2 Comments

Chapter 188 – Congenital Optic Disc Anomalies

Chapter 188 – Congenital Optic Disc Anomalies

 

MICHAEL C. BRODSKY

 

 

 

 

 

DEFINITION

• Unusual configurations of the optic disc(s) typically present since birth.

 

KEY FEATURE

• Small, pale, or unusually shaped optic discs may reflect mere curiosities or significant anomalies associated with visual defects.

 

ASSOCIATED FEATURE

• Abnormalities of the surrounding retina (e.g., in morning glory syndrome), anterior segment (e.g., iris coloboma), face, or brain may occasionally be seen.

 

 

 

INTRODUCTION

The principles outlined here apply to the evaluation and management of children who have congenital optic disc anomalies.[1]

Age Association

Children who have bilateral optic disc anomalies generally present in infancy with poor vision and nystagmus; those who have unilateral optic disc anomalies generally present during the preschool years with sensory esotropia.

Central Nervous System Malformations

Central nervous system malformations are common in patients who have malformed optic discs. Small discs are associated with a variety of malformations that involve the cerebral hemispheres, pituitary infundibulum, and midline intracranial structures (e.g., septum pellucidum, corpus callosum).

Optic discs of the morning glory configuration are associated with the transsphenoidal form of basal encephalocele, whereas optic discs with a colobomatous configuration are associated with systemic anomalies in a variety of coloboma syndromes. Investigation using magnetic resonance imaging (MRI) is advisable for infants who have small optic discs and for infants who have large optic discs wo have either neurodevelopmental deficits or midfacial anomalies that are suggestive of basal encephalocele. This generalization applies to patients with unilateral as well as bilateral optic disc anomalies.

Functional Amblyopia

Any structural ocular abnormality that reduces visual acuity in infancy may lead to a superimposed amblyopia. A trial of occlusion therapy is warranted in most young patients who have unilateral optic disc anomalies and decreased vision in the affected eye.

OPTIC NERVE HYPOPLASIA

Optic nerve hypoplasia is a congenital anomaly that has become recognized as a major cause of blindness in children.[1] Histologically, it is characterized by a subnormal number of optic nerve axons with normal mesodermal elements and glial supporting tissue.[2] The ophthalmoscopic appearance is that of a small, gray, or pale optic nerve head, which is often surrounded by a yellowish mottled peripapillary halo, flanked on either side by a ring of pigment (double-ring sign)[2] ( Fig. 188-1 ). Visual acuity may range from 20/20 to no light perception.[2] Because visual acuity depends only on the degree of papillomacular nerve fiber bundle hypoplasia, it does not necessarily correlate with the overall size of the disc. [1]

The term septo-optic dysplasia (de Morsier syndrome) describes the constellation of optic nerve hypoplasia, absence of the septum pellucidum, and partial or complete agenesis of the corpus callosum. [2] MRI of the brain in optic nerve hypoplasia frequently shows coexistent cerebral hemispheric abnormalities (most often schizencephaly) and absence of the pituitary infundibulum with or without posterior pituitary ectopia.[3] The presence of an ectopic posterior pituitary gland, which appears as a hyperintense nodule at the median eminence on T1-weighted images, indicates that posterior pituitary function is intact.[3] Cerebral hemispheric abnormalities indicate that neurodevelopmental deficits are likely, and absence of the pituitary infundibulum with an ectopic posterior pituitary gland indicates congenital hypopituitarism. Absence of the septum pellucidum does not place the child at higher risk for neurodevelopmental or endocrinologic

 

 

Figure 188-1 Optic nerve hypoplasia (note double-ring sign).

 

1256

problems unless the cerebral hemispheres or pituitary infundibulum are also abnormal. [3]

A reduction in the diameter of the hypoplastic optic nerve and chiasm is demonstrated reliably by MRI, which establishes the presumptive diagnosis of optic nerve hypoplasia.[1]

The association of septo-optic dysplasia with pituitary hormone deficiencies warrants endocrinologic evaluation in children who have both optic nerve hypoplasia and absence of the pituitary infundibulum on MRI. Growth hormone deficiency is most common, followed by deficiency of thyroid-stimulating hormone, corticotropic hormone, and vasopressin. In infants who have septo-optic dysplasia, a history of neonatal jaundice suggests hypothyroidism and neonatal hypoglycemia indicates corticotropin deficiency. Children who have corticotropin deficiency are at risk for sudden death from hypoglycemia and shock during intercurrent illness; parents should be instructed to administer injectable parenteral corticosteroids at the onset of febrile illness. [4]

MORNING GLORY DISC ANOMALY

The morning glory disc anomaly is a congenital excavation of the posterior globe that involves the optic disc.[5] Embryologically, the morning glory disc anomaly may result from an anomalous, funnel-shaped expansion of the distal portion of the optic stalk, which causes the opening of its lumen into the cavity of the optic vesicle to be abnormally large. Closure of the embryonic fissure occurs normally; however, progression of the closure into the distal portion of the stalk does not obliterate the space within the fissure because of the increased dimensions of this space.[5]

The optic disc is enlarged, orange or pink in color, and either excavated or situated within a funnel-shaped area of excavation ( Fig. 188-2 ).[5] A variably elevated annular zone surrounds the disc with irregular areas of pigmentation and depigmentation. A white tuft of glial tissue overlies the center of the disc. The retinal blood vessels appear increased in number, arise from the periphery of the disc, run an abnormally straight course over the peripapillary retina, and tend to branch at acute angles. It is often difficult to distinguish arteries from veins. The macula may be incorporated into the excavated defect (macular capture).[5] Although mistakenly referred to as a variant of optic disc coloboma, the morning glory disc anomaly is truly a distinct anomaly, as evidenced by its sporadic occurrence, its lack of association with iris or retinal colobomas, and its systemic associations. [5]

The morning glory disc anomaly is associated with transsphenoidal encephalocele,[1] and with hypoplasia of the ipsilateral intracranial vasculature (which can be visualized by magnetic resonance angiography).[5] [6] Children who have this occult basal encephalocele have characteristic facies, which consist of mild

 

 

Figure 188-2 Morning glory disc anomaly.

hypertelorism with a depressed nasal bridge, a midline notch in the upper lip, and sometimes a midline cleft in the soft palate. Respiratory symptoms of transsphenoidal encephalocele in infancy may include rhinorrhea, nasal obstruction, mouth breathing, or snoring. Most affected children have no overt intellectual or neurologic deficits, but panhypopituitarism is common. Patients who have morning glory discs are also at risk for acquired visual loss. Nonrhegmatogenous retinal detachments develop in approximately one third of eyes with morning glory discs and usually involve the peripapillary retina.[5] Controversy exists about the source of subretinal fluid; however, intraoperative findings in one case showed that the vitreous cavity, subarachnoid space, and subretinal space were all interconnected. (See Chapter 187 .)

OPTIC DISC COLOBOMA

In optic disc coloboma, the disc appears enlarged and a sharply demarcated, glistening white, bowl-shaped excavation occurs ( Fig. 188-3 ).[7] The inferior rim of the disc is thinner than the superior rim, which reflects the position of the embryonic fissure relative to the primitive epithelial papilla. The excavation may extend inferiorly to involve the adjacent choroid and retina, in which case microphthalmia is frequently present. In some instances, the entire disc is excavated, but the colobomatous nature of the defect can still be appreciated ophthalmoscopically because the excavation is deeper inferiorly. The excavation is contained within the colobomatous optic disc, as opposed to the morning glory disc anomaly, in which the disc falls within the excavation.[7] Visual acuity may be minimally or severely affected, depending upon the extent of the lesion. Although the optic disc area appears enlarged, optic disc coloboma is actually an inferior segmental form of optic nerve hypoplasia. The only remaining neural tissue lies superiorly in a C-shaped or moon-shaped crescent ( Fig. 188-3 ).

Optic disc coloboma may arise sporadically or be inherited in an autosomal dominant fashion and may be accompanied by iris or retinochoroidal colobomas in the same or fellow eye. Often it is associated with systemic anomalies in a number of genetic syndromes (CHARGE [coloboma of the eye, heart anomaly, choanal atresia, retardation, and genital and ear anomalies] association, Walker-Warburg syndrome, Goltz focal dermal hypoplasia, Goldenhar’s syndrome, linear nevus sebaceus syndrome), but rarely is it associated with transsphenoidal encephalocele.[1]

OPTIC PIT

An optic pit appears as a round or oval, gray, white, or yellowish crater-like depression in the optic disc ( Fig. 188-4 ).[7] Optic pits

 

 

Figure 188-3 Optic disc coloboma.

 

1257

commonly involve the temporal optic disc but may be situated in any sector.[8] Temporal optic pits are often associated with adjacent peripapillary retinal pigment epithelium changes.[8] In unilateral cases, the involved disc is slightly larger than the normal disc.[8]

Visual field defects are variable and often correlate poorly with the location of the pit; the most common defect appears to be a paracentral arcuate scotoma connected to an enlarged blind spot. Acquired depressions in the optic disc that are indistinguishable from optic pits have been documented in eyes with normal-tension glaucoma.[1] Histologically, an optic pit is a herniation of rudimentary neuroectodermal tissue into a pocket-like depression within the nerve substance[8] ( Fig. 188-5 ). Its pathogenesis is unknown.

Optic pits are not associated with brain malformations, and their discovery does not warrant neuroimaging. Approximately 45% of eyes with optic pits develop serous retinal detachments.[6] Some serous retinal detachments associated with optic pits resolve spontaneously, but the visual prognosis remains poor.[8] The subretinal fluid most likely originates from the vitreous cavity or the subarachnoid space that surrounds the optic nerve. Lincoff et al. [9] demonstrated that fluid from the optic pit initially produces an inner layer retinal separation (retinoschisis) that overlies the posterior pole. An outer layer macular hole subsequently develops through which this intraretinal fluid communicates with the subretinal space to form a sensory macular detachment that gradually enlarges. [9] This key observation has changed the preferred surgical therapy of serous macular detachments from photocoagulation

 

 

Figure 188-4 Optic pit.

 

 

Figure 188-5 Optic pit. Herniation of retinal tissue through an enlarged scleral opening along one side of the optic nerve. (Courtesy of Dr JB Crawford, from Irvine AR, Crawford JB, Sullivan JH. The pathogenesis of retinal detachment with morning glory disc and optic pit. Retina. 1986;6:146–50.)

at the disc margin (which was performed to block the flow of subretinal fluid from the disc to the macula) to internal gas tamponade (which is used to displace mechanically subretinal fluid from beneath the macula).[1] (See Chapter 187 .)

MEGALOPAPILLA

Megalopapilla is a generic term that connotes an abnormally large optic disc that lacks the inferior excavation of optic disc coloboma or the numerous anomalous features of the morning glory disc anomaly.[1] This condition is usually bilateral and often associated with a large cup-to-disc ratio. Patients who have megalopapilla are often suspected to have glaucoma. Unlike the situation in glaucoma, however, the optic cup is usually round or horizontally oval with no vertical notch or encroachment ( Fig. 188-6 ). Visual acuity is generally normal in megalopapilla but may be mildly decreased in some cases. Visual fields are usually normal except for an enlarged blind spot, which enables the examiner to rule out low-tension glaucoma or a compressive lesion. Megalopapilla is only rarely associated with brain anomalies, and neuroimaging is not warranted unless midline facial anomalies are present.

CONGENITAL TILTED DISC SYNDROME

The tilted disc syndrome is a nonhereditary bilateral condition in which the superotemporal optic disc is elevated and the inferonasal disc is displaced posteriorly, which results in an optic disc of oval appearance with its long axis obliquely orientated ( Fig. 188-7 ). [10] This configuration is accompanied by situs inversus

 

 

Figure 188-6 Megalopapilla.

 

 

Figure 188-7 Congenital tilted right optic disc. Note the inferonasal retinochoroidal depigmentation. (Left optic disc is the mirror image.)

 

1258

 

 

Figure 188-8 Congenital optic disc pigmentation.

of the retinal vessels, congenital inferonasal conus, thinning of the inferonasal retinal pigment epithelium and choroid, and myopic astigmatism. These features presumably result from a generalized ectasia of the inferonasal fundus that involves the corresponding sector of the optic disc.

Familiarity with this condition is important because affected patients may present with the suggestion of bitemporal hemianopias, which involve primarily the superotemporal quadrants. However, these field defects, when observed carefully, do not respect the vertical meridian (as do chiasmal lesions). Furthermore, large and small isopters are fairly normal, but medium-sized isopters are constricted selectively because of the ectasia of the midperipheral fundus. Repeated visual field tests after correcting for the myopic refractive error often eliminate the field defect, which confirms its refractive nature. In some cases, retinal sensitivity is decreased in the area of the ectasia, which causes the defect to persist despite refractive correction. Rare cases of the tilted disc syndrome have been documented in patients who have congenital suprasellar tumors; neuroimaging is therefore warranted when the associated bitemporal hemianopia respects the vertical meridian.[10]

CONGENITAL OPTIC DISC PIGMENTATION

Congenital optic disc pigmentation is a condition in which melanin anterior to or within the lamina cribrosa imparts a gray appearance to the disc ( Fig. 188-8 ). True congenital optic disc pigmentation is extremely rare, but it has been described in a patient who had an interstitial deletion of chromosome 17. Congenital optic pigmentation is compatible with good visual acuity but may be associated with coexistent optic disc anomalies that decrease vision.[11]

Most cases of gray optic discs are not caused by congenital optic disc pigmentation.[11] For reasons that are understood poorly, optic discs of infants who have delayed visual maturation or albinism and those of some normal neonates have a diffuse gray tint when viewed ophthalmoscopically. In these disorders, the gray tint disappears within the first year of life without visible pigment migration. Beauvieux[12] first observed this phenomenon in premature infants and subsequently in albinotic infants who were apparently blind and who developed normal vision as the gray color disappeared. He attributed the gray appearance of these neonatal discs to delayed optic nerve myelination with preservation of the “embryonic tint.”

Patients who have “optically gray optic discs” have unfortunately been lumped together with those who have congenital optic disc

 

 

Figure 188-9 Aicardi syndrome.

pigmentation. These two conditions can usually be distinguished ophthalmoscopically because the melanin deposition is often irregular and displays some degree of granularity. [11]

AICARDI SYNDROME

The major features of Aicardi syndrome are infantile spasms, agenesis of the corpus callosum, modified hypsarrhythmia on electroencephalography, and a characteristic optic disc appearance that consists of multiple depigmented chorioretinal lacunae clustered around the disc ( Fig. 188-9 ).[13] Associated systemic anomalies include vertebral malformations (e.g., fused vertebrae, scoliosis, spina bifida) and costal malformations (e.g., absent ribs, fused or bifurcated ribs).[13] Severe mental retardation is almost invariable. The intriguing association between choroid plexus papilloma and Aicardi syndrome has been documented in numerous patients.[1] In addition to agenesis of the corpus callosum, neuroimaging abnormalities in Aicardi syndrome include cortical migration anomalies (pachygyria, polymicrogyria, cortical heterotopia) and central nervous system malformations (cerebral hemispheric asymmetry, Dandy-Walker syndrome, colpocephaly, midline arachnoid cysts).[1] The inheritance pattern of Aicardi syndrome is attributed to an X-linked mutational event that is lethal in males.[1]

 

 

REFERENCES

 

1. Brodsky MC. Congenital optic disc anomalies. Surv Ophthalmol. 1994;39:89–112.

 

2. Lambert SR, Hoyt CS, Narahara MH. Optic nerve hypoplasia. Surv Ophthalmol. 1987;32:1–9.

 

3. Brodsky MC, Glasier CM. Optic nerve hypoplasia: clinical significance of associated central nervous system abnormalities on magnetic resonance imaging. Arch Ophthalmol. 1993;111:66–74.

 

4. Brodsky MC, Conte FA, Hoyt CS, et al. Sudden death in septo-optic dysplasia: report of five cases. Arch Ophthalmol. 1997;115(1):66–70.

 

5. Pollock S. The morning glory disc anomaly: contractile movement, classification, and embryogenesis. Doc Ophthalmol. 1987;65:442–53.

 

6. Massaro M, Thorarensen O, Liu GT, et al. Morning glory disc anomaly and moyamoya vessels. Arch Ophthalmol. 1998;116(2):253–4.

 

7. Brown G, Tasman W. Congenital anomalies of the optic disc. New York: Grune & Stratton; 1983:91–126.

 

8. Brodsky MC. Magnetic resonance imaging of colobomatous optic hypoplasia. Br J Ophthalmol. 1999;83(6):755–6.

 

9. Lincoff H, Lopez R, Kreissig I, et al. Retinoschisis associated with optic nerve pits. Arch Ophthalmol. 1988;106:61–7.

 

10. Young SE, Walsh FB, Knox DL. The tilted disc syndrome. Am J Ophthalmol. 1976;82:16–23.

 

11. Brodsky MC, Buckley EG, McConkie-Rosell A. The case of the gray optic disc. Surv Ophthalmol. 1989;33:367–72.

 

12. Beauvieux J. La pseudo-atrophie optique des nouveau-nes (dysénésie myélinque des voies optiques). Ann Ocul (Paris). 1926;163:881–921.

 

13. Carney SH, Brodsky MC, Good WV, et al. Aicardi syndrome: more than meets the eye. Surv Ophthalmol. 1993;37:419–24.

Advertisements

2 comments on “Chapter 188 – Congenital Optic Disc Anomalies

  1. I’ll right away grab your rss as I can not find your email subscription link or e-newsletter service. Do you’ve any? Kindly let me know so that I could subscribe. Thanks.

  2. How could I have missed this blog! Its awsome. Your design is flawless, its like you know exactly what to do in order to make people flock to your site! I also like the perspective you brought to this subject. Its like you have an insight that most people havent seen before. I love to read a site like this.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: