Aspects of corneal changes in onchocerciasis

The distribution of living and dead microfilariae in 160 cases of ocular onchocerciasis has been studied. A model for coding the densities in 9 different areas of the cornea has been used. The average numbers of microfilariae and onchocercal punctate opacities per square millimetre were assessed. The highest densities were found in the superficial one-third of the corneal stroma at the periphery of the nasal and temporal parts of the cornea. Sclerosing keratitis was also recorded, and the average age of the patients in this group was significantly higher than in the group with non-sclerosing onchocercal involvement. Corneal thickness measurements showed that the presence of microfilariae or onchocercal punctate opacities or a faint uveitis did not influence the values. In sclerosed areas the corneal thickness varied greatly and was dependent on the degree of the vascularisation. The routes of entry of microfilariae into the eye are discussed on the basis of the distribution patterns of microfilariae and onchocercal opacities.