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Editors Selection IGR 20-2

Examination methods: RNFL in rodents

Comment by Linda Zangwill on:

14061 In vivo imaging and quantitative evaluation of the rat retinal nerve fiber layer using scanning laser ophthalmoscopy, Kawaguchi I; Higashide T; Ohkubo S et al., Investigative Ophthalmology and Visual Science, 2006; 47: 2911-2916

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Obtaining in-vivo quantitative evaluation of the RNFL in rodents is a challenge. Kawaguchi et al. (755) have shown that scanning laser ophthalmoscopy (SLO) can be used to semi-quantitatively measure retinal nerve fiber layer (RNFL) thinning in the rat. This report documents experiments consisting of 16 rats. The right eye of 12 rats was induced with experimental glaucoma using the optic nerve crush method while the left eye was the untreated control. Fundus images of both eyes were recorded using an argon blue laser SLO before, and at 1, 2 and 4 weeks after optic nerve crush. By changing refractive values, the focus plane of the SLO was sequentially moved and the range of refractive values recorded. Although this was a subjective procedure with the focus determined by comparison with standard reference images, the intra-observer and inter-observer reproducibility was good (kappa = .92 and .83 respectively). The 12 rats were sacrificed at 1, 2 and 4 weeks (4 each week) for histologic determination of RNFL thickness, and for obtaining counts of the number of cells in the ganglion cell layer. The difference in refractive values was found to correlate strongly with histologic RNFL thickness (r = 0.86). However, ganglion cell counts decreased significantly after 1 week, whereas SLO RNFL (indirectly measured as change in refractive values) and histologic RNFL thickness remained unchanged at one week after the crush. The authors conclude that the SLO is a valuable tool for in vivo imaging and quantitative evaluation of the rat RNFL. As the authors point out, the clinical usefulness of RNFL evaluation using SLO is limited as there are other techniques such as optical coherence tomography and scanning laser polarimetry that provide reproducible RNFL measurements for patient management. However, the rodent model is valuable for studying glaucoma and other optic neuropathies. The development of reproducible methods to measure the RNFL in vivo is important to improve the relevance of rodent models for studying optic nerve damage.

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