenous Toxins (Toxic Amblyopias) Top


Toxic amblyopias comprise a group of diseases caused by the absorption of exogenous poisonous substances which have a specific effect of destroying nerve tissue elements near or in the optic nerve. In some of them, like tobacco and alcohol the disease is pri­marily retinal and follows poisoning of ganglion cells of the retina which re­sults in degeneration of the nerve fibers, seen only after they have obtain­ed their medullary sheaths behind the lamina cribrosa. In others it is due to a direct action on the nerve fibers them­selves. In general these substances at­tack the nerve fibers or the ganglion cell layer of the retina and cause either papillomacular scotomas or peripheral visual field loss. The exact mechanism of destruction by those substances is not known but they are believed to be either neurotoxic or vasoconstrictive giving rise to degeneration.

The toxic agents belong to two main groups. The first group includes agents that produce central field defects, while the toxins of the second group produce a peripheral contraction of the visual fields. The group that produces central field defects mainly comprises of agents like tobacco and alcohol besides the rarer substances like carbon disulphide (as seen in rayon industry), iodoform, lead, thallium and inorganic arsenic preparations. Pathologically there is extreme degeneration of the retinal ganglion cells and the nerve fibers, which may extend upto the external geniculate body. The other group that causes peripheral contraction of fields contains drugs like quinine, ethyl-hydrocuprein (optochin), salicy­lates, barbituric compounds, felixmas, organic arsenic preparations and ani­line dyes. Here the pathology reveals chromatolysis and degeneration of ganglion cells and nerve fibers. In later stages there is thickening of the walls of the blood vessels and oblitera­tion of the lumen.

Recently with the advent of broad spectrum antibiotics, some toxic chan­ges in the nerve have been observed, especially when streptomycin is given over a long period in cases of tuber­culous meningitis. More recently optic atrophy has been reported following chloromycetin also.

As regards streptomycin in tuber­culous meningitis and blindness, there has been a controversy whether optic nerve involvement is due to strepto­mycin or is it due to the tuberculous process involving the meninges near the cysterna chiasmatis. Others believe that "Isonex" is the cause of damage to the optic nerve and not streptomy­cin.

The following two instances in our experiences prove conclusively the mat effect of streptomycin, in some cases at least, on the optic nerve.

(Case 7) A nurse from the Turner Sanatorium for Tuberculous patients was being treated for phlyctenular keratitis in one eye with streptomycin and other anti-tuberculous line of treat­ment. She was developing defective vision when pas-isonex were disconti­nued and she still continued to lose her vision. It was at this stage that we saw her first when her vision was reduced to finger counting only in both the eyes. The anti-tuberculous line of treat­ment was not doing her keratitis the slightest good. Her optic disc in the eye that had no keratitis was very pale. The fundus in the other eye was not visible due to the keratitis. On discon­tinuing streptomycin her vision im­proved rapidly. Desensitising therapy with tuberculin improved her keratitis and she could resume her work as a nurse within a month. This case not only proves the toxic effect of strepto­mycin on the optic nerves in this parti­cular case but also shows that phlycte­nular keratitis was not a manifestation of tuberculosis but was only an allergic manifestation, to tuberculin in this case, which got improved with desensi­tization to tuberculin.

(Case 8) The second case is a sad case and even more convincing. The patient, a young man of 16 years was consulted for complete bilateral optic atrophy in both the eyes with no per­ception of light. The history was that he had suffered from tuberculous meningitis for which he was treated with streptomycin and 'pas-isonex.'

The boy recovered but he got a recur­rence. This time when the treatment was restarted he complained of misty vision. The treatment was continued in spite of this, when he complained of further loss of vision. The boy refused to take any more streptomycin as he thought he was getting blind. The boy said that his vision improved on dis­continuing streptomycin. Some resi­dual effects of the tuberculous infection remained and somehow the physician in charge could not be convinced that streptomycin was causing the blurring of vision. He said that streptomycin was known to affect the acoustic nerve but not the ophthalmic. He was in­clined to put the blurring of vision down as functional. He proposed to give more streptomycin but the boy re­fused, but he was induced to take it after being assured that it was not streptomycin but some other injection. The boy, ignorant that he was getting streptomycin under a false assurance complained of immediate amaurosis after receiving this single dose of streptomycin. When we saw him at this stage for the first time, the vision was irretrievably lost, the fundus presenting the appearance as in quinine amblyo­pia--chalky white discs with attenuat­ed vessels.

This case teaches us one useful les­son besides driving the nail in the fact that streptomycin does cause optic atrophy. It shows that courses of streptomycin injections separated by intervals of rest, progressively become more damaging. In this case the very first injection in the third course preci­pitated complete and irreversible blind­ness. It is a form of Herxheimer re­action, which is due to individual sus­ceptibility which seems to get built up in some individuals with every course separated by an interval.

A severe deficiency of vitamins in the diet, particularly of thiamine as in severe starvation and in extreme de­gree of pellagra may cause optic neu­ritis usually of the axial type with loss of central vision just as similar lesions in the mid-brain give rise to various types of ophhalmoplegias like that of Wernicke's acute haemorrhagic anterior polioencephalitis. A partial optic atrophy which may eventually develop into a complete one leads to perma­nent visual defect.

The essential TREATMENT of these amblyopias is to recognise and stop the toxic agent completely and to give high doses of the B-Complex group of vitamins, particularly, thia­mine and B 12. Also found useful is the administration of peripheral vaso dilators like amyl nitrite, sodium nit­rite and retrobulbar injections of acetylcholine, etc.


  Course-Prognosis­-treatment Top


In optic atrophy disease, the changes in visual function usually occur very slowly over weeks or months, except in cases of severe injury and acute toxoemia like quinine and methyl alcohol. It is difficult to assess prog­nosis on the basis of ophthalmoscopic findings alone. Atrophic cupping, at­tenuation and reduced number of ves­sels on the disc, and pallor with papilloedema are all signs of unfavourable prognostication. Optic atrophy se­condary to vascular, traumatic, dege­nerative and some of the severe toxic causes, usually has a very bad prog­nosis. Visual loss due to optic atrophy secondary to pressure against the optic nerve may be restored, particularly if the cause is relieved early. No treat­ment is effective for optic atrophy ex­cept to treat the underlying cause and on the general line of treatment as done for toxic amblyopias.

From the series of cases under re­view we have found that glaucomatous optic atrophy was the commonest fol­lowed next in order by vascular, toxic and syphilitic. Due to efficient and energetic antisyphilitic treatment, the last has become very infrequent. The least common causes were those due to intracranial tumours, trauma, meningi­tis and septic foci of infection, parti­cularly from the posterior ethmoidal and sphenoidal sinuses. Finally, there was a group of cases where the etiology could not be determined.


  Conclusions Top


In conclusion it may be noted that there is much that is unpredictable about the course of lesions of the optic nerve. Some lesions are acute and ir­reversible, others appear progressive at first but are completely curable func­tionally although a tell-tale optic atrophy may prevail. There are still others which gain in severity with every repetition of the noxious lesion. One is tempted to explain these on patho­logical basis.

The acute lesions, traumatic or toxic are neuropathic and primarily damage the ganglion cells and the nerve fibers.

The second variety of lesions pri­marily affect the vascular supply which at first are of a spastic nature, func­tional and capable of recovery. They are clinically recognised by a "de­pression" of the field and fall in line with Traquair's postulation that all field defects could be explained on a vascular basis. If the noxious agent is removed the function improves but some auxiliary blood vessels may get obliterated and result in some perman­ent pallor of the disc resulting in dis­proportion between visual function and disc colour, as illustrated in cases 1 and 2 on page 57. Fortunately, an appre­ciable amount of time can elapse (about 3 weeks) before the nerve be­gins to show signs of degeneration after the initial impairment of the blood supply.

In the third variety the noxious toxin is neurovascular, first affecting mainly the blood vessels but during the rest­ing phase the nerve gets progressively sensitized to the noxious agent so that with subsequent attacks or administra­tion of the same toxin the nerve be­comes more vulnerable and the subse­quent lesions become neuropathic, acute and permanent as described un­der streptomycin toxicity.

Arguing on these lines, the unpre­dictability of optic nerve lesions refer­red to above, will not appear so un­predictable, the prognosis not so inde­finite and the treatment not so irra­tional. I hope this presentation will help us to face our cases of optic nerve lesions with greater confidence.


  Summary Top


Anatomical, physiological, patholo­gical and etiological considerations in optic nerve atrophies of various kinds are considered. These are illustrated by clinical experiences wherever appli­cable.

Three types of noxious agents can cause damage to the optic nerve: (1) Neuropathic, (2) vascular, (3) vasculo­neuropathic. The prognosis is best in the second group where a time limit of about three weeks is available to meet the challenge. In the third group a progressive sensitization of the optic nerve takes place with every repetition of the toxic agent after an interval.

I thank my colleague and friend Dr. S. N. Cooper for allowing me to use some of his clinical material which we have seen together and for some of the diagrams in the text. I also thank him for his editorial suggestions.[20]

 
  References Top

1.
Cordes, F. E. (1952): Atrophy in In­fancy, Childhood and Adolescence (Survey of 81 cases): Am. J. Ophth. 35: 1272.  Back to cited text no. 1
    
2.
Duke Elder. W. S.: Text Book of Ophthalmology, Vol. III, Diseases of the Inner Eve; Henry Kimpton. (1940).  Back to cited text no. 2
    
3.
Cooper S. N. (1956): Proc. All-India Ophth. Soc. 16, 4 and It.  Back to cited text no. 3
    
4.
Francois, J. and Neetans, A. (1954): Vascularization of Optic Pathway: Br. J. Ophth. 38: 472.  Back to cited text no. 4
    
5.
Francois. J. and Neetans. A. and Cot­lette, J. M. (1955): Vascular supply of Optic Pathway (Studies by Micro­arteriography of the Optic Nerve): Br. J. Ophth. 39: 220.  Back to cited text no. 5
    
6.
Helmick. E. (1957): Tabetic Optic Atrophy: A.M.A. Arch. of Ophth.. 57: 282.  Back to cited text no. 6
    
7.
Hogan. M.::nd Zimmerman, L. (1962): Ophthalmic Pathology: W. B. Saunders Co., pp. 623-627.  Back to cited text no. 7
    
8.
Hughes. B. (1949): The. Diagnosis of Optic Atrophy: Trans. Ophth. Soc. U.K. Vol. 69, 411.  Back to cited text no. 8
    
9.
Kant. A. (1949): Evaluation of Optic Atrophy; Am. J. Ophth.. 32: 1479.  Back to cited text no. 9
    
10.
Kestcnbaum A. (1946): Clinical Me­thods of Neuro-Ophthalmologic Exami­nation: New York. Grune & Stratton, P. 81.  Back to cited text no. 10
    
11.
Kwitten. J. and Barest. H. (1958): The Neuropathology of Laber's Disease; A.M.A. Arch. Ophth., 59: 309.  Back to cited text no. 11
    
12.
Moore, J. (1937): An Etiologic Study of a series of Optic Neuropathies; Am. J. Ophth. 20: 1099.  Back to cited text no. 12
    
13.
Paton. L. (1922): Tabes and Optic Atrophy; Br. J. Ophth.. 6: 289.  Back to cited text no. 13
    
14.
Sugar, H. (1957): The Glaucomas, Hoeber-Harper, Second Edition, p. 103.  Back to cited text no. 14
    
15.
Vail, D. (1948): The Blood Supply of the Optic Nerve; Am. J. Ophth., 31: 1.  Back to cited text no. 15
    
16.
Walsh, B. (1957): Clinical Ncuro­Ophthalmology; 2nd Edition, The Wil­liams and Willcins Company, 324-334.  Back to cited text no. 16
    
17.
Wolff, E. (1958): The Anatomy of the Eye and the Orbit: H. K. Lewis. pp. 286-360.  Back to cited text no. 17
    
18.
Wolff, E. (1944): The Pathology of the Rye: H. X. Lewis, 215-243.  Back to cited text no. 18
    
19.
Wolff, E. (1947): Schnabal's Cavernous Atrophy: Trans. Ophth. Soc. U. K. 67: 133.  Back to cited text no. 19
    
20.
Woods, Alan C. (1948): Optic Neuro­pathies. Am. J. Ophth.. 31: 1053.  Back to cited text no. 20
    


    Figures

  [Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9], [Figure - 10]



 

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