Information relating to adipose eyelids:
Little published information appears available on the nature or function of adipose
eyelids. Stewart (1962) noted its presence and variations in
various families of fishes (
herring-like isopondyls [Clupeodea], mullets [Mugulidae], jacks [Carangidae],
mackerels [Scombridae - although we have noted its absence in Spanish mackerels,
and tunas], ten-pounders [Elopidae], anchovies [Engraulidae], butterfishes
[Stromateidae], threadfins [Polynemidae], bonefishes [Albulidae], and Salmonidae).
Stewart continues on to report that examination of this tissue from Pacific herring
Clupea pallasii, revealed , " . . . it has different refractive indices for light polarized in
mutually perpendicular planes", and that " . . . the amount of light absorbed by the
adipose eyelid varies with the plane of polarization of the light." Following examination
of tissue from species representing several families (Salmonidae, Mugilidae, and
Polymnemidae, John Morrison, U.S. Fish and Wildlife Service, Olympia (Washington)
Fish Health Center, found that "adipose" eyelids, rather than being fatty, primarily
consists of " . . . a stroma (matrix) of extremely fine, microfibrils of collagen. Scant
numbers of fibrocyes, which function in forming and maintaining the collagen are also
present. There is abundant interfibril ground substance, which may be described as
jelly-like material consisting of related glycosaminoglycan molecules (complex of
polysaccharides) that contain aminosugars. The microfibrils within the stroma are in
layers. There are scant numbers of blood vessels and sinuses. The tissue is covered
by an epithelium." (personal communication).

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