Purpose: Thorough this experimental study, the physic features of a modified 23-gauge vitrectomy probe were evaluated in vitro.Methods: A modified vitrectomy probe to increase vitreous outflow rate with a smalldiameter probe, that also minimized tractional forces on the retina, was created and tested. The "new" probe was created by drilling an opening into the inner duct of a traditional 23-gauge probe with electrochemical or electrodischarge micromachining. Both vitreous outflow and tractional forces on the retina were examined using experimental models of vitreous surgery.Results: The additional opening allowed the modified probe to have a cutting rate of 5,000 cuts per minute, while sustaining an outflow approximately 45% higher than in conventional 23-gauge probes. The modified probe performed two cutting actions per cycle, not one, as in standard probes. Because tractional force is influenced by cutting rate, retinal forces were 2.2 times lower than those observed with traditional cutters.Conclusion: The modified probe could be useful in vitreoretinal surgery. It allows for faster vitreous removal while minimizing tractional forces on the retina. Moreover, any available probe can be modified by creating a hole in the inner duct.RETINA 0:1-10, 2016 S utureless pars plana vitrectomy (PPV) reduces postoperative inflammation at sclerotomy sites, decreasing patient postoperative discomfort and recovery time. 1-6 Unfortunately, these advantages are often mitigated by longer operation times, which are mainly caused by reduced vitreous outflow rates. The smaller diameter of the probe leads to a decreased vitreous outflow and possibly exposes the surrounding retinal tissue to higher tractional forces because of the resulting higher aspiration pressures. 7,8 Poiseuille law, which governs flow inside of a pipe, is applicable to a vitrectomy probe and states that volumetric flow is proportional to tube radius to the fourth power (r 4 ). Therefore, the vitreous aspiration rate is decreased by a factor of 6.6 with a 25-gauge vitreous cutter, compared with the aspiration rate obtained with a 23-gauge vitreous cutter, because of its smaller port and tube radius. To achieve acceptable values of the vitreous outflow, higher aspiration values (at least 600 mmHg) can be used and, because flow is also inversely proportional to tube length, the length of both the probe tube and the aspiration ducts can be reduced. Vitrectomy probes are pipes that are not always open. The end of the probe is equipped with a guillotine that continuously opens and closes, and the percentage of

Introduction Plasma tests have demonstrated high diagnostic accuracy for identifying Alzheimer's disease pathology. To facilitate the transition to clinical utility, we assessed whether plasma storage duration and temperature affect the biomarker concentrations. Methods Plasma samples from 13 participants were stored at +4°C and +18°C. Concentrations of six biomarkers were measured after 2, 4, 6, 8, 10, and 24 h by single molecule array assays. Results Phosphorylated tau 181 (p‐tau181), phosphorylated tau 231 (p‐tau231), neurofilament light (NfL), and glial fibrillary acidic protein (GFAP) concentrations were unchanged both when stored at +4°C and +18°C. Amyloid‐β 40 (Aβ40) and amyloid‐β 42 (Aβ42) concentrations were stable for 24 h at +4°C but declined when stored at +18°C for longer than 6 h. This decline did not affect the Aβ42/Aβ40 ratio. Discussion Plasma samples can be stored for 24 h at +4°C or +18°C and result in valid assay results for p‐tau181, p‐tau231, Aβ42/Aβ40 ratio, GFAP, and NfL. HIGHLIGHTS Plasma samples were stored for 24 h at +4°C and +18°C, mimicking clinical practice. Concentrations for Alzheimer's disease biomarkers were measured at six time‐points. p‐tau181, p‐tau231, NfL, and GFAP concentrations were unchanged during the experiment. Storage at +18°C affected Aβ40 and Aβ42 concentrations while storage at +4°C did not. The Aβ42/Aβ40 ratio was unaffected. These plasma tests seem suitable for use in general practice.

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