Hospital for Sick Children's, The: Atlas of Pediatric Ophthalmology & Strabismus, 1st Edition

9

Optic Nerve

Alex V. Levin

Thomas W. Wilson

  1. Raymond Buncic

Agnes Wong

Wai-Ching Lam

The optic nerve arises as an outpouching of the anterior neural tube. The optic stalk, formed at the fourth week of gestation, is continuous with the forebrain at one end and the optic vesicle at the other. The optic vesicle, derived from neuroectoderm, forms the neurosensory retina and retinal pigmented epithelium. As early as the sixth week of gestation, ganglion cells in the optic vesicle become the first retinal cells to differentiate and their axons begin to reach the formative occipital cortex by the eighth week. Neural crest cells form the optic nerve sheath. Abnormalities of this process cause congenital anomalies of the optic nerve and optic disc.

Optic nerve function is often affected by underlying systemic illness or by local processes, including compression, inflammation, or the effects of other intracranial disease. The optic nerve may respond to the many pathologic processes by becoming edematous, hyperemic, or, with time, atrophic. Loss of optic nerve fiber is more readily appreciated in children because of visible changes in the normally thick nerve fiber layer in children. Congenital anomalies of the optic nerve may also be associated with underdevelopment of the macula.

Although sophisticated evaluation such as optical coherence tomography, Doppler ultrasound, and neuroimaging are helpful, any physician can assess the optic nerve using the ophthalmoscope.

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Figure 9.1 Normal Nerve Fiber Layer

This photograph demonstrates a normal optic nerve and macula. The nerve fiber layer is thickest in the perifoveal area. The thickness is demonstrated by the relationship of the retinal blood vessels usually buried within the retina and overlying light reflexes. The central reflexes form a doughnut-shaped mound, with a perifoveal inner circular reflex and an outer reflex where the curvature of the macula evens out. Within the fovea, the nerve fiber layer is absent, thus highlighting the healthy surrounding circular macular mound (mound of Buncic) of the thick nerve fiber layer. Flattening of this mound indicates loss of thickness of the retinal nerve fiber layer and decrease in the number of axons into the optic nerve (Figs. 9.15 and 9.21).

 

Figure 9.2 Optic Nerve Aplasia

Optic nerve aplasia is characterized by a complete absence of the optic nerve and retinal blood vessels. Eyes with aplastic optic nerves do not have any visual potential. This computed tomography scan illustrates the complete absence of the optic nerve structures bilaterally. As the globe is present and represents the end of the optic stalk, optic nerve aplasia is due to either failure of retinal ganglion cell development or abnormal invagination of the ventral fissure. Histopathologically, a vestigial nerve and optic nerve sheath may be found. This very rare disorder has only been observed sporadically.

 

Figure 9.3 Optic Nerve Hypoplasia

Optic nerve hypoplasia is characterized by a small optic disc (thick arrow). It is often surrounded by a yellowish mottled peripapillary halo, bordered by a ring of increased or decreased pigmentation (the “double-ring” sign, thin arrow). The outer ring represents the normal junction between the sclera and lamina cribrosa, whereas the inner ring represents the termination of an abnormal extension of retina and pigmented epithelium over the lamina cribrosa. The hypoplasia may be unilateral or bilateral. The retinal vessels are often anomalous, as shown here. Visual acuity does not always correlate with the size of the optic disc, whereas the thickness of the macular mound may be helpful. Optic nerve hypoplasia is frequently associated with the de Morsier syndrome (septo-optic dysplasia), which refers to the constellation of hypoplastic anterior visual pathways, absence of the septum pellucidum, and thinning or agenesis of the corpus callosum. Ectopia of the posterior pituitary gland on magnetic resonance imaging may indicate pituitary deficiency. Other brain abnormalities may coexist.

 

Figure 9.4 Optic Nerve Coloboma

Optic disc coloboma represents incomplete fusion of the embryonic fissure. The superior portion of the nerve appears normal, whereas the inferior portion is often yellowish white, excavated, and surrounded inferiorly by colobomatous choroid and retina. Systemic associations include CHARGE (coloboma, heart defects, atresia choanae, retarded growth and development, genitourinary abnormalities, and ear defects). Optic nerve coloboma can be part of a wide spectrum of coloboma ranging from involvement of the iris anteriorly to the macula posteriorly, with or without microphthalmia. The optic disc may appear enlarged, and if located within a larger chorioretinal coloboma, it may look quite dysplastic or even be unrecognizable.

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Figure 9.5 Morning Glory Disc

The morning glory disc anomaly is a congenital, funnel-shaped excavation of the posterior fundus that incorporates the optic disc. It is characterized by a central white glial tuft, retinal vessels that exit radially from the borders of the optic nerves, and peripapillary pigmentation. The optic nerve is larger than normal and also has a funnel shape when visualized by neuroimaging or ultrasound. Morning glory disc is usually unilateral, more common in females, and less common in patients of African descent. Visual acuity can vary from normal to hand motion. Morning glory disc can be associated with basal encephalocele, and a midline notch in the upper lip is a signature sign. Vision loss can also occur from serous retinal detachment. Rarely, a morning glory disc can be contractile.

 

Figure 9.6 Optic Pit

An optic pit (arrow) is an oval depression within the optic nerve. It is usually grayish in color and typically located centrally or temporally. An optic pit is usually unilateral and the affected disc is often slightly larger. Complications include serous detachment of the retina if associated with a temporally located pit. A macular hole can occur as a result of the serous retinal detachment. Without retinal detachment, optic pits rarely affect vision.

 

Figure 9.7 Megalopapilla

Megalopapilla is a larger than normal optic disc. The cup-to-disc ratio is often increased, although there is no increased risk for pediatric glaucoma. Visual acuity and visual field are usually normal except for an enlarged blind spot. The cause of this disorder is unknown, although familial megalopapilla has been rarely described. It is not associated with coloboma (Fig. 9.4).

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Figure 9.8 Bifid Disc

Bifid disc, or doubling of the optic disc, is due to abnormal division of the optic nerve during ocular development. Both optic nerves typically have their own blood supply. As shown here, there is usually a white band between the two discs as well as some contiguous tissue. Visual acuity is subnormal. Only sporadic cases have been described.

 

Figure 9.9 Congenital Tilted Disc

The tilted disc syndrome is a nonhereditary, usually bilateral disorder of the optic nerve. The optic disc is elevated superotemporally and depressed inferonasally, with an inferior scleral crescent. The disc is oval in shape and its long axis tends to be oriented obliquely. There is usually associated situs inversus (Fig. 9.10) of the retinal vessels. A pseudobitemporal hemianopia may be observed. This is considered to be a refractive scotoma related to regional myopia localized to the inferonasal retina. The hemianopia does not respect the vertical meridian and is reduced or eliminated with the use of minus lenses.

 

Figure 9.10 Situs Inversus

Situs inversus is a variation of the course of the temporal retinal blood vessels. Normally, the temporal retinal blood vessels are directed temporally. In situs inversus, however, the temporal blood vessels course nasally first before turning temporally. Situs inversus is associated with tilted disc syndrome (Fig. 9.9) but can occur in entirely normal eyes. Retinal traction can cause a secondary acquired situs inversus. Primary congenital situs inversus has no visual significance.

 

Figure 9.11 Prepapillary Vascular Loops

Prepapillary vascular loops are extensions of the normal retinal blood vessels into the vitreous. They often have a spiral configuration but do not extend to the posterior capsule and are therefore differentiated from persistent hyperplastic primary vitreous (Chapter 7: Lens, Figs. 7.14 and 7.15). These loops are remnants of the primitive hyaloid vascular system. The majority of the loops are arterial and can be associated with retinal artery occlusion. Otherwise the loops are entirely benign.

 

Figure 9.12 Anomalous Vessels

The number of variations in optic nerve and retinal vasculature are almost infinite. This photograph illustrates an increased number and enlarged caliber of retinal vessels. This pattern can be seen in Down syndrome, congenital retinal macrovessels, and racemose angioma. In congenital retinal macrovessels, a single vessel is typically involved, whereas in racemose angiomatosis, the retinal vessels are more dilated and tortuous. This photograph was taken from a child with normal vision.

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Figure 9.13 Bergmeister Papilla

Bergmeister papilla is caused by incomplete regression of the posterior hyaloid artery during ocular development. It may vary from a small glial tuft on the surface of the disc to a large stalk extending into the vitreous cavity. A blood vessel can be seen on occasion within the fibrous stalk. It is a sporadic, nonhereditary abnormality with no visual significance.

 

Figure 9.14 Hyaloid Glial Veil

A glial veil is a sheetlike membrane overlying the optic disc. Glial veils are formed by incomplete regression of hyaloid vascular structures and represent a variant of Bergmeister papilla (Fig. 9.13). They are visually insignificant, although the physiologic blind spot may be enlarged. Usually, as pictured here, the veil is translucent. It is a sporadic, nonhereditary abnormality.

 

Figure 9.15 Gray Optic Nerve

The optic nerve in this photo is from a patient with oculocutaneous albinism (Chapter 15: Dermatology, Fig. 15.17). The gray appearance of the optic nerve is typical of albinism and can also be seen in premature infants, chromosomal aberrations, or other genetic syndromes. In the premature infants, the gray appearance of the optic disc typically resolves with maturation of the visual system. Gray optic nerve may also be smaller than normal.

 

Figure 9.16 Optic Nerve Nevus

This photograph shows an optic disc nevus, which contains nevus cells. Note the dark pigmentation at the center of the optic cup. The differential diagnoses include melanocytoma (Fig. 9.38), malignant melanoma, or combined hamartoma of the retinal pigment epithelium. It is a benign, nonprogressive, and nonhereditary condition. The pathophysiology is unknown and no treatment is indicated.

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Figure 9.17 Pseudopapilledema

The optic nerves pictured here illustrate pseudopapilledema with absence of the cup and an appearance of disc elevation with blurring of the disc margins. However, the retinal vessels are not obscured (as would be seen in disc swelling) and the retinal blood vessel pattern is anomalous. These eyes are often hyperopic and may be occasionally microphthalmic. They are not more prone to swelling or pediatric glaucoma. There may or may not be visual consequence. Familial pseudopapilledema may occur.

 

Figure 9.18 Physiologic Cupping

This photograph demonstrates an enlarged optic cup in the absence of glaucoma. Physiologic cupping is characterized by very clear, often sharp, edges of the cup. The cup is elongated horizontally as opposed to vertically, the latter being often seen in glaucoma. Although this type of optic nerve is commonly seen in myopes, other refractive errors or emmetropia may be observed. This anomaly is inherited in an autosomal dominant fashion. Examination of the parents may obviate the need for neuroimaging, visual field testing, or glaucoma evaluation.

 

Figure 9.19 Peripapillary Crescent

Peripapillary crescent is caused by a gap between the optic disc edge and the retinal pigment epithelium. The neurosensory retina is still continuous to the edge of the optic disc. The area surrounding the disc temporally in this photograph shows a direct view to the underlying choroid and scleral tissue. The vision is typically normal. Myopia is more common. There may be an increased risk for glaucoma in adulthood. This is a nonhereditary anomaly, which may be unilateral or bilateral.

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Figure 9.20 Peripapillary Staphyloma

Posterior staphylomas are deep excavations of the globe surrounding a normal or anomalous nerve head. Visual acuity is typically reduced to counting fingers. It may be seen in high myopia, in optic nerve coloboma, or in isolation. The optic nerve may appear tilted or enlarged and, as shown here, the vessels may have a radiating pattern similar to the morning glory disc (Fig. 9.5).

 

Figure 9.21 Peripapillary Atrophy

The optic nerves in these photographs are pale and lack the normal orange-pink color. There is significant nerve fiber layer dropout causing the peripapillary atrophy. Note how the light reflexes line up along the vessels due to the thinning of the nerve fiber layer. Differential diagnoses include previous episodes of optic neuritis, an orbital compressive lesion, ischemia, nutritional deficiencies, hereditary optic neuropathy, trauma, and toxic optic neuropathies.

 

Figure 9.22 Dominant Optic Atrophy (Kjer Optic Atrophy)

Dominant optic atrophy typically presents with decreased vision in the first decade of life. Children often do not have any visual symptoms and the diagnosis may be made on routine examination. Visual acuity is typically between 20/40 and 20/80. A blue-yellow color vision defect is most common. The optic nerve shows sectoral pallor temporally, referred to as “pie in the sky” atrophy. There are no associated systemic findings.

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Figure 9.23 Mild Optic Nerve Swelling

Causes of optic nerve swelling in children include papilledema from increased intracranial pressure, optic neuritis, malignant hypertension, and diabetic papillopathy. The optic disc pictured here is elevated and the disc margins are blurred with obscuration of the retinal vessels as they course through the edematous optic disc. Venous pulsations are usually absent. The optic cup is absent and early engorgement of the retinal veins is apparent.

 

Figure 9.24 Moderate Optic Disc Swelling

Moderate optic nerve swelling is demonstrated in this photograph with significantly more nerve fiber layer swelling and obscuration of the disc margin and retinal arterioles, as well as peripapillary flame-shaped hemorrhages. A small cotton wool spot is present inferonasally, as a result of nerve fiber layer ischemia (incorrectly named a “soft exudate” in past nomenclature).

 

Figure 9.25 Severe Optic Disc Swelling

In severe optic nerve swelling, peripapillary hemorrhage (left image) or lipid exudates (right image) can be seen within the nerve fiber layer radiating toward the macula, forming a partial macular star. Spreading of peripapillary edema may cause circumferential wrinkling of the retina (Paton lines). Differential diagnosis includes neuroretinitis, often due to infection such as cat scratch disease. There is extensive nerve fiber layer edema with almost complete obscuration of the retinal vessels on the disc and in the immediate peripapillary area. There is no visible disc margin or optic cup. The retinal veins, particularly in the left image, are markedly engorged and tortuous. With the exception of an enlarged blind spot, visual function may be remarkably preserved in optic nerve swelling.

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Figure 9.26 Chronic Optic Disc Swelling

Chronic optic nerve swelling leads to irreversible damage of the optic nerve with a resultant optic neuropathy. Visual acuity, visual field, and color vision may be severely affected. The optic nerve is pale and is still elevated. The color and configuration have led to the name “champaign cork” disc, illustrated best in the left image. The disc margins are blurred and there is significant dropout of the nerve fiber layer. This occurs after weeks to months of increased intracranial pressure without treatment. Vascular tortuosity, as seen in the left image, may or may not persist.

 

Figure 9.27 Papillitis/Optic Neuritis

Pediatric optic neuritis represents an acute swelling of the optic nerve due to local factors. It is usually bilateral, and visible optic disc swelling is typically present. Clinical findings include optic nerve dysfunction (decrease in visual acuity, decreased color vision, and visual field loss and relative afferent pupillary defect). Unlike optic neuritis in adults, pediatric patients typically do not have pain with eye movement. The most common causes of pediatric optic neuritis are postinfection (chickenpox, measles, mumps, rubella, mononucleosis, and cat scratch disease), postvaccination, and rarely multiple sclerosis or other neurologic disorders. Workup should include magnetic resonance imaging of the brain and lumbar puncture.

 

Figure 9.28 Late Optic Neuritis

This optic nerve shows significant pallor following an episode of optic neuritis. Visual acuity often returns to normal but other visual functions such as color vision and contrast sensitivity may remain subnormal. Optic nerve pallor may be the only residual sign of previous optic neuritis. Note the peripapillary atrophy (Fig. 9.21). A relative afferent pupillary defect can be seen in acute or late optic neuritis if the optic nerves are affected unilaterally or asymmetrically.

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Figure 9.29 Neuroretinitis

Neuroretinitis is characterized by a combination of optic disc swelling and associated macular star. The optic nerve swelling (mild in this photograph) is typically unilateral and clinically there is decreased vision and pain with eye movement. The optic nerve swelling resolves over several months and the exudate resolves over months to years. It is not associated with other demyelinating processes such as multiple sclerosis. Common infections preceding neuroretinitis include cat scratch disease, Lyme disease, and mumps. Workup should be targeted to identify the infectious agent.

 

Figure 9.30 Anterior Ischemic Optic Neuropathy

Anterior ischemic optic neuropathy is very rare in children. This optic nerve shows significant pallor with peripapillary hemorrhage and engorgement of the veins. However, edema is not a prominent feature. Visual recovery is less than that seen in optic neuritis and recurrences are common. Patients with anterior ischemic optic neuropathy are generally systemically well, although diabetes mellitus and blood dyscrasias that cause increased serum viscosity must be excluded.

 

Figure 9.31 Buried Optic Disc Drusen

Optic nerve drusen are small lobular collections of a hyalinelike material within the optic nerve. They are a common cause of pseudopapilledema and can be inherited as an autosomal dominant trait. They are often bilateral, although they may be asymmetrical. The visual acuity is typically normal. Loss of visual acuity can be secondary to hemorrhage, or less commonly, subretinal neovascular membrane. Visual field abnormalities include arcuate defects and enlarged blind spot. In cases where clinical confirmation is difficult, ultrasound or computed tomography scan, as shown here, may reveal calcified bodies within the optic disc.

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Figure 9.32 Optic Disc Drusen

Optic nerve drusen are characterized by yellowish-white elevations. The disc surface is often irregular and there is usually no optic cup. Although the border of the optic disc is obscured or irregular, no true disc edema is present and the vasculature is usually normal. Autofluorescence can be demonstrated and there is no leakage on fluorescen angiography. An important caveat is that all forms of pseudopapilledema may have coexisting true edema (i.e., optic nerve edema).

 

Figure 9.33 Myelinated Nerve Fibers

Optic nerve myelination normally begins at the lateral geniculate body and progresses as far as the lamina cribrosa. Myelinated nerve fibers represent abnormal intraocular myelination of the retinal nerve fiber layer. The areas of nerve fiber myelination are opaque and white and have a characteristic feathery edge. These areas are usually, but not always, adjacent to the optic disc. A visual field defect may correspond to the area of myelination, and occasionally, amblyopia may be present, especially in association with high myopia. Myelination of the nerve fiber layer is more common in Down syndrome and Gorlin-Goltz syndrome (multiple basal cell nevi).

 

Figure 9.34 Retrograde Trans-Synaptic Degeneration

These photographs demonstrate retrograde synaptic degeneration following a lobectomy in the first decade of life involving the optic radiation. Retrograde degeneration affects the synoptic fibers in the right lateral geniculate nucleus. Anteriorly it involves the temporal retinal fibers from the right eye and the nasal retinal fibers from the left eye (i.e., the left optic disc resides in the blind hemiretina). Degeneration of the fibers results in the characteristic pattern seen here. The temporal part of the right optic disc is pale and the left optic nerve shows bow-tie atrophy as a reflection of the retinal nerve fiber pattern feeding into the optic disc.

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Figure 9.35 Leber Hereditary Optic Neuropathy

Leber hereditary optic neuropathy is a mitochondrial disorder that is maternally inherited. Unlike other mitochondrial disorders, it affects men more frequently than women. Although the disorder can present at almost any age, it is typically observed in the second and third decades of life, with unilateral or bilateral decrease in optic nerve function. The vision typically is less than 20/100 and recovery is limited. Funduscopic examination shows pseudoedema of the optic nerve and nerve fiber layer, with peripapillary telangiectatic vessels in the acute phase (not shown here). There is characteristically no leakage on fluorescein angiography. Differential diagnoses include optic neuritis, anterior ischemic optic neuropathy, nutritional and alcohol amblyopia, and toxic exposure.

 

Figure 9.36 Optic Nerve Glioma

Optic nerve glioma is the most common optic nerve tumor of children. It is commonly associated with neurofibromatosis 1. Patients may present with progressive proptosis, loss of vision, or strabismus. Clinical examination shows reduction of visual acuity and color vision. The optic nerve is typically pale but may have disc swelling, as shown here in the left image, when the glioma abuts on the globe. Optociliary shunt vessels may be observed (right image).

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Figure 9.37 Optic Nerve Glioma

MRI scan of the left orbit shows an enlarged optic nerve due to glioma. The nerve may be symmetrically enlarged or have a fusiform or tortuous appearance. On coronal views, there may be an effusion within the nerve sheath. The glioma is hyperintense on CT scan and can extend backward to involve the intracranial visual pathway including the optic chiasm and/or radiations as well as the hypothalamus. Magnetic resonance imaging with gadolinium is the preferred neuroimaging technique.

 

Figure 9.38 Melanocytoma

Melanocytoma is a lesion of the optic disc that is composed of magnocellular nevus cells. The tumor has a dramatic jet-black appearance, which is characteristic. Visual acuity is typically normal and malignant transformation is rare. However, the tumor may increase in size slightly over time. Differential diagnoses include optic nerve nevus (Fig. 9.16) and malignant melanoma.

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Figure 9.39 Optic Atrophy

The end stage to many optic nerve diseases is complete optic atrophy. Note the diffuse white color of this disc, making the cup almost indistinguishable. Also note the changes in the light reflexes as they line up along the blood vessels, indicating severe loss of the nerve fiber layer.