Savini Giacomo, Barboni Piero, Zanini Maurizio
Centro Salus, Bologna, Italy.
J Refract Surg. 2007 May;23(5):461-6. doi: 10.3928/1081-597X-20070501-07.
Given that the standard keratometric refractive index of 1.3375 is no longer valid after excimer laser surgery, we aimed to investigate how this value changes postoperatively and if any correlation to the attempted correction exists.
The pre- and postoperative data of 98 patients who underwent either myopic photorefractive keratectomy (PRK) or LASIK were reviewed. Using postoperative videokeratography, the corneal radius (r) was obtained; the corrected corneal power (Pc) was measured by separately calculating the dioptric power of the anterior and posterior corneal surfaces. The postoperative index of refraction (n(post)) was derived from these values using the formula: n(post) = (rPc) +1.
As the amount of refractive change increases, n(post) progressively decreases (P < .0001, r = 0.9581). Linear regression provided the subsequent formula to calculate the postoperative index of refraction: n(post) = 1.338 + 0.0009856 x attempted correction.
Myopic PRK and LASIK induce a decrease in the keratometric refractive index. This reduction correlates to the amount of attempted correction. When the latter is known, calculating n(post) may enable the measurement of corneal power and thus provide an additional method for calculating intraocular lens power in eyes that have undergone myopic PRK or LASIK.
鉴于准分子激光手术后标准角膜曲率计折射率1.3375不再有效，我们旨在研究该值术后如何变化以及与预期矫正量是否存在任何相关性。
回顾了98例行近视性准分子激光角膜切削术（PRK）或准分子原位角膜磨镶术（LASIK）患者的术前和术后数据。使用术后角膜地形图获得角膜半径（r）；通过分别计算角膜前表面和后表面的屈光力来测量矫正后的角膜屈光力（Pc）。术后折射率（n（post））使用以下公式从这些值中得出：n（post）=（rPc）+1。
随着屈光变化量增加，n（post）逐渐降低（P <.0001，r = 0.9581）。线性回归得出了计算术后折射率的后续公式：n（post）= 1.338 + 0.0009856×预期矫正量。
近视性PRK和LASIK导致角膜曲率计折射率降低。这种降低与预期矫正量相关。当已知预期矫正量时，计算n（post）可用于测量角膜屈光力，从而为计算接受近视性PRK或LASIK手术眼的人工晶状体屈光力提供一种额外方法。
