Environmental Aspects of Corneal Opacities in Captive South African Fur Seals (Arctocephalus pusillus pusillus)
The associations of corneal opacities with different environmental factors were evaluated in three adult South African fur seals (Arctocephalus pusillus pusillus). The fur seals were housed in an outdoor, fresh water recirculating system using bromine as the sterilant. Between August and November the severity of the corneal opacities of both eyes was subjectively assessed daily in each animal. Potential association between the severity of these lesions and different variables were measured by Pearson's correlation coefficients. A strong seasonal pattern was obvious for all three animals; the lesions being the most severe during the summer and the mildest during the winter. The degree of corneal opacities positively correlates with the daily maximum temperature, the global solar radiation, and the length of time with bright sunshine for all three animals. The degree of corneal opacities was poorly correlated with the length of time spent in the outdoor pool (Table 1). The interpretations of these results were limited by the strong correlations between most of the variables evaluated. Even though our results did not rule out other potential etiologies, they did support the hypothesis of repetitive alterations of the corneal epithelium caused by excessive exposure to solar radiation. These alterations to the epithelial protective layer would lead to the over hydration of the corneal stroma, especially if the lesioned eye was immersed in a hypotonic fluid like fresh water. Any factors that would decrease the concentration of free-radical scavengers at the surface of the cornea could also have a negative impact on the integrity of the corneal epithelium and could therefore enhance the formation of corneal edema.
Table 1. Correlation coefficients (r) between the severity of the corneal opacities and different variables in three South African fur seals