Hugger P, Kohnen T, La Rosa F A, Holladay J T, Koch D D
Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
Am J Ophthalmol. 2000 Jan;129(1):68-75. doi: 10.1016/s0002-9394(99)00268-8.
To determine which corneal curvature values most closely correlate to change in manifest refraction after excimer laser photorefractive keratectomy.
In a prospective study at the Cullen Eye Institute, excimer laser photorefractive keratectomy was performed on 27 eyes of 27 patients (mean age, 38.07+/-6.65 years). Preoperative refractive errors ranged from -2.25 diopters to -8.75 diopters (mean, -5.74+/-2.09 diopters). Preoperatively and 1 month postoperatively, we determined the spherical equivalent of the subjective manifest refraction (corrected for a 12-mm vertex distance) and measured corneal power using standard keratometry (Bausch & Lomb Keratometer; Rochester, New York) and computerized videokeratography (EyeSys Corneal Analysis System; Premier Laser Systems Inc, Houston, Texas). We collected 15 corneal values: standard keratometry and 14 computerized videokeratography values calculated using the axial, instantaneous, and refractive formulas. All calculations were performed with 1.3375 and 1.376 for the refractive index of the cornea. For each of the corneal values, we subtracted the change in corneal power from the change in manifest refraction and calculated for this difference the means, SDs, correlations, and regressions.
Mean differences between change in refraction and change in corneal power were lower when for a refractive index of 1.376 than for 1.3375, were lowest for the most central measurement points, and displayed a high SD. A value of 1.408 for the refractive index would be required to optimize the correlation between change in manifest refraction and effective refractive power of the central 3 mm of the cornea.
For individual patients who have undergone photorefractive keratectomy, changes in corneal values determined by computerized videokeratography or by standard keratometry do not reliably predict change in manifest refraction.
确定哪些角膜曲率值与准分子激光屈光性角膜切削术后明显屈光不正的变化最密切相关。
在库伦眼科研究所进行的一项前瞻性研究中，对27例患者的27只眼（平均年龄38.07±6.65岁）实施了准分子激光屈光性角膜切削术。术前屈光不正范围为-2.25屈光度至-8.75屈光度（平均-5.74±2.09屈光度）。术前及术后1个月，我们确定了主观明显屈光不正的等效球镜度（针对12毫米顶点距离进行校正），并使用标准角膜曲率计（博士伦角膜曲率计；纽约罗切斯特）和计算机化视频角膜地形图（EyeSys角膜分析系统；得克萨斯州休斯顿市Premier激光系统公司）测量角膜屈光力。我们收集了15个角膜值：标准角膜曲率计测量值以及使用轴向、瞬时和屈光公式计算得出的14个计算机化视频角膜地形图测量值。所有计算均采用角膜折射率1.3375和1.376。对于每个角膜值，我们从明显屈光不正的变化中减去角膜屈光力的变化，并计算此差值的均值、标准差、相关性和回归分析。
当角膜折射率为1.376时，屈光不正变化与角膜屈光力变化之间的平均差值低于折射率为1.3375时，在最中央测量点差值最低，且标准差较高。需要角膜折射率为1.408才能优化角膜中央3毫米的明显屈光不正变化与有效屈光力之间的相关性。
对于接受过屈光性角膜切削术的个体患者，通过计算机化视频角膜地形图或标准角膜曲率计确定的角膜值变化并不能可靠地预测明显屈光不正的变化。
