Holladay J T, Dudeja D R, Chang J
Houston Eye Associates, Texas 77025, USA.
J Cataract Refract Surg. 1999 May;25(5):663-9. doi: 10.1016/s0886-3350(99)00011-5.
To demonstrate the functional vision and corneal changes following laser in situ keratomileusis (LASIK) determined by contrast sensitivity, glare testing, and corneal topography.
University of Texas Medical School, Houston, Texas, USA.
Seven patients ranging in age from 20 to 61 years who had bilateral LASIK were evaluated preoperatively and 1 day, 1 week, and 1 and 6 months postoperatively. Visual acuity, using letters on the Baylor Visual Acuity Testor (BVAT) at 98% (standard acuity) and 13% contrast, and the contrast threshold were determined at 3 light levels (darkness, medium brightness acuity testor [BAT], high BAT). Pupil sizes were measured at each level, and corneal topography was performed at each visit.
The greatest changes were found 1 day postoperatively: The contrast threshold worsened by a mean of 0.6 lines +/- 1.0 (SD) (P = .05) in darkness, 0.4 +/- 0.7 lines (P = .05) at medium BAT, and 0.8 +/- 0.7 lines (P = .002) at high BAT. The 98% contrast acuity decreased a mean of 1.4 +/- 1.6 lines (P = .01) in darkness, 1.0 +/- 2.0 lines (P = .09) at medium BAT, and 0.8 +/- 2.3 lines (P = .22) at high BAT. The 13% contrast acuity decreased a mean of 2.2 +/- 2.6 lines (P = .01) in darkness, 1.3 +/- 1.9 lines (P = .02) at medium BAT, and 1.4 +/- 2.5 lines (P = .07) at high BAT. The predicted corneal acuity (PCA) obtained from corneal topography decreased by a mean of 3.3 +/- 3.1 lines (P = .002), and the asphericity (Q-value) increased by an average of +0.35 +/- 0.67 (P = .07). All values returned to the preoperative levels by 1 week except PCA, asphericity, visual acuity at 13%, and contrast threshold in darkness, which improved slightly but had not returned to baseline by 6 months. The 98% contrast acuity at medium BAT improved by 0.2 +/- 1.0 lines (P = .34) and 0.3 +/- 0.8 lines (P = .16) at high BAT at 1 month. The 98% contrast acuity values remained 0.3 lines over baseline through 6 months. Corneal topography showed that all corneas became oblate after LASIK to a mean Q-value of +0.47 +/- 0.40 (P = .0001) and PCA was decreased by 1.6 +/- 1.1 lines (P = .0002) at 6 months.
Functional vision changes do occur after LASIK. The optical quality of the cornea is reduced and the asphericity becomes oblate. Changes in functional vision worsen as the target contrast diminishes and the pupil size increases. These findings indicate that the oblate shape of the cornea following LASIK is the predominant factor in the functional vision decrease.
通过对比敏感度、眩光测试和角膜地形图，展示准分子原位角膜磨镶术（LASIK）后功能性视力及角膜的变化。
美国得克萨斯州休斯敦市得克萨斯大学医学院。
对7例年龄在20至61岁之间接受双侧LASIK手术的患者进行术前及术后1天、1周、1个月和6个月的评估。使用贝勒视力测试仪（BVAT）在98%（标准视力）和13%对比度下测定视力，并在3种光照水平（暗环境、中等亮度视力测试仪[BAT]、高亮度BAT）下测定对比阈值。在每个水平测量瞳孔大小，并在每次就诊时进行角膜地形图检查。
术后1天发现最大变化：暗环境下对比阈值平均恶化0.6行±1.0（标准差）（P = 0.05），中等亮度BAT下为0.4±0.7行（P = 0.05），高亮度BAT下为0.8±0.7行（P = 0.002）。98%对比度视力在暗环境下平均下降1.4±1.6行（P = 0.01），中等亮度BAT下为1.0±2.0行（P = 0.09），高亮度BAT下为0.8±2.3行（P = 0.22）。13%对比度视力在暗环境下平均下降2.2±2.6行（P = 0.01），中等亮度BAT下为1.3±1.9行（P = 0.02），高亮度BAT下为1.4±2.5行（P = 0.07）。从角膜地形图获得的预测角膜视力（PCA）平均下降3.3±3.1行（P = 0.002），非球面性（Q值）平均增加+0.35±0.67（P = 0.07）。除PCA、非球面性、13%对比度下的视力和暗环境下的对比阈值外，所有值在1周时恢复到术前水平，后者虽有轻微改善，但在6个月时仍未恢复到基线。1个月时，中等亮度BAT下的98%对比度视力提高0.2±1.0行（P = 0.34），高亮度BAT下提高0.3±0.8行（P = 0.16）。98%对比度视力值在6个月内一直比基线高0.3行。角膜地形图显示，LASIK术后所有角膜均变为扁圆形，6个月时平均Q值为+0.47±0.40（P = 0.0001），PCA下降1.6±1.1行（P = 0.0002）。
LASIK术后确实会发生功能性视力变化。角膜的光学质量降低，非球面性变为扁圆形。随着目标对比度降低和瞳孔大小增加，功能性视力变化会恶化。这些发现表明，LASIK术后角膜的扁圆形是功能性视力下降的主要因素。
