15 Aplicacion En Neuro Oftalmologia

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CHAPTER 15 APPLICATION OF CONFOCAL LASER TOMOGRAPHY IN NEURO-OPHTHALMOLOGY Dr. Roberto Ebner

15.1 Introduction to confocal tomography (CLT) in neuro-ophthalmology 15.1.1 Acquisition and treatment of images CLT enables the study of those diseases manifested at the level of the optic disc and its surroundings. Although the image acquisition process is consistent with the general rules for CLT (see chapter 2), some entities may require for their study wide capture angles (15 or 20 degrees instead of 10 degrees used routinely), in order to cover all the manifestations of the process in the same image. This is the case in edematous disc processes, where the disc diameter is larger than under normal conditions (figure 7.6). 15.1.2 Contour line In edematous optic disc processes, the scleral spur is difficult or impossible to identify, therefore, the contour line cannot be drawn as described according to the technique (for example, in glaucomatous cases). The area to be studied should then be enclosed by drawing a circle (obtained from the pertinent submenu). In the specific case of optic disc edemas, the circle should be located at the level of Patton’s line or beyond it (figure 15.1). 15.1.3 Selection of the area to be measured The measurements (linear, area or volume parameters) are performed within the defined contour line. There structure enclosed by the contour line can be measured in a global or partial manner. The complete interior of the contour line (360 degrees) may be of interest, or a selected sector may be indicated (in the Measure submenu) in order to perform a partial measurement (figure 15.2). 15.2 Clinical cases and CLT in neuro-ophthalmology 15.2.1 Optic disc elevations Edema: Optic disc edema produced by the hypertension of the cerebrospinal fluid, either in the case of idiopathic intracranial hypertension, also known as pseudotumor cerebri, or in the case of hypertension due to an occupying mass, yield CLT images with a characteristic "volcanic" appearance (not chronic or atrophic chronic), when the edema is well developed [1-3]. The central portion of the image obtained, the volcano crater,

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Fig. 15.1: The image at the top left-hand shows how the contour line should be drawn. It should follow the scleral spur. The top right-hand image shows the complete drawing. The planes enabling one to achieve a better image of the neuroretinal rim margin can be chosen from the series of 32 images shown between the previously described images. The images at the bottom are from a case with optic disc edema, where the contour line should be drawn outside the over-elevated area. corresponds to the remaining disc cup. Its base (the base of the volcanic cone) has an area much greater than the area of a normal disc. The value of the parameter ‘volume above surface’, provides the volume (in mm3) of all of the structures elevated above the retinal surface, thus providing the measurement of the ‘volume of the edema’ for each case and according to the evolution stage (figure 15.3). Different three-dimensional images may be acquired at different time in a longitudinal study in such a way, that the behavior of the causal process and its effect on the optic nerve can be monitored. In the case of pseudotumor cerebri, the effectiveness of the treatment (with the use of osmotic diuretics, steroids, etc.) may be evaluated by means of CLT by comparing the volume of the papilledema at variable time intervals. If worsening is observed, then treatment may be modified (medication dosage increase or indication of decompressive surgery of the optic nerve sheath). Otherwise, a decrease in the volume of the edema will be indicative of treatment effectiveness. Changes in volume of the papilledema can be detected early enough so that clinical changes may not yet have appeared (worsening of visual acuity, visual field defects or color vision disorders). This monitoring is also valid in the case of tumors in the CNS that cannot be subjected to surgery and which are treated with radiotherapy and/or chemotherapy. For longitudinal studies to evaluate the changes in the volume of a disc, we may just stick to the value of said parameter (volume above surface) for each examination, or we may use the comparison submenu (topographic difference image) in order to display the observed height changes as graphs or numbers. The difference images presented show the locations where a volume decrease is detected in red color, while the locations where

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Fig. 15.2: Selection of a segment of the optic disc image (inferior nasal and temporal octants) in order to measure volumes. Within this segment there is a tumorous formation.

Fig. 15.3 there is a volume increase appear in green color. If differences in volume only involve fibers, the ‘measure’ submenu numerically (in mm3) provides the volume differences between the examinations (as well as the time elapsed between examinations). Values indicating volume increase are positive and those indicating volume decrease are negative (figure 15.4). When the disc edema has led to optic disc atrophy, the optic disc is flat. In some cases, it is accompanied by radiated folds (which take a long time to disappear). Pseudoedema of the optic disc (drusen): The presence of hyaline bodies (drusen) buried into the optic disc, lead to an over-elevation of the optic nerve head. Classically, the presence of these hyaline bodies has constituted one of the differential diagnoses between optic disc edema and optic disc pseudoedema. In computerized tomography and in

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Fig. 15.4

Fig. 15.5 ultrasonography, there are signs that are characteristic of this entity (hyaline bodies) at the level of the optic head nerve, revealed as calcifications in the computerized tomography [4] or evidencing the presence of Skalka´s sign in echography [5, 6]. Just like the papilledema had a volcanic appearance in CLT, the drusen has the appearance of a kidney, with the characteristic orientation of its pelvis (renal) always towards the macular sector. It should be considered that the classical descriptions of optic nerve head drusen [7] indicate the absence of a physiological cup in these discs. Miller stated that the drusen mainly produce a protrusion in the nasal sector of the optic disc [8]. The topography (in CLT) shows that the ‘slit’ revealed in the temporal sector (area corresponding to the papillo-macular bundle entrance) completes the shape, here suggested, of a ‘renal pelvis’ which is a modified variant of the central cup (figure 15.5). The differential diagnosis between edema and pseudoedema of the optic disc with CLT is based on the topographic aspect that each entity has. The volcano image for the

189 former (developed optic disc edema) and the kidney aspect for the latter, signal the first distinctive aspect. The volumetric analysis shows a second difference. Whereas the measured volumes for the developed optic disc edema are (6.92 ± 1.62) mm3, the volumes reached by the drusen are (1.41 ± 0.76) mm3 (figure 15.1). These two characteristics (topographic appearance and volumes) are the elements contributed by CLT to the differential diagnosis between these entities. The values in figure 15.6 have been obtained from consecutive cases of papilledema (5 cases) and pseudopapilledema (8 cases).

Edema Pseudoedema Control group

n 9 16 16

VAS mean ± SD 6.92 ± 1.62 1.41 ± 0.76 0.04 ± 0.03

Med 7.02 1.11 0.04

VAR mean ± SD Med 11.56 ± 3.48 11.78 2.73 ± 1.93 2.03 0.47* ± 0.18 0.31

Fig. 15.6: VAS: Volume above surface. VAR: Volume above reference. VAS and VAR are expressed in mm3. n: number of cases. * The 0.47 value above is the result for this series by the author of this chapter (R.E.) for this series and corresponds to the concept of neuroretinal rim volume. This value shows a slight difference with the one included in figure 7.6 (0.48 mm3). Papillitis: In some cases, the characteristics of the optic disc in papillitis are impossible to distinguish from those of papilledema. It is the clinical aspect of these entities that enable a differential diagnosis to be made. On other occasions, papillitis presents an elevated disc with no central cup, where any recognizable architecture of the area has been lost. Laser scanning tomography shows the enlarged aspect of these optic discs which sometimes have the aspect of a nuclear mushroom (figure 15.7). The cross sections (height profiles) performed on these optic discs reveal strange formations evidencing the absence of a central cup. The ascending walls of the disc (as opposed to the ‘volcano’ or ‘kidney’ signs) are almost vertical at the acute stage. Here, like in papilledemas, the measurement of the volumes is critical for follow-up. In a case of papillitis, an over-elevation of the macular area, papillo-macular bundle, simultaneous with the optic disc inflammatory process, was observed (figure 15.7). This lead to the later development of a macular star, which allows to predict that this papillitis is not due to demyelinization [9, 10]. Disc elevations in orbital tumors: In cases of orbital tumors compressing the optic nerve due to their adjacent location, such as large cavernous angiomas, optic disc congestion with an over-elevated disc may occur [11] (figure 15.8). If there is contact with the posterior portion of the eyeball effecting pressure against it, folds in the posterior pole will develop. Generally, the peridiscal folds observed surround the optic disc. The folds further away from the optic disc usually have a radial arrangement. The optic disc overelevation, as well as the folds, take a long time to disappear once these tumors are extirpated.

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Fig. 15.7: Top: ‘nuclear mushroom’ appearance of papillitis. A profile performed diagonally (menu ‘interactive measurements’, option ‘distance’) reveals the type of optic disc elevation and the absence of a central cup. The macular area of the same patient (bottom) also shows an elevation (see profile), in association with radiated folds.

Fig. 15.8: Disc elevations due to the presence of an orbital tumor. The image on the right corresponds to an optic nerve sheath meningioma with the vascular anomalies at the level of the optic disc. The image on the left shows the optic nerve head in a case of orbital cavernous angioma, with circular folds beneath the elevated disc. Unlike intraocular tumors (like cavernous angiomas) [12], optic nerve sheath meningiomas, surround the nerve and strangulate it [13, 14]. The compression thus origi-

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Fig. 15.9: Reflectivity image (on the right) of an AION after a few hours of evolution. The image on the left shows the optic disc of the right eye of the same patient which was obtained in order to measure volumes (green: volume above surface; blue: volume above reference; red: volume below reference) and which enables to obtain the cup/disc ratio (c/d). It is outstanding how low the c/d ratio is (see text: ‘risk disc’). nated may cause a disc elevation (before reaching the atrophic stage) and a vascular phenomenon known as Hoyt-Spencer´s Sign may be observed [15]. 15.2.2 Vascular processes: anterior ischemic optic neuropathy (AION) In the non arteritic form of AION, a regional acute infarction (rarely global) of the optic disc occurs [16, 18]. During the acute picture, the CLT identifies the sectors undergoing the ischemic process (which affects the posterior ciliary artery system) and it reveals the elevated areas of the neuroretinal rim. Sometimes, the swollen areas correspond with the resulting perimetric picture (altitudinal defect), although this is not always the case. As for the fellow eye, the CLT allows one to obtain the cup/disc ratio objectively, thus identifying the so-called ‘risk discs’ [19, 22] (figure 15.9). 15.2.3 Optic disc atrophies - Traumatic optic neuropathy (TON) - Multiple sclerosis (MS) - Leber’s hereditary optic neuropathy (LHON) - Toxic optic neuropathy (TXON) - Post-edema optic disc atrophy In cases of post-traumatic optic atrophies (closed orbitofacial trauma or blunt trauma), as well as in those caused by demyelivating neuropathies (DN) and in the toxic ones (related to alcohol and tobacco consumption) or those studied in LHON case, neuroretinal rim defects at the level of the papillo-macular bundle develop (figure 15.10). This finding is clinically related to the presence of central scotomas in the visual field of the affected eyes.

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Fig. 15.10: Top left: Papillomacular bundle defect in a case of toxic neuropathy. Top right: Atrophic disc with disparition of the neuroretinal rim temporally in a case of Leber’s lenditary optic neuropathy. Bottom: Atrophic disc in MS. Note the collapse of neuroretinal rim at the papillomacular entrance. In no case the diseases listed resemble the atrophies observed in glaucoma or low tension glaucoma since neither cup depth nor volume increase, nor does the cup shape measure vary in a positive sense (see chapter 8, sections 8.1 and 8.2). Post-edema atrophy is not different from the previously described ones in its tomotopographic characteristics, but unlike the above mentioned atrophies it may be accompanied by retinal folds (right from the edematous stage) [23], generally radiated from the disc and which take long to disappear. 15.2.4 Optic disc malformations with neuro-ophthalmologic manifestations Tilted disc (situs inversus of the optic disc): The most frequent disc malformation was found in discs implanted in an oblique position or ‘tilted discs’. They have a characteristic oval shape and the amount of tilt is variable. As CLT displays 32 consecutive (sufficiently thick) sections, it is easy to localize the difference in height where the different portions of the neuroretinal rim are located in these optic discs, thus enabling to determine the scleral spur limits accurately. Nevertheless, when a malformation is very marked, one of the rim’s lips may be hidden so that the scleral spur is impossible to determine (with the contour line). Morning Glory Syndrome: Another frequent malformation is the presence of a large and deep disc in the shape of a truncated cone, known as ‘Morning Glory’. In two out of the three examined cases, the contralateral eye was pathological (retinal detachment in one case, increasing temporal myopia in the other, which in the third case was associated with an optic disc pit) [24-25].

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Fig. 15.11: Top row: topographical and reflectivity images of the left eye in a patient with Morning Glory syndrome obtained in primary eye position. Middle row, from left to right: images obtained in adduction, primary position and abduction of the left eye showing the volume variations according to the eye position. Bottom row: pseudo-threedimensional images showing the volumetric changes of the cup according to the eye position; from left to right: adduction, primary position and abduction of the left eye. A patient came for consultation due to a brief-lasting amaurosis on the side of the malformation. Examination with the HRT in this particular case was carried out in three different eye positions (primary eye position [PPM], abduction [ABD] and aduction [ADD]) since the patient reported darkening of vision when his eye was in abduction. A striking change of volume in the disc, depending on the eye position, was observed. The disc’s behavior (in its variations for each position) was similar to the behavior of a plunger, not in its ability to produce a vacuum, but regarding the changes produced in the soft portion of this element when (attached to a surface) it suffers the tension originated in the hard portion (the handle) when it is shifted from side to side (figure 15.11). The structural modifications of these malformed discs have already been reported by Wise and Pollack [26-27]. These optic disc variations (symptomatic or not) were not observed in two other cases with the same malformation. Megalopapilla: In a case of esotropia detected from birth in the right eye (RE) of a four-year-old girl whose visual acuity was luminous perception at the temporal sector, though her neurologic and pediatric examinations (including neuroimaging) were normal, the CLT showed the presence of a flat atrophic disc with only remnant fibers only at the nasal sector (accounting for the temporal light vision of the patient) and of a surface three times its normal size (see figure 7.6), the characteristic signs of a megalopapilla [28-29] (figure 15.12).

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Fig. 15.12: Note the value of ‘disk area’ in this case of megalopapilla. 15.2.5 Chiasmatic syndrome It was observed that in patients with tumors at the sellar region, the topographic images obtained when using the menu ‘stereometric parameters’, sub-menu ‘measure’ (in 360 degrees), showed a characteristic green region (volume above surface) and part of the blue region (volume above reference - volume below surface) had more volume in the nasal sectors of each eye. The central cup had a strange truncated shape at the level of the nasal portion (figure 15.13). This topographic condition was repeated in cases of active sellar tumors (compressing and shifting the chiasm), and the topographic condition worsened in a postoperative case, probably due to the manipulation of the area. Conversely, in operated cases where the chiasm is not shifted (but where there are visual/perimetric sequelae), disc atrophies without the above mentioned characteristics of a nasal optic disc protrusion are found. In one case the patient was a child on whom perimetry could not be performed due to his low vision. Upon ophthalmoscopy he seemed to have a simple optic disc atrophy. The CLT evidenced the disc condition described above (increase of the neuroretinal rim at the nasal sector and a nasal deformation of the central cup). Magnetic resonance revealed a craniopharyngioma. In another chiasmatic syndrome case due to the growth of an inactive adenoma, the topographic images revealed the same pattern, whereas clinically one of the eyes showed a temporal visual field defect and the other eye had light perception. The topographic features of these patients are highly suggestive of an ongoing sellar pathology. In patients with visual field damage, with or without disc atrophy upon CLT but with a previous surgery for the process causing the chiasmatic syndrome, the signs described above were not present.

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Fig. 15.13: CLT of the right eye (top) and left eye (bottom) of a patient with a sellar mass. Note the volume distribution (green) of VAS with a vertical clear cut limit of nasal crowding with an accompanying shift of the central cup temporally (see text). We do not know the meaning of this finding, since the fibers coming into the optic nerve, which are responsible for conveying information from the temporal hemifield (nasal fibers), are not exclusively bound to the nasal disc margin. 15.2.6 Homonymous Hemianopsias (HH) In patients with either congenital HH or HH in its late evolution stage (enough to present trans-synaptic atrophy), the neuroretinal rim had a different behavior in the optic nerve head of each eye. This had already been observed by other authors through ophthalmoscopy [30-31]. The eye homolateral to the hemianopsia (contralateral to the lesion), with CLT shows a defect in the area of the papillo-macular bundle caused by a reduction in the volume of the incoming axons, with a resulting oval-shaped cup. In the eye contralateral to the hemianopsia (eye on the side of the lesion) the axonal reduction (expressed by the reduction in the volumes of the neuroretinal rim), is detected above and beneath the entrance area of the papillo-macular bundle and it results in a triangular appearance of the cup (figures. 15.14, 15.15 and 15.16). The cup patterns - oval in the eye on the side of the hemianopsia and triangular in the eye on the side of the lesion - make up the topographic pattern of congenital HH or of those caused by old lesions (capable of producing trans-synaptic atrophy).

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Fig. 15.14: Confocal tomography of the right eye in a patient with left homonymous hemianopsia and optic disc manifestations of trans-synaptic atrophy. The topographic (A), reflectivity (B) and volumetric identification (D) images, as well as the pseudo-3D image (C) show the triangular shape of the cup caused by a reduction in the volumes of the neuroretinal rim in its superior and inferior temporal portions.

Fig. 15.15: Confocal tomography of the left eye of the same patient shown in figure 15.14. The topographic (A), reflectivity (B) and volumetric identification (D) images, as well as the pseudo-3D image (C) show the oval shape (horizontal major axis) of the cup caused by a reduction in the volumes of the neuroretinal rim in its central temporal portion.

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Fig. 15.16: Confocal tomography of the left eye in a patient with right homonymous hemianopsia due to congenital absence of left occipital lobe. The topographic (A), reflectivity (B) and volumetric identification (D) images, as well as the pseudo-3D image (C) show the same triangular shape of the cup as in the case illustrated in figure 15.14. The tomography of the right eye of this patient could not be reproduced due to opacity of the media (cataract).

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