Canis ISSN: 2398-2942

Cornea: spontaneous chronic corneal epithelial defects (SCCEDs)

Synonym(s): Indolent ulcer, non-healing ulcer, persistent corneal erosions, recurrent corneal erosion

Contributor(s): Paul Gerding, Rhea Morgan, David L Williams, James Oliver

Introduction

  • Spontaneous chronic corneal epithelial defects (SCCEDs, also termed healing corneal ulcers, indolent ulcers, refractory ulcers and Boxer ulcers) are frequently encountered in canine practice.
  • Cause: SCCEDs typically have no apparent underlying cause and affect middle-aged to older dogs averaging 8-9 years of age.
  • All breeds can be affected but the Boxer is consistently overrepresented in studies.
  • Signs: SCCEDs are characterized by the presence of an epithelial erosion which is surrounded by loose, non-adherent epithelium and. without appropriate treatment, can persist for longer than 6 months.
  • Fortunately, SCCEDs are usually straightforward to diagnose and treat successfully.

Pathogenesis

Etiology

  • A primary inciting cause is rarely identified.
  • Primary disorder of the basement membrane of corneal epithelial cells.
  • Secondary effects of corneal stromal edema on the epithelium.

Predisposing factors

General
  • Age.
  • Breed (Boxer).

Specific

Pathophysiology

  • Most of the theories about the causes of SCCEDs have arisen from the discovery of alterations in corneal anatomy and expression of various factors compared to that of normal cornea.
  • The epithelium adjacent to the lesion demonstrates poor attachment to underlying stroma, loses its normal ordered architecture and is often thickened (Bentleyet al2001)
  • Immunohistochemical studies have revealed either a complete lack of basement membrane or adhesion complexes or only small, discontinuous segments of basement membrane.
  • The corneal stoma usually exhibits a superficial, hyalinised, acellular zone composed of collagen fibrils and with a thickness of around 4 um. It is thought that this layer may prevent a barrier to epithelial cells from forming adhesion complexes.
  • An experimental study involving mechanical epithelial debridement on normal corneas failed to result in similar hyaline layers suggesting that this layer does not develop as a consequence of a chronic epithelial defect but actually may play an important role in the underlying pathophysiology of SCCEDs (Bentleyet al2002).
  • It was originally postulated that SCCEDs may represent a form of epithelial basement membrane dystrophy as is reported in humans and this theory has been further investigated. Extensive ultrastructural studies of specimens from unaffected areas of corneas affected with SCCEDs have revealed no evidence of dystrophy and the average age of affected dogs (8 to 9 years) make a dystrophic aetiology unlikely (Bentleyet al2001).
  • Another study looked at changes in corneal innervation in SCCEDs (Murphyet al2001). A dense, abnormal plexus of substance P and calcitonin gene-related peptide immunoreactive nerve fibers has been found to develop in the corneal stroma surrounding the lesion. Substance P was found to be elevated in epithelial cells of dogs with SCCEDs and topical treatment of SCCEDs with substance P, with or without insulin growth factor, resulted in resolution suggesting this factor to be involved in the pathophysiology of SCCEDs.
  • Other studies have shown that the epithelium of dogs with SCCEDs fails to express certain factors that are involved in normal epithelial migration. E-cadherin, beta-catenin, beta -actin and desmoplakin have been shown to be deficient and, levels of tissue growth factor-beta (TGF-beta), which is required for expression of these factors, are decreased in tears of dogs with SCCEDs (Chandleret al2010). It has therefore been postulated that abnormalities in TGF-beta are involved in the pathogenesis of SCCEDs and that treatment with tetracyclines, which increase TGF-beta expression, might be beneficial in their treatment. Fibronectin, an important factor in early migration and formation of temporary epithelial adhesions, has been found on the surface of erosions in SCCEDs (Bentleyet al2001). This finding suggests that early healing is occurring but that reformation of adhesion complexes is delayed resulting in recurrent loss of poorly attached epithelium.

Timecourse

  • A SCCED should be suspected for a superficial corneal ulcer which has no identificable cause and does not heal within 7 days.
  • Without appropriate treatment, SCCEDs may persist for weeks to months.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Gosling A A, Labelle A L, Breaux C B (2013) Management of spontaneous chronic corneal epithelial defects (SCCEDs) in dogs with diamond burr debridement and placement of a bandage contact lens. Vet Ophthalmol 16 (2), 83-88 PubMed.
  • Chandler H L, Gemensky-Metzler A J, Bras I D et al (2010) In vivo effects of adjunctive tetracycline treatment on refractory corneal ulcers in dogs. JAVMA 237 (4), 378-386 PubMed.
  • Ledbetter E C, Munger R J, Ring R D et al (2006) Efficacy of two chondroitin sulfate ophthalmic solutions in the therapy of spontaneous chronic corneal epithelial defects and ulcerative keratitis associated with bullous keratopathy in dogs. Vet Ophthalmol (2), 77-87 PubMed.
  • Bentley E (2005) Spontaneous chronic corneal epithelial defects in dogs: a review. JAAHA 41 (3), 158-165 PubMed.
  • Regnier A, Cazalot G, Cantaloube B (2005) Topical treatment of non-healing corneal epithelial ulcers in dogs with aminocaproic acid. Vet Rec 157 (17), 510-513 PubMed.
  • Bromberg N (2002) Cyanoacrylate tissue adhesive for treatment of refractory corneal ulceration. Vet Ophthamol 5, 55-60 PubMed.
  • Bentley E, Abrams G A, Covitz D et al (2001) Morphology and immunohistochemistry of spontaneous chronic corneal epithelial defects (SCCED) in dogs. Invest Ophthalmol Vis Sci 42 (10), 2262-2269 VetMedResource.
  • Murphy C J, Marfurt C F, McDermott A et al (2001) Spontaneous chronic corneal epithelial defects (SCCED) in dogs: clinical features, innervation, and effect of topical SP, with or without IGF-1.  Investigative Ophthalmology and Visual Sciences 42 (10), 2252-2261 PubMed.
  • Stanley R G, Hardman C, Johnson B E (1998) Results of grid keratotomy, superficial keratectomy and debridement for the management of persistent corneal erosions in 92 dogs. Vet Ophthalmol 1 (4), 233-238 PubMed.


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