臺灣博碩士論文加值系統

我們用眼睛看物體時，光線行經角膜、水晶體，最後呈像在視網膜上。光線行進通過眼球構造，其影像面與平滑參考影像到達焦點時，會有快慢落差產生，稱之為像差(aberration)。像差的多寡是影響視網膜影像品質的重要因素：像差越大，影像越模糊。
　　角膜表面是產生像差的主要來源。角膜像差(corneal aberration)是眼球像差(ocular aberration)中最重要的一部分，其測量可以利用電腦輔助角膜圖譜攝影(computer-assisted videokeratography) 拍攝角膜圖譜，再利用軟體加以轉換及分析，以一組多階(orders)的Zernike 係數(Zernike coefficients , Znm)來表示。Zernike coefficients彼此之間為向量關係，各係數相加必需以向量方式計算，其結果為稱為 Root Mean Square - RMS，可以用來評估視覺品質。例如球面像差(SA)之RMS值＝ 。
　　近年來，對於像差的研究越來越多，原因是藉由新的測量儀器（例如角膜圖譜儀、像差儀aberroscope）及新的手術技術（如準分子雷射excimer laser），使得修正像差而增進矯正視力的夢想似乎越來越可行。除了臨床的應用方面，對像差的基礎研究也方興未艾：有研究指出角膜像差在個別眼睛上的變異很大，而在左右兩眼之間有高度的相關性。也有報告指出，部分角膜像差與年齡之間有正相關。但查遍文獻，尚未有角膜像差的遺傳方面報告，引起吾人研究的興趣。
　　雙胞胎一向被認為是研究遺傳方面的最佳對象。釵h家族和雙胞胎研究指出，屈光狀態(近視及散光)主要受到遺傳因素的影響；另外一些研究則指出，遺傳與環境因子均會影響屈光度數。而吾人對於角膜像差是否像屈光度數一樣受到遺傳因素的影響感到興趣，嘗試以雙胞胎為對象來進行研究。
　　共邀請52組雙胞胎(同卵30組及異卵22組)參與研究。以口腔黏膜細胞萃取DNA作胎性鑑定後，做一系列眼科檢查，包括：視力測量、自動電腦驗光、眼科超音波檢查、細隙燈檢查、角膜弧度測定及角膜圖譜攝影。角膜圖譜資料以CTView 軟體轉換成Zernike係數。分析及比較球面度數，散光度數，角膜弧度，角膜散光及角膜高階像差於同一人左右眼之間以及同卵和異卵雙胞胎之間的相關，並觀察上述變數與年齡有無關連性。
　　角膜圖譜及電腦驗光結果發現，不論是同卵或異卵雙胞胎，左右眼球面度數有高度相關，散光度數有中等程度的相關。我們推測，個別眼球的局部狀況（如眼皮鬆緊）或解剖位置（如水晶體位置）會影響左右兩眼散光度數的相關性。在角膜弧度與角膜散光方面，同卵雙胞胎的相關性均較異卵為高，顯示這方面可能受到遺傳因素的影響。這個結果較釵h西方國家（如英國、瑞典）的報告來的低，而和亞洲國家（如新加坡及本國）的報告相似，顯示人種及環境不同可能影響遺傳力的高低。同卵或異卵雙胞胎同一人左右眼的高階像差均有中等程度的相關。以雙胞胎之間右眼來分析，不論是同卵或異卵雙胞胎，也有中等程度的相關。以遺傳率來計算，僅只有球面像差(SA)受到遺傳因素的影響（遺傳率h2：0.44），其他高階像差與遺傳之關係尚無法由本研究確認。而球面像差所代表的是角膜中央部分的像差，是否在此部分遺傳因素有較明顯的影響力，需要再進一步的研究。
　　高階像差與年齡分析顯示，球面像差(SA)及慧星像差(coma)與年紀呈低度正相關。角膜弧度，角膜散光兩者與年紀無相關。
　　本篇是文獻上首篇探討角膜高階像差與遺傳之研究。由結果看來，角膜像差並非全部受到遺傳因素影響，環境因素及眼球表面狀態等可能也扮演了重要的角色。角膜弧度、角膜散光與球面度數則受到中、低程度遺傳因素的影響，環境可能仍然參與了大部分的表現。在左右眼相關性上，無論是球面度數、角膜弧度、角膜散光均有高度相關；而散光度數與角膜表面像差則有中等程度的相關性。

Purpose: To described a twin study to exam the heritability of the anterior corneal aberration and corneal curvature, and investigate the symmetry of corneal aberrations and refractive errors between in right and left eyes. Method: 30 monozygotic and 22 dizygotic twin pairs, ages 18 to 67 years, were invited to attend this study. An automatic refractor measured the refractive error, corneal curvature and corneal astigmatism. CTView program was used to compute anterior corneal aberration from corneal topographic data. The parameters of the corneal aberration included root mean square(RMS) of higher order aberrations(HOAs, 3rd to 6th orders), spherical aberration(SA) and coma. Result: High correlations were found between right and left eyes for spherical power, mean corneal curvature and cornel astigmatism (Pearson r > 0.9, all p< 0.01). Our data also demonstrated the existence of mirror symmetry of HOAs, SA and coma between right and left eyes of each individual.. The heritability of spherical power, corneal curvature, corneal astigmatism and SA was 0.2, 0.16, 0.42 and 0.42, respectively. Other anterior corneal aberrations did not present genetic effect. Conclusion: This is the first study to evaluate the genetic effect on the distribution of the anterior corneal aberration and our results proved a genetic predisposition in SA.

目 錄 1
摘要 2
第一章　緒論 4
　第一節　視學品質的評量 4
　第二節　像差的定義與測量 4
　第三節　角膜像差的計算及應用 5
　第四節　雙胞胎研究在遺傳方面的重要性 6
　第五節　角膜前表面像差及角膜散光與遺傳的相關性 7
第二章　材料及方法 9
　第一節　研究對象 9
　第二節　胎性鑑別 9
　第三節　眼科檢查 10
　第四節　資料分析 11
第三章　研究結果 12
　第一節　屈光度數與散光度數 12
　第二節　角膜弧度及角膜散光 12
　第三節　角膜表面高階像差的Zernike係數 13
　第四節　角膜弧度、角膜散光及角膜高階像差與年紀的相關性 14
第四章　討論 15
第五章　未來展望 18
第六章　英文簡述 20
第七章　參考文獻 24
第八章　圖表 28

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