Abstract
Optic nerve (ON) aplasia is a rare congenital anomaly. It is characterised by the absence of optic nerve, nerve fibre layer, ganglion cells, and retinal blood vessels. ON aplasia is usually unilateral. Bilateral cases are very rare. We report such a rare case with bilateral ON aplasia and corpus callosum hypogenesis. An 11-month-old male child presented with a history of not seeing or following objects since birth. On examination, the child had microcornea and the absence of an optic disc in both the eyes. In addition, the right eye showed partial aniridia and few rudimentary retinal vessels in the posterior pole, while the left eye showed a chorioretinal coloboma but no evidence of any retinal blood vessels. Flash visual evoked potential was nonrecordable in both the eyes. MRI brain and orbit showed congenital aplasia of the ON on both sides with poorly developed optic chiasm, optic tract, and lateral geniculate body along with the features of corpus callosum hypogenesis. Child had no other systemic or endocrinological abnormalities.
Keywords: Coloboma, corpus callosum hypogenesis, optic nerve aplasia, partial aniridia
Optic nerve (ON) aplasia is a rare congenital anomaly. It is characterised by the absence of optic nerve, optic disc, nerve fibre layer, retinal ganglion cells, and retinal blood vessels. It is associated with a relative afferent pupillary defect and no light perception.[1,2] It may be an isolated ocular anomaly or may be seen in association with other ocular or nonocular abnormalities. ON aplasia is usually unilateral. Bilateral cases are very rare. Unilateral variant is characterised by normal brain and central nervous system (CNS) development, while a bilateral form is often accompanied by CNS abnormalities.[1] We, hereby, report a case of bilateral ON aplasia with corpus callosum hypogenesis and no other systemic abnormalities at presentation.
Case Report
An 11-month-old male child presented to us with a history of not seeing or following objects since birth. He is the first child of the parents and born out of nonconsanguinous marriage. He had uneventful prenatal, perinatal, and postnatal history, and had a full-term normal delivery. He had normal developmental milestones till date except vision. There was no history of seizures, focal deficits, or any other gross motor or sensory abnormalities barring visual complaints.
On ocular examination, both the eyes had searching movements and nystagmus. The child did not follow the light or any object and was unable to fix at any target. Anterior segment examination in both the eyes showed microcornea and clear lens. The right eye showed irregular pupil, partial aniridia with only a thin rim of iris superiorly and absent pupillary reaction. The left eye had normal iris, round pupil, and a sluggish pupillary reaction.
Fundus examination in both the eyes showed tessellated appearance, the absence of an optic disc with only areas of chorioretinal atrophy and hypopigmentation at the corresponding areas of the fundus. The left eye fundus in addition showed a chorioretinal coloboma involving the macula. There was no evidence of any retinal blood vessels either in the disc area or the retina in the left eye while the right eye showed few rudimentary retinal vessels emanating from the corresponding disc area [Fig. 1]
Figure 1.
Fundus photograph of the right eye (a) shows absent optic disc (arrow), tessellated fundus, hypopigmented patches, and rudimentary retinal vessels (arrowhead) emanating from the disc; fundus photograph of the left eye (b) shows absent optic disc and retinal vessels (arrow), chorioretinal coloboma (arrowhead) involving the macula, tessellated fundus, and multiple hypopigmented patches; flash visual evoked potential (VEP) in both the eyes (c) is unrecordable
Flash visual evoked potential (VEP) was nonrecordable in both the eyes. MRI brain and orbit showed congenital aplasia of the ON on both sides with poorly developed optic chiasm, optic tract, and lateral geniculate body (LGB). In addition, MRI brain showed thinning of the distal body and splenium of corpus callosum suggestive of corpus callosum hypogenesis. [Fig. 2] USG B scan in both the eyes revealed the absence of optic nerve head (ONH) shadow.
Figure 2.
MRI brain and orbit (a) and (b) shows absent optic nerve (arrowheads) while (c) shows thinning of a distal body (arrowhead) and splenium (arrow) of the corpus callosum
A systemic evaluation revealed no motor, sensory, cardiovascular, neurological, or any endocrinological abnormalities.
Discussion
ON aplasia implies the complete absence of the ON and disc, ganglion cells, and nerve fibre layer along with retinal vessels. On histopathological examination, only a vestigial dural sheath entering the sclera in its normal position is seen along with the features of retinal dysplasia in the form of rosettes.[1,3] Multiple theories have been suggested regarding the pathogenesis of ON aplasia – defective embryonal fissure formation, failure of the mesenchymal anlage of the hyaloid system to enter the embryonal fissure, or primary retinal ganglion cell agenesis.[4]
True ON aplasia is characterised clinically by blindness (no light perception), absent disc, absent central and branch retinal vessels, and afferent papillary defect.[4,5,6] The left eye of the child in our case showed no light perception, abnormal pupillary reaction, absent disc, and absent retinal vessels. MRI brain and orbit in the left eye showed absent ON with poorly developed chiasm and LGB; USG B scan showed the absence of ONH shadow while VEP in the left eye was unrecordable. Our case, thus, had a true ON aplasia in the left eye based on clinical as well as MRI, USG, and VEP findings. However, the right eye of the child in our case showed all clinical, radiological, and electrophysiological features of ON aplasia except the presence of rudimentary retinal vessels in the posterior pole. Histopathological examination to look for the absence of ganglion cells and nerve fibre layer along with the presence of a vestigial dural sheath may help to differentiate true ON aplasia from severe ON hypoplasia. This is, however, not feasible in this case. Based on the absence of light perception, partial aniridia, absent pupillary reflex, absence of disc on fundus examination, absent ON on MRI and USG, and nonrecordable VEP from the right eye, we have assumed it to be a case of ON aplasia in the right eye as well.
Other ocular abnormalities seen in ON aplasia include microphthalmos, ptosis, squint, microcornea, iris hypoplasia, iris coloboma, aniridia, retinochoroidal coloboma, and persistent hyperplastic primary vitreous.[2,6,7] Our case had microcornea, tessellated fundus, and chorioretinal atrophic patches in both the eyes; iris hypoplasia in the right eye; and retino choroidal coloboma in the left eye.
Unilateral ON aplasia in the majority of cases is accompanied by otherwise normal brain development. Bilateral cases are very rare and are associated with widespread congenital CNS malformations such as hydrancephaly and hypopituitarism.[8,9] Only very few cases of true bilateral ON aplasia as isolated CNS anomaly have been reported in the past in the literature.[1,2] Our case also had bilateral ON aplasia with only corpus callosum hypogenesis on MRI but no clinical signs of CNS or endocrinological abnormalities at presentation.
Corpus callosum hypogenesis or dysgenesis can be associated with developmental delay, speech delay, visual and hearing problems, feeding problems, seizures, and abnormal muscular tonus.[10] Our case had an only visual impairment and no other features of corpus callosum dysgenesis as listed before. Cases with documentation of bilateral ON aplasia are updated in Table 1.[1,2,5,6,7,8,9] However, the case reported by Storm et al.[8] strictly speaking represents optic disc hypoplasia because there was a normal pupillary reflex in addition to the presence of a small disc.
Table 1.
Bilateral aplasia of optic nerve
| Author and year of publication | No. of cases | Associated CNS* and other anomalies | Ocular abnormalities |
|---|---|---|---|
| Storm, 1984[8] | 1 | Hydranencephaly | Small optic disc, absent retinal vessels |
| Brodsky, 2004[9] | 1 | Hypo-pituitarism, posterior pituitary ectopia | Absent optic disc and retinal vessels |
| Sanjari, 2006[1] | 1 | Absent | Absent optic disc and retinal vessels |
| Meire, 2011[5] | 2 | Absent | Absent optic disc and retinal vessels |
| Ghassemi, 2012[7] | 1 | Corpus callosum agenesis, thalamic and chiasmal lesions | Absent optic disc and retinal vessels |
| Khandgave, 2014[2] | 1 | Absent | Absent optic nerve head and retinal vessels, microcornea, anterior embryotoxon in both the eyes; partial aniridia and coloboma in the left eye |
| Sadasivan, 2018[6] | 1 | Absent | Absent optic nerve head and retinal vessels, microcornea in both the eyes; iris and lens coloboma in the left eye |
*CNS−Central nervous system
Management of such cases involves mainly the evaluation and management of any associated neurological or endocrine problem. As there is no specific management of ocular problems, the parents are counselled mainly regarding education, vocational rehabilitation, and mobility training of blind children. Also, regular and annual systemic evaluation is advocated in such cases to detect any clinical signs of CNS abnormality at the earliest and manage accordingly.[2]
Conclusion
Bilateral ON aplasia is rare, with most reported cases having major CNS malformations. Very few cases of bilateral ON aplasia in a normal child like our case have been reported before. We, however, advocate regular systemic evaluation along with vocational rehabilitation, parent counselling and mobility training for such special children.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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