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Peggy Bouzika, Joseph F Rizzo, Joan W Miller, Demetrios Vavvas, Dean M Cestari; Laser-induced optic nerve head injury in mice: challenges in establishing photothrombotic models to study optic neuropathies. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5068.
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© ARVO (1962-2015); The Authors (2016-present)
In vivo photothrombotic models have been extensively used to study diseases of the optic nerve (ON) such as non-arteritic anterior ischemic optic neuropathy. In these models photodynamic therapy (PDT) is applied to the ON, leading to optic nerve head (ONH) capillary occlusion, with minimal laser thermal effects on surrounding tissues. The use of mice presents extra difficulties given the animals’ small eye size and unique ONH blood supply. We present here a series of findings arising from the laser treatment itself of mouse ONH, which may interfere with the establishment of proper optic neuropathy models.
Laser (532nm) was applied to the ONH of C57BL/6 mice for various durations without the prior injection of a photosensitizer. The laser power was set at 50mW and the spot size used was 300um. The laser was focused either on the anterior part of the ONH structure, closer to the peak of the hyaloid artery remnant, or slightly deeper into the ONH. Fundoscopy, optical coherence tomography (OCT) and fluorescein angiography (FA) were performed to record any ONH findings. Retinal whole-mounts were also analyzed by immunohistochemistry using the Brn3a marker.
Laser treatment for one second led to slight ONH whitening 24h after application, with ONH late leakage on FA but without retinal edema on OCT. Increasing the duration of laser treatment to three seconds caused increased ONH whitening, and occasional branch retinal vein occlusion. There was loss of retinal ganglion cells one week after laser treatment of 3 seconds, as assessed by Brn3a staining of retinal whole-mounts. Finally, we observed that the position of the laser focus on the ONH also plays an important role on the type of lesion induced; laser applied while focused more anteriorly on the ONH led to more instances of retinal vessel occlusion, as well as to retinal lesions extending well beyond the peripapillary area.
Establishing a photosensitizer model of ONH in mice is challenging due to the fact that even brief application of commonly available lasers at lowest settings lead to ONH photothermal injury that contributes significantly to the final lesions induced.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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