Optometry - Journal of the American Optometric Association
Volume 79, Issue 10 , Pages 576-580, October 2008

Superior segmental optic nerve hypoplasia: The topless disc syndrome

  • Joseph Sowka, O.D.

      Affiliations

    • Corresponding Author InformationCorresponding author: Joseph Sowka, O.D., Nova Southeastern University College of Optometry, 3200 South University Drive, Ft. Lauderdale, Florida 33328.
    • ,
  • Lori Vollmer, O.D.
    • ,
  • Sherrol Reynolds, O.D.

Nova Southeastern University, Ft. Lauderdale, Florida

Article Outline

Abstract 

Background

Optic nerve hypoplasia is a well-known congenital maldevelopment presenting with an abnormally small optic nerve head occupying the central aspect of a normally sized chorioscleral canal. Characteristically, the optic nerve head is surrounded by scleral anlage with a “double ring sign.” Less commonly appreciated, however, is the fact that optic nerve hypoplasia may be sectorial rather than total and involving only the superior aspect of the optic disc with corresponding inferior visual field loss.

Case Report

A 51-year-old woman presented with a previous diagnosis of idiopathic optic atrophy superiorly in the left eye. Detailed observation revealed that the disc was not atrophic superiorly but actually hypoplastic, and the patient received a conclusive diagnosis of superior segmental optic nerve hypoplasia.

Conclusions

It must be appreciated that optic nerve hypoplasia can also affect solely the superior aspect of the disc with subsequent functional deficits. It is important to differentiate this syndrome from true optic atrophy to ensure proper management.

Keywords: Superior segmental optic nerve hypoplasia, Topless disc syndrome, Optic nerve hypoplasia

 

Optic nerve hypoplasia (ONH) is the one of the most common congenital optic nerve abnormalites.1, 2 ONH is characterized by a lower number of optic nerve axons, as the condition is believed to represent a dysplasia of the retinal ganglion cell layer with an associated loss of the nerve fiber layer secondary to some interruption in the development of the fetus.2 Patients present with variable symptoms, depending on the severity of the condition. Visual acuity may range from normal to no light perception in the affected eye.1, 2, 3

The hypoplastic optic nerve is smaller than expected, with the vasculature appearing very large relative to the disc.4, 5 The optic disc is frequently encircled by a circumpapillary ring of scleral tissue described as a halo and termed a double-ring sign. The normally bright reflex from the nerve fiber layer is characteristically diminished.2 There is a distinct subcategory of ONH known as superior segmental optic nerve hypoplasia (SSONH) with structural dysfunction limited to only the superior aspect of the disc. Although SSONH has been written about in reports dealing with optic hypoplasia,6, 7 a review of the literature using keywords “superior segmental optic (disc) hypoplasia,” and “topless disk” finds only 8 published reports devoted to this entity. Thus, it is important to call to the attention of clinicians this entity to avoid misdiagnosis and unnecessary medical testing, such as serology, looking for infectious and inflammatory diseases as well as neuroimaging looking for mass lesions.

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Case report 

A 56-year-old Hispanic female presented for a comprehensive ophthalmic evaluation with complaints of her eyes itching and burning, floaters of long duration, and reading difficulties. She had previously used cyclosporine 0.05% (Restasis®, Allergan Inc., Irvine, California) for dry eyes, but was not using the medication currently. She had been involved in an automobile accident 20 years before with nonpermanent injury to the left side of her face. She also reported a history of “asymmetric optic nerves” and had undergone an extensive, but inconclusive, evaluation for this issue. She had no diagnosed systemic conditions and reported allergies to iodine and sulfa medications. Her family medical history was significant only for colon cancer and diabetes, both in her brother. The patient did not recall whether her mother had been diabetic.

Previous records of ophthalmic care were available for review at examination. In 1999, the patient was noted to have asymmetric optic disc cupping (judged at 0.25/0.25 in the right eye and 0.45/0.45 in the left eye) with statistically normal intraocular pressures. Threshold perimetry was performed to rule out glaucoma. Visual field testing found a dense inferior temporal defect O.S. and a normal visual field O.D. (see Figure 1). At that time, it was felt that the visual field defect was inconsistent with glaucoma and, upon further examination, it was determined that the left disc manifested superior disc pallor in excess of cupping. At that time, the patient was referred to a neuro-ophthalmologist.

Upon evaluation, the neuro-ophthalmologist agreed that there was superior disc pallor O.S. corresponding to the visual field loss. The proposed etiologies at that time were congenital defect, traumatic nerve lesion, old vascular or demyelinating event, or direct nerve compression. Cranial nerve testing was normal at that time. Magnetic resonance imaging of the brain, orbits, and chiasm with and without contrast was performed. There was no demonstrated mass effect or evidence of ischemic or demyelinating events. Without a conclusive etiology, the neuro-ophthalmologist followed up with the patient periodically for 1 year and saw no evidence of change in either the visual field or disc appearance and concluded that the neuropathy was nonprogressive. The patient then returned to the referring optometrist and was followed up for “occult neuropathy” on an appropriate periodic basis for several years.

At her examination in 2007, she expressed some anxiety over the unresolved issues of her left optic neuropathy; however, because it did not impact her visual function and was apparently stable, she ignored the situation for the last several years. Regardless, at this examination, she desired another opinion on the condition.

Best-corrected visual acuities were 20/20-2 O.D. and 20/20 O.S. with a low hyperopic correction. An age-appropriate change in her bifocal add solved her reading difficulties. Pupils were equal, round, and reactive to light without relative afferent defect. Confrontation visual field testing failed to reveal any losses. Extraocular muscles were without restriction. Color vision testing with pseudoisochromatic plates found normal color perception in each eye. Biomicroscopy results showed a slightly shallow anterior chamber in each eye. Gonioscopic analysis found pigmented trabecular meshwork 360° in both eyes with a steep iris approach but no evidence of peripheral anterior synechiae, angle closure, or propensity to close. The corneas were clear, but there was a diminished tear break-up time consistent with dry eye syndrome. Intraocular pressures by Goldmann applanation were 12 mmHg O.D. and 13 mmHg O.S. Dilated fundus examination found a pink and distinct optic disc and intact neuroretinal rim tissue O.D. with cupping estimated at 0.25/0.25. The left disc manifested cupping at 0.45/0.45. The left disc area was slightly larger than the right, accounting for some degree of cupping asymmetry. The superior aspect of the disc showed relative pallor from 10 o'clock to 2 o'clock. However, there was not complete pallor throughout this sector. Rather, the perceived pallor had a sharp horizontal demarcation line running from 10 o'clock to 2 o'clock and did not extend to the cup. Therefore, the disc did not manifest complete sectorial pallor. Additionally, detailed disc inspection not only showed perceived pallor but a discontinuity in the tissue of the disc. That is, the pink and perfused rim tissue appeared very smooth and regular, whereas the seemingly pale aspect appeared to be rough and, in fact, a different type of tissue distinct from rim tissue, appearing more similar to scleral tissue (see Figure 2). Additionally, there was peripapillary atrophy O.S. The remainder of the fundus examination findings were normal in each eye except for mild vitreous syneresis OU accounting for her complaints of floaters.

  • View full-size image.
  • Figure 2. 

    A and B, Disc photographs show superior hypoplasia O.S., with arrows pointing to delineation of flattened disc and scleral anlage filling the chorioscleral canal.

Threshold perimetry was performed, showing a dense inferior temporal defect O.S. and a normal visual field O.D. There appeared to be no changes compared with the analysis performed 8 years earlier (see Figure 3). Therefore, based on the unchanging visual field defect and unusual superior segmental pallor with apparent differentiation of tissue, the patient had SSONH diagnosed, rather than pallor associated with optic atrophy. It was determined that the relative superior pallor was not actually atrophy of the neuroretinal rim from ischemic, compressive, or similar causes, but rather a colobomatous formation with prominence of scleral tissue and a manifestation of ONH.

The patient was educated to the findings and assured that she had an identified, nonprogressive anomaly. She expressed relief at the information. She is currently being followed up with at appropriate intervals for shallow (though nonoccludable) anterior chamber angles. Laser peripheral iridotomy is not indicated at this time. Artificial tears were recommended for dry eyes.

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Discussion 

Superior segmental optic nerve hypoplasia is a distinct subcategory of ONH. This congenital anomaly is characterized by a relative superior entrance of the central retinal artery, pallor of the superior optic disc, superior peripapillary scleral halo, and thinning of the superior retinal nerve fiber layer (RNFL). These findings are variably present.8, 9, 10, 11, 12, 13, 14, 15 This appearance may be confused with true optic atrophy of infectious, inflammatory, or compressive etiology. Because of the absence of tissue and hypoplasia involving only the superior aspect of the disc, SSONH has been synonymously termed the topless disc syndrome, a moniker attributed to W.F. Hoyt and published by Landau et al.9, 15 The pathogenesis of SSONH remains undefined.12

Patients with SSONH typically have excellent and unaffected visual acuity. The main functional deficit appears to be an associated inferiorly located visual field defect, arcuate or altitudinal in nature, in the affected eye(s).9, 11, 12, 15

A summary review of 38 patients with SSONH found a female predilection (in 74% of cases).15 The condition has been noted to occur both unilaterally and bilaterally with relatively equal frequency.8, 12 The prevalence of this condition likely has been underestimated. One population analysis in Japan that reviewed photographs of 14,431 subjects involving 28,396 eyes for SSONH found a prevalence of 0.3% of subjects and 0.2% of all eyes reviewed.8

There has been a strong association between SSONH and maternal diabetes.10, 11, 15 Landau et al.15 also noted a lower birth weight, shorter gestation time, and poorer control of maternal diabetes as associated risk factors for SSONH, although these risk factors were not independent of one another. In fact, at the time of publication of their report (1998), SSONH was only reported to have occurred in offspring of diabetic mothers.15 However, in 1999, Hashimoto et al.9 reported on 4 patients with SSONH that was found incidentally due to inferior visual field defects; these patients did not have a history of maternal diabetes. There have been reports of familial cases, suggesting genetic involvement.12, 14

As expected, optic coherence tomography (OCT) shows superior defects in the optic disc and associated superior thinning of the RNFL.12 OCT scans in the vertical meridian through the affected optic disc shows an asymmetric topographic configuration consistent with the structural abnormalities in the superior aspect of the disc. The RNFL contiguous with the superior aspect of the disc is thinned and, in some cases, the retinal pigment epithelium and choroid extend toward and intrude on the center of the optic cup, suggesting superior narrowing of the scleral canal. This may contribute to the superior peripapillary halo or crescent present in this condition.12 Superior segmental optic nerve hypoplasia can be so mild that it may be missed initially clinically and be discovered only incidentally upon visual field testing or nerve fiber layer analysis.12

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Conclusion 

This case details a patient who received a mistaken diagnosis of partial sectorial optic atrophy. This misdiagnosis was likely made because of widespread unfamiliarity with this distinct clinical syndrome. This is not surprising when one considers that only 8 reports devoted to this entity have been published and only passing mention is made in comprehensive reviews of ONH. However, this benign condition must be considered in patients manifesting seeming pallor, atrophy, or hypoplasia affecting only the superior aspect of the optic disc with concordant inferior visual field defects, especially when asymptomatic and with a history of maternal diabetes. In cases of adult patients, recognition of this condition can obviate the need for neuroimaging or other diagnostic testing. In children, however, the diagnosis of any form of optic nerve hypoplasia should prompt a complete evaluation for any other associated developmental anomalies.

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References 

  1. Dutton GN. Congenital disorders of the optic nerve: excavations and hypoplasia. Eye. 2004;18(11):1038–1048
  2. Kim MR, Park SE, Oh SY. Clinical feature analysis of congenital optic nerve abnormalities. Jpn J Ophthalmol. 2006;50(3):250–255
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  10. Kim RY, Hoyt WF, Lessell S, et al. Superior segmental optic hypoplasia. A sign of maternal diabetes. Arch Ophthalmol. 1989;107(9):1312–1315
  11. Purvin VA. Superior segmental optic nerve hypoplasia. J Neuroophthalmol. 2002;22(2):116–117
  12. Unoki K, Ohba N, Hoyt WF. Optical coherence tomography of superior segmental optic hypoplasia. Br J Ophthalmol. 2002;86(8):910–914
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PII: S1529-1839(08)00416-8

doi:10.1016/j.optm.2008.05.008

Optometry - Journal of the American Optometric Association
Volume 79, Issue 10 , Pages 576-580, October 2008

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