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The Official Scientific Journal of Delhi Ophthalmological Society
Unilateral Optic Nerve Aplasia In An Otherwise Normally Developed Eye
Suresh Ramchandani, Prajakta Paritekar, Priyanka Patkar, Neha Dhiware 
 Shivam Eye Foundation and MGM Medical College and Hospital, Kamothe, Navi Mumbai, Maharashtra, India

Corresponding Author:
Suresh Ramchandani
Shivam Eye Foundation & MGM Medical 
College and Hospital, Kamothe, 
Navi Mumbai, Maharashtra, India 
Email id: shivameyefoundation@gmail.com
Received: 20-OCT-2016 Accepted: 21-SEP-2017 Published Online: 05-MAR-2018
DOI: http://dx.doi.org/10.7869/djo.340
Abstract
We report a unique case of unilateral optic nerve aplasia in an otherwise normally developed child. It was an incidental finding in a preterm child who was being screened for retinopathy of prematurity. Anterior segment of the affected eye was normal. However pupillary light reflexes- direct and consensual were absent. Ultrasound B scan and MRI confirmed the absence of optic nerve, in an otherwise normally developed eye.
Keywords : unilateral, optic nerve, aplasia

Introduction
Optic nerve aplasia is a rare developmental anomaly characterized by absence of optic nerve, central retinal vessels and retinal ganglion cells that is seen most often in a unilaterally malformed eye. It can be unilateral or bilateral. The visual pathway in unilateral optic nerve aplasia may assume a primitive form of neuronal organisation characterized by an increase in contralateral retinogeniculostriate projection. Bilateral optic nerve aplasia is usually associated with microphthalmos in at least one eye whereas unilateral optic nerve aplasia is associated with a variety of ocular anomalies in addition to microphthalmos.
We report a unique case of unilateral optic nerve aplasia in an otherwise normally developed eye.

Case Report
A 6 week old female child born of a non-consanguinous marriage at 30 weeks of gestation by vaginal delivery was referred to us for screening of retinopathy of prematurity. The pregnancy was uneventful without any history of drug intake or exposure to radiation. The birth weight was 1.2 kgs, and the baby was given inhalational oxygen therapy in neonatal intensive care unit. On examination of the right eye, both direct light reflex and concensual light reflex was absent; whereas in the left eye, both direct and consensual light reflexes were present. RAPD was seen in the right eye. Extra ocular movements were full. Rest of anterior segments of both eyes were normal on torch light examination (Figure 1).
Dilated fundus examination showed a normal left eye (Figure 2). Fundus picture of right eye showed absence of optic nerve head, absence of retinal vessels and few chorioretinal atrophic patches (Figure 3). A clinical diagnosis of right eye optic nerve aplasia was made and USG B-Scan and MRI were done. USG B-scan of the right eye showed normal size of eyeball, absence of optic nerve, normal extraocular muscles and echo free vitreous cavity (Figure 4), while that of the left eye was normal (Figure 5).
MRI orbit showed a normally developed left eye, while the right eye showed absence of optic nerve upto the optic chiasma (Figure 6).









Discussion
Development of the eye starts at 22 days of intrauterine life. Outpouchings develop from a pair of shallow groves appearing on the sides of the primitive forebrain, forming the optic pits. Proliferation of cells occur in the optic pit, producing a large spherical bulge connected to the neural tube by a short, cylindrical optic stalk. The optic nerve develops from the embryonic optic stalk. As the stalk lengthens, the lumen gets progressively occupied by the axons growing from the ganglion cells of the retina. This process is completed by the eighth week. These axons reach the brain, and a rudimentary optic chiasma is established. Studies show that expression errors of certain genetic factors can give rise to optic nerve hypoplasia.1-3 Optic nerve aplasia is a rare congenital anomaly that typically occurs unilaterally in healthy patients. It may also occur bilaterally, but this is rare and almost always associated with various ocular and CNS anomalies.4 Only a handful cases of bilateral aplasia in an otherwise normal infant have been reported worldwide. Only one case of bilateral chiasma and tract aplasia in an otherwise healthy infant with one microphthamic and one normal sized eye has been reported.5 It does not have any gender or racial predilection.6

The pathogenesis is controversial. Scheie and Adler suggested that it may be due to failure of development of mesodermal elements that supply the connective tissue and hyaloid vessels.7 However, Mann’s theory, which suggests that failure of the foetal fissure to form causes misdirection of the nerve fibres and it leads to their failure to reach the lateral geniculate body and their necrosis, is more accepted.8 In a normal size eye with optic nerve aplasia, the initial development of the eye is normal with primitive multipotent retinal ganglion cells. Hotchkiss and Green postulated a failure of mesodermal induction secondary to a third order neuronal defect which is probably responsible for development of optic nerve aplasia.9

Reports have described a variety of ocular defects on the affected side. These include microphthalmos, enophthalmos, ptosis, esotropia, microcornea, diminished corneal sensation, immature irido-corneal angle, iris hypoplasia, iris coloboma, aniridia, cataractous lens, persistent hyperplastic primary vitreous, avascular retina, no definite optic nerve, geographic areas of hyperplasia, hypoplasia or normal pigmentation of RPE and visualisation of choroidal vasculature in regions of RPE.6 Significant extraocular abnormalities have also been described. All the cases of unilateral optic nerve aplasia reported so far show microphthalmos or other ocular anomalies, usually with systemic abnormalities, prominently CNS. To the best of our knowledge, ours is a rare case showing unilateral optic nerve aplasia without any ocular or systemic anomalies. The brain was normally developed. The cause of this can be because of a degenerative mechanism occurring in a normally developed eye due to some reason.

References
  1. Torres M, GÃ mez-Pardo E, Gruss P. Pax2 contributes to inner ear patterning and optic nerve trajectory. Development 1996; 122:3381.
  2. Deiner MS, Kennedy TE, Fazeli A, Serafini T, Tessier-Lavigne M, Sretavan DW. Netrin-1 and DCC mediate axon guidance locally at the optic disc: loss of function leads to optic nerve hypoplasia. Neuron 1997; 19:575.
  3. Brittis PA, Silver J. Multiple factors govern intraretinal axon guidance: a time-lapse study. Mol Cell Neurosci 1995; 6:413.
  4. Alqahtani J. Optic nerve aplasia: A case report and literature review. J Pediatr Neurosci 2008; 3:150-3.
  5. Sanjari MS, Flavarjani KG, Parvaresh MM, Kharazi HH, Kashkooli MB. Bilateral aplasia of optic nerve chiasm, and tracts in otherwise healthy infant. Br J Ophthalmol 2006; 90:513–4.
  6. Howard MA, Thompson JT, Howard RO. Aplasia of the optic nerve. Trans Am Ophthalmol Soc 1993; 91:267–81.
  7. Scheie HG, Adler FH. Aplasia of optic nerve. Arch Ophthalmol 1941; 26-61.
  8. Mann I. The development of the human eye. New York: Greene and Stratton, Inc;1964.p.29.
  9. Hotchkiss LH, Green WR. Optic nerve aplasia and hypoplasia. J Pediatr Ophthalmol Strabismus 1979; 16:225-40.


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Suresh Ramchandani, Prajakta Paritekar, Priyanka Patkar, Neha DhiwareUnilateral Optic Nerve Aplasia In An Otherwise Normally Developed Eye.DJO 2018;28:64-66
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Suresh Ramchandani, Prajakta Paritekar, Priyanka Patkar, Neha DhiwareUnilateral Optic Nerve Aplasia In An Otherwise Normally Developed Eye.DJO [serial online] 2018[cited 2019 Jan 17];28:64-66. Available from: http://www.djo.org.in/articles/28/3/UnilateralOpticNerveAplasiaInAnOtherwiseNormallyDevelopedEye.html
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