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GUANPING FENG, Jesse B Schallek; Retinal thickness increases in anesthetized but not awake-behaving mice. Invest. Ophthalmol. Vis. Sci. 2019;60(9):188.
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© ARVO (1962-2015); The Authors (2016-present)
Anesthesia is widely used to provide ocular stability in animals for in vivo study. Unfortunately, many anesthetics have physiological side effects in the eye such as changes of intraocular, perfusion and arterial pressure that could alter retinal thickness. Here, we measured total retinal thickness with OCT in mice spanning 2 hours with and without anesthesia.
Four healthy C57BL/6J mice (40–46 weeks old) were imaged using OCT (Heidelberg Spectralis) centered at 10○ eccentricity (superior retina). A spatially registered OCT volume corresponding to a cube with 1024Χ97 A-scans (20○Χ20○) was imaged every 5-20 minutes up to two hours. Head-fixed, awake mice were positioned on a rotational treadmill that permitted OCT imaging (Schallek et al. 2018 ARVO). Anesthesia was induced with a single intraperitoneal injection of 100 mg/kg ketamine and 10 mg/kg xylazine (KX). Three mice were imaged again >1 week later with the same parameters, using intraperitoneal saline injection as a control. Retinal thickness was measured at each time interval using a custom graph-search algorithm to analyze OCT B-scans. Retinal thickness was defined as the distance between the vitreo-retinal surface and the outer segment-retinal pigment epithelial boundary.
All four mice subjected to anesthesia showed a continuous increase over two hours. At 80-120 minutes, a significant increase was observed of 8.0±4.1μm (mean±SEM, p=0.034) (Fig.1), corresponding to an average 3.9±2.0% thickening (Fig. 2). No significant thickness increase was observed in awake-behaving control mice that received saline injections (p=0.179, n=3).
We show a repeatable effect of apparent retinal thickening after administration of KX. Further studies will need to examine the impact of other widely used anesthetics such as isoflurane. Although the mechanism of this effect is not yet known, progressive retinal thickening due to anesthesia must be accounted for in future in vivo measurements. Alternately, this effect can be avoided by using an awake-behaving imaging paradigm.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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