Segmental Optic Nerve Hypoplasia
Posted inInteresting Cases Interesting Papers

Segmental Optic Nerve Hypoplasia

 

  • Definition: Superior Segmental Optic Nerve Hypoplasia (SSONH), also known as “topless optic disc,” is a congenital condition characterized by reduced regional ganglion cells (RGCs) in the superior optic disc.

 

  • Characteristic Findings (4 key features):

    • Superior entrance of the central retinal artery.

    • Superior optic disc pallor.

    • Thinning of the superior retinal nerve fiber layer (RNFL).

    • Inferior altitudinal or sectoral visual field (VF) defects.

  • Epidemiology: Rare condition, often underdiagnosed; commonly associated with maternal diabetes.

  • Etiology/Pathophysiology:

    • Pathogenesis is unclear but linked to maternal diabetes, suggesting a developmental insult to the superior optic nerve during embryogenesis.

    • Involves overproduction and subsequent elimination of retinal axons, as seen in human fetal optic nerve development.

  • Risk Factors:

    • Maternal diabetes mellitus (strong association, especially gestational diabetes).

    • High glucose levels may affect retinal patterning during embryogenesis, leading to neuronal death or altered retinal Müller cell function.

  • Clinical Presentation:

    • Patients typically have normal visual acuity but present with inferior visual field defects (altitudinal or sectoral).

    • Often asymptomatic unless visual field loss is significant, detected during routine screening.

  • Diagnostic Tools:

    • Fundus Examination: Shows superior disc pallor and superior entrance of the central retinal artery.

    • Optical Coherence Tomography (OCT): Reveals thinning of the superior RNFL and confirms optic disc hypoplasia.

    • OCT Angiography: Demonstrates reduced radial peripapillary capillary density in the superior segment.

    • Visual Field Testing: Confirms inferior altitudinal or sectoral defects, a critical diagnostic clue.

  • Differential Diagnosis:

    • Glaucoma: SSONH can mimic glaucomatous optic neuropathy due to RNFL thinning and VF defects but lacks progressive rim loss or elevated intraocular pressure.

    • Other optic nerve hypoplasias, optic atrophy, or congenital disc anomalies.

  • Management:

    • No specific treatment; management focuses on monitoring for associated conditions (e.g., diabetes-related complications).

    • Regular follow-up with OCT and VF testing to assess stability, as SSONH is non-progressive.

  • Prognosis:

    • Stable condition with no progression over time, unlike glaucoma.

    • Visual field defects are permanent but typically do not worsen.

  • Historical Context: First described by Petersen and Walton in 1977 in children born to diabetic mothers; termed SSONH by Robert K. in 1989.

Citation

Vickers, A., Zhou, A., Al-Zubidi, N., & Tripathy, K. (2024). Superior Segmental Optic Nerve Hypoplasia (SSONH). EyeWiki, American Academy of Ophthalmology. Last edited December 3, 2024. Retrieved from https://eyewiki.aao.org/Superior_Segmental_Optic_Nerve_Hypoplasia

  • Patient Presentation: A 15-year-old boy with high myopia (-11.00 diopters), axial length of 27.14 mm, and anisometropic amblyopia in the right eye, presenting with best-corrected visual acuity of 20/200.

  • Ocular Findings:

    • Segmental temporal optic nerve hypoplasia, characterized by a crescent-shaped disc with temporal hypoplasia.

    • Nearly absent optic cup, an exceptionally rare finding.

    • Left eye was unremarkable, indicating unilateral involvement.

  • Diagnostic Imaging:

    • Color fundus photograph and red-free image: Show a crescent-shaped disc with temporal hypoplasia (red arrowhead).

    • Optical Coherence Tomography (OCT): Confirms segmental temporal hypoplasia of the optic disc with a nearly absent cup.

  • Clinical Context: Segmental optic nerve hypoplasia is a rare variant of optic nerve hypoplasia, distinct from diffuse hypoplasia or aplasia.

  • Associated Conditions:

    • High myopia and elongated axial length (27.14 mm) may contribute to optic disc anomalies.

    • Anisometropic amblyopia likely explains poor visual acuity in the affected eye.

  • Rarity: Segmental temporal hypoplasia with an almost absent cup is exceptionally rare, making it a critical point for differentiation from other optic nerve anomalies.

  • Differential Diagnosis:

    • Optic nerve aplasia, diffuse optic nerve hypoplasia, or myopic disc changes.

    • Consider other congenital optic disc anomalies (e.g., morning glory disc anomaly, optic pit).

  • Management Implication: No specific treatment for segmental hypoplasia; focus on managing amblyopia and monitoring for myopic complications (e.g., retinal detachment, myopic maculopathy).

Citation

Palaniva, S., & Rajendran, A. (2024). Segmental Optic Nerve Hypoplasia. Ophthalmology Retina, e31. https://doi.org/10.1016/j.oret.2024.08.002