Crocodile Shagreen

Key Points at a Glance

Key Points of This Disease

• Crocodile shagreen is a benign corneal degeneration characterized by polygonal gray-white opacities in the posterior corneal stroma.
• The name derives from the opacity pattern resembling crocodile skin.
• It occurs bilaterally and symmetrically with aging and is usually asymptomatic.
• It does not cause vision loss and requires no treatment.
• Differentiation from François central cloudy corneal dystrophy is important.

1. What is Crocodile Shagreen?

Crocodile shagreen is a benign corneal degeneration first reported by Weizenblatt in 1927 and named by Vogt in 1930. It presents as bilateral, symmetrical polygonal gray-white opacities in the central posterior corneal stroma ¹⁾. The pattern resembles crocodile skin, hence the name.

Most commonly, it appears with aging. It can also occur with band keratopathy or after traumatic corneal injury. Cases associated with pseudoxanthoma elasticum, glaucoma, and polymorphic amyloid degeneration have been reported.

It is a non-familial degenerative condition, genetically distinct from Central Cloudy Dystrophy of François, which shows autosomal dominant inheritance ^1,2). Since both have similar ultrastructural findings, family history and age of onset are important for differentiation ²⁾.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

Usually asymptomatic. It does not cause vision loss. It is often discovered incidentally during slit-lamp examination.

Clinical Findings

• Polygonal opacities: Gray-white polygonal pattern in the central posterior corneal stroma
• Opacity edges: Ill-defined, with clear areas between opacities
• Bilateral and symmetrical: Similar pattern in both eyes
• Corneal surface: Epithelium is normal; opacities are confined to the deep stroma (posterior stroma)

Q Does crocodile shagreen affect vision?

A

Usually it does not cause vision loss. Since the opacities are confined to the posterior corneal stroma and do not significantly affect corneal transparency, most cases remain asymptomatic. It is often discovered incidentally during slit-lamp examination, and treatment is not required.

4. Diagnosis and Examination Methods

Diagnosis is based on identification of polygonal opacities in the posterior corneal stroma using slit-lamp microscopy.

Differential diagnosis:

• François central cloudy dystrophy of the cornea: Autosomal dominant inheritance. Clinical appearance is similar but affects only the central cornea and has a family history. Most important in differentiation from crocodile shagreen.
• Band keratopathy: Subepithelial deposition of calcium salts. Presents with a band-shaped pattern along the palpebral fissure, with a clear zone between the opacity and the limbus.
• Polymorphic amyloid degeneration: Presents with polymorphic opacities in the deep corneal stroma.

Other conditions reported to show similar anterior corneal findings include fluorescein staining patterns after pressure patching, ocular hypotony, flattening of keratoconus by hard contact lenses, and X-linked megalocornea.

Histopathology:

Electron microscopy reveals the presence of vacuoles containing electron-dense material within the corneal stroma¹⁾. The vacuoles are more densely distributed toward the posterior stroma and are concentrated anterior to Descemet’s membrane¹⁾. Sawtooth-like structural changes of the collagen lamellae are observed, and the electron-dense fibrillogranular material within the vacuoles is thought to originate from collagen degeneration products and accumulation of mucopolysaccharides¹⁾.

6. Pathophysiology and Detailed Mechanism

Crocodile shagreen is considered a non-familial degenerative disease. With aging, structural changes occur in the collagen lamellae of the corneal stroma, leading to a sawtooth arrangement. Electron-dense material accumulates between the lamellae, which is clinically recognized as polygonal gray-white opacities.

The clear linear areas between the opacities correspond to regions where the normal structure between lamellae is preserved. The localization of opacities to the posterior corneal stroma is presumed to be because the collagen lamellae in the posterior layer are more susceptible to age-related changes.

Medical disclaimer

The content of this article is intended for educational information for healthcare professionals and does not replace individual diagnosis or treatment. Actual clinical decisions should be made under the responsibility of the attending physician.

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7. References

1. Belliveau MJ, Brownstein S, Agapitos P, Font RL. Ultrastructural features of posterior crocodile shagreen of the cornea. Surv Ophthalmol. 2009;54(5):569-575.
2. Meyer JC, Quantock AJ, Thonar EJ, Kincaid MC, Hageman GS, Assil KK. Characterization of a central corneal cloudiness sharing features of posterior crocodile shagreen and central cloud dystrophy of François. Cornea. 1996;15(4):347-354.