Short and long term corneal biomechanical analysis after overnight orthokeratology

INTRODUCTION

Several studies have been conducted to evaluate the clinical outcomes and microstructural changes occurring after overnight orthokeratology (OK)

. This scientific evidence shows the efficacy and safety of this type of corneal refractive treatment

. However, the scientific evidence of changes occurring in the mechanical properties of the cornea with OK is still limited and showing even contradictory outcomes

. Whereas some authors have concluded in different studies that OK alters some corneal biomechanical properties

, other authors have reported just the opposite

.Chen

concluded in a case series that short term OK(STOK) treatment induced a reduction of corneal hysteresis(CH) parameters measured with the Ocular Response Analyzer(ORA) from Reichert. In contrast, Lam

concluded in another randomized study that STOK had no significant effect on corneal tangent modulus, with changes in CH and corneal resistance factor (CRF) measured with the ORA device being related to their intrinsic measurement variability.

A total of 54 eyes of 54 patients with ages ranging from 18 to 35y (mean age: 24.9±4.4y) were evaluated in the current study.The sample included a total of 22 men (40%) and 32 women(60%). Mean spherical equivalent in the whole sample was-3.00±1.40 D. As previously mentioned, three groups of eyes were differentiated: CG (18 eyes), STOK group (18 eyes), and LTOK group (18 eyes). Table 1 summarizes the main clinical data characterizing these three groups.

SUBJECTS AND METHODS

Demographic, Visual, Refractive, and Corneal Curvature Data No significant differences were found between groups in age (

=0.25) or gender (

=0.93; Table 1). In contrast,significantly poorer CDVA was found in STOK compared to CG and LTOK (

＜0.01). Likewise, significantly flatter keratometric readings were obtained in STOK and LTOK groups compared to CG (

＜0.01; Table 1).

隨著人工智能、大數據技術的發展，作為新資源、新技術和新理念的混合體，大數據不僅在企業的管理過程中，而且在國家、社會治理中其評價、預測、決策功能也發揮著越來越大的價值。這一新技術的應用，也給法學研究帶來了新的挑戰。其中，如何明確大數據權利屬性，如何保護個人信息，如何明確數據法律關系中各主體的行為邊界，成為一個非常現實的命題，具有很強的學理與現實意義。

Subjects

This retrospective, observational and comparative study enrolled a total of 54 subjects that were divided into three groups: control group (CG), including 18 non-contact lens wearers; STOK group, including 18 subjects treated with OK with a short time follow-up; and long term OK (LTOK)group, including 18 subjects treated with OK for a long-time follow-up.

Tomographic biomechanical index (TBI): calculated by combining tomographic and biomechanical parameters and using an artificial intelligence approach to optimize ectasia detection

.

Inclusion criteria for all groups were Caucasian men or women with an age between 18 and 35 years old, myopia between 0.75 and 6.00 D, and astigmatism below 2 D. Exclusion criteria included previous ocular surgery, strabismus, keratoconus or any other ectatic corneal disease, active ocular or systemic pathology, and pregnancy. In CG, only healthy non-contact lens wearers with any active ocular or systemic disease were included. In STOK and LTOK groups, patients were treated with OK for two weeks and for more than 1y, respectively.

Clinical Protocol A complete examination was performed in all patients including the following tests and measurements:manifest refraction, measurement of corrected distance visual acuity (CDVA) using an ETDRS chart at 4 metres,measurement of axial length (AXL) and anterior chamber depth (ACD) with an optical biometer (IOL Master 700,Carl Zeiss Meditec, Jena, Germany), corneal topographic analysis (Pentacam HR, Oculus Optikgerate Optikgerate GmbH, Wetzlar, Germany, software version 1.25r15), and measurement of the corneal biomechanical properties with the CorVis

ST system (Oculus Optikgerate GmbH, Wetzlar,Germany, software version 1.6r2223). Three consecutive measurements were performed on each eye by 2 experienced examiners and only those with image quality graded as “OK”were collected. The CorVis

ST is a non-contact tonometer that allows the clinician to analyze the response of the cornea to an air pulse. A high-speed Scheimpflug camera records corneal movements, corneal flattening length, and velocity over time

. This camera captures more than 4300 frames per second, providing reliable measurements of intraocular pressure (IOP) and corneal thickness

. Concerning the biomechanical parameters provided by this system, the following were considered in the current analysis:

First applanation time (AT1): time in which the first applanation is reached.

Amplitude of deformation 1 (AD1): amplitude of deformation at the first applanation time.

式中:Q*,GH,ΔM分別為雙堆垛機執行出庫任務運行時間的數學期望、貨架重心高度、成組貨架質量差的絕對值，已于式(10)中詳細描述；分別為當代棲息地中，對應各目標函數的最大值。以此為HSI，可以保證：①HSIQ*最大的貨位分配方案雙堆垛機執行出庫任務運行時間的數學期望最小；②HSIGH最大的貨位分配方案貨架重心高度最低；③HSIΔM最大的貨位分配方案成組貨架質量差的絕對值最小。

OK does not seem to alter significantly the corneal biomechanical properties, but special care should be taken when analyzing biomechanical parameters influenced by corneal thickness such as amplitude of deformation, ARTh or CBI, because they change significantly after treatment but mainly due to the reduction and pachymetric progression induced by the corneal molding secondary to OK treatment.

Second applanation time (AT2): time in which the second applanation is reached.

Maximum deflection amplitude (MaxDA): the maximum amount of the corneal movement compensating for the whole eye movement during the measurement.

Velocity of corneal apex at the first applanation time (AV1).

Velocity of corneal apex at the second applanation time (AV2).Corneal stiffness parameter (SPA1): resulting pressure on the cornea divided by the deflection amplitude at the first applanation

.

文獻[19]顯示，當模型的水平范圍為8～10倍隧道直徑時，即可獲得較高的計算精度。本文建立了二維彈塑性動力有限元模型，模型水平方向為80 m，豎直方向為60 m，盾構隧道直徑為6 m。

Strain stress index (SSI): this index represents the stress-strain curve and describes the elastic properties of the cornea. The curve is shifted to the right if the cornea is soft, and to the left if the cornea is stiff.

“二表哥吐了一口唾沫，然后把手中的耙子扔在地上，娟兒尖叫了一聲。我嚇傻了，想跑，但二表哥發現了我，我嚇得汗毛都豎了起來。二表哥跑過來，把我拉進柴垛后，我以為他想把我也殺死，但他只是讓我脫衣服，我害怕得要死，只好聽他的話。

在最新的DNV GL有關浮式風機的規范中指出[10]，錨鏈斷裂等故障工況，應該在設計工況中考慮。……