From 2D Fundus Photography to 3D Structural Anatomy: Implementing the ICON-PM Consensus in Retina Practice

The global burden of axial myopia is projected to surge dramatically over the coming decades, driven by a rising prevalence in younger generations who are now transitioning into older, higher-risk cohorts. As retina specialists, our clinical vocabulary has long been shaped by historical classifications developed in an era when color fundus photography was the gold standard. However, these legacy systems—while landmark achievements in their respective times—have significant limitations: they represent two-dimensional projections of complex three-dimensional disease processes, fail to resolve deeper layers like the choroid, and often rely on ethnocentric, pigmentation-dependent features.

To address these challenges, the International Consensus on Nomenclature for Adult Pathologic Myopia (ICON-PM) assembled a panel of 32 experts from 13 countries. Using a rigorous Delphi process, the panel established a unified, imaging-based lexicon grounded in optical coherence tomography (OCT) and multimodal imaging. This post breaks down the core clinical shifts, the six structural domains of pathologic myopia, and how to apply this modern nomenclature in daily retina practice.

1. Redefining High Myopia vs. Pathologic Myopia

One of the first major clarifications established by the ICON-PM framework is the separation between biometric thresholds and structural disease:

High Myopia: For consistency in epidemiologic and research contexts, high myopia is defined as a spherical equivalent of −6.00 D or greater, or an axial length of 26.5 mm or more. This threshold represents a conceptual risk inflection point, although the dioptric and axial metrics do not perfectly align.
Pathologic Myopia: A clinical diagnosis of pathologic myopia rests on the presence of characteristic structural alterations or degenerative changes of the posterior segment associated with an increased risk of irreversible vision loss.

Crucially, biometric cutoffs are not required for a diagnosis of pathologic myopia; some eyes with modest elongation exhibit degenerative changes, while other highly elongated eyes remain structurally intact.

The Problem of Ethnocentricity and 2D Limitations

Historical systems like Tokoro’s or META-PM heavily incorporated fundus tessellation as an early stage of myopic degeneration. However, tessellation—a striped pattern caused by the visibility of large choroidal vessels through thinned retinal pigment epithelium (RPE)—is heavily modulated by pigmentation. It can be a normal fundus variation in Northern Europeans but is rarely seen in healthy Japanese individuals. ICON-PM explicitly discourages the use of racially biased phenotypic markers like tessellation for staging, instead advocating for pigment-independent, quantitative OCT criteria.

2. The Choroidal Paradigm: Thinning vs. Ischemic Tissue Loss

The posterior choroid undergoes progressive thinning and loss driven by mechanical axial elongation and staphyloma formation, compounded by aging. SFCT (subfoveal choroidal thickness) in highly myopic eyes is inversely associated with visual acuity and microperimetric threshold sensitivities in a non-linear fashion.

Severity Bands for Research Grading

The consensus introduces the term myopic choroidal thinning to replace descriptive terms like “leptochoroid”. It is defined on OCT as a generalized reduction in choroidal thickness without scleral visibility, falling below the age-adjusted 95% reference range for emmetropes (or below 100 µm in adults if normative databases are unavailable). For research grading, the consensus proposes three severity bands:

Mild Thinning: 100–61 µm
Moderate Thinning: 60–31 µm
Severe Thinning: ≤30 µm (high-risk threshold linked to precipitous visual decline)

When SFCT drops below approximately 30 µm, a physiological threshold is crossed where the choroid can no longer support itself, the RPE, or the outer retina, leading to cell death.

Focal Chorioretinal Loss (Formerly “Patchy Atrophy”)

Rather than “patchy atrophy,” which is syntactically paradoxical and misuses the term “atrophy,” the consensus establishes myopic focal chorioretinal loss. This represents an ischemic tissue loss endpoint where the choroid, RPE, and outer retina involute. On OCT, it is characterized by the attenuation or loss of the outer retina, complete loss of the RPE band, and the near-total absence of the choroid, leading to relative hypertransmission into the sclera.

3. The Six Structural Domains of pathologic Myopia

The ICON-PM framework organizes the structural complications of pathologic myopia into six distinct, overlapping domains. This modular system ensures that multiple processes coexisting in a single eye can be described and graded independently.

Domain 1: Atrophic Domain

This domain moves beyond generic pattern descriptions to advocate for a precise combination of pattern, location, and etiology modifiers. For instance, a lesion previously labeled simply as “macular atrophy” should be described as “foveal center-involving focal chorioretinal loss secondary to myopic choroidal neovascularization”.

Key features include:

Myopic Bruch’s Membrane Defects: Large mechanical ruptures in Bruch’s membrane where RPE cannot persist due to the loss of its structural scaffold.
Atrophic Creep: The slow expansion of atrophy over an intact Bruch’s membrane due to chronic, advancing peripapillary choroidal thinning that extends under the fovea in later life.

Domain 2: Mechanical Expansion Domain

Axial elongation alters the global shape of the eye from an oblate to a prolate ellipsoid, upon which localized contour irregularities are superimposed.

Posterior Staphyloma: A localized outpouching of the sclera with a local radius of curvature smaller than the surrounding tissue. Staphylomas act as biomechanical risk enhancers and amplifiers for tractional and atrophic processes, but they are not a prerequisite for diagnosing pathologic myopia.
Tilted Disc and Inferior Staphyloma: These represent related manifestations of localized posterior scleral deformation involving the optic nerve head region. It features an oblique orientation of the disc (nasal elevation, temporal displacement, and torsion), with an inferior staphyloma creating two regions of differing posterior curvature separated by a transition zone of localized scleral thickening.
Dome-Shaped Macula (DSM): An anterior convex protrusion of the macula that can exist within a staphyloma. Multidirectional OCT scanning is mandatory to diagnose DSM and differentiate it from ridge-like configurations. DSM is frequently complicated by subretinal fluid, pigmentary changes, and secondary CNV.
Lacquer Cracks: These are mechanical ruptures of Bruch’s membrane occurring when local tensile stress exceeds the elastic limit of the tissue. Because staphylomas form early in life while lacquer cracks develop much later, age-related compositional changes (including thinning and discontinuities of the elastic layer of Bruch’s membrane) play a major role in their pathogenesis. They are often accompanied by acute subretinal hemorrhage and serve as primary sites for neovascular ingrowth.
Temporal Crescent: Reflects the physical exposure of the underlying sclera and peripapillary scleral flange due to a temporal shift of the Bruch’s membrane opening (BMO); it is a biomechanical displacement, not an atrophic process.

Domain 3: Traction Domain

The mechanical expansion of the outer ocular wall stretches the internal tissue layers. A profound compliance and surface-area mismatch exists between the highly distensible sclera/choroid and the relatively noncompliant internal limiting membrane (ILM) and retinal blood vessels. This mismatch generates three primary forces within the retina: tangential traction, shear forces, and a vertical tensile force.

Myopic Macular Schisis (MMS): Laminar thickening and cavitation within the retina. It typically involves inner retinal splitting (occurring between the ILM and nerve fiber layer) and outer retinal splitting (at the level of the Henle’s fiber and outer nuclear layers). Inner schisis generally spares vision, whereas foveal-involving outer schisis degrades visual acuity and carries a high risk of progression.
Myopic Traction Maculopathy (MTM): Defined as the spectrum of structural macular changes (intraretinal schisis, foveal detachment, or macular hole) caused by this posterior mechanical mismatch.
Paravascular Abnormalities: The rigid, non-compliant nature of retinal vessels leads to localized traction. This manifests as paravascular microfolds (where vessels “tent up” the inner retina like a sheet on a clothesline), paravascular cavitation, and paravascular lamellar defects that can occasionally progress to full-thickness holes and localized detachment.
Surgical Nuances for Myopic Macular Holes: Highly myopic macular holes have historically lower surgical closure rates than emmetropic holes. Contemporary techniques utilize ILM flap transposition and require the avoidance of indocyanine green (ICG) staining due to its documented light-activated cytotoxicity to the thinned, vulnerable RPE.

Domain 4: Neovascular Domain

Myopic choroidal neovascularization (mCNV) is a major cause of sudden visual loss, affecting an estimated 5% to 11% of high myopes over their lifetime.

Pathogenesis and Diagnostics: Neovascular vessels originate in the choroid, growing under the RPE, subretinal space, or both. They can break through Bruch’s membrane de novo or utilize a pre-existing lacquer crack. While fluorescein angiography (FA) remains a standard, OCT angiography (OCTA) is invaluable for non-invasive, structural visualization of the neovascular network.
Management: Untreated mCNV carries an extremely poor prognosis, with 90% of patients dropping to ≤20/200 within 5 to 10 years. First-line therapy is anti-VEGF injections, which yield rapid anatomical and visual improvements and are vastly superior to photodynamic therapy (PDT).
Atrophic Progression: Despite successful anti-VEGF therapy to combat exudation, the underlying mechanical stress and choroidal thinning remain unabated, and the regressed fibrovascular membrane frequently transitions into a localized zone of focal chorioretinal loss (macular atrophy).

Domain 5: Optic Nerve Domain

Evaluating the optic nerve in highly myopic eyes is one of the greatest challenges in ophthalmic practice.

Optic Nerve and Peripapillary Pits: Localized defects involving focal dehiscence of the lamina cribrosa or adjacent stretched sclera. They represent direct mechanical structural failure of the optic nerve tissues independent of intraocular pressure (IOP).
PHOMS (Peripapillary Hyperreflective Ovoid Mass-like Structures): Represent the physical lateral herniation of retinal nerve fiber layer axons at the nasal disc margin. It is a structural consequence of the tilted disc configuration and should not be misdiagnosed as neuro-ophthalmic pathology.
PICC (Peripapillary Intrachoroidal Cavitation): A yellowish, localized lesion found inferior or inferotemporal to the disc. Swept-source OCT demonstrates that PICC is caused by a localized backwards bowing of the sclera, creating a cavitation in the overlying thinned choroid; it must not be confused with peripapillary CNV, choroidal tumors, or congenital optic disc anomalies.
Glaucoma Assessment Challenges: Optic disc distortion (tilt, torsion, and vertical elongation) blunts classic cupping parameters. Normative databases for visual fields and OCT nerve fiber layer thickness are unadjusted for axial length, and segmentation errors are common in highly atrophic eyes. Diagnosis must rely on stereoscopic examination, looking for disc hemorrhages, and tracking longitudinal structural and functional changes over time.
Pathophysiology (Vascular vs. Mechanical):
- Vascular: The expansion of the circle of Zinn-Haller radially away from the nerve, combined with the stretching and thinning of the peripapillary scleral flange (delta zone), geometrically restricts centripetal arterial access to the lamina cribrosa, causing chronic ischemia.
- Mechanical: Laplace’s Law ($\sigma = Pr / 2t$) dictates that wall stress ($\sigma$) increases as the radius ($r$) increases and the wall thickness ($t$) decreases. The thinned, stretched lamina cribrosa in high myopia exists in a high-baseline prestressed state, making it highly vulnerable to strain.
Myopic Optic Neuropathy: ICON-PM formally recognizes this as a distinct, non-glaucomatous optic neuropathy driven by direct biomechanical insults, axonal stretching, temporal compression from Bruch’s membrane, and ischemia, occurring independently of IOP.

Domain 6: Retinal Detachment Domain

Rhegmatogenous retinal detachment (RRD) risk is highly elevated in axial myopes. The consensus emphasizes two distinct mechanical pathways of detachment:

Younger Patients (Atrophic Round Holes): Occur frequently in young high myopes without posterior vitreous detachment (PVD), often in areas of lattice degeneration.
Older Patients (Flap Tears): Occur in the setting of PVD, which develops significantly earlier in myopes than in emmetropes.

Prophylactic Laser Guidelines

Evidence for routine prophylactic laser photocoagulation of asymptomatic lattice degeneration is limited. Management should be strictly individualized. Prophylaxis is generally not indicated for simple lattice in patients with myopia > -6 D, but it may be highly beneficial for eyes exhibiting atrophic holes with localized subretinal fluid, or in patients with a personal or family history of retinal detachment.

4. The Critical Differential: Inflammatory Choroidopathies

Retina specialists must remain highly vigilant against misdiagnosing active inflammatory chorioretinopathies as degenerative pathologic myopia, particularly in young myopic women.

MCP (Multifocal Choroiditis and Panuveitis) and PIC (Punctate Inner Choroidopathy): Both produce peripapillary scarring, punched-out lesions, and secondary neovascularization. MCP features inflammatory vitreous cells, while PIC typically does not.
OCT Differentiation: High-resolution OCT is crucial to differentiate active inflammatory chorioretinopathies from myopic degeneration. PIC and MCP demonstrate active sub-RPE or subretinal hyperreflective inflammatory infiltrates. Additionally, active inflammation often causes localized loss of the ellipsoid zone, leading to visual field defects (such as blind spot enlargement) that are much larger than the visible fundus lesions.
Scar Patterning: Peripapillary atrophy in MCP or PIC creates a highly characteristic multilobular appearance with pigment borders, whereas pathologic myopia typically features a unilobular crescent.
Therapeutic Implications: Standard mCNV is highly responsive to minimal anti-VEGF injections. In contrast, neovascularization secondary to PIC or MCP recurs frequently and mandates aggressive, early intervention combining anti-VEGF with initial systemic or local corticosteroids and long-term immunosuppression to suppress active chorioretinal inflammation and prevent the formation of new lesions.

Clinical Takeaways for Your Practice

Ditch the Fundus Camera for the OCT: Color fundus photography alone is insufficient to diagnose, grade, or manage pathologic myopia. Definitions must be anchored in three-dimensional OCT and OCTA anatomy rather than two-dimensional fundus color changes.
Standardize Your Nomenclature: Adopt the “Pattern-Location-Etiology” modifier system for atrophic changes, and abandon vague terms like “myopic conus” in favor of anatomically specific zone descriptions (gamma and delta zones).
Recognize Myopic Optic Neuropathy: Do not attribute every visual field defect or progressive axonal loss in a highly myopic eye to primary open-angle glaucoma. Biomechanical stretch and microvascular insufficiency can cause direct, non-glaucomatous optic neuropathy.

Bibliography

Spaide, R. F., Agarwal, A., Chen, S.-J., Lai, C. C., Cohen, S. Y., Couturier, A., Eter, N., Freund, K. B., Ikuno, Y., Jonas, J. B., Kodjikian, L., Lai, T. Y. Y., Moussa, M., Munk, M., Ogura, Y., Priglinger, S., Querques, G., Rizzo, S., Rossi, T., Ruamviboonsuk, P., Ruiz-Moreno, J. M., Sacconi, R., Sadda, S., Sarraf, D., Souied, E., Terasaki, H., Ting, D., Yannuzzi, L., Holz, F. G., Keane, P. A., Liebmann, J. M., Ohno-Matsui, K., & Sebag, J. ICON-PM: International Consensus on Nomenclature for Adult Pathologic Myopia. Progress in Retinal and Eye Research, Advance online publication.