Optic nerve aplasia: A case series.

Optic nerve aplasia (ONA) is a congenital optic nerve anomaly characterized by the absence of optic nerve head, retinal blood vessels, retinal ganglion cells, and optic nerve fibers in a malformed eye. Clinically, the condition presents with the absence of perception of light, afferent pupillary defect and a fundus appearance of absent optic nerve head, and retinal vessels with associated ocular and nonocular abnormalities. Systemic anomalies have been reported with bilateral ONA, whereas unilateral ONA is seen in otherwise healthy individuals. We report three cases of ONA with varied clinical presentations.

Optic nerve aplasia (ONA) is a rare, nonhereditary developmental anomaly characterized by congenital absence of the optic nerve, retinal blood vessels, retinal ganglion cells, and optic nerve fibers in a blind eye causing lifelong visual handicap. Unilateral ONA is generally associated with otherwise normal brain development, whereas bilateral ONA is accompanied by central nervous system (CNS) malformations[1] though variations may exist. Ocular or nonocular abnormalities may coexist. Herein, we report three cases of ONA with varied clinical presentations.

Case Reports

Case 1

A 6-year-old girl, born to a nonconsanguineous marriage, was brought in with the complaints of apparent small size with occasional deviation of the right eye since birth. Examination revealed absent perception of light, pseudoptosis, and total afferent pupillary defect (TAPD) in the right eye. The left eye had vision 20/20 with normal clinical findings.

The right eye had 50 prism diopters exotropia with modified Krimsky. Exophthalmometry by Leudde's measured 8 mm (right eye), 10 mm (left eye) suggestive of enophthalmos of the right eye [Fig. 1].

Figure 1

Fundus appearance of absent optic nerve head and retinal vessels in the right eye, normal fundus of the left eye, and coronal magnetic resonance imaging showing the absence of optic nerve in the expected location in the right eye. Optic nerve is of normal caliber and seen in the intraconal fat in the left eye, marked with arrow (Case no: 1)

Fundus examination of the right eye showed a complete absence of the optic nerve and retinal blood vessels with chorioretinal atrophic patches and a highly tessellated background retina. The left eye fundus was within normal limits.

Ultrasound B-scan showed the absence of the optic nerve shadow in the right eye. Computerized tomography imaging of the brain and orbit at the level of the optic nerve showed enophthalmos of the right eye. The anterior segment of the right optic nerve in its intraorbital course was absent, posterior segment appeared as a thin cord. No significant anomaly of the brain was noted. T1 weighted, coronal magnetic resonance imaging (MRI) revealed complete absence of the optic nerve in the right eye in the expected location in the intraconal fat, thus confirming the absence of the orbital part of the optic nerve [Fig. 2].

Figure 2

Normally appearing fundus in the right eye and absence of optic nerve in the left eye (Case no: 2)

Case 2

A 5-year-old child with unremarkable birth history was brought in with the complaints of having no vision in the left eye which appeared small in size since birth. There was a past history of trauma with stone and ocular surgery in the right eye. On examination, best-corrected visual acuity in the right eye was 20/40 with Cardiff cards and no perception of light in the left eye. Right eye showed linear macular corneal scar at 11 o' clock limbus. Iris tissue was deficient from 9 to 11 o'clock hours and the pupil was irregular. Lens was clear and fundus examination was within normal limits. Left eye corneal diameter was 12 mm vertically and 9 mm horizontally. There was partial aniridia from 7 to 2 o' clock hours [Fig. 3]. Fundus examination revealed the complete absence of the optic nerve and retinal vessels and areas of chorioretinal atrophy in the macula and mid-peripheral retina.

Figure 3

Fundus photograph of the right eye and left eye showing complete absence of the optic nerve head and retinal vessels and coronal magnetic resonance imaging showing bilateral absence of optic nerve (Case no: 3)

Intraocular pressure was 12 mmHg in the right eye and 50 mmHg in the left eye by applanation tonometry.

Case 3

A 5-month-old girl child was brought with a complaint of not having developed social smile. This child was born to a nonconsanguineous marriage by normal term delivery with an uneventful perinatal period. General and systemic examinations were within normal limits. On ocular examination, the child was not fixing or following the light. There was microcornea in both the eyes with the persistent pupillary membrane in the right eye and typical iris coloboma with lens coloboma in the left eye. Fundus examination revealed clear media with absent optic nerve head and retinal blood vessels and tessellated background retina in both the eyes. Optic nerve head shadow was not made out by ultrasound B-scan in either eye. Axial length was 20 mm in both eyes. MRI revealed the bilateral absence of optic nerves and chiasma and no abnormality of the brain.

Discussion

ONA is an infrequently reported congenital optic nerve dysplasia presumed to be the result of some insult occurring at around the 3–4 months of gestation, affecting normal retinal development and angiogenesis, causing degeneration of retinal ganglion cells.[2] The various theories proposed to explain the pathogenesis of ONA are failure of development of mesodermal elements,[3] failure of formation of fetal fissure,[4] primary failure of ganglion cells,[5] and failure of mesodermal induction,[6] though no unified hypothesis exists. Histopathological examination usually demonstrates a vestigial dural sheath entering the sclera in its normal position, retinal dysplasia, and rosette formation.[7]

Literature review has revealed 38 cases of ONA being reported till date.[8] Unilateral ONA is usually associated with normal brain development, whereas bilateral ONA is reported to be associated with congenital hypopituitarism and posterior pituitary ectopia,[1] meningoencephalocele, and septo-optic dysplasia. Esotropia, enophthalmos, trabeculodysgenesis, partial aniridia, cataract, microcornea, and retinal rosettes/uveoretinal coloboma are the ocular abnormalities associated with unilateral cases.[1] Mutations in PAX6 and OTX2 genes have been implicated, though the exact genetic basis is unknown.[9]

The prognosis of ONA is poor and management is directed towards identifying any associated systemic abnormality. Ocular prosthesis for esthesis and shatterproof glasses along with mobility training and vocational rehabilitation are recommended for optimized social development.

Here we report three cases of ONA with varied presentations. The first case had unilateral ONA with no ocular or systemic anomalies. The second case had unilateral ONA in association with ipsilateral ocular anomalies and glaucoma. The third was unique in that, CNS was within normal limits in spite of bilaterality. Indian literature review is limited with regard to ONA and related abnormalities. The only reported case has been that of bilateral ONA exclusively associated with microphthalmos.[10]

Conclusion

A thorough systemic evaluation along with neuroimaging is recommended in children with ONA to rule out CNS malformations and endocrinological abnormalities.

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.