Normal color variations of the canine ocular fundus, a retrospective study in Swedish dogs

BACKGROUND: A retrospective study was made to demonstrate normal variations of the color and size of the tapetal area and color of the nontapetal area in the ocular fundus in dogs, correlating them to breed, age and coat color. METHODS: The study was based on protocols of five hundred and thirty-nine adult dogs describing eye examinations made during the years 1997-2001. The dogs were examined using an indirect ophthalmoscope in order to find heritable eye diseases. The following characteristics were recorded: breed; age; coat color; color and size of the tapetal area and color of the nontapetal area. Normal color variations in the fundus were studied and categorized with regard to breed, age and coat color. Chi-square analysis was used comparing distributions between factors. Differences between mean values were analysed with Student's t-test or one-way-ANOVA. A logistic regression analysis was performed on the color of the tapetal area with the color of the coat and breed. RESULTS: Twenty breeds were represented. The mean age was 42.8 months. The most common colors of the tapetal area were yellow-green and orange, and the most common colors of the nontapetal area were dark brown and black. The analysis revealed that coat-color and breed concomitantly did not significantly influence tapetal color. Brown coated dogs often had a striped red and brown nontapetal area. The color of the tapetal area influenced the color of the nontapetal area. Smaller-sized breeds (such as Papillon) had a smaller tapetal area. A tapetal area was completely absent in 1.9%. The age did not influence the color of the tapetal area. CONCLUSIONS: Color of the tapetal area was influenced by both coat color and breed, but neither of these was statistically more influential than the other. The color of the tapetal area influenced the color of the nontapetal area. The size of the tapetal area correlated to breed and to body size.