Lam Andrew Kc, Leung Stanley Yy, Hon Ying, Shu-Ho Lu, Wong Kit-Ying, Tiu Pui-Kwan, Lam David Cc
a Centre for Myopia Research, School of Optometry , The Hong Kong Polytechnic University , Hong Kong , China.
b Department of Mechanical and Aerospace Engineering , The Hong Kong University of Science and Technology , Hong Kong , China.
Curr Eye Res. 2018 Apr;43(4):474-481. doi: 10.1080/02713683.2017.1418895. Epub 2017 Dec 28.
Influence of orthokeratology on corneal biomechanics is equivocal using Ocular Response Analyzer, ORA. Implementing indentation method, corneal tangent modulus was measured and monitored in short-term orthokeratology.
Sixteen young subjects with refractive errors between -4D to -5D sphere and astigmatism within -1.50D were recruited. One randomly selected eye wore orthokeratology lens (treatment), and the fellow eye wore conventional rigid gas permeable lens (control). Lenses were worn for 30 and 60 minutes and one night separately with a week of washout period in between. The first two visits were randomly scheduled and before the overnight visit. Eyes were kept closed during all the lens wearing periods. Corneal radius, thickness, and biomechanics (using both ORA and an indentation device) were compared between eyes prior to each visit, and then before and after lens wear. Associations between baseline corneal biomechanics and central cornea from overnight visit were investigated.
Corneal parameters were similar in each visit before lens wear. Significant corneal flattening was observed in treatment eyes, and flattening increased with wearing time. Control eyes showed no significant corneal curvature changes. Corneal resistance factor (CRF) reduced by 0.42mmHg (± 0.68mmHg) after 30 minutes of orthokeratology treatment. Corneal hysteresis (CH) reduced by 0.42mmHg (+/- 0.63mmHg) in control eyes from overnight wear. Both eyes showed stable tangent modulus, E, throughout the study. A lower CH (r = 0.51, p = 0.046) and a higher E (r = 0.53, p = 0.037) at baseline was significantly associated with greater corneal flattening along the flattest meridian in treatment eyes.
Short-term orthokeratology had no significant effect on corneal tangent modulus. Changes in CH and CRF could be related to their intrinsic measurement variability. Corneal tangent modulus provided another measure of corneal biomechanics. Long-term study is required to investigate predictive role of corneal biomechanics in orthokeratology.
使用眼反应分析仪（ORA）评估角膜塑形术对角膜生物力学的影响尚无定论。采用压痕法，在短期角膜塑形术中测量并监测角膜切线模量。
招募了16名年龄较小的受试者，其球镜度数在-4D至-5D之间，散光度数在-1.50D以内。随机选择一只眼睛佩戴角膜塑形术镜片（治疗组），另一只眼睛佩戴传统硬性透气性镜片（对照组）。镜片分别佩戴30分钟、60分钟以及一晚，期间间隔一周的洗脱期。前两次就诊随机安排，且在过夜就诊之前。在所有佩戴镜片期间眼睛保持闭合状态。在每次就诊前以及佩戴镜片前后，比较双眼的角膜半径、厚度和生物力学（使用ORA和压痕装置）。研究过夜就诊时基线角膜生物力学与中央角膜之间的关联。
在佩戴镜片前的每次就诊中，角膜参数相似。治疗组眼睛出现明显的角膜变平，且变平程度随佩戴时间增加。对照组眼睛未显示出明显的角膜曲率变化。角膜塑形术治疗30分钟后，角膜阻力因子（CRF）降低了0.42mmHg（±0.68mmHg）。过夜佩戴后，对照组眼睛的角膜滞后（CH）降低了0.42mmHg（±0.63mmHg）。在整个研究过程中，双眼的切线模量E均保持稳定。基线时较低的CH（r = 0.51，p = 0.046）和较高的E（r = 0.53，p = 0.037）与治疗组眼睛沿最平子午线方向更大程度的角膜变平显著相关。
短期角膜塑形术对角膜切线模量无显著影响。CH和CRF的变化可能与其固有的测量变异性有关。角膜切线模量提供了另一种角膜生物力学测量方法。需要进行长期研究以探讨角膜生物力学在角膜塑形术中的预测作用。
