Case report

A 40 year old African-American woman with no visual complaints went to her local optometrist for a routine eye examination. At the optometrist’s office she was told that “in the back of her right eye she had a dark spot with a ring around it” and was referred to a retinal specialist. The retinal specialist found a mildly decreased visual acuity and a “swollen disc” in the right eye and the patient was referred for neuro-ophthalmic consultation. To her knowledge, she previously had never had a dilated funduscopic examination.

Best corrected visual acuity was 20/30 distance and J1 near in the right eye and 20/20 distance and J1+ near in the left eye. There was a 0.9 log unit right relative afferent pupillary defect. Her colour vision, external examination, slit lamp biomicroscopy, intraocular pressures, and motility were all normal in both eyes. Funduscopic examination was normal in the left eye with an optic nerve cup to disc ratio of 0.4. The appearance of her right optic nerve (Fig 1) was that of an elevated ring around the centre of the disc, interrupted from about 7 o’clock to 9 o’clock by an area of pigmentation. The vasculature was mildly obscured as it crossed the elevation. There was no venous engorgement, haemorrhage, cotton wool spots, or exudate. Funduscopic examination gave the appearance of a peripapillary excavation of retina and retinal pigment epithelium surrounding the elevated ring from about 12 o’clock to 7 o’clock. The macula and periphery were normal. Automated perimetry showed an enlarged blind spot and a relative superior altitudinal defect on the right and a full field on the left.

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Figure 1

Photograph of the patient’s right optic disc. An elevated annulus of apparent fibroglial tissue surrounds most of the disc although it appears to spare part of the papillomacular bundle. An excavation of retina and retinal pigment epithelium surrounding the optic disc can be appreciated from about 12 o’clock to 7 o’clock.

Fluorescein angiography showed staining of optic nerve tissue but no leakage of fluorescein outside the disc margin, confirming the absence of true disc swelling (Fig 2). Magnetic resonance imaging of the brain and orbits with gadolinium showed no pathology. B-scan ultrasonography excluded optic disc drusen. Optical coherence tomography (OCT) of the optic nerve showed the elevated annulus of tissue seen on fundus examination and also showed a peripapillary excavation of the retinal pigment epithelium (RPE) adjacent to the optic nerve (Fig 3). This was thought to be most consistent with MGDA.

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Figure 2

Fluorescein angiography of the patient’s right eye. Both early (left; 32.6 seconds after injection) and late (right; 6 minutes and 14 seconds after injection) images show no evidence of fluorescein leakage outside the disc margin.

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Figure 3

Optical coherence tomography (OCT) of the patient’s right optic nerve. Representative OCT shows retinal pigment epithelium lining an excavation surrounding the optic nerve, characteristic of morning glory syndrome.

Comment

Morning glory disc anomaly is a congenital anomaly of the optic disc that is typically unilateral (for review see Brodsky¹). The majority of patients have a visual acuity between 20/200 and counting fingers in the affected eye, although cases with 20/20 vision and no light perception have been reported. It is more common in females than males and is less common in African-Americans than white people.^2–4 This condition is not typically an inherited condition or part of a multisystem genetic disorder, although it has been reported as part of the renal-coloboma syndrome⁵ and trisomy 4q.⁶

The term “morning glory syndrome” was coined for its ophthalmoscopic resemblance to the morning glory flower.⁷ In MGDA the optic nerve lies centrally within an excavation of the posterior globe. The size of the excavation varies from being relatively small, as in this particular case, to cases in which the excavation encompasses the macula, termed macular capture. In most cases there is a central fibrous tuft that obscures the central part of the disc⁸ and a variable amount of peripapillary pigment.

While MGDA is usually diagnosed by funduscopic examination alone, our case was atypical and not diagnosed immediately for several reasons: the patient had good visual acuity in the affected eye; she was African-American; there was no central fibrous tuft; and there was only a mild amount of peripapillary pigmentation. It is likely that our patient’s visual acuity was spared because of relative sparing of the papillomacular bundle (Fig 1). Indeed, the peripapillary annulus of tissue surrounding the optic nerve spared a small area temporally from about 7 to 9 o’clock. In this region there was some pigment disturbance, but little if any apparent fibrosis, compared to the rest of the optic nerve. While a previous study of eight patients⁹ suggested there was “no correlation between optic disc configuration and visual acuity” there was no patient in that study with a documented visual acuity better than 20/100.

Another atypical feature of our patient is the small amount of peripapillary pigment seen in the affected eye. The only area of pigmentation is between 7 and 9 o’clock. The remaining clock hours have elevated fibrovascular tissue but no visible pigment. This finding is not unexpected, as the visible peripapillary pigment in MGDA dissipates over time. This decrease in peripapillary pigment over time is believed to be secondary to a metaplasia of hamartomatous RPE into fibroglial tissue and hyperplasia of the fibroglial tissue. Our patient was 40 years old at diagnosis of MGDA and it is possible that she had more peripapillary pigment when she was younger. It is also possible that the peripapillary excavation of this patient was larger when she was younger, as the glial hyperplasia tends to progressively elevate the disc over time.¹⁰

There is controversy regarding the aetiology of MGDA. Some believe it is a form of optic disc coloboma.^11,12 This theory is supported by evidence that MGDA is seen along a continuum of other optic disc anomalies including coloboma in the renal coloboma syndrome.⁵ Based on the findings of a scleral defect, vascular anomalies, central glial tuft, and adipose and smooth muscle tissue in histopathological specimens, it has been hypothesised that MGDA may be a primary mesenchymal disorder or an abnormality in the relative growth between the mesoderm and ectoderm.^8,9 Another theory proposes that an abnormal enlargement of the distal optic stalk during eye development allows the inner layer of the optic cup to enter, causing an excavation at the entry site.³ One problem with determining the aetiology has been the lack of clinical confirmation (primarily a lack of fundus photography) in previous histopathological reports.^8,13–16 In this report we present OCT data that confirm these pathological findings in MGDA. Common to all of the histopathological reports is a layer of RPE that lines the peripapillary excavation. This histological feature is confirmed in the present case with OCT, which shows RPE extending posteriorly within the peripapillary scleral excavation as it approaches the optic nerve (Fig 3). We are currently evaluating other patients with MGDA using OCT and comparing these findings with the OCT appearances of other optic nerve anomalies, including optic disc coloboma.

MGDA is sometimes associated with a basal encephalocele^17–21 and up to a third of patients with MGDA will develop a retinal detachment.^2,4,22 Hence, the first step in the management of MGDA is recognising these associated conditions. Our patient did not have the characteristic facial features (flattened nasal bridge or cleft lip) nor did she have any neurological, endocrine, or respiratory symptoms to suggest she had a basal encephalocele and an magnetic resonance imaging confirmed its absence. Funduscopic examination showed no evidence of retinal detachment, and she will be followed carefully for this potential complication.

Although this is an atypical case, with no central fibrous tuft and little peripapillary pigment, this patient demonstrates the peripapillary excavation characteristic of MGDA. To our knowledge this is the first report of OCT of an eye with MGDA and confirms previous histopathological reports of MGDA showing RPE lining the central peripapillary excavation. Ongoing studies at our institution are using OCT to quantify the changes that occur with MGDA over time and to compare the features of MGDA with those of other optic nerve anomalies, including optic disc coloboma.