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N.P. Turunen, T. Karjalainen, A. Tuulonen, P.J. Airaksinen, U. Napankangas; Imaging and Evaluation of Rat Retinal Nerve Fiber Layer After Total and Partial Optic Nerve Transection . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1826.
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We examined whether axon degeneration in the retinal nerve fiber layer (RNFL) occurs in line with retinal ganglion cell death seen after optic nerve transection in a rat and can be documented in RNFL photography.
Normal fundus and RNFL pictures of 20 adult female Brown Norway rats were taken to assure the quality and reproducibility of the method. The left optic nerve of 6 rats was transected as previously described. A partial transection of the nerve was done for a group of animals by ligating the nerve with a suture of its nasal (N = 6) or temporal (N = 6) half. After operation, RNFL photografs were taken by an experienced technician every second day for four weeks with a Canon CF–60 Fundus Camera with Canon EOS–1D MARK II (495 nm, blue filter). The pictures were screened in a blinded manner by two glaucomatologists, who were not aware of the experimental procedure or animal identity. Postoperative pictures were compared to preoperative and those of the contralateral eye of each individual animal. At the end of follow–up the rats were sacrificed and the eyes collected for immunohistochemical analysis.
High/good quality rat nerve fiber layer photographs were achieved in most cases. Based on the density of RNFL, four groups (abundant or moderate RNFL, diffuse or total axon loss) could reproducibly be defined by two individual observers. Each group contained animals of the same postoperative period. In further image analysis, it was found that total optic nerve axotomy produced a diffuse total axon loss between postoperative days 10–11 and 14–15. Partial transection of the optic nerve also seems to lead to total RNFL loss, although later than total transection, i.e. by day 18–22.
To our knowledge, this is the first successful, reproducible study of RNFL imaging in adult rats. Our results indicate, that total optic nerve transection leads to total RNFL loss within 14–15 days, which is in line with the retinal ganglion cell loss seen after axonal injury. Partial optic nerve transection also seems to produce total axon loss, possibly due to secondary degeneration.
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