Lincoff H A, Kreissig I, Smith R J, Serag Y R, Laroche D
Department of Ophthalmology, New York Hospital, New York, USA.
Klin Monbl Augenheilkd. 1996 Feb;208(2):100-6. doi: 10.1055/s-2008-1035178.
Increased use of gases in retinal/vitreous surgery requires a good clinical estimate of intraocular gases. This is needed, if a supplement of gas is intended, its disappearance to be predicted (e.g. to 10% to permit travelling by plane) or the amount to be calculated to cover a break. Clinical estimation of gas in the pupil is limited by its size. Accuracy of pupil measurements will be tested and compared with experimental results obtained by estimating the level of gas meniscus at the retina.
Ten cadaver eyes (5 phakic, 4 aphakic, 1 pseudophakic) were fixed in a plastic mold, vitrectomized and injected with multiple randomized volumes of air. Two observers measured the level of meniscus in disc diameters above or below the superior margin of disc and then anteriorly in the pupil in millimeters from the superior limbus. Measurements were converted to milliliters through tables constructed on mathematical models of the phakic and aphakic eye.
Observations at the retina and in the pupil were equally accurate for intermediate gas volumes, for which the meniscus fell within the pupil (P = 0.372). Measurements at the retina proved less vulnerable to error induced by misalignment of the observer's eye. Above the pupil observations at the retina were still reliable for small bubbles up to 4 dd above the disc (error < 5% in the aphakic, < 10% in the phakic eye). Below the pupil observations at the retina yielded a result increasing less than the injected volume because of refraction at the anterior segment gas interface (error > 10% of the ocular volume).
Observations of the level of gas meniscus at retina with indirect ophthalmoscopy is an accurate method for estimating intraocular gas volumes. It extends the range of measurement significantly beyond the pupil. Tables based on a mathematical model convert disc diameters to milliliters.
视网膜/玻璃体手术中气体使用的增加需要对眼内气体进行良好的临床评估。如果打算补充气体、预测其消失情况（例如降至10%以允许乘坐飞机）或计算覆盖裂孔所需的气体量，就需要进行这种评估。瞳孔中气体的临床评估受其大小限制。将测试瞳孔测量的准确性，并与通过估计视网膜处气体弯月面水平获得的实验结果进行比较。
将10只尸体眼（5只正视眼、4只无晶状体眼、1只人工晶状体眼）固定在塑料模具中，进行玻璃体切割并注入多组随机体积的空气。两名观察者测量视盘上缘上方或下方视盘直径数目的弯月面水平，然后从前房角向上测量瞳孔中距角膜上缘的毫米数。通过根据正视眼和无晶状体眼的数学模型构建的表格，将测量值转换为毫升。
对于弯月面位于瞳孔内的中等气体体积，视网膜和瞳孔处的观察同样准确（P = 0.372）。视网膜处的测量结果证明较不易受观察者眼睛未对准引起的误差影响。在瞳孔上方，对于视盘上方达4个视盘直径的小气泡，视网膜处的观察仍然可靠（无晶状体眼中误差<5%，正视眼中误差<10%）。在瞳孔下方，由于前段气体界面处的折射，视网膜处的观察结果增加量小于注入体积（误差>眼体积的10%）。
间接检眼镜观察视网膜处气体弯月面水平是估计眼内气体体积的准确方法。它显著扩展了测量范围，超出了瞳孔范围。基于数学模型的表格可将视盘直径转换为毫升。
