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Editors Selection IGR 9-3
Basic research: Retinal ganglion cell imaging
Comment by Francesca Cordeiro on:
14057 In vivo imaging and counting of rat retinal ganglion cells using a scanning laser ophthalmoscope, Higashide T; Kawaguchi I; Ohkubo S et al., Investigative Ophthalmology and Visual Science, 2006; 47: 2943-2950
The paper by Higashide et al. (750)describes a method using a scanning laser ophthalmoscope to assess the number of labeled RGC in vivo in a rat model of optic nerve crush. This is not a novel idea with labeled RGCs having previously being identified in vivo using conventional fluorescence microscopy, SLO and more recently adaptive optics. However, the method of validation is creditable, with the authors showing a point-by-point comparison of the SLO image overlay and the histological retinal flatmount. Their analysis also identified microglial cells and they showed that newly emerged fluorescent spots in the SLO images colocalized with lectin-stained microglia histologically. Using the overlay system they counted the number of RGCs in SLO images in sample areas at 0.5 to 1.5 mm from the center of the optic disc and compared them with histology. RGC counts in SLO images were derived by subtracting the number of newly emerged fluorescent cells from total cell counts.
A major drawback with the study is the authors 'sampled' only select areas of the retina, where cells were seen to be intensely stained and well focused inSLO images. This was then used to be representative of the whole eye. Work by Danias et al. have clearly shown that the whole retina needs to be assessed rather than sample areas; the strength of their technique would have been more powerful had a much greater area of the retina had been included in the analysis.
At present, there is no way this technique could be applied to patients due to the procedure of retrograde labeling. However, the technique has implications for the assessment of chronic models of optic nerve disease. As in vivo imaging is becoming more popular in providing an objective evaluation of experimental glaucoma, the improvements in technology should mean that the current limitations such as inadequate focusing of wide field will soon be overcome, providing glaucoma scientists with important tools in the investigation of the cellular processes and management of this disease.
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