轉斜眼球運動是利用內直肌與外直肌使眼球同時向內(convergence)或向外(divergence)轉動，使我們能夠感知到不同距離的物體。
Convergence insufficiency (CI)的病患往往有頭痛、模糊視覺、複視以及眼睛疲勞等症狀。此類的患者同時也會表現出有高度的外隱斜視(exophoria)、眼球內聚的能力減弱、眼球可以凝視的範圍減少等現象。 他們轉斜眼球運動與正常人相比之下呈現出較慢的動態。在臨床上，視覺治療(Vision therapy)被用來減輕病患的症狀，它能夠減少隱斜視(phoria)的程度、增加眼球可以凝視的範圍以及恢復眼球內聚的能力。視覺治療確實幫助病人減輕了症狀，但是並沒有太多的科學去研究跟其相關的機制。同時，關於轉斜眼動的神經控制機制至今仍存在著爭議。本研究的目的是研究與轉斜眼動相關的神經控制機制以及比較一些已經建立好的轉斜眼動模型。本研究所提出的方法將可以針對CI病人的進行研究。
本研究中總共包含三個主題，第一個主題對於divergence進行了量化分析同時也研究了divergence 跟convergence對於平滑移動的目標、純步階目標還有短暫停留的步階目標所產生的反應。第二個主題研究了在眼球適應於不同的凝視位置所產生的眼動動態改變。在第三個研究中我們重建並比較了兩個不同的轉斜眼動(vergence)模型。
在divergence的量化結果中，我們發現了眼球在追描一個平滑移動的目標時，眼球表現出了平滑追瞄同時伴隨一些類步階(step-like)的動態反應，而這些類步階的動態反應與純步階(step)的動態反應有相似的主程序(main sequence)關係。另一方面，這個類步階反應的動態跟它所開始的起始位置有相關。最後我們也發現了在進行divergence時，對於純步階目標還有短暫停留的步階目標所產生的動態反應也表現出相似的主程序關係。在對於phoria adaptation的研究中，我們使眼球適應於不同的凝視位置而產生phoria adaptation，並發現此反應造成divergence暫態成分動態上的改變。而divergence動態上的改變與視覺目標的初始位置相關。在第三個研究的結果中顯示，我們所重建的兩個模型都能夠經由適當的參數調整而得到合理的動態反應，而其中使用到preprogrammed成份的模型在模擬不同振幅的反應時需要較少的修正。兩個模型都沒有辦法模擬雙重步階(double step)跟開迴路(open loop)的動態反應。
在本研究當中所使用的分析方法可以應用於有視覺異常的病人。藉由分析在視覺治療前後的動態改變，可以幫助我們更加了解視覺治療對於視覺系統所產生的影響。因為我們更加的了解關於視覺系統的控制機制，希望本研究的成果能夠更進一步的幫助病人的診斷與治療。

Vergence eye movements enable depth perception utilizing the medial and lateral recti muscles to rotate the eyes inward (convergence) or outward (divergence). Patients with convergence insufficiency (CI) report symptoms such as headache, blur, diplopia and eye strain. They show high exophoria, receded near point of convergence and reduce fusional range. Their symmetrical disparity vergence movements have reduced dynamics compared to healthy controls. Vision therapy is used to remediate patient’s symptoms resulting in a reduced phoria level, increased fusional ranges and reduced near point of convergence. Vision therapy helps patients yet there is little science investigating the mechanism behind the improvement. Furthermore, controversy exists in the literature about the basic neural control of vergence eye movements. The purpose of this research is to study the basic science of vergence eye movements and compare the established models. Three studies are involved in this thesis. The first study sought to quantify divergence eye movements and differences between divergence and convergence to smoothly-moving ramp, step and disappearing step stimuli. The second study sought to study how sustained convergence over a range of positions influenced disparity divergence eye movements generated from two different initial positions, one near and one far. The third study constructed and compared two established models of vergence, a switched-channel feedback model and a dual-mode configurative model consisting of a preprogrammed element in parallel with a continuous feedback loop.
Our quantification of divergence eye movement shows that 1) a smooth tracking behavior was observed for slow ramps while the fast ramps elicited smooth tracking combined with a high-velocity, step-like behavior, 2) the high-velocity components observed in the faster ramps had a similar main sequence as divergence steps, 3) divergence dynamics to disappearing steps starting at the subject’s near dissociated phoria level were similar to corresponding step responses and 4) the high-velocity components from divergence ramps were dependent on initial vergence position, whereas the high-velocity components from convergence ramps were not. The phora adaptation study shows that 1) phoria adaptation induced by sustained convergence over a range of different positions causes nonlinear changes in divergence transient dynamics and 2) the modification of divergence was dependent on the stimulus initial position. Our comparison on two vergence models indicates that after parameter adjustments, both models could accurately simulate step responses of subjects with a range of response dynamics. The model with a preprogrammed element required less modification when stimulus amplitude changed. Neither model could simulate the naturally occurring double responses nor the open-loop data reported in the literature.
The analysis techniques in this thesis provide new methods to study the dynamics of eye movements in patients with vision dysfunction. By analyzing the dynamics of eye movements before and after vision therapy, the effect of vision therapy can be better understood and may result in more efficient and personalized treatments for improving the vision function in patients.

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