Topographic analysis of the retinal ganglion cell layer and the optic nerve in the sandlance, Limnichthyes fasciatus (Creeiidae, Perciformes)

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    Abstract

    The sandlance or tommy fish Limnichthyes fasciatus (Creeiidae, Perciformes) is a tiny species that lives beneath the sand with only its eyes protruding and is found throughout the Indopacific region.

    The retina of the sandlance possesses a deep convexiclivate fovea in the central fundus of its minute eye (1.04 mm in diameter). A Nissl‐stained retinal whole mount in which the pigment epithelium had been removed by osmotic shock was used to examine the retinal topography of the ganglion cell layer. There was a foveal density of between 13.0 × 104 cells per mm2 (S.D. ± 1.8 × 104 cells per mm2), counted in the retinal whole mount, and 15.0 × 104 cells per mm2, counted in transverse sections, which diminished to a peripheral density of 4.5 × 104 cells per mm2 (S. D. ± 0.8 × 104 cells per mm2). The total population of axons within the optic nerve was assessed by electron microscopy. Optic axon densities ranged from 2 × 106 axons per mm2 in the caudal apex to over 16 × 106 axons per mm2 within a specialized region of unmyelinated axons in the rostral apex. The topography of the proportion of unmyelinated axon population (26%) follows closely that of the total population of optic nerve axons. There was a total of 104,452 axons within the optic nerve compared with 102,918 cells within the retinal ganglion cell layer. A close relationship is revealed between ganglion cell soma areas and axon areas where the organization in the optic nerve and retina may reflect some functional retinotopicity.
    Original languageEnglish
    Pages (from-to)226-241
    Number of pages15
    JournalThe Journal of Comparative Neurology
    Volume278
    Issue number2
    DOIs
    Publication statusPublished - 8 Dec 1988

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