A number of authors have speculated on the cause(s) of the higher prevalence of ocular disease in some populations of captive pinnipeds as compared with wild conspecifics. Rigorous research to verify these speculations and identify the etiologies of ocular lesions has not been conducted. Despite this lack of directed studies, most authors commenting on these conditions have suggested that ocular disorders in captive pinnipeds are environmentally induced. Salinity, water quality, light intensity, nutrition, and spatial characteristics have all been suggested to influence the ocular health of captive pinnipeds, even though in some cases similar or even harsher conditions may be encountered in the wild without apparent effect. Traumatic and infectious causes are frequently cited as the origin of ocular lesions in wild seals and sea lions, and yet similar opportunities for corneal damage or infection exist for captive specimens.

An epidemiologic questionnaire designed to identify specific risk factors was created with a view toward improving the ocular health of pinnipeds held in captivity. The questionnaire was intended to characterize the captive environment (water type and treatment, holding facilities), husbandry (stocking density, nutrition) and medical care (procedures and medications) for each of the species studied. The harbor seal, Phoca vitulina and the California sea lion Zalophus califomianus, were selected because they are maintained in greater numbers and in more diverse holding facilities than other pinniped species. The survey yielded more than 8000 data points characterizing the holding facilities and animal management programs of 20 of the 40 institutions which received the survey. These data define the captive environment for 107 harbor seals held in 26 separate systems, and 193 California sea lions in 49 systems. Many of the facilities, and sometimes different systems within a facility, represented distinct sets of environmental conditions making it difficult to combine data into larger sets for more robust statistical analysis. Subsequent analysis and statistical comparisons focused on specific variables considered to have greatest importance, based on the clinical and husbandry experience of the investigators. The prevalence of current ocular conditions for each species was analyzed in relation to the following variables:

 Water - Fresh versus Salt

 Pool location - indoor versus outdoor versus mixed in/out

 Pool capacity in gallons

 Pool capacity as a function of stocking densities

 Water quality control - turbidity, flocculation, open versus closed systems, rates of replacement, chlorine disinfection, ozone disinfection, animal stocking densities.

The most commonly reported condition in Phoca vitulum was cataracts, visible as a clouding of one or both lenses. In Zalophus californianus, corneal lesions predominated. These were recognizable as one of three separate entities occurring in one or both corneas: corneal edema which was manifested as a diffuse, often transitory cloudiness; corneal ulceration or erosion, a discontinuity of the corneal surface sometimes extending deep into the corneal stroma; and corneal scarring which frequently can be a permanent sequel to severe ulcerations or the result of major trauma.

While segregation of the data sets along these parameters allowed calculation of ocular disease prevalence rates, serious concerns arose over the possibility that certain ocular diseases were underreported. Of particular concern is the completeness of the diagnostic information, especially as this applies to the full recognition of cataracts. Our concern was generated by the apparently low rates of ocular disease reported by some institutions in contrast to the widely held perception among health care workers in the marine mammal community that cataracts are a common wo and aquarium-wide problem. Because they are frequently examined outside, the pupils of pinnipeds may be highly constricted. The combination of constricted pupils, certain light conditions, and the presence of accompanying corneal lesions can make cataracts very difficult to detect, thereby complicating accurate diagnosis. Some of the retrospective ocular disease data was found to be suspect to the point where further analysis was not justified. Existing record systems at many of the respondent institutions apparently are not designed for the ready and reliable extraction of such retrospective data.

Histopathologic examination of eleven eyes substantiated antemortem diagnoses of several ocular disorders, but revealed no features which were pathognomonic of the exact etiology of these disorders.

The epidemiologic analysis of survey responses demonstrated a significant statistical association (p<.01) between the maintenance of harbor seals in fresh water holding facilities and an increased risk of cataract development. The reported overall prevalence of cataracts in this species was 24% with approximately a three times higher prevalence in fresh water holding facilities than in salt water. No such association was demonstrated for similarly held California sea lions. No association was demonstrated between fresh water maintenance and corneal edema in harbor seals whereas a very strong association (p<.00001) exists for California sea lions maintained in fresh water.

Suspected sampling bias concerns relating to the fresh water-cataract association in harbor seals were confirmed by eliminating data from one responding institution. Recalculation following this trial deletion resulted in the loss of the statistically significant association.

We will continue to attempt to increase our sample size and to improve on the accuracy of previously submitted data with the hope of garnering sufficient additional data to refine these and any subsequently developed associations between ocular disease and the captive environment. The assistance of health care and husbandry personnel at a greater percentage of facilities holding harbor seals and California sea lions will be required if we are to successfully complete our task.