Megalopapilla

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Article initiated by:

Qiancheng Wang

All contributors:

Qiancheng Wang, Samantha Marie Arsenault, Adam.Cantor, Julia.Faust, Nagham Al-Zubidi, MD, Amanda Ely, M.D., Samantha Marie Arsenault, Mary Labowsky, MD

Assigned editor:

Amanda Ely, M.D., Mary Labowsky, MD

Review:

Assigned status Up to Date

 by Amanda Ely, M.D. on September 1, 2026.

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Megalopapilla (MP) is a rare congenital anomaly characterized by an enlarged nerve head and abnormal disc shape. It is typically a benign condition but must be differentiated from other diseases of the optic nerve that can cause vision loss such as glaucoma.

Disease Entity

Megalopapillae

Disease

Megalopapilla (MP) is a rare, congenital, non-progressive anomaly characterized by an enlarged optic nerve head (disc diameter >2.5mm) with or without an abnormal disc shape and can occur in one or both eyes. MP can mimic glaucomatous changes of the optic nerve, with an increase cup area, volume, and shape however the optic nerve maintains a normal rim area and volume. Megalopapilae is a diagnosis of exclusion, therefore no structural abnormalities consistent with an alternative diagnosis can be present. It is commonly divided into 2 phenotypes:

Type 1: Normal configuration with enlarged disc, high C/D ratio, disc surface and/or neuroretinal rim pallor.

Type 2: An upwardly displaced cup that obliterates the neuroretinal rim, typically unilateral and with higher frequency of cilioretinal arteries.

MP is a benign condition with unknown etiology, though rare familial cases, including bilateral megalopapilla in twin siblings with a similarly affected paternal grandfather, suggest a possible hereditary component. MP has also been reported in individuals with congenital glaucoma, basal encephalocele, and pulverulent cataract.

Patients are typically asymptomatic, but MP can cause a physiologically enlarged blind spot in some individuals and rarely reduced visual acuity. While this entity may resemble glaucomatous neuropathy on fundoscopy, MP has no optic nerve fiber loss or retinal nerve fiber layer thinning. Therefore, MP is a pseudoglaucomatous condition and possibly a variant of normal, representing an extreme example of physiologic cupping.

Etiology

The mechanism behind MP has not been elucidated and it may be a normal developmental variation during embryogenesis resulting in an increased number of optic nerve fibers. Another proposed mechanism is altered optic axonal migration in early embryogenesis in children with basal encephalocele. MP has also been reported alongside contralateral optic nerve hypoplasia in the same patient, suggesting that MP may fall within a broader spectrum of dysgenetic optic disc anomalies arising from aberrant embryologic development. MP has been reported in a set of twins and their paternal grandfather, suggesting a possible hereditary component.

Risk Factors

There is no known epidemiological association or risk factors. However, a study of a genetically isolated Marshallese population found 22 out of 54 eyes to have an optic disc >2.10 mm and 36 patients with a cup to disc ratio of >0.6.

History

Typically, megalopapilla is an incidental finding on clinical exam without pathology. A thorough review of ocular history, past medical history and family history should be performed to rule out other causes of an anomalous appearing optic disc, such as glaucoma or high myopia-associated large optic disc. Given rare reports of familial occurrence, eliciting a family history of optic disc anomalies may be informative. Because MP can coexist with other optic nerve anomalies (e.g., contralateral optic nerve hypoplasia) and midline defects such as basal encephalocele, the history should also screen for relevant neurologic or developmental concerns.

Physical Examination

Megalopapilla should not cause visual impairment and the intraocular pressure should be in the normal range. Fundoscopy typically reveals an enlarged disc, high C/D ratio, disc surface and/or neuroretinal rim pallor, displaced cup with or without obliteration of the neuroretinal rim. These findings make it extremely difficult to distinguish MP from a glaucomatous optic nerve by fundoscopy alone.

Diagnostic Procedures

Heidelberg retinal tomography (HRT) is an excellent tool for differentiating megalopapilla from pathological causes of an anomalous optic nerve. Unlike glaucoma, MP eyes have preserved optic disc area, rim area, and rim volume demonstrated on HRT. One study of 50 MP eyes and 80 normals eyes show rim area (mm²) of 1.96 ±0.36 in the megalopapilla group and 1.90 ± 0.22 in the normal group (p= 0.25) and rim volume (mm³) of 0.15 ± 0.07 in the megalopapilla group and 0.14 ± 0.07 in the normal group (p= 0.48). When distinguishing MP from glaucoma specifically among eyes with large discs (>2.82 mm²), the most discriminating HRT parameters are the cup-to-disc area ratio, height variation contour, RNFL cross-sectional area, and cup volume. Rim area, rim volume, and cup shape measurement are significantly smaller in glaucomatous large discs, whereas cup area and cup-to-disc ratio overlap and are less specific.

Optical coherence tomography (OCT) of the peripapillary retinal fiber layer (pRNFL) is another tool that can assist in differentiating glaucoma from MP. OCT studies show normal to increased thickness of the pRNFL in individuals with MP compared to normal. In one study of 50 MP eyes and 80 normal eyes in children, the average RNFL thickness(µm) is 117.34 ±11.88 (MP) versus 106.83 ± 13.48 (normal) (p <0.01; CI:-15.85 to -5.18). In children, the increased RNFL thickness is attributed to larger discs having more ganglion cells. .

Visual field testing may show an enlarged physiologic blind spot in some patients. However, MP patients typically do not present with peripheral field loss.

Differential diagnosis

• Glaucoma (Congenital; JOAG; POAG; secondary glaucomas)
  • Physicians should also be aware of the shared similarities between MP and glaucoma: increased cup area, cup volume, and cup shape.
• Morning glory syndrome
• Optic nerve coloboma
• Staphyloma
• Optic nerve glioma
• Tilted disc syndrome
• Myopia

Management

Megalopapilla requires no treatment, as it is a benign, non-progressive congenital anomaly. The primary management goal is to establish an accurate diagnosis and to distinguish MP from acquired cupping optic neuropathies, particularly glaucoma, that share an enlarged cup, increased cup volume, and altered cup shape. Because the anomalous large disc creates a persistent diagnostic challenge for detecting superimposed disease, such as chronic open-angle glaucoma, baseline documentation is prudent. Routine visual fields and OCT pRNFL could be considered in addition to the routine eye exam to establish baseline measurements for potential future disease monitoring. However, there is no evidence that patients with MP are at increased risk for other eye conditions.

Prognosis

The prognosis of MP is excellent. There should be no progression of MP or visual changes beyond the natural loss of ganglion cells and rim area associated with normal aging. A study comparing 39 children with MP to 39 adults with MP found children with MP to have significantly larger optic rim area and smaller cup compared to adults with MP who had a similar disc size. These findings suggest that enlargement of the cup of the optic disk and reduction of the rim area can occur through life.

The main long-term consideration is not MP itself but the difficulty it imposes on detecting incident glaucoma. Given that a subset of large-cupped eyes convert to glaucoma over time, patients benefit from baseline imaging and individualized follow-up so that true progression can be distinguished from the stable, congenital large disc of MP.