Lam Andrew K C, Chan Rufina, Chiu Roger
Department of Optometry and Radiography, Hong Kong Polytechnic University, Hong Kong, China.
J Cataract Refract Surg. 2004 Mar;30(3):645-52. doi: 10.1016/S0886-3350(03)00554-6.
To study the effect of posture and artificial tears on handheld automated keratometry.
Department of Optometry and Radiography, Hong Kong Polytechnic University, Hong Kong, China.
Thirty-five subjects were recruited to have corneal curvature measurement in 1 eye (randomly selected) by a Medmont topographic keratometer and a Nidek handheld keratometer. In handheld keratometry, the measurements were taken with the subject in a sitting and lying posture (both with and without the use of artificial tears). The sequence of measurements was randomly assigned, but the application of artificial tears was always the last. The steepest and flattest corneal curvatures were compared between the 4 conditions. The corneal power was converted to orthogonal power vector components and rectangular Fourier form (M, J(0), J(45)) for another comparison.
There was a significant difference in the steepest and flattest meridians between the 4 conditions (P<.01). However, the mean difference between the handheld keratometer and the topographic keratometer was less than 0.50 diopter, and the intraclass correlation coefficient (ICC) was very high (0.96), indicating good clinical reliability. When analyzed in rectangular Fourier form, the difference was also significant but the ICCs were lower (0.97, 0.89, and 0.64 for M, J(0), and J(45), respectively). The greatest difference was when subjects were in the lying posture and had received artificial tears.
Handheld keratometry provided different results from topographic keratometry. The difference was greatest with the use of artificial tears. Cataract surgeons should take this into consideration, especially when using the handheld keratometry in the operating theater in patients under general anesthesia. Results show that the power vector method is best for studying corneal shape.
研究姿势和人工泪液对手持式自动角膜曲率计测量结果的影响。
中国香港理工大学验光与放射学系。
招募35名受试者，使用Medmont角膜地形图仪和尼德克手持式角膜曲率计对其一只眼睛（随机选择）进行角膜曲率测量。在手持式角膜曲率测量中，分别在受试者坐姿和卧姿下（均分为使用人工泪液和不使用人工泪液两种情况）进行测量。测量顺序随机分配，但人工泪液的使用总是在最后。比较4种情况下最陡和最平的角膜曲率。将角膜屈光力转换为正交屈光力矢量分量和矩形傅里叶形式（M、J(0)、J(45)）进行另一项比较。
4种情况下最陡和最平子午线之间存在显著差异（P<0.01）。然而，手持式角膜曲率计与角膜地形图仪之间的平均差异小于0.50屈光度，组内相关系数（ICC）非常高（0.96），表明临床可靠性良好。以矩形傅里叶形式分析时，差异也很显著，但ICC较低（M、J(0)和J(45)分别为0.97、0.89和0.64）。差异最大的情况是受试者处于卧姿并使用了人工泪液。
手持式角膜曲率测量结果与角膜地形图测量结果不同。使用人工泪液时差异最大。白内障手术医生应考虑到这一点，尤其是在全身麻醉下的手术室中对手持式角膜曲率计的使用。结果表明，屈光力矢量法最适合研究角膜形状。
