- Email: [email protected]
Stochastical interpretation of retinal tear
STOCHASTICAL
INTERPRETATION
OF RETINAL TEAR
INTRODUCTION Detachment refers to the clinical process of separation of the neural (sensory) retina from the pigemented epithelial layer. This separation can be conceived as a state of discontinuity, while the normal retina is termed a continuum. Retinal tears, particularly horse-shoe tears, are pathognomic of retinal detachment in progression, i.e. a state of transition from continuum to discontinuum. Statistically, this simultaneous occurrence of the two orders of continuum results in a horse-shoe configuration of the tear. The substantial clinical evidence of retinal tears progressing toward detachment, and the virtual non-existence ofU-shaped or horse-shoe tears in detachments caused by colobomas, neoplasms and malignant melanoma, where no discontinuity exists histologically, substantiate the theoretical analysis. THEORY The neural architecture of the retinal tissue, although very complex, is exceptionally ordered. Embryological invagination of the (primary) optic vesicle produces a structure of two layers lying in opposition. The outer layer of this neuroectoderm continues to maturity as a deeply pigmented layer of the epithelium and becomes the definitive pigment cell lamina. The inverted, inner, neuroectodermal layer is the many layered neural (sensory) retina. These two layers are mutually interdependent and functionally integrated in a fully functional normal retina. Separation of the neural laminae from the pigment cell lamina of the retina is clinically termed ‘detachment’, thus in a sense it is re-opening of the lumen of the optic vesicle, with the plane of cleavage being intravitreal.
or lattic degeneration’ is by now well described. The flap or tear itself is thought to be caused by vitreous traction on the retina at the point of the tear. What is not seriously considered is the unique U-shape or horse-shoe shape of the flap. It is the purpose of this communication to suggest theoretical conceptions, for this aspect of the tear, which possess heuristic value towards better understanding and management of retinal detachment. For a normal retina the undetached laminae of the neural (sensory) retina and the pigment epithelium are conceived as a continuum. The two laminae of the optic vesicle are in close opposition and are fenestrated to each other histologically. The retinal attachment is normally influenced by acid mucopolysaccharides (AMPS) acting as a biological ‘glue’? retinal pigment epithelial cell sheaths excert a contractile for&’ and dynamic forces as positive vitreous pressure lo . The detached retina constitutes a discontinuum of separate elements. In the continuum the retinal tissue is continuously distributed throughout space so that a certain density must exist at every point. The discontinuum or detachment requires that the retinal medium is concentrated in certain regions. In the clinical state of retinal tear these two concepts co-exist, for the tear is localized to certain regions and not the entire fundus,as in large bullous detachment and large retinal tears. Therefore, the state of order in a U-shaped retinal tear is a process consisting of the transition of the system from the first stage (continuum) to the second stage (discontinuum) in the region specific to the tear. Mathematical
characterization
can easily be deter-
Detachment of the retina occurs for a variety of reasons. Primarily it could be trauma, vitreous traction, vitreoretinal factors, neoplasmas or idiopathic. Aphakia and high myopia are equally important predisposing factors. In a simple detachment like the rhegmatogenous detachment, with which we are concerned here, the separation of the laminate is governed by causative factors such as fluid production behind the laminae. Also important are the weight of the (subretinal) fluid in relation to the erect posture of man; the anatomical limitations of the disc and ora-serratta, and the degree of retinal setting and chorioretinal adhesions presentl, not forgetting pathognomic retinal holes and breaks. The incidence, distribution and appearance of retinal flaws play a key role in pre-operative diagnosis and management of the detachment. The ubiquitous retinal tear or break has been identified as the causative factoti of the detachment and its relationship to the extensions of the vitreous base or tufts3; pigmented spots4; meridonial fold?; enclosed bays of the ora-serrata6 0 1987 Butteworth 0111-5425/87/030283-02
& Co (Publishers) $03.00
STATE
/
@p‘7. &&ve- +
Figure 1
Probability
of simultaneous
occt~rr~~ncc of two states
Ltd ,J. Biomcd.
Eng.
IqX7.
\‘oI
0. ,Juh
283
1
Letters to the Editor
mined by statistics for each of these states independently. The probability distribution for simultaneous occurrence can also be determined easily. The probability distribution, when translated graphically, gives a conceptual pattern to the transition state, and it is no surprise that the resulting pattern is that of an inverted conic (Figure I), which is the pattern of the retinal tear. The coexistance of these two states of order is so singularly specific that no other pattern is possible. The spherical contour of the retinal fundus and the fenestration between the laminae give a distorted or ragged conic to the tear. It is also possible that the raggedness of the tear is influenced by the presence of the positive vitreous pressure acting normally on the retinal tissue and the force of compression which tries to keep the tissue adherent during the event of actual stripping. The contention of this hypothesis is not to evolve a theory for the aetiology of a horse-shoe tear but to seek a justification for the pattern of the tear from statistical theory; the justification for which is already well established from the clinical data. CLINICAL
All these reports indicate that clinically a horseshoe tear is a predisposing symptomatic sign towards detachment and that the state of simultaneous occurrence of the two orders of continuum coincides with the clinical stage of the appearance of the tear. It cannot be otherwise. The study by Hyamsi4 of 873 retinal detachment-prone eyes followed from 1 to 6 years shows that of the various retinal lesions, holes or breaks present, only 14 progressed towards detachment in an apparently normal retina. Unfortunately, Hyams does not report the form of the lesion, such as round holes, with or without opercular; retinal breaks or retinal tears as distinct from retinal tears of horse-shoe form.
J.
Finally, it is very important to discuss clinical detachment occurring in neoplasms and colobomas. Histologically in these disease states the description separation or detachment is semantically improper. In other words, in these cases no transition to discontinuum occurs. It is for this reason that in malignant melanomas retinal tear of the horse-shoe type is almost a non-occurrence, although one report of such a clinical finding has been reported15. finding has been reported15. CONCLUSION We can infer from such a successful theoretical interpretation certain pertinent points for the surgical management of tears which have a propensity towards detachment. It is also important to investigate how the retinal tear and the state of discontinuum itself would behave, prognostically, from a further analysis of the theoretical model so established. Laxmipuram
Biomcd. Eng. 1987, Vol. 9, July
P. SriVatsa
Stanford University Medical Center, PaloAlto, CA 94085, USA, and Retinitis Pigmentosa Foundation, 164 South Cross Road, Bangalone, 560 004, India
INFORMATION
Davis’s paper” on over 176 eyes with retinal breaks without detachment or with subclinical detachment, of 6 months to 16 years follow-up, reports that 3 1 eyes (18%) progressed to sub-clinical, asymptomatic, peripheral or symptomatic clinical detachment. In this series the detachment almost always occurred with symptomatic horse-shoe tears while progression to detachment with round holes, with or without opercula, was rare. In another study of over 162 breaks and 115 aphakic eyes with retinal breaks by Byer ‘* the author concludes, ‘the presence or absence of the horse-shoe tear determines the progression to rhegmatogenous retinal detachment’. Admittedly, both Byer and Davis do not think that it is important to indicate the number of contralateral eyes with horse-shoe tear, as distinct from other forms of tear and breaks. Nevertheless, both conclude that a fresh horse-shoe retinal tear is pathognomic of retinal detachment. In the third series of over 204 eyes left untreated for retinal lesions like lattice degeneration, Byeri3 notes that only one was with a horse-shoe tear and it ultimately progressed towards detachment.
284
However, one case of specific horse-shoe tear progressing towards detachment was reported.
I
2 3
4 5
6
7
8
9
10
11 12 13 14
15
Bedford, M.A. and Chignell, A.H. U-shaped retinal tears. Br. J. Ophthalmol. 1970, 54, 200 Schepens, C.L. and Marden, D. Data on the natural history of retinal detachment. Arch. Ophthaimol. 198 1, 66, 63 1 Foos, R.Y. Vitreous base, retinal tufts and retinal tears: pathological relationships. In: Retinal Congress Eds. R.C. Pruett and C.D.J. Regan. Appleton Century Crofts: New York, USA. 1974, 259-280 Lincoff, H. and Gleser, R. Finding the retinal hole. Arch. Ophthalmol. 197 I, 85, 565 Spenser, L.M., Foos, R.Y. and Straatsma, B.R. Meridonial folds, meridonial complexes and associated abnormalities of the periphereal retina. Am. J. Ophthalmol. 1970, 70, 697 Spenser, L.M., Foos, R.Y. and Straatsma, B.R. Enclosed bays of the ora-serrata: relationship to retinal tears. Arch. Ophthalmol. 1970, 83, 421 Straatsma, B.R., Foos, R.Y. and Shabo, A.L. Lattice degenerations of the retina. Am. J. Ophthalmol. 1974, 77, 617 De-Guillebon, H. and Zauberman, H. Experimental retinal detachment: bio-physical aspects of retinal peeling and stripping. Arch. Ophthalmol. 972, 81, 545 Spitznas, M., Hogan, M.S. Outer segments of photoreceptors and retinal pigment epithelium: interrelationships in the human eye. Arch. Ophthalmol. 1970, 84,810 Hayashi, QT., Anliker, M. and S&is, J.W. Model studies of retinal setting under various dynamic forces. Arch Ophthalmol. 1979, 81, 58 Davis, M.D. The natural history of retinal breaks without detachment. Trans. Am. Ophthalmol. Sot. 1973, 71, 343 Byer, N.E. Progression of asymptomamatic retinal breaks. Arch Ophthalmol 1974, 92, 208 Byer, N.E. Change in and prognosis of lattice degeneration of the retina. Trans. Am. Acad Ophthalmol. Otolog. 1974, 78,114 Hyams, S.W., Meir, E. and Wry, M. Chorioretinal lesions predisoposing to retina1 detachment. Am. J. Okhthalmol 1974, 78, 429 Duke-Elder, S. Systems in Ophthalmology. Vol. 3. Kimpon: London, UK. 1961, 2561
INTERPRETATION
OF RETINAL TEAR
INTRODUCTION Detachment refers to the clinical process of separation of the neural (sensory) retina from the pigemented epithelial layer. This separation can be conceived as a state of discontinuity, while the normal retina is termed a continuum. Retinal tears, particularly horse-shoe tears, are pathognomic of retinal detachment in progression, i.e. a state of transition from continuum to discontinuum. Statistically, this simultaneous occurrence of the two orders of continuum results in a horse-shoe configuration of the tear. The substantial clinical evidence of retinal tears progressing toward detachment, and the virtual non-existence ofU-shaped or horse-shoe tears in detachments caused by colobomas, neoplasms and malignant melanoma, where no discontinuity exists histologically, substantiate the theoretical analysis. THEORY The neural architecture of the retinal tissue, although very complex, is exceptionally ordered. Embryological invagination of the (primary) optic vesicle produces a structure of two layers lying in opposition. The outer layer of this neuroectoderm continues to maturity as a deeply pigmented layer of the epithelium and becomes the definitive pigment cell lamina. The inverted, inner, neuroectodermal layer is the many layered neural (sensory) retina. These two layers are mutually interdependent and functionally integrated in a fully functional normal retina. Separation of the neural laminae from the pigment cell lamina of the retina is clinically termed ‘detachment’, thus in a sense it is re-opening of the lumen of the optic vesicle, with the plane of cleavage being intravitreal.
or lattic degeneration’ is by now well described. The flap or tear itself is thought to be caused by vitreous traction on the retina at the point of the tear. What is not seriously considered is the unique U-shape or horse-shoe shape of the flap. It is the purpose of this communication to suggest theoretical conceptions, for this aspect of the tear, which possess heuristic value towards better understanding and management of retinal detachment. For a normal retina the undetached laminae of the neural (sensory) retina and the pigment epithelium are conceived as a continuum. The two laminae of the optic vesicle are in close opposition and are fenestrated to each other histologically. The retinal attachment is normally influenced by acid mucopolysaccharides (AMPS) acting as a biological ‘glue’? retinal pigment epithelial cell sheaths excert a contractile for&’ and dynamic forces as positive vitreous pressure lo . The detached retina constitutes a discontinuum of separate elements. In the continuum the retinal tissue is continuously distributed throughout space so that a certain density must exist at every point. The discontinuum or detachment requires that the retinal medium is concentrated in certain regions. In the clinical state of retinal tear these two concepts co-exist, for the tear is localized to certain regions and not the entire fundus,as in large bullous detachment and large retinal tears. Therefore, the state of order in a U-shaped retinal tear is a process consisting of the transition of the system from the first stage (continuum) to the second stage (discontinuum) in the region specific to the tear. Mathematical
characterization
can easily be deter-
Detachment of the retina occurs for a variety of reasons. Primarily it could be trauma, vitreous traction, vitreoretinal factors, neoplasmas or idiopathic. Aphakia and high myopia are equally important predisposing factors. In a simple detachment like the rhegmatogenous detachment, with which we are concerned here, the separation of the laminate is governed by causative factors such as fluid production behind the laminae. Also important are the weight of the (subretinal) fluid in relation to the erect posture of man; the anatomical limitations of the disc and ora-serratta, and the degree of retinal setting and chorioretinal adhesions presentl, not forgetting pathognomic retinal holes and breaks. The incidence, distribution and appearance of retinal flaws play a key role in pre-operative diagnosis and management of the detachment. The ubiquitous retinal tear or break has been identified as the causative factoti of the detachment and its relationship to the extensions of the vitreous base or tufts3; pigmented spots4; meridonial fold?; enclosed bays of the ora-serrata6 0 1987 Butteworth 0111-5425/87/030283-02
& Co (Publishers) $03.00
STATE
/
@p‘7. &&ve- +
Figure 1
Probability
of simultaneous
occt~rr~~ncc of two states
Ltd ,J. Biomcd.
Eng.
IqX7.
\‘oI
0. ,Juh
283
1
Letters to the Editor
mined by statistics for each of these states independently. The probability distribution for simultaneous occurrence can also be determined easily. The probability distribution, when translated graphically, gives a conceptual pattern to the transition state, and it is no surprise that the resulting pattern is that of an inverted conic (Figure I), which is the pattern of the retinal tear. The coexistance of these two states of order is so singularly specific that no other pattern is possible. The spherical contour of the retinal fundus and the fenestration between the laminae give a distorted or ragged conic to the tear. It is also possible that the raggedness of the tear is influenced by the presence of the positive vitreous pressure acting normally on the retinal tissue and the force of compression which tries to keep the tissue adherent during the event of actual stripping. The contention of this hypothesis is not to evolve a theory for the aetiology of a horse-shoe tear but to seek a justification for the pattern of the tear from statistical theory; the justification for which is already well established from the clinical data. CLINICAL
All these reports indicate that clinically a horseshoe tear is a predisposing symptomatic sign towards detachment and that the state of simultaneous occurrence of the two orders of continuum coincides with the clinical stage of the appearance of the tear. It cannot be otherwise. The study by Hyamsi4 of 873 retinal detachment-prone eyes followed from 1 to 6 years shows that of the various retinal lesions, holes or breaks present, only 14 progressed towards detachment in an apparently normal retina. Unfortunately, Hyams does not report the form of the lesion, such as round holes, with or without opercular; retinal breaks or retinal tears as distinct from retinal tears of horse-shoe form.
J.
Finally, it is very important to discuss clinical detachment occurring in neoplasms and colobomas. Histologically in these disease states the description separation or detachment is semantically improper. In other words, in these cases no transition to discontinuum occurs. It is for this reason that in malignant melanomas retinal tear of the horse-shoe type is almost a non-occurrence, although one report of such a clinical finding has been reported15. finding has been reported15. CONCLUSION We can infer from such a successful theoretical interpretation certain pertinent points for the surgical management of tears which have a propensity towards detachment. It is also important to investigate how the retinal tear and the state of discontinuum itself would behave, prognostically, from a further analysis of the theoretical model so established. Laxmipuram
Biomcd. Eng. 1987, Vol. 9, July
P. SriVatsa
Stanford University Medical Center, PaloAlto, CA 94085, USA, and Retinitis Pigmentosa Foundation, 164 South Cross Road, Bangalone, 560 004, India
INFORMATION
Davis’s paper” on over 176 eyes with retinal breaks without detachment or with subclinical detachment, of 6 months to 16 years follow-up, reports that 3 1 eyes (18%) progressed to sub-clinical, asymptomatic, peripheral or symptomatic clinical detachment. In this series the detachment almost always occurred with symptomatic horse-shoe tears while progression to detachment with round holes, with or without opercula, was rare. In another study of over 162 breaks and 115 aphakic eyes with retinal breaks by Byer ‘* the author concludes, ‘the presence or absence of the horse-shoe tear determines the progression to rhegmatogenous retinal detachment’. Admittedly, both Byer and Davis do not think that it is important to indicate the number of contralateral eyes with horse-shoe tear, as distinct from other forms of tear and breaks. Nevertheless, both conclude that a fresh horse-shoe retinal tear is pathognomic of retinal detachment. In the third series of over 204 eyes left untreated for retinal lesions like lattice degeneration, Byeri3 notes that only one was with a horse-shoe tear and it ultimately progressed towards detachment.
284
However, one case of specific horse-shoe tear progressing towards detachment was reported.
I
2 3
4 5
6
7
8
9
10
11 12 13 14
15
Bedford, M.A. and Chignell, A.H. U-shaped retinal tears. Br. J. Ophthalmol. 1970, 54, 200 Schepens, C.L. and Marden, D. Data on the natural history of retinal detachment. Arch. Ophthaimol. 198 1, 66, 63 1 Foos, R.Y. Vitreous base, retinal tufts and retinal tears: pathological relationships. In: Retinal Congress Eds. R.C. Pruett and C.D.J. Regan. Appleton Century Crofts: New York, USA. 1974, 259-280 Lincoff, H. and Gleser, R. Finding the retinal hole. Arch. Ophthalmol. 197 I, 85, 565 Spenser, L.M., Foos, R.Y. and Straatsma, B.R. Meridonial folds, meridonial complexes and associated abnormalities of the periphereal retina. Am. J. Ophthalmol. 1970, 70, 697 Spenser, L.M., Foos, R.Y. and Straatsma, B.R. Enclosed bays of the ora-serrata: relationship to retinal tears. Arch. Ophthalmol. 1970, 83, 421 Straatsma, B.R., Foos, R.Y. and Shabo, A.L. Lattice degenerations of the retina. Am. J. Ophthalmol. 1974, 77, 617 De-Guillebon, H. and Zauberman, H. Experimental retinal detachment: bio-physical aspects of retinal peeling and stripping. Arch. Ophthalmol. 972, 81, 545 Spitznas, M., Hogan, M.S. Outer segments of photoreceptors and retinal pigment epithelium: interrelationships in the human eye. Arch. Ophthalmol. 1970, 84,810 Hayashi, QT., Anliker, M. and S&is, J.W. Model studies of retinal setting under various dynamic forces. Arch Ophthalmol. 1979, 81, 58 Davis, M.D. The natural history of retinal breaks without detachment. Trans. Am. Ophthalmol. Sot. 1973, 71, 343 Byer, N.E. Progression of asymptomamatic retinal breaks. Arch Ophthalmol 1974, 92, 208 Byer, N.E. Change in and prognosis of lattice degeneration of the retina. Trans. Am. Acad Ophthalmol. Otolog. 1974, 78,114 Hyams, S.W., Meir, E. and Wry, M. Chorioretinal lesions predisoposing to retina1 detachment. Am. J. Okhthalmol 1974, 78, 429 Duke-Elder, S. Systems in Ophthalmology. Vol. 3. Kimpon: London, UK. 1961, 2561