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ARTICLE
Year : 1959  |  Volume : 7  |  Issue : 3  |  Page : 66-71

A definition of "tapetoretinal degenerations"


From the Ophthalmological Clinic of the University of Ghent, Belgium

Date of Web Publication8-May-2008

Correspondence Address:
J Francois
From the Ophthalmological Clinic of the University of Ghent
Belgium
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Source of Support: None, Conflict of Interest: None


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How to cite this article:
Francois J, Verriest G. A definition of "tapetoretinal degenerations". Indian J Ophthalmol 1959;7:66-71

How to cite this URL:
Francois J, Verriest G. A definition of "tapetoretinal degenerations". Indian J Ophthalmol [serial online] 1959 [cited 2021 Jun 14];7:66-71. Available from: https://www.ijo.in/text.asp?1959/7/3/66/40727

Tapetoretinal degenerations arc degenerative affections of the ocular fundus, of hereditary origin. All authors agree to this definition but it remain, necessary to outline with some exactness the significance of such, terms as degenerative affection, ocular fundus and hereditary origin; only in this way can it be ensured that there is no discussion or confusion as to which affections should be considered tape­toretinal degenerations and which not. In this respect there are still some differences of opinions.


  Heredity Top


It is not always easy, to recognize a hereditary affection or to give it an exact definition. The following factors must be taken into account:

1. A hereditary affection is not necessarily familial, as it may be due to a unique combination of various hereditary factors.

Even if a single gene is, causative, this may be manifested only in a certain individual or exist only due to a mutation in a germinal cell, sec that there is no continuity in ascendant. There may also be a retrograde mutation, by which very fact con­tinuity in descendants is excluded.

With regard to tapetoretinal de­generations it may be pointed out that there are sporadic but frequent cases of juvenile macular degeneration.

2. A pathological gene sometimes exerts its influence only if certain exogenous factors create a disposition favourable to its action. Although there are manifestly hereditary senile macular degenerations, there are other forms which remain isolated but which are in no way distinguishable from the former type. It may well be that the same affection is involved of which an indispensable factor is of vascular origin.

3. The pathological gene may exert its influence only on a part of the tissues which it usually contacts (mosaic heredity or genetic dyssysm­metry).

In this respect it should he borne in mina that segmented retinitis pigmentosa is a genuine familial here­ditary degeneration whereas unilateral retinitis pigmentosa is always sporadic.

4. Various different members of the same sibship, apparently bearing the same pathological gene, may show completely different clinical features (variability of the phenotype corres­ponding with a genotype determined by changes in expressivity).

The majority of the various forms of peripheral tapetoretinal degenera­tion and central retinitis pigmentosa are therefore seen in intrafamilial association with typical retinitis pigmentosa. Macular degenerations of the STARGARDT type, however, seem to be less markedly individual­ized.

A genetic analysis of retinitis pigmentosa shows that it is impossible, on the other hand, to accept any absolute unity of tapetoretinal dege­nerations. There are three genetic types of pigmental retinal degeneration (dominant, recessive and sex-linked type); the symptomatology of each of these varieties is different; the domi­nant type, for example, is more benign than the recessive form.

It is today known that the gene of choroideremia is not the same as that of FUCHS' atrophia gyrata in that both are localized on different chro­mosomes, although there are "clinical" reasons to believe that these conditions are two varieties of the same affection.

Although at first sight one may be astonished at the enormous variety of tapetoretinal degenerations, yet it is likely that the number of corresponding genes is considerably less, and that even different genes may have an essentially similar mechanism of action so that the notion of unity of tapeto­retinal degenerations may pass from the genetic to the biochemical level.

From a genetic point of view, tape­toretinal degenerations are always well separated from other affections of the ocular fundus such as malformations (e.g. coloboma of the choroid) or functional anomalies (e.g. protanopia).

It has repeatedly been pointed out that the apparent intrafamilial rela­tionship between retinitis pigmentosa and essential hemeralopia can have no significance as long as the diagnosis "idiopathic" hemeralopia is not demonstrated beyond doubt by an absolutely normal ocular fundus, complete absence of progressivity and characteristic functional signs such as selective affection of the scotopic components of the electroretinogram. So far, no observation described in the literature has combined all these requirements.

5. A hereditary affection may be due not so much to a pathological gene carried by a chromosome as to a cytoplasmic factor. LEBER's disease doubtless constitutes an example in this respect.

All cases involve a disorder of the normal enzymatic process, the starting­point of which is found in the ribo­nucleic constituents. From this point of view we know still another fundamental difference between the genes, the plasmogens and the viruses. The last-mentioned, it should be pointed out, may well be at the source of congenital diseases. Yet it is generally easy to distinguish a retinal degeneration due to a viral embryo­pathy from a true heredofamilial tapetoretinal degeneration .


  II. Localization of Lesions in the Ocular Fundus Top


According to LEBER's classical conception, the essential lesions of tapetoretinal degeneration are localized at the level of the tapetum (pigmental epithelium) and the retina (particularly the outer layers). We believe that the choroid should be included, and that these conditions should be referred to as tapetoretinochoroid or, more simply, as retinochoroid degeneration. It is actually impossible to separate here­ditary choroid degenerations (choroid sclerosis) from retinal degenerations; the choroid is also seriously affected in choroideremia, in FUCH'S atrophia gyrata and in numerous forms of retinitis pigmentosa. It is not yet known what the possible influence of choroid degeneration on retinal de­generation may be, or vice versa, but it is hoped that electroretinographic examinations made in the early stages of the affection may afford more definite information in this respect.

The localization of lesions in cases of tapetoretinal degeneration is highly variable.

1. Whereas the entire retina is affected in the terminal stage of peripheral degeneration, it is only the macular region which is involved in the majority of cases of central degeneration.

2. In retinitis pigmentosa the retinal affection begins and remains predominant at the level of the external retinal layers. In TAY­SACHS' amaurotic idiocy, however, only the ganglion cells are affected.

There are also reasons to believe that, in STARGARDT's macular degeneration the retinal affection is more marked in the internal lavers when the affection is characterized at the onset by dyschromatopsia of the green-red (as in affections of the optic nerve), whereas peripheral tapetore­tinal degenerations give dyschroma­topsia of the blue-yellow axis.

3. From a functional point of view there are still other differences between the peripheral and the central types of affection. An absence of ERG response and hemeralopia are characteristic of peripheral tapetoretinal degeneration. In macular degeneration there is as a rule a normal ERG, and frequently nyctalopia.

The only characteristic found in all forms of tapetoretinal degeneration is the terminal abolition of all visual functions in the retinal area affected. In this respect there exists a funda­mental difference between tapetoretinal degenerations and what we know as congenital sensory anomalies (in which cases the functional deficiency is always partial, stationary and selective).

It should also be pointed out that other parts of the eyeball may be involved in degeneration. As regards the optic disc, this may develop not only the well-known girate atrophy but also excrescences known as Drusen, which are relatively frequent. As regards the lens, this may not develop complicated cataracts but also cataracts developing in a very rapid fashion towards complete maturity (a case of retinitis pigmentosa of dominant heredity, a case of FUCHS' atrophia gyrata in a girl aged 15). We have seen, on two occasions, a combination of FUCHS' complicated heterochromia and tapetoretinal degeneration.

The correlation between tapetoretinal degeneration and certain extra-ocular lesions is well-known. The following facts should meanwhile be taken into account:

1. ERG changes which are charac­teristic of retinitis pigmentosa may also be seen in STARGARDT's macular degeneration.

2. Certain somatic hereditary af­fections do not, on first consideration, belong to the group of cerebroretinal degenerations; yet they may be asso­ciated with a degenerative chorioretinal affection. Mention may be made in this respect of HURLER's multiple dysostosis, which is sometimes accom­panied by tapetoretinal degeneration, hemeralopia and absence of ERG responses (2 personal observations). Also the MARFAN syndrome, which is often associated with more or less generalized choroid sclerosis; the GROENBLAD-STRANDBERG syn­drome and that of EHLERS­DANLOS. The histopathological lesions seen in angioid striate retinitis are almost identical with those of senile macular degeneration and SORSI3Y's pseudo-inflammatory here­ditary degeneration, a similarity so marked that the lesions of the RRUCH membrane cannot be considered pathognomonic of angioid striae.


  III. The Degenerative Nature of the Lesions Top


It is possible to distinguish with certainty between a degeneration and a malformation, an anomaly, inflam­mation or neoplasm; a hereditary basis, however, may be involved in all affections.

The significance. of the above terms, which are sometimes used in a variable sense, should first be considered.

A malformation, is a macroscopic deformity resulting from a develop­mental disorder interfering with the formation of an organ; mention can be made, in this respect, of the colo­bomatous affections of the eyeball.

An anomaly is a minor, not very severe malformation such as, for example, a remnant of the hyaloid artery. Metabolic disorders such as albinism constitute true anomalies. With regard to retinal affections we reserve the term sensory anomalies for submicroscopic, microscopic or ultra­microscopic malformations; in this respect we could mention the macular hypoplasis seen in albinism, and protanopia.

Inflammation and neoplasia are fundamentally characterized by typical histological lesions found in each stage.

Degeneration is a primary, pro­gressive and usually premature change in a tissue which has previously appeared to develop in a normal manner (abiotrophy). This excludes changes which are manifestly second­ary to neoplasia or to inflammation of infectious origin (e.g. syphilis).

The cause of malformations is multiple and a specific: a genetic factor as well as an infectious, chemical or even mechanical factor may he involved the most important feature being the time at which these factors interfere in the course of embryonic development.

Even when familial antecendents are not taken into account it is as a rule possible to distinguish a hereditary lesion from a non-hereditary, provided the lesion be multiple. Certain asso­ciations are in fact pathognomonic in that they make it possible to differentiate genetic syndromes, such as MARFAN' s disease, from embryo­pathic syndromes due to such condi­tions as maternal rubeola.

However this may be, true tapeto­retinal degenerations are not malfor­mations. They can be distinguished from retinal dystrophy as seen in malformations of the eyeball which are of viral origin and which arc recognizable not only on the basis of their morphology but also by demon­stration of the causative agent, often revealed by careful questioning of the mother, by the isolated occurrence of the affection and by the concomitance of other malformations of the car and particularly of the heart.

Functional anomalies o f the retina are clue to strictly genetic factors, possible variations in phenotype being completely independent of the environ­ment. Apart from hereditary trans­mission by a constant mechanism and with constant expressivity, the follow­ing fundamental characteristics should be mentioned: concomitant somatic affection absent or excessively reduced, stationary condition with complete absence of aggravation between birth and death, selective affection, and partial affection, of the visual func­tions, absence of degenerative lesions, with a macroscopically normal ocular fundus. These requirements are met in the case of essential hemeralopia, OGUCHI's disease, achromatopsia and dyschromatopsia. The objection may be made that, in OGUCHI's disease, the ocular fundus shows a yellow discoloration; this, however, is merely due to intsantaneous accumulation of substances derived from the metabolism of visual pigments, no degeneration is involved.

In the case of achromatopsia there are sometimes degenerative macular changes. "These changes are mild and by no means essential: they are often lacking. The same holds true for annular scotoma such as is seen in certain cases of achromatopsia.

The condition known as "fundus albipunctatus cum hemeralopia" can not be considered a functional anomaly in our opinion. The affection of visual functions is not selective, strictly speaking, as there may be concentric narrowing of the field of vision. The lesions of the ocular fundus are pro­bably degenerative. There are also cases showing intermediary forms between fundus albipunctatus and albescent punctate retinitis; this, then, is an indisputable tapetoretinal degene­ration.

Functional affections of the retina, as compared with the normal retina, would seem to be diseases based on deficiency or replacement. There is a lack of pigment, of a receptor or of a neuronic transmission type. In the anomalous trichromatic systems, the essential lesion consists of replacement of a normal by an abnormal funda­mental colour. All these functional anomalies would seem to depend on a disturbance in histobiochemical differ­entiation.

Inflammation can of course be due to infectious causes, but also to non­infectious, biochemical causes; in the latter case it may be hereditary. SORSBY in particular has demonst­rated the existence of hereditary inflammations, showing that it is sometimes difficult to distinguish a pseudo-inflammatory retinal dystrophy of dominant heredity from true tapeto­retinal degeneration and common chorioretinitis.

The conceptions of congenital inflam­mation and malformation of infectious origin are sharply distinct, as the embryonic organism does not react to a virus or to a bacterium by inflammatory manifestations of the granulomatous type.

Even if the above described defini­tions are accepted and observed there remain cases of difficult interpretation. In LEBER's congenital tapetoretinal degeneration for example, there is an admittedly very early abiotrophy, and the degenerative process largely deve­lops during intra-uterine life; the analogy of the affection with typical retinitis pigmentosa is evidently in favour of this hypothesis.

With regard to fundus albipunctatus cum hemeralopia, the smiliarity with albescent punctate retinitis also suggests progressivity of lesions at a given moment; yet this is merely a hypothesis

The pathogenesis of tapetoretinal degenerations is still completely obscure. When we state that these cases involve progressive changes in a tissue previously developed in an apparently normal fashion, we only forward a simple hypothesis; nothing makes it possible to exclude an anomalous constitution of the tissue from the onset. It is for this reason that the hypothesis comprises the word " apparently" .

However, even if there exists a latent change of the retina from the onset, the fundamental difference between tapetoretinal degeneration and function­al anomalies still persists, as the latter involve not so much a latent and ultimately active condition as a complete albeit submicorscopic) mal­formation.

The conclusion seems justified that tapetoretinal degeneration must be defined as follows: a hereditary, primary, progressive and usually pre­mature change in a chorioretina which previously appeared to develop in a normal manner.

Since this definition includes no inflammation, SORSBY's pseudo­inflammatory chorioretinal dystrophy can be included among the tapeto­retinal degenerations.

When adding the choroid, we can also include in this range cases of hereditary choroid sclerosis and even malignant myopia which is after all regularly seen in FUCHS' atro­phiagyrata and frequently in retinitis pigmentosa.

The familial cases of senile macular degeneration and angioid striate retin­itis are well described by the definition suggested.

The reasons why LEBER's con­genital dystrophy and fundus albipunc­tatus cum hemeralopia should be classified among the tapetoretinal degenerations, have already been listed.

KARPE & ZETTERSTROM's con­genital retinal dysfunction does not seem to be a tapetoretinal degeneration, as visual functions in these cases improve with increasing age.

The retinal lesions in phacomatosis cannot be included either, as they generally show a tumorous lesion.

The following is the classification which we wish to propose for hereditary chorioretinal degenerations:


  A. Hereditary Chorioreti­nal Degenerations of Pre­dominantly Peripheral Loc­alization Top


I. Retinitis Pigmentosa.

1. Generalized retinitis pigmen­tosa

a) classical retinitis pigmen­tosa

1) of dominant heredity.

2) of recessive heredity.

3) of sex-linked heredity.

b) LEBER's congenital retinopathy.

c) senile pigmental retino­pathy.

d) combined retinitis pigmen­tosa (cerebroretinal forms),

2. Localized retinitis pigmentosa:

a) segmented retinitis pigmentosa.

b) pericentral retinitis pigmentosa,

II. Punctate Retinitis.

1. Albescent punctate retinitis.

2. Fundus albipunctatus cum hemeralopia.

III. Generalized Choroid Sclerosis.

IV. Fuchs' Gyrate Atrophy.

V. choroideremia.



  B. Hereditary Chorio­retinal Degenerations of Predominantly Central Localization Top


I. Central Retinitis Pigmentosa.

II. Sorsby's Pseudo-Inflamatory Dystrophy.

III. Angioid Striate Reti­nitis.

IV. Central and Peripapil­lary Choroid Sclerosis.

V. Hereditary Macular Degenerations,

in a wide variety of morphological types which can be classified on the basis of the following factors:

a) age at which symptoms occur (STARGARDT'S macular de­generation, senile macular degeneration, etc.).

b) mode of heredity.

c) concomitant somatic signs (infantile amaurotic idiocy).

VI. Choroidosis producing myopia.


  Summary Top


Tapetoretinal degenerations are hereditary, primary, progressive and generally premaure changes in a chorioretina previously apparently showing normal development.

The various tapetoretinal degenera­tions differ in genetic, anatomical, functional and somatic aspects which seem to refute the notion of absolute unity. Such a unity may perhaps be found, however, on the biochemical level

It is not difficult to distinguish tapetoretinal degenerations from retinal or choroid malformations, sensory anomalies of the retina, tumours and chorioretinal inflammations of infecti­ous orign.

Apart from the classical types of tapetoretinal degeneration the same group should be made to include LEBER's congenital retinal dystrophy, fundus albipunctatus cum hemeralopia, senile macular degeneration, angioid striate retinitis and choroiditis produc­ing myopia.[5]

 
  References Top

1.
Duke-Elder (Info) Text book of Ophthalmology Vol. 3. P. 3330. Kimpton, London.  Back to cited text no. 1
    
2.
V. Graefe (1862) A.f.O., 8, 242.  Back to cited text no. 2
    
3.
Haag (1915) K. Al. Aug., 54, 133. Cited by Duke-Elder (1940)  Back to cited text no. 3
    
4.
Sugar H. S. (1951) The Glaucomas, p 126. C. V. Mosby, St. Louis.  Back to cited text no. 4
    
5.
Weinstein (1953) Glaucoma Pathology C Therapy Translated by J. Folde. p. 61. C. V. Mosby, St. Louis.  Back to cited text no. 5
    




 

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Heredity
II. Localization...
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