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Keely M. Bumsted O'Brien, Hie Rin Lee; Development Of The Fovea And Visual Resolution In The Tropical Seahorse (Hippocampus taeniopterus). Invest. Ophthalmol. Vis. Sci. 2011;52(14):5425.
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Seahorses are visually guided feeders requiring high resolution vision to prey upon small, fast moving crustaceans. The seahorse retina contains a convexiclivate fovea characterized by a rod-free depression where inner retinal layers are thinned in the center and thickened on the edges. The aim of this study was to analyze the changes in foveal morphology and reactive distance, a behavioral measure of visual resolution, during development.
Three age groups of tropical H. Taeniopterus (Ht) seahorses were analysed. Group 1 (n=5) was composed of juvenile fish - 6 cm in length, Group 2 (n=5) fish were 10 cm in length and Group 3 (n=5) fish were adults - 15 cm in length. Reactive distance was tested for each group. Eyes were then processed for frozen sections or flat-mounted. Wholemounts were stained with propidium iodide and photoreceptor (PR) densities determined.
The reactive distance in the larger/older fish was generally the longest, meaning that the bigger fish were able to detect smaller prey at the same distance compared with the smaller/younger fish. Morphologically, the depression of the pit became deeper and more pronounced in the larger fish. Overall foveal PR density in Group 1 fish was 174,000 cells/mm2. This foveal PR density increased to 180,000 cells/mm2 in Group 2 and 243,000 cells/mm2 in Group 3.
Ht fovea development is similar to that of other foveate retinas in that there is a deepening excavation of the fovea and an increase in PR with age. This change in morphology is correlated with an increased visual function.
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