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M. Salinas-Navarro, M. Jiménez-López, F. J. Valiente-Soriano, L. Alarcón-Martínez, I. Cánovas, J. M. Bernal, M. I. Soro, M. Avilés-Trigueros, M. P. Villegas-Pérez, M. Vidal-Sanz; Laser Photocoagulation of Perilimbal and Episcleral Veins Induced Elevation of the Intraocular Pressure. Effects on the Retinal Ganglion Cell Population of the Albino Mouse. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4353.
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To study the effects of elevated intraocular pressure on the survival of retinal ganglion cells.
In adult swiss mice (30-45 g) one eye received laser photocoagulation (532nm wavelength, 300mW power, 0.5 second duration, 100 µm diameter spot size) of limbar and episcleral veins. Intraocular pressure (IOP) in both eyes was measured with a Tonolab prior to and at 24h and 48h, and at 1, 2, 4, 6, or 8 wks after lasering. Mice were divided in groups I and II, and analyzed at 4 and 8 weeks, respectively. To identify the population of retinal ganglion cells, 3% Fluorogold was applied over the surface of both Sci one week prior to animal processing. Retinas were prepared as whole-mounts, examined and photographed under a fluorescence microscope (Axioscop 2 plus, Zeiss, Germany) equipped with a digital high-resolution camera and a motorized stage, connected to an image analysis system with an automatic frame-grabber device (Image-Pro Plus, ver. 18.104.22.168). Retinas were imaged by adjacent, nonoverlapping frames captured in raster pattern. Each of these frames was counted with image analysis software Image-Pro Plus (IPP). And an isodensity contour plot was generated for each retina (SigmaPlot 2002 for Windows, ver 9.0).
Laser treatment induced an increase in mean intraocular pressure of approximately 30% over baseline that was maintained throughout the period of study. In group I Basal IOP values were (mean ±SD) 14.1±1.2 (n=5), increased to 24 ±4.2 at 48 hours and decreased to basal values by one week. Similar values were observed in Group II, with basal IOP values of 14.7 ±0.9 (n=5) that increased to 26.7 ±11.6 at 48 hours and decreased to basal values by one week. In group I, the mean retinal ganglion cell population in the lasered retinas (26,631±23,560; n=5) represented 55% of the values found in their contralateral control eyes (48,485±5,125; n=5). In group II the mean retinal ganglion cell population in the lasered retinas (19,974±18,040; n=5) represented 44% of the values found in their contralateral control eyes (45,666±2,017; n=5).
Lasering of the perilimbar and episcleral veins in swiss mice results in elevation of the intraocular pressure that leads to the loss of approximately 50% of the original RGC population. This RGC loss, which did not seem to progress between 4 and 8 weeks, was focal (in sectors with the apex located in the optic disc) as well as diffuse within the retina.
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