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M.A. Johnson, L. Wilson, J.G. Morris; Visual Contrast Sensitivity Loss in Chesapeake Bay Watermen . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1919.
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Purpose: Pfiesteria piscida is a dinoflagellate that is thought to release a neurotoxin responsible for fish kills and human illness in inshore waters of the mid–Altantic region of the eastern United States. Shoemaker and Hudnell (Environ Health Perspect 109:539(2001)) have advocated use of visual contrast sensitivity (VCS) to diagnose individuals with Pfiesteria–related toxicity. However, contrast sensitivity is a non–specific test that is affected by many factors such as lenticular light scatter and ophthalmic disease, and cataracts are known to occur at an earlier age in this population. (Taylor HR. Trans Am Ophthalmol Soc 87:802 (1989) We evaluated lens and retinal status in watermen enrolled in the Maryland Pfiesteria Cohort Study to determine if VCS loss is pathognomonic of Pfiesteria toxicity, and to determine the prevalence of other factors known to affect VCS. Methods: 89 of the 104 participants in the MD Pfiesteria Cohort Study were enrolled and tested at the beginning and end of the 2003 fishing season, i.e. pre– and post–exposure in the event of a Pfiesteria bloom. All subjects having 20/30 or worse visual acuity were refracted to obtain their best–corrected acuity, and the optical correction was used during measurement of the distance Functional Acuity Contrast Tests (FACT) and the distance Pelli–Robson Contrast Sensitivity Chart. Scheimphlug photography of the anterior chamber using the Nidek EAS–1000 system was performed in the slit and retroillumination modes of illumination. Fundus photographs were taken with the Nidek NM200 digital non–mydriatic fundus camera. Intraocular pressures (IOP) were measured with applanation tomography using a Tonopen (Medtronic, Inc.) A modified version of the NEI Visual Function Questionnaire was administered. Results: Nine percent (7/89) had evidence of moderate to severe open angle glaucoma (0.6 to 0.9 cup/disk ratios with IOPs up to 29 mmHg), much higher than the 1 – 2 % reported for the general population. 44/189 eyes had posterior subcapsular cataracts, and 177/188 eyes had increased lenticular light scattering. Pelli–Robson contract sensitivity was significantly correlated with light scattering, but scattering accounted for only 15% of the variance in the data. Measurements were considerably more variable using the FACT chart. Conclusions: As a Pfiesteria outbreak did not occur in 2003, the effect of Pfiesteria toxicity on VCS could not be determined. However, both (undiagnosed) ocular pathology and early cataracts occur in this population at a much higher rate than in the general population, facts that would confound interpretation of VCS.
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