Ocular Pathology

Anatomy and pathology of the human eye. Use it to review eye pathology for Ophthalmology Board Review or OKAP.

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Saturday, December 30, 2006

What is sclerocornea?

Definition: Sclerocornea is defined as a non-progressive scleralization of the cornea in which the peripheral cornea and sometimes the entire cornea is opacified by thick collagen bundles and vascularization without antecedent inflammation.
Incidence/ Prevalence: The incidence in males and females is equal and 90% of cases are bilateral. Although the prevalence and incidence seem to elude the current literature, 1.4 % of randomly selected hospitalized eye patients had this condition (Reference 1).
Etiology: Approximately one half the cases are stated to be familial; autosomal dominant and recessive patterns of inheritance have been described. The other ½ of cases are sporadic.
Clinical Findings: The most common ocular association is cornea plana, found in 80% of cases. Keratometry reveals low values between 20 and 39 D. The limbus or corneal scleral sulcus is usually poorly defined, with superficial vessels extending from sclera, episclera, and conjunctiva to traverse into part or all of the cornea. Visual symptoms are dependent of the associated corneal flattening and of course whether the visual axis is affected by scleralization. Associated ocular abnormalities include aniridia, Axenfeld’s anomaly, cataract, coloboma, esotropia, glaucoma, microphthalmos, posterior embryotoxon, Rieger’s anomaly, and strabismus. Sclerocornea has been associated with facial anomalies, mental retardation, deafness, and cerebellar anomalies. Sclerocornea has been associated with a number of syndromes including Dandy-Walker, Hurler, Hallermann-Streiff and many others.

Histopathology: The anterior stromal collagen fibrils are irregularly arranged (number 1) and markedly thickened (3-6 times normal thickness). Cornea and sclera are difficult to distinguish. The collagenization is more prominent anteriorly (number 1) and dissipates posteriorly (number 2). Blood vessels (arrows 3) are seen in the superficial stroma. The pathology may be confined to the periphery with various degrees of central involvement. In the trichrome stained section one sees a wedge of scleralization (arrow 4) adjacent to the more central area (number 5). Bowman's layer is absent (arrow 6) as may be Descemet's membrane in the affected area. Critical to the diagnosis is the absence of inflammation, differentiating this entity from stromal keratitis. Note the complete absence of inflammatory cells in these photomicrographs.
Treatment: Penetrating keratoplasty has been performed for central corneal involvement but some authors feel the visual prognosis is probably not sufficient to warrant the procedure.
Prognosis: If the process is confined to the periphery, vision may be minimally affected. With success defined as graft clarity, the rate of success of penetrating keratoplasty is about 50% for sclerocornea (Ref 2).

1. Ozeki H et al. Japanese Journal of Ophthalmology 1997:41:422-425.
2. Michaeli et al: J Pediatr Ophthalmol Strabismus. 2005;42:34-44.

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