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Journal Français d'Ophtalmologie
Volume 41, n° 1
pages 62-77 (janvier 2018)
Doi : 10.1016/j.jfo.2017.08.003
Received : 6 June 2017 ;  accepted : 17 August 2017
Revues générales

Sclerotic scatter
Dispersion sclérale
 

E. Denion a, b, c, d, , G. Béraud e, f, g, M.-L. Marshall h, G. Denion i, A.-L. Lux a, b
a Service d’ophtalmologie, CHU de Caen, avenue de la Côte-de-Nacre, 14033 Caen cedex 9, France 
b Pôle de formation et de recherche en santé, faculté de médecine, Unicaen, 2, rue des Rochambelles, CS 14032, 14032 Caen cedex, France 
c Inserm, U 1075 COMETE, pôle de formation et de recherche en santé, 2, rue des Rochambelles, CS 14032, 14032 Caen cedex, France 
d Centre ophtalmologique du pays des olonnes (COPO), 9, rue du Maréchal-Leclerc, 85100 Les Sables-d’Olonne, France 
e Médecine interne et maladies infectieuses, CHU de Poitiers, 86000 Poitiers, France 
f EA2694, université droit et santé Lille 2, 59000 Lille, France 
g Interuniversity Institute for Biostatistics and Statistical Bioinformatics, Hasselt University, Hasselt, Belgium 
h Ernst & Young, 102, Rivonia road, Dennehof, 2196 Sandton, South Africa 
i Cabinet de médecine générale, rue de la Grâce de Dieu, 14610 Epron, France 

Corresponding author.
Summary

Sclerotic scatter involves the scattering of incident light by the limbal sclera followed by entry of part of the scattered light into the cornea, where some of the light travels through total internal reflection to the other side, where it scatters a second time in the limbal sclera. It is then visible in the form of a limbal scleral arc of light. Sclerotic scatter has been used for decades to spot and delineate corneal opacities, which disrupt and scatter the light travelling through total internal reflection. To implement the technique, the slit beam and the binoculars of the slit lamp should be dissociated so that the limbal sclera is illuminated, while the binoculars are centered on the cornea. The technique does not provide any information as to the depth of corneal opacities and therefore needs to be complemented by direct illumination. The second sclerotic scatter may also be used clinically, for instance for diode cycloablation, the posterior part of the arc of light projecting 0.5mm behind the scleral spur. This article aims to describe the phenomenon of sclerotic scatter, explaining how the slit-lamp should be set to use this technique, describing its clinical applications (in the opacified cornea and in the normal sclera), showing that the limbal scleral arc of light of sclerotic scatter may be seen under certain circumstances in daily life with the naked eye and, finally, explaining how the arc of light differs from peripheral light focusing (“Coroneo effect“).

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Résumé

La dispersion sclérale se base sur la dispersion d’une lumière éclairant la sclère limbique, suivie d’une entrée d’une partie des rayons lumineux dans la cornée où certains rayons traversent la cornée par réflexion totale interne jusqu’à l’autre côté où une seconde dispersion survient dans la sclère limbique et est visible sous la forme d’un croissant clair. La dispersion sclérale est utilisée depuis des décennies pour détecter et délimiter des opacités cornéennes qui s’interposent sur le trajet de la lumière cheminant par réflexion totale interne et la dispersent. Pour mettre en œuvre cette technique, le système d’éclairement et le système optique du biomicroscope doivent être désolidarisés afin que le limbe puisse être éclairé, tandis que la cornée reste au centre du champ du microscope. La technique n’apporte aucune information sur la profondeur des lésions et doit donc être complétée par une étude des opacités par examen direct. La seconde dispersion sclérale peut aussi être utilisée cliniquement, par exemple pour effectuer un cyclo-affaiblissement au laser diode, la partie postérieure de l’arc lumineux limbique se projetant 0,5mm en arrière de l’éperon scléral. Cet article a pour but de décrire le phénomène de dispersion sclérale, d’expliquer comment le biomicroscope doit être réglé pour mettre en œuvre cette technique, de décrire les applications cliniques de la dispersion sclérale, de montrer que le croissant clair de la dispersion sclérale peut être vu à l’œil nu, dans la vie quotidienne, dans certaines conditions, et finalement d’expliquer en quoi le croissant clair diffère de la concentration de la lumière périphérique (« effet Coroneo »).

The full text of this article is available in PDF format.

Keywords : Sclerotic scatter, Cornea, Sclera, Corneal scar, Peripheral light focusing

Mots clés : Dispersion sclérale, Cornée, Sclère, Taie cornéenne, Concentration de la lumière périphérique


Introduction

From an ophthalmologist's point of view, sclerotic scatter is first and foremost a biomicroscopic technique aimed at spotting and mapping corneal opacities, wherever they may lie within the cornea. This technique is based on the scattering of light – travelling into the cornea by total internal reflection – by the corneal opacities [1]. At first glance, then, sclerotic scatter appears to be a misnomer. Nevertheless, renaming sclerotic scatter “corneal scatter” would be most unfair. Firstly, in sclerotic scatter, no scattering of light occurs in the cornea unless opacities are present [2, 3]. Secondly, the primum movens of sclerotic scatter is indeed sclerotic scatter: scatter that takes place at the limbal sclera. And the endpoint of sclerotic scatter, after the light has moved from one limbus to the other through total internal reflection into the cornea, is sclerotic scatter: scatter that takes place at the opposite limbus. Sclerotic scatter, which involves two systematic scatterings of light into the limbal sclera versus an opacity-dependant scattering of light into the cornea, is consequently not a misnomer. This article aims at describing the phenomenon of sclerotic scatter, explaining how the slit-lamp should be used in its implementation, describing the clinical applications of sclerotic scatter (in the opacified cornea and in the normal sclera), showing that the limbal arc of light related to this phenomenon may under certain circumstances in everyday life be seen with the naked eye, and, finally, explaining how sclerotic scatter differs from peripheral light focusing.

The sclerotic scatter phenomenon

Basil Graves, a British Ophthalmologist (Figure 1), described sclerotic scatter in a book chapter published in 1936 [1]. Among other sources we consulted [2, 3, 4, 5, 6, 7, 8], Graves is probably the author to have best explained the primum movens of sclerotic scatter as the striking of light at the limbal sclera, resulting in light scattering in no particular direction (Figure 2, Figure 3) [1]. A small part of the scattered light can enter the peripheral cornea (Figure 2) [1]. Depending on their direction, the light rays then may travel into the cornea through total internal reflection (Figure 3) [1, 9]. The genius of Basil Grave was to find a means of trapping light in the cornea, subsequently use the cornea as a solid curved volume to guide light from one limbus to the other in a fashion similar to that reported by Swiss physicist Jean-Daniel Colladon in 1842 for a parabolic water stream [10]. Owing to the close refractive indices of the cornea and aqueous humour (respectively 1.376 and 1.336 [11]), the light rays must strike the interface between the cornea and aqueous humour in a strongly oblique direction (≤13.8°) so as to undergo total internal reflection, whereas on the interface between the cornea and air, the direction of the critical angle is much larger (48.4°) [9]. The light rays remaining trapped in the cornea by total internal reflection reach the other side of the cornea and undergo a second scattering by the limbal sclera (Figure 2, Figure 3). The contingent of rays scattered back to the examiner's eyes can then be seen as a limbal arc of light (Figure 2, Figure 3). Alternative pathways contributing to this limbal arc may exist: refraction followed by reflection on the iris or sclerotic scatter followed by reflection on the iris followed by total internal reflection within the anterior chamber [9]. Nevertheless, the contribution of such pathways seems negligible [9]. Per-operatively, we have consistently observed that filling the anterior chamber with trypan blue, a dense dye, does not change limbal arc appearance (Figure 4a–d). Such a finding shows that total internal reflection within the cornea – as opposed to the alternative trans-cameral pathways – is indeed the main pathway [9] contributing to the limbal arc.



Figure 1


Figure 1. 

Basil Graves. Photography taken at the Oxford ophthalmology congress in 1937 and provided by Richard Keeler, honorary curator at the Royal College of Ophthalmologists. The man with the white handkerchief is Basil Graves, 48 years old at the time.

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Figure 2


Figure 2. 

Sclerotic scatter. A red laser aiming beam is applied at the nasal limbal sclera where it is scattered, travels into the cornea through total internal reflection in every possible directions, reaches the opposite side where it scatters a second time in the limbal sclera where it appears as a red light arc.

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Figure 3


Figure 3. 

Schematic cross-section of sclerotic scatter. The incident light (1) is scattered by the limbal sclera (2) in every direction. Most of the directions are incompatible with entry into the cornea (red arrows) but some light does enter the cornea (yellow arrow). Among these rays, some are refracted and leave the cornea (3). Other travelling through total internal reflection may be stopped and scattered by a corneal opacity (4) or may reach the other limbus where they scatter a second time (5) and are visible to the examiner in the form of a limbal scleral arc of light.

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Figure 4


Figure 4. 

Sclerotic scatter with an undisrupted and then trypan blue-filled anterior chamber: a: the slit lamp attached to the operating microscope illuminates the temporal limbus and elicits a limbal scleral light arc on the opposite side; b: the anterior chamber is filled with trypan blue using a Ryckroft canula; c: the anterior chamber is completely filled with trypan blue; d: the slit light beam is again applied at the temporal limbus, which results in a limbal scleral light arc unchanged compared to the initial situation.

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How should a slit lamp be used to implement sclerotic scatter?

Prior to producing sclerotic scatter, the examiner should decouple the biomicroscope binoculars from the illumination system by unscrewing the thumb wheel through which it is secured (Figure 5). The illumination system may then be moved clockwise or counterclockwise fashion around a vertical axis (Figure 6). Doing so can decentre the slit beam on the scleral limbus on the nasal or temporal side while focusing the binoculars centrally, in front of the cornea (Figure 7) [2, 4, 6]. If the eye is normal, the cornea does not scatter any light [2, 3] and therefore remains dark against a dark background [2] while a limbal light arc is visible at the limbal sclera opposite the illuminated side (Figure 6) [1] (Figure 7).



Figure 5


Figure 5. 

Decoupling of the biomicroscope binoculars from the illumination system. Decoupling is achieved by unscrewing the thumb wheel securing the illumination system (yellow curved arrow).

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Figure 6


Figure 6. 

Decentring the illumination system. The decentring is achieved by moving the illumination system around a vertical axis (blue dotted line), either counterclockwise as illustrated here (yellow dotted lines/curved arrows) or clockwise.

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Figure 7


Figure 7. 

Sclerotic scatter in a normal eye. The light beam is directed on one limbus while, through decoupling, the binoculars are centered on the cornea, which does not scatter any light and conveys light to the other limbus, where an arc of light is visible.

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As already mentioned, only a fraction of the incident light scattered at one limbus is able to enter the cornea to travel internally [1] and only a portion of the light rays entering the cornea remains trapped in the cornea[9]. For these reasons, in order to perform sclerotic scatter, the light beam applied to the limbal sclera should be as bright as possible [2, 3], which presents the drawback of at times being difficult to tolerate for photophobic patients [3].

The clinical applications of sclerotic scatter

The clinical applications of sclerotic scatter may be divided into two categories: those related to the corneal scatter occurring only if the cornea has opacities, and those related to the second sclerotic scatter occurring at the limbus opposite the side where the light beam is shone.

Regarding the clinical applications related to corneal scatter, it should first and foremost be mentioned that the normal cornea is optically quiet, [3] i.e. it does not scatter any light [2, 3]. If, the cornea has opacities, not matter how deep they may lie within the cornea, the light rays travelling through total internal reflection will be disrupted and scattered by the opacities (Figure 3). This will cause the opacities to light up [3] as some of the light is scattered forward to the binoculars [4] and as the opacities stand out against a dark field [2, 6], especially if the pupil is dilated [2]. This technique is great to spot even subtle opacities [2, 3] and to delineate and map them out [2]. It nonetheless does not give any information as to the depth of opacities and must therefore be completed by other slit-lamp techniques, especially direct illumination with a thin light slit to further characterize the opacities [3] (Figure 8, Figure 9). Examples of the use of sclerotic scatter in examination of endothelial, stromal and epithelial opacities are respectively displayed in Figure 8, Figure 9, Figure 10, Figure 11, Figure 12 and Figure 13, Figure 14. In complex cases with opacities located at different depth in the cornea, sclerotic scatter clarifies the situation by clearly mapping the opacities (Figure 15). Sclerotic scatter may also be used to properly set the amount of corneal removal in photokeratic keratectomies [12]. In such cases, a sterile light pipe may be applied at the scleral limbus to induce sclerotic scatter. This strongly contributes to mapping the opacities before laser treatment and mapping possible residual opacities after a first ablation, in which case a second ablation may be applied [12].



Figure 8


Figure 8. 

Examination of an endothelial lesion through sclerotic scatter, then direct illumination: a: sclerotic scatter clearly shows a cluster of slight central corneal opacities standing out against the dark background of the pupil; b: direct illumination shows that the opacities are endothelial pigments.

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Figure 9


Figure 9. 

Per-operative views of a herpetic corneal scar: a: using direct illumination and retro-illumination, the scar is barely visible; b: using sclerotic scatter, the scar stands out against the dark pupil and the scar limits are sharply demarcated.

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Figure 10


Figure 10. 

Corneal scar caused by a metallic wounding agent. Sclerotic scatter shows the penetration site, roughly vertical and sprinkled with numerous tiny metallic debris shining against the dark background, and the stromal scar, roughly rectangular and extended to the right of the penetration site.

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Figure 11


Figure 11. 

Stromal dystrophic lesion: a: under diffuse illumination, the peripheral yellowish lesion extends from the 9 to the 3 o’clock meridian; b: under sclerotic scatter, the lesion is luminous against a dark background facilitating the analysis of its outline, slightly irregular and, between 1 and 2 o’clock, showing two focal interruptions.

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Figure 12


Figure 12. 

Corneal scar caused by glass debris: a: under diffuse illumination, the scar is barely visible, even against the dark dilated pupil background; b: under sclerotic scatter, the complex shape of the scar as well as that of the scars of the nylon stiches (removed) are clearly visible.

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Figure 13


Figure 13. 

Superficial punctate keratitis. Sclerotic scatter clearly displays numerous epithelial defects against the dark pupil and iris background.

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Figure 14


Figure 14. 

Cornea verticillata and round corneal scar. Sclerotic scatter displays the characteristic brownish combed appearance of amiodarone-related cornea verticillata as well as a round stromal scar located just above and caused by a small superficial metallic foreign body removed a few years before.

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Figure 15


Figure 15. 

Complex corneal lesion: a: under diffuse illumination, the lesion is difficult to analyse partly because a nuclear cataract is present and brightens the background; b: under sclerotic scatter, the lesion appears to be much less large than previously thought, is split into two stromal scars (the largest is on the left) and numerous roughly vertical arcuate endothelial lines of pigment. These lesions stand out against the dark background, with sclerotic scatter providing very little lens illumination.

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Regarding the clinical applications of the second sclerotic scatter occurring at the limbus opposite the side where the light beam is shone, Ayoub and Said found that irrespective of the meridian, the posterior limit of sclerotic scatter projects approximately 0.5mm behind the scleral spur [5]. Per-operatively, sclerotic scatter may be induced with a slit lamp (Figure 16) or a light pipe. As it is more easily elicited under mesopic (or scotopic) rather than photopic conditions, the operating room should be kept as dark as possible [9]. This may help to identify the scleral spur, an anatomical landmark helping to perform T-flux implantation [13] or deep sclerotomy [14]. It may also contribute to performance of diode laser cycloablation [9], a procedure involving proper positioning of the probe in front of the pars plicata ciliaris [15]. To do so, the probe should be positioned immediately posterior to the posterior limit of the light arc [9] (Figure 16).



Figure 16


Figure 16. 

Use of sclerotic scatter to guide diode laser cycloablation: a: using sclerotic scatter in the dark operating rooms allows clear visualisation of the limbal scleral arc of light opposite the illuminated side; b: the laser probe is put immediately posterior to the posterior limit of the limbal scleral arc of light, which stands 0.5mm behind the scleral spur.

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Sclerotic scatter in everyday life and its differentiation from peripheral light focusing

With an average mean of 2.8, humans have the largest width/height ratio of the palpebral fissure among primates [16, 17]. This factor, in addition to the strong forward position of the human eyeball in the orbit [18], and the fact that the human lateral orbital margin is very rearward [19, 20] leaves the human cornea very exposed [21, 22]. Accordingly, humans have a large temporal visual field [22], which is enlarged through eye motion [23, 24]. Another consequence of the aforementioned factors, particularly the extraordinarily elongated human palpebral fissure [16, 17], is the visibility of the conjunctiva and underlying sclera located nasally and temporally to the cornea. Para-corneal sclera exposure is the sine qua non condition for sclerotic scatter to occur [1] and allows the second sclerotic scatter (limbal scleral arc of light) – after the light has crossed the cornea by total internal reflection – to at times be visible in everyday life, using one's bare eye [9]. The limbal scleral arc of light requires extreme contrast between the ambient light and the lateral light that triggers sclerotic scatter. It is more easily elicited in mesopic rather than photophic conditions. Furthermore, it occurs much more easily in some eyes [9] as though, for reasons still unknown, some eyes were able to “process” the lateral light much more efficiently than others.

For the scleral limbal arc to be elicited and to be visible to the bare human eye, the following conditions must be met: the limbal sclera must be visible on both sides of the cornea; one side must be lit (i.e. submitted to the lateral light triggering sclerotic scatter), while the other side is in the shade (i.e. submitted to ambient light only); on the side in the shade, some sclera must be visible beyond the limbus for the contrast between the limbal arc of light and the more peripheral sclera to be spotted. The orientation of the light triggering sclerotic scatter is not important as long as it lights the limbal sclera on one side, while leaving the limbal sclera on the other side in relative shade (Figure 17, Figure 18, Figure 19, Figure 20, Figure 21). If the contrast is not sufficient, the effect will not be visible (Figure 18). For a given lateral light orientation, either sclerotic scatter with a limbal scleral arc of light (Figure 22 a) or a second effect called peripheral light focusing [25] (or “Coroneo effect“) will occur (Figure 22b). Peripheral light focusing refers to the concentration by the cornea of light and ultraviolet albedo (i.e. the light that is reflected and scattered by surfaces [26]). More precisely, the light liable to be concentrated has a postero-lateral orientation roughly peaking at 120° from the sagittal plane [27]. This light is concentrated by the cornea, travels through the anterior chamber and ends at the opposite limbus, where its intensity reaches roughly 20 times that of the incident postero-lateral light [25] (Figure 23). This concentrated light, which is likely to be involved in the pathogenesis of pterygium [26], is best visible in the primary position of gaze, as illustrated in Figure 24. Peripheral light focusing occurs almost exclusively on the nasal side [26] as the very rearward lateral orbital margin avoids lateral vision obstruction [19, 20], whereas on the nasal side, the nose stops the postero-lateral light (except if the eye is moved in extreme abduction). Most of the time, the light inducing peripheral light focusing is albedo, but it may also be direct sunlight, provided that the sun is sufficiently low-lying, at sunrise or sunset (Figure 22b and Figure 25).



Figure 17


Figure 17. 

Sclerotic scatter in everyday life. In this left eye, the lateral light illuminates the nasal limbus. The left part of the eyeball is in the shade, which allows the limbal scleral arc of light to be clearly visible.

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Figure 18


Figure 18. 

Sclerotic scatter in everyday life. In the left eye, the light strikes the nasal limbus, where it induces sclerotic scatter and leaves the temporal part of the eyeball in the shade, which explains why the temporal limbal scleral arc of light is easily seen. In the right eye, the light strikes the temporal limbus, where it induces sclerotic scatter and leaves the nasal part of the eyeball in the shade. However, reflection of light on the nose base makes the shade less deep, to such an extent that the nasal limbal sclera arc of light is not visible.

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Figure 19


Figure 19. 

Sclerotic scatter in real life. In this right eye, the light strikes the temporal limbus with a mostly vertical/slightly lateral direction, elicits sclerotic scatter and results in a nasal limbal scleral arc of light standing out in this shaded area.

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Figure 20


Figure 20. 

Sclerotic scatter in everyday life. In this individual, limbal scleral arc of light is visible at the temporal limbus of the left eye and also–despite less contrast owing to reflection of the lateral light on the nose base–at the nasal limbus of the right eye.

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Figure 21


Figure 21. 

Sclerotic scatter in real life. In the left eye, the light strikes the nasal limbus with a mostly vertical/slightly lateral direction, induces sclerotic scatter and results in a temporal limbal scleral arc of light standing out in this shaded area. In the right eye, the light strikes the temporal limbus, where it induces sclerotic scatter. Reflection of the light on the nose diminishes the shade on the nasal side and makes the contrast insufficient for the nasal limbal scleral arc to be seen by the human eye.

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Figure 22


Figure 22. 

Sclerotic scatter in real life: a: in the left eye in the primary position of gaze, the lateral light strikes the temporal limbus in a lateral fashion and induces sclerotic scatter. A limbal scleral arc of light is visible on the nasal side, which stands in relative shade. This relative shade also allows the subject to see a tiny red spot just temporal to the plica semilunaris, corresponding to the internal projection of the pupil area; b: a moment later, under the same lighting conditions, the subject has turned her head and has moved her eye in adduction. The postero-lateral light is concentrated by the cornea in a trans-cameral fashion to the nasal limbus, where it appears as a clear spot is peripheral light focusing (“Coroneo effect”).

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Figure 23


Figure 23. 

Schematic drawing of peripheral light focusing. The postero-lateral light (1) is refracted by the temporal cornea (2), concentrated through the anterior chamber (3) and reaches the nasal limbus where light intensity is roughly 20 times that of the incident light (4).

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Figure 24


Figure 24. 

Peripheral light focusing in everyday life. In this subject, the postero-lateral albedo strikes the temporal cornea, is concentrated through the anterior chamber and is concentrated at the nasal limbus, where it appears as a bright light spot.

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Figure 25


Figure 25. 

Peripheral light focusing in everyday life. An example of peripheral light focusing, with the characteristic nasal bright spot of concentrated light, caused not by albedo, but by direct light.

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The range of orientation of the lateral or postero-lateral light orientation triggering the limbal scleral arc of light (sclerotic scatter) or the concentrated scleral light spot (peripheral light focusing) overlap. Depending on this orientation, the two effects may be visible simultaneously (Figure 26a) or not (Figure 26b).



Figure 26


Figure 26. 

Co-existence of sclerotic scatter and peripheral light focusing in everyday life: a: in this right eye, the slightly postero-lateral light induces sclerotic scatter on the temporal side, which results in a limbal scleral arc of light clearly visible on the nasal side. Peripheral light focusing is visible on the iris as a triangular light pattern whose summit projects on the nasal sclera, on the 3 o’clock meridian, but is barely visible as the light concentration does not reach its peak for this light incidence and because the sclerotic scatter limbal arc provides a clear background; b: in the same eye, eye adduction results in a much more postero-lateral angle of the incident light. Under this angle, sclerotic scatter is not induced whereas peripheral light focusing reaches its peak, and is clearly visible as a concentrated light spot at the nasal limbus just above the 3 o’clock meridian.

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Conclusion

Niels Bohr's motto, “contraria sunt complementa” (translating, “opposites are complementary“) applies to sclerotic scatter, a phenomenon in which light and shadow intermingle, as on the taijitu displayed on Bohr's coat of arms [28]. As a slit-lamp technique, sclerotic scatter requires a powerful light applied at the scleral limbus. If corneal opacities are present, the light they scatter is easily seen on the dark background, especially if the pupil is dilated. Corneal opacities may thereby be efficiently spotted and precisely delineated. The depth of these opacities within the cornea may then be assessed using a thin slit of light. The limbal scleral arc of light appearing on the non-illuminated side is the result of the scattering by the sclera of the light having travelled in the cornea through total internal reflection. This arc is in the shade and is easily seen, especially if the room is dark. The posterior part of this arc is located 0.5 behind the scleral spur, an important anatomical landmark in glaucoma surgery and diode laser cycloablation.

In life, the limbal scleral arc may be seen with the naked eye provided that the contrast between the lateral light triggering the phenomenon and the ambient light leaving the other side in relative shade is high enough.

Disclosure of interest

The authors declare that they have no competing interest.


Acknowledgement

The authors thank Jeffrey Arsham, a medical translator, for reading and reviewing the original English-language text.


 Part of the information displayed in this article was presented during the 114th congress of the “Société française d’ophtalmologie” (Paris, May 2008) in a film entitled “Effet coroneo : une idée lumineuse !” and during the 122th congress of the “Société française d’ophtalmologie” (Paris, May 2016) in a film entitled “Cette obscure clarté cornéenne et sclérale”.
 Une partie des informations contenues dans ce texte ont été présentées au 114e congrès de la Société française d’ophtalmologie (Paris, mai 2008) dans une communication filmée intitulée « Effet Coroneo : une idée lumineuse » et au 122e congrès de la Société française d’ophtalmologie (Paris, mai 2016) dans une communication filmée intitulée « Cette obscure clarté cornéenne et sclérale ».

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