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    Retina/Vitreous

    Investigators examined the autoregulation of blood flow at the optic nerve head in response to IOP spikes during vitrectomy among type 2 diabetics.

    Previous research using an animal model of diabetes has shown that autoregulation of blood flow at the optic nerve head (ONH) may be disrupted in response to elevation of IOP. Because IOP is known to fluctuate during ocular surgery, this study aimed to determine if spikes in IOP during a vitrectomy would have a measurable impact on blood flow.

    Study design

    The cohort comprised 13 type 2 diabetic patients and 30 control subjects who underwent 25-gauge vitrectomy. Among the 13 study subjects, diabetic retinopathy was either absent (n=5) or mild (n=8).

    Mean blur rate (MBR)—an index of optic nerve blood flow assessed using laser speckle flowgraphy (LSFG-NAVI, Softcare)—was measured in the ONH vascular and tissue areas. Measurements were taken at baseline as well as 5 and 10 minutes after an IOP elevation of 15 mm Hg was induced with increased perfusion pressure (Constellation vented gas–forced infusion and IOP control system, Alcon)

    Outcomes

    Vascular MBR was significantly lower in diabetic subjects than controls at both time points after IOP elevation (both P<0.05). A similar observation was noted for tissue MBR.

    Additionally, the recovery rate for vascular MBR was significantly lower in the diabetic group compared with controls (P=0.009) and was negatively correlated with hemoglobin A1c and fasting plasma glucose levels (P=0.028 and P=0.038, respectively).

    Limitations

    This study only looked at type 2 diabetic patients without diabetic retinopathy or with mild background DR, so the impact of having PDR or DME remains unclear.

    IOP was measured using the Tono-Pen AVIA (Reichert) in supine position—more accurate methods would have been desirable.

    Authors also did not assess how the patients' medications—to treat hypertension, diabetes, hyperlipidemia or sedative agents administered during surgery—may have affected the autoregulation of blood flow in response to changes in ocular perfusion pressure during vitrectomy.

    Clinical significance

    This study utilized laser speckle flowgraphy to demonstrate that there is impaired autoregulation of blood flow at the optic nerve during vitrectomy among patients with type 2 diabetes. Additional studies that assess higher stages of DR are warranted, since patients with complications of PDR are typically the ones undergoing vitrectomy. If these findings hold true, they would reinforce the need for more rigorous preoperative counseling and surgical planning that addresses the increased risk of postoperative ischemia and optic neuropathy.