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M. Salinas–Navarro, A. Triviño, A.I. Ramírez, J.J. Salazar, J.M. Ramírez, M.P. Villegas–Pérez, M. Vidal–Sanz; Long Term Efects of Laser–Induced Ocular Hypertension: Retrograde Degeneration of Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1560.
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© ARVO (1962-2015); The Authors (2016-present)
To study the effects of laser photocoagulation–induced ocular hypertension on the survival of adult rat retinal ganglion cells (RGC).
In adult Sprague–Dawley rats, the intraocular pressure of the left eye was chronically elevated by laser photocoagulation (532nm wavelength, 400mW power, 0.5 sec duration, 100 µm diameter spot size) of the trabecular meshwork, the limbar and episcleral veins. Intraocular pressure in both eyes was measured with a Tono–Pen prior to and at 6, 12, 24, 48, and 72h and at 7, 14, 21, 30, 60 or 90 days after lasering. Animals were analyzed at 2 or 3 months after lasering. Retinal ganglion cell survival was investigated by examining RGCs labeled with fluorogold applied to both superior colliculi 1 week before sacrifice and with dextran tetramethylrhodamine (DTMR) 3000 molecular weight (MW) applied intraorbitally to the ocular stump of the transected left optic nerve 5 days after FG application and 2 days prior to sacrifice. The optic nerve and the nerve fiber layer were examined with neurofilament antibodies (RT97).
Within the first 72 hours after lasering IOP increased between 73 to 100% over baseline. At 1, 2 and 3 weeks the IOP was approximately 35, 30 and 25% over baseline and by 30 days the IOP reached normal levels. In all retinas analyzed at 2–3 months after lasering there were large wedge sectors of the retina lacking RGCs retrogradely labelled with FG or DMTR. Although there was certain variability among different animals in the size and location of these sectors, most of these were localized in the superior retina. The mean number (±SD) of FG–labelled RGCs in lasered retinas was 17,957±17,574 (n=23) and 18,686±16,486 (n=14), at 2 and 3 months, respectively, which approximate 24% of the RGC population found in control retinas (79,659±4,915; n=12). Neurofilament staining showed large sectors of the optic nerve lacking RGC axons.
Laser photocoagulation of episcleral and limbal veins results in high levels of IOP during the first 72h and in moderate levels of IOP for the following 21 days. These increments of IOP result in altered retrograde axonal transport in pie shaped sectors of the retina and in a dramatic loss of RGCs.
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