眼球之聲波動力學與訊號量測

Abstract

在此論文中，其目的為探討眼球受到聲波激發之動態力學反應，並進行眼球 之基本訊號量測，將此應用於青光眼之預防與診療，目前在市面上以接觸式及侵 入式眼壓器居多，接觸式及侵入式眼壓量測技術包含觸碰式、氣吹式、超音波感 測以及應變規量測式，其中接觸式及侵入式之方法較容易使患者在進行眼壓測量 時造成不適與不便，故在此研發一非接觸式及非侵入式之方法以不會造成患者不 適的情況下進行眼壓量測，且在未來可提供臨床上之應用，可進行24 小時之眼壓 監控。 藉由建立眼球之數學模型來模擬眼球在人體上之動態力學反應，首先，設定 眼球之薄膜材料，然後建立眼球在人體之模型邊界條件，並且將眼球之初使形狀 加入到數學模型中，利用此模型得知眼球在不同之模態響應，再進行模態響應以 及特徵頻率之分析，並且選取適當操作範圍之特徵頻率進行實驗操作，眼球之機 械參數和幾何參數在數學模型中會影響特徵頻率之範圍，故在最後也藉由比較不 同參數下之模態響應以及特徵頻率之關係。 在檢體實驗中，主要分為四個部分，眼球之無眼皮掃頻實驗、重製性實驗、 以及有眼皮掃頻實驗和場型之測量，首先，眼球之無眼皮實驗是用來驗證此非接 觸式及非侵入式之方法是否具有可行性度第一步，藉由進行掃頻實驗來量測出特 徵頻率隨著眼球內部壓力之變化，藉由眼球之無眼皮實驗可知，運用非接觸式及 非侵入式之方法量測是可行的，故在眼球之重製性實驗中，藉由將眼球內部壓力 升高在將眼球內部壓力降低之方法來進行重製性實驗，觀察在同一眼球操作在不 同時間點且在相同壓力下，特徵頻率之分布是否有在一固定範圍來判斷實驗是否 具有重複性，眼球之有眼皮掃頻實驗是用於比較眼球之無眼皮實驗，此實驗目的 在於模擬人體之真實情況，在運用非接觸式及非侵入式之方法量測眼壓時，判斷 患者眼睛閉上與否會不會造成眼壓量測時之誤差，藉由將眼皮覆蓋在眼球表面來 進行掃頻實驗，掃頻實驗在此論文中以驗證不同之模態響應，首先，假設眼球為 軸對稱之球體，故可將眼球簡化為二維結構，眼球在不同的壓力下進行掃頻實驗 會產生出不同之模態響應，在不同的模態響應下會產生出不同的場型，藉由環狀 機構來量測在眼球在不同角度下之訊號強度來建立場型之分布，且利用此場型之 iii 結果，就可驗證之後在不同眼球進行掃頻實驗時是在哪一模態響應。 在動物性實驗中，受體以兔子為主，量測兔子在一天之眼壓波動，在開始進 行動物性實驗前，進行了兩個星期的白日與夜晚的調整，早晨七點時會將兔籠外 的燈光打開，並且在晚上七點時會在兔籠外面罩上黑色的布，以這樣的方式使兔 子漸漸培養早上七點至晚上七點是屬於白天和晚上七點至隔天早上七點會是屬於 晚上的習慣，在實驗過程中藉由將激發元件貼附在兔子之眼球和耳朵之間的皮膚 上進行激發，運用激發元件之振動促使兔子之頭顱振動，此時，眼球周圍產生盆 地效應，產生匯聚能量之現象，且因為眼球周圍組織之幾何分布，訊號由眼球正 前方射出，此時所發射之訊號因為兼具眼框特徵、玻璃體、水晶體和角膜特徵， 故透過接收並分析，則可得知兔子眼球之模態響應與特徵頻率，並藉由特徵頻率 在一天的分布來分析兔子一天的眼壓波動。 由檢體實驗結果可看出，運用一非接觸式及非侵入式之方法來進行眼壓之量 測是具有可行性的，且利用重製性實驗來強調此方法是可以重複進行量測眼球之 特徵頻率，並且可加以運用在臨床實驗，在另一方面，患者是否將眼睛睜開都不 會嚴重的影響實驗，故此技術是可以運用在晚上進行量測的，在晚上量測的過程 中，不需要將患者叫醒即可進行眼壓之量測，不僅可以減少先前患者進行量測時 之不便與不適，也可以運用在平日進行眼壓之量測，此外，運用此方法進行動物 性實驗有了初步的結果，可輕易的利用眼球之特徵頻率來描述兔子在一天之眼壓 波動。

This thesis is to discuss the response of eyeball which is activated by acoustic in-depth exploration. We aim to develop a non-invasive and non-contact real–time IOP monitoring system, which is used to prevent and diagnose the symptom of glaucoma. Nowadays, the majority of detecting devices are invasive and contact-based, such as applanation tonometer, air-puff tonometer and contact lens tonometer and etc. The methods of invasive and contact-based are often uncomfortable and inconvenient to patients. Therefore we develop a non-invasive and non-contact technology of acoustics to conduct the 24-hours IOP monitoring. By establishing the mechanical model of eyeballs, we can simulate the human eye. First, we choose the material of mechanical model then establish the boundary conditions of human eye, and then we combine the influence of the initial curvature to the mechanical model. Thus, we have the access to obtain the response in different mode shapes and analyze the correlation between mode shapes and characteristic frequencies. Different mechanical parameters of eyeballs will induce different response of mechanical model as well, so, we can compare with the variables of Young’s modulus, radius and thickness, further to analyze the difference of mode shapes. In vitro experiment can be separated into four parts as follows: in vitro experiment without eyelid, the repeatability of in vitro experiment, in vitro experiment with eyelid and the radiation field experiment. We use the in vitro experiment to confirm whether the method of non-invasive and non-contact is feasible or not, and detect the characteristic frequency by spectrum sweeping. Via in vitro experiment, on the other hand, the repeatability of in vitro experiment reveals the trend of the characteristic frequency which increases gradually with the increased pressure then decreases v constantly with the decreased pressure. The results of the IOP fluctuation show a similar trend to the characteristic frequency. Therefore, we confirm that in vitro experiment can be conducted repeatedly, and the clinical experiment is feasible. Besides, in vitro experiment without eyelid is used to compare with in vitro experiment with eyelid. By analyzing the difference between the experiment of with eyelid and without eyelid, we determine whether patients open their eyes or close their eyes would influence the results during the clinical experiment. On the other hand, the radiation field reveals different properties of field in different mode shapes. The experiment confirms that different pressure in eyeballs will induce different mode shapes during activation, and by observing radiation field, we can determine whether the characteristic frequency belong to the eyeball or not. In the animal experiment, our purpose is to observe the IOP fluctuation on rabbit by using the non-invasive and non-contact method. Four experiments show the similar trend of IOP fluctuation during four weeks. The IOP fluctuation which is detected by using the non-invasive and non-contact method maintains in a stable fluctuation which is located at the low level in diurnal period and at the high level in nocturnal period. In the first week, the trend of the characteristic frequency and the IOP display the same circadian rhythm, but the correlation between them is not quite match. So subsequently, we enhance the quality of experiment, and the correlation in week 2 to week 4 become more obvious in IOP fluctuation between the characteristic frequency and IOP, so we can further observe the IOP fluctuation on rabbits in circadian rhythm certainly.