University Eye Hospital, Freiburg, Baden-Württemberg, Germany.
J Glaucoma. 2013 Sep;22(7):584-90. doi: 10.1097/IJG.0b013e31824cef11.
Among other corneal biomechanical properties, Goldmann applanation tonometry (GAT) has been shown to depend on corneal edema. New tonometry devices have been designed, such as the Tono-Pen XL, iCare, and ocular response analyzer (ORA), to measure the intraocular pressure (IOP) accurately. This study aims to investigate the influence of corneal edema on the accuracy of these IOP-measuring devices in an in vitro model.
A model of an artificial anterior chamber was developed using a guided trephination system. Eight donor corneas not suitable for keratoplasty were clamped into this artificial anterior chamber. All corneas showed signs of stromal edema. Intracameral pressure (ICP) was adjusted manometrically to 10, 20, 30, 40, and 50 mm Hg. The central corneal thickness (CCT) was determined by ultrasonic pachymetry. For each manometrically defined ICP, tonometry was performed using the iCare, Tono-Pen XL, GAT, and ORA.
The mean CCT increased from 616.1±29.6 µm to 626.9±36.1 µm. At 10 mm Hg, GAT yielded a higher ICP than those manometrically adjusted (10.4±3.3 mm Hg); at all other ICP levels, GAT yielded lower ICP levels than those adjusted. The Tono-Pen XL and iCare showed the greatest difference at 10 mm Hg, with the Tono-Pen XL yielding a value of 14.0±4.0 mm Hg and the iCare yielding a value of 12.5±2.6 mm Hg. All other results of the 2 devices fell within a range of ±2 mm Hg from the adjusted ICP. The ORA provided accurate results only at "physiological" ICP levels with a maximum difference of 2.6 mm Hg at 30 mm Hg. At higher ICP levels, corneal hysteresis decreased significantly with increasing ICP. None of the measurement devices revealed a statistically relevant dependence on CCT in this experimental setting.
The Tono-Pen XL and the iCare yielded the most accurate ICP values across all the adjusted ICP values. This may be because of their relatively small contact area with the cornea and, consequently, greater independence from corneal biomechanical properties. The ORA yielded accurate measurement results only at physiological ICP levels. As anticipated, GAT underestimated ICP. The Tono-Pen XL and the iCare should therefore be used to determine IOP in patients suffering from corneal edema, such as bullous keratopathy or Fuchs endothelial dystrophy.
在其他角膜生物力学特性中，压平眼压计（GAT）已被证明与角膜水肿有关。已经设计了新的眼压计设备，如 Tono-Pen XL、iCare 和眼反应分析仪（ORA），以准确测量眼压（IOP）。本研究旨在研究角膜水肿对这些眼压测量设备在体外模型中的准确性的影响。
使用引导环钻系统开发了人工前房模型。将 8 个不适合角膜移植的供体角膜夹入该人工前房。所有角膜均有基质水肿的迹象。通过压力计法将眼内压（ICP）调节至 10、20、30、40 和 50 mmHg。通过超声测厚仪确定中央角膜厚度（CCT）。对于每个压力计定义的 ICP，使用 iCare、Tono-Pen XL、GAT 和 ORA 进行眼压测量。
平均 CCT 从 616.1±29.6 µm 增加到 626.9±36.1 µm。在 10 mmHg 时，GAT 产生的 ICP 高于压力计调整的 ICP（10.4±3.3 mmHg）；在所有其他 ICP 水平下，GAT 产生的 ICP 水平均低于调整后的 ICP。Tono-Pen XL 和 iCare 在 10 mmHg 时差异最大，Tono-Pen XL 产生的数值为 14.0±4.0 mmHg，iCare 产生的数值为 12.5±2.6 mmHg。这两种设备的所有其他结果均在与调整后的 ICP 相差±2 mmHg 的范围内。ORA 仅在“生理”ICP 水平提供准确的结果，在 30 mmHg 时最大差异为 2.6 mmHg。在较高的 ICP 水平下，角膜滞后随 ICP 的增加而显著降低。在这种实验设置下，没有一种测量设备显示出与 CCT 有统计学意义的相关性。
Tono-Pen XL 和 iCare 在所有调整后的 ICP 值上产生了最准确的 ICP 值。这可能是因为它们与角膜的接触面积相对较小，因此对角膜生物力学特性的依赖性较小。ORA 仅在生理 ICP 水平提供准确的测量结果。如预期的那样，GAT 低估了 ICP。因此，在患有角膜水肿的患者（如大疱性角膜病变或 Fuchs 内皮营养不良）中，应使用 Tono-Pen XL 和 iCare 来确定 IOP。
