13 Congenital Anomalies Of The Optic Nerve

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CHAPTER 13 CONGENITAL ANOMALIES OF THE OPTIC NERVE

13.1 Introduction It often occurs that ophthalmologists or particularly, pediatric ophthalmologists, have to examine newborns, mainly children with low vision due to congenital optic disc anomalies. There are three major references: The book by Orellana [1]; the paper by Apple and Rabb (1982) [2] and the paper by Brodsky (1994) [3]. In the last 10 years, CNS defects of patients with congenital optic disc anomalies were studied by means of magnetic resonance imaging. In this way, every type of malformation was associated with malformation defects of the CNS. 13.2 Concepts for diagnosis and treatment a) Unilaterality or bilaterality. When the anomalies are unilateral, the child generally presents esotropia during infancy, while bilateral anomalies appear earlier, as the loss of vision is accompanied by nystagmus. b) Malformations of the CNS accompany in most cases, congenital anomalies of the optic nerve. For this reason, magnetic resonance imaging should be performed in all cases. c) Color vision is usually maintained. This is useful for differential diagnosis as it is the opposite to what occurs in acquired optic neuropathies, where there is a marked dyschromatopsia. d) Amblyopia usually accompanies these vision-reducing anomalies in the first years of age and during childhood. Therefore, it is important to keep this in mind, as it may be of help to the child with occlusion. 13.3 CNS malformations in congenital optic disc anomalies When congenital optic disc anomalies occur with small optic discs, they are accompanied by malformations of the brain hemispheres, pituitary infundibulum, septum pellucidum and corpus callosum. Those accompanied by large optic nerves, and in the case of the Morning Glory syndrome, present a transphenoid basal encephalocele, and in cases of colobomas, they are associated with congenital colobomastous syndromes (figures 13.1 and 13.2).

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Fig. 13.1

Fig. 13.2 13.4 Classification Congenital anomalies of the optic nerve I. Hypoplasia of the optic nerve II. Cupped anomalies a Morning Glory Syndrome b Optic disc colobomas c Peripapillary staphylomas III. Megalopapillas IV. Optic disc pits V. Tilted disc syndrome VI. Optic nerve dysplasia

151 VII. VIII. IX.

Congenital optic nerve pigmentation Aicardi’s syndrome Pseudo-papilla

I. Hypoplasia of the optic nerve Ophthalmoscopy reveals a small and gray optic nerve. After studying normality, we have concluded that the mean surface of the optic nerve is 2.05 mm2. If the normal standard deviation is taken into account, a micropapilla can be considered to be any optic disc with a surface under 1.59 mm2 and a megalopapilla, any optic disc over 2.51 mm2. Regarding the micropapilla, the values we have found are rather consistent with the values of <1.40 mm2 obtained by Jonas [4] (mean 2.89 mm2, minus two standard deviations, equals 1.40 mm2). It is accompanied by a stained hale, tortuous vessels and the double ring sign. Pathological anatomy accounts for this sign: the external ring corresponds to the place where the lamina cribrosa is continuous with the sclera and the internal ring is due to the fact that the retina and the pigmentary epithelium abnormally extend over the lamina cribrosa [5, 6]. This double ring sign is exactly the opposite to what is observed in the Morning Glory syndrome (see II.a). Sometimes, the hypoplasia of the optic nerve can be segmentary, superior or inferior, with the corresponding visual field damage. Otherwise, the visual field is characterized by a general fiber constriction and defects. Hypoplastic optic nerves are accompanied by endocrin alterations, which are also congenital anomalies, such as hypothyroidism and a deficiency of the growth hormone [7, 8, 9]. The visual acuity is varied, since it ranges from light perception to 20/20, which calls for refraction correction as soon as possible. In regards to etiology, the literature makes reference to alcohol and drugs during pregnancy and to insulin-dependant mothers [10], and to the anomalies of the CNS accompanying small optic discs or hypoplastic optic discs, which are located in the brain hemispheres at the pituitary infundibulum and at the septum pellucidum [11]. As to pathogenesis, hypopolastic optic discs are gestational lesions in the structures of the middle line of the CNS altering axon migration [12, 13, 14] (figure 13.3). Among cupped optic disc congenital anomalies, the Morning Glory syndrome, optic disc colobomas and peripapillary staphylomas, can be mentioned. II.a Morning Glory Syndrome The Morning Glory Syndrome (MGS) is a congenital alteration of the eyeball manifested as a posterior mushroom-shaped cup incorporating the optic disc. It can be unilateral or bilateral. The visual acuity is almost always reduced, it ranges from finger counting to 10/100, although cases with a visual acuity of 20/20 have been reported. MGS is more frequent in women. It was described for the first time by Graether in 1963 [15]. Later Kindler,in 1970 [16] named it Morning Glory because of its resemblance to a violet bell-shaped flower which grows wild and which, in Argentina, is generally found at railway crossings. Ophthalmoscopic examinations reveal a big orange or pink optic nerve with a mushroom-shaped cupping, surrounded in its anterior end by a thick pigmentary hale. Numerous radial vessels, increased in number if compared to normal, where it is difficult to distinguish vessels from arteries, emerge from it. In the central part there is a

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Fig. 13.3 white, slightly prominent area that looks like a veil, which is glial tissue; sometimes this malformation involves the macula and in this case it is known as macular capture [17, 18]. In some cases, a retinal detachment occurs, due to small holes near the optic nerve (in 26 % to 38 % of cases, as reported in the literature [19, 20]). In other cases, there is a communication between the vitreous body and the subarachnoid space [21]. Ultrasonography shows this syndrome as a funnel in the posterior part of the eyeball, that can sometimes be qualified, and in this case it is also visible with computerized tomography of the orbit. In the retinograph of a MGS, the posterior cup has the appearance of a mushroom with a white veil in the central area corresponding to glial tissue. A dark adjacent area surrounded by a choroidal depigmentation shows a macular sequestration with a small coloboma. In a patient with unilateral MGS, the confocal tomography in the topographical image, protrusion of the rigna as a very dark area (figure 13.4) and in a horizontal section a marked depression between the funnel area and the retina surrounding it, can be seen. Another patient had MGS in the right eye and a double optic nerve in the left eye, as described by Bonamour and coworkers [22], with a superior optic disc, a smaller one beneath this one, and below it, a choroidal coloboma. In 1963, Graether [15] was the first to describe a transient amaurosis with venous dilatation in the MGS and in 1994, Ebner, R. Sampaolesi and J.R. Sampaolesi (in press) described a transient amaurosis with arteriolar contraction depending on the sight position. In chapter 15 of this book, Dr. Ebner will describe this case in greater detail. In Brodsky’s article of 1994 which we mentioned earlier [3], the author refers to mid-facial anomalies (hypotelorism, depressed nose, palpebral alterations) as other manifestations of this syndrome. In figure 13.5 the main features of the MGS are described. The MGS manifests in the CNS as a transphenoid form of basal encephalocele, for which surgery is counterindicated, rarely as absence of chiasma, agenesis of the corpus callosum and dilatation of the lateral ventricules. It is sometimes also accompanied by a herniation of the hypothalamic structures (palate clefts, bone defects in the base of the

153

Fig. 13.4

Fig. 13.5 skull). Brodsky also reports that sometimes there is a rhinorrhea due to basal obstruction caused by a polyp, the extirpation of which could be lethal. An interesting paper, by an Argentine author, Dr. Alezzandrini, describes RFG alterations in detail [23]. II.b Optic disc colobomas Ocular manifestations: It is an abnormal coaptation of the proximal area of the optic vecicle slit. The optic disc is enlarged, with sharp borders, of a bright white color and with a deep cup. The cup is decentered towards the bottom, making the neuroretinal rim disappear in that place. This defect generally presents a choroidal coloboma at the deepest part of the optic disc, and it is sometimes associated with a coloboma of the iris. Ultrasonography and computerized tomography show a posterior pole cup of the eye as in the Morning Glory Syndrome and, contrary to this syndrome, it is generally bilat-

154

Fig. 13.6

Fig. 13.7 eral. The visual acuity depends on the integrity of the papillomacular bundle. The retinal vessels are normal. They are sometimes accompanied by a macular serous detachment. Systemic manifestations: Optic disc colobomas may be accompanied by the Charge’s syndrome [24, 25], Walker-Warburg’s syndrome [26], Aicardi’s syndrome [27, 28], or the linear Nevus sebaceous syndrome[29]. Sometimes the coloboma has an atypical connection with an orbital cyst [30]. In optic disc colobomas, as already said, a choroidal coloboma equal or larger in size than the optic disc in its inferior part, is usually present. Sometimes there is no optic disc coloboma but this small inferior coloboma is present. One of these cases is shown on the vertical section of both depressions at the bottom of the optic disc, as well as on a threedimensional representation, the measurement of the optic disc area and of the area of the coloboma (figure 13.6). The main features are described in figure 13.7.

155

Fig. 13.8

Fig. 13.9 II.c Peripapillary staphylomas It is a very infrequent unilateral condition and it is manifested by a deep cup surrounding the optic disc, especially in its inferior part. The cup is surrounded by a pigmentary hale and, conversely to what happens in the Morning Glory syndrome, there is no central glial white veil. The visual acuity may be normal or reduced and in the visual field there is a centrocecal scotoma. It is often associated with a coloboma of the iris, the retina and of the ciliary body, and only very rarely does a basal encephalocele appear, as a manifestation of the CNS [31]. In a highly myopic case combined with glaucoma, we have observed a staphylomatous depression around the optic disc in the center of which there was a flat glaucomatous optic disc. Figure 13.8 shows the pertinent confocal tomographies. In figure 13.9 the main characteristics are shown.

156

Fig. 13.10

Fig. 13.11 III Megalopapillas When the optic disc area is greater than 2.5 mm2, we are dealing with a megalopapilla. There are two types of megalopapillas: Type I: the optic disc bears a normal configuration; it is bilateral. The cup/disc ratio is high, so this fact must be kept in mind when making the differential diagnosis with low tension glaucoma (cup/disc ratio: mean 0.16 + 2 S.D. = 0.6 maximum). The entire optic disc surface is pale, and the cup is either round or oval. Type II: It is characterized by a decentered cup towards the top of the optic disc. That is to say, contrary to what occurs in optic nerve colobomas where the cup is decentered towards the bottom. The cilioretinal arteries are more common in megalopapillas [32]. The neuroretinal rim is reduced or has almost completely disappeared in the top part. It usually occurs monolaterally.

157 Many megalopapillas appear in normal subjects with a normal visual field. It is one of the wide range of optic discs [33]. It should be kept in mind that megalopapillas may develop in congenital glaucomas, mainly in reoperated cases. This megalopapilla is acquired because as the sclera distends, with the consequent axial length and ocular volume increase, Elschnig’s Ring enlarges, and so does the entire optic disc surface. Figure 13.10 shows the images, and their characteristics are shown in figure 13.11. IV. Optic disc pits Ophthalmoscopy: It is manifested as a round or oval gray, white or yellow depression; it is usually located on the temporal area. It is accompanied by peripapillar pigmentary changes and in 50% of cases, one or two cilioretinal arteries come from the pit [34]. It is generally unilateral. Visual field: The visual field defects correlate with the position of the pit, according to the fibers crossing the area. There is a blind spot enlargement and arcuate scotomas are the most common defects. We have sometimes found central scotomas. Retina: In 25% to 75% of cases a macular serous edema [35, 36] leading to a macular detachment occurs. Lincoff [37] has studied this subject in depth and proved that the retinal separation is similar to a retinoschisis, that a retinal hole of the external layers of the macula leading to a central scotoma, may develop. The retina around the macular hole is detached. Gas injections and laser photocoagulation is recommended in these cases. Retinofluoresceinography: An early hypofluorescence and a late hyperfluorescence of the pit usually take place. There is no fluorescein passage to the vitreous nor to the macula. Pathological anatomy: The dysplasic retina is herniated inside a pocket or cavity that extends towards the back, frequently inside the subarachnoid space through a defect of the lamina cribrosa [38, 39] (figures 13.12 and 13.13). V. Tilted disc syndrome It is a bilateral condition where the superior temporal part of the optic nerve is elevated and the inferior nasal part is shifted in a posterior direction. This gives the optic disc an oval shape with its greater axis in an oblique position. Ophthalmoscopy: In the conditions mentioned before, the optic disc has its greater axis in an oblique position. There is a situs inversus of the optic disc vessels with an inferonasal congenital conus and retinal epithelium and choroid thinning in the inferonasal area that may be accompanied by an inferonasal albinism. Visual field: The visual field presents a bitemporal hemianopsia or a superior quadrantanopsia. This visual field defect is a refractive scotoma secondary to a localized regional myopia in the inferotemporal retina. If a -4 diopter lens is used, the scotoma disappears and in this way, its refractive nature is confirmed. There is, then, a myopic astigmatism with the greater axis parallel to the ectasia [40]. In my opinion, the tilted optic disc syndrome is related to nasal ectasia of the fundus. This syndrome was described by Riise in 1975 [41]; at that time Dr. Argento and Dr. Mayorga were residents under my charge, so I informed them on this subject and I referred some of my patients to

158

Fig. 13.12

Fig. 13.13 them for their study. This, along with their studies on other patients, resulted in the publication of a very interesting article [42] (figures 13.14 and 13.15). VI. Optic nerve dysplasia VII. Congenital optic nerve pigmentation Gray in albinism; due to late myelinization. VIII. Aicardi’s syndrome Depigmented lagoons around the optic disc. Pathological anatomy: lack of choroid and of pigmentary epithelium in the lagoons. Sometimes congenital optic disc alteration. Lethal in males. Systemic manifestations (CNS): Corpus callosum agenesia.

159

Fig. 13.14

Fig. 13.15 Other ocular manifestations: microphthalmos; retrobulbar cyst; pseudoglioma; bifid spine; detachment of the macular retina; pupillary membrane; iris sinechiae; iris colobomas. Other general manifestations: escholiosis; microcephalia; muscular hypotonia; mental retardation. IX. Pseudo-papilla The main features are described in figure 13.16. A 20 degrees tomography is shown in figure 13.17 which contains both discs (the papilla and the pseudo-papilla). In figure 13.18 both discs are displayed separately, in two 10 degrees field examinations (real optic disc on the top of the image, pseudopapilla at the bottom).

160

Fig. 13.16

Fig. 13.17

Fig. 13.18

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