Introduction

Tumors of the eye (ICD-9 190) are infrequent (Chapters 18 and 58).

Histology, classification and diagnosis

Squamous cell carcinoma of the conjunctiva occurs with moderate frequency in parts of Africa. Intraorbital tumors are almost always retinoblastomas in children under 10 years of age, arising from the retina. In adults they are predominantly malignant melanomas arising from the choroid. Rarely, metastases from an ocular melanoma may manifest in the liver up to 20 years after diagnosis and treatment of the primary.

Descriptive epidemiology

Incidence rates for retinoblastoma are usually less than one and there is up to eight-fold geographical variation, but registration artefacts cannot be excluded. Intraocular melanomas are, however, rare in Africans and Asians. There is usually a modest male excess.

Etiological inferences

Familial studies on retinoblastoma estimate a role of inheritance by autosomal dominance in about 50% of the cases. Most of the genetic forms are bilateral. Survivors of bilateral retinoblastoma have an excess risk of osteogenic sarcoma.

Known and suspected causes

Tumors of the conjunctiva (and eyelids) are related to sunlight. The cause of ocular melanoma is unknown (Osterlind, 1987).

The pathogenesis of childhood retinoblastomas is discussed in Chapter 18. These neoplasms provide the best example of the two-hit theory of mutagenesis, although the triggering agent is unknown.