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 09, 2006

What is spheroidal degeneration?

Spheroidal Degeneration is also known as Labrador keratopathy, Bietti nodular hyaline bandshaped keratopathy, climatic droplet keratopathy, proteinaceous corneal degeneration, elastotic degeneration, Fisherman’s keratopathy, and Eskimo’s corneal degeneration

Definition: Described in 1955 by Bietti, this relatively common condition features characteristic oil deposits at the limbus which are characterized histologically as mauve globular degeneration and are strongly associated with UV exposure.

Incidence/Prevalence: Typically, the lesions are associated with high UV exposure climates and/or reflected light such as observed in desert, ocean and snow. The incidence rises with age. Prevalence is 7% in areas of South Africa. The prevalence is higher in Greenland than Copenhagen.

Etiology: The theory is that UV exposure results in altered proteins depositing at the limbus. The proteins contain a high content of sulfur. Repeated arc welding burns may result in a similar condition.

Clinical Findings: 0.1-0.6 mm yellow oil droplets deposit near the limbus in the 3 and 9 o’clock positions in older individuals. Spheroidal degeneration is usually bilateral in the primary form. The areas may appear band shaped and often are associated with pingueculae but presumably and incredulously not pterygia!
Three types have been described:

1. primary corneal involvement
2. corneal involvement secondary to an underlying process such as a chronic infection
3. conjunctiva
Histopathology: Amorphous mauve colored globules are seen in the superficial corneal stroma or substantia propria close to the limbus in hematoxylin and eosin sections (number 2). The globules are often confluent. The globules are not dissolved by elastase. It is very easy to confuse these globules with calcification especially when they are in the cornea near Bowman's layer. However, careful examination shows that they lack the granular quality and deep purple color of calcium crystals but rather are amorphous centrally homogeneous deposits.

The globules may stain focally and usually peripherally with congo red (arrow 3). This may lead to misconclusions that the deposits are amyloid but there is no dichroism with polarized light (number 4). The birefringence seen in the photograph originates from keratin and collagen not the spheroidal degeneration nodules.

Autofluorescence (number 5) reveals bright fluorescence under ultraviolet light. The proteins of the globules contain a high sulfur content.

Treatment: Corneal involvement that affects vision has been treated by removal including procedures such as penetrating keratoplasty, without recurrence.

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