正常的眼內壓（Intraocular pressure, IOP）是維持眼球正常形態的一種非常重要的因素，異眼內壓的形成是指眼球內包含物對於如房水、晶狀體、玻璃體及眼內血容量對於眼外壁施加的一種均恆穩定力量，維持眼窩一個比較恆定的數值，讓眼球中各種透明趨光質發揮最大的光學性質，常的眼內壓和眼科疾病之間是有一定的相關和影響性，若眼壓長時間高於或低於正常平均值，對於視覺功能容易造成傷害性的影響，例如青光眼（glaucoma）的發生便是常見的例子，然而異常性眼壓的異常不單指高眼壓，低眼壓也視為其中之一，臨床眼科對低眼壓的定義是，眼內壓平均低於5mmhg或其眼壓低於平均值30％以下，即處於低眼壓的狀況，目前研究多著墨於高眼壓所造成的影響，不同造成高眼壓的動物模式也不斷被討論及研究，但相對於研究低眼壓則少有學者關注，尤其在形態上更乏人問津，恩此我們將利用大白鼠睫狀體剝離後，造成大白鼠眼內壓壓下降，利用穿透式及掃瞄式電子顯微鏡去觀察大白鼠眼球長時間處於低眼壓狀況下，其形態上的變化。實驗前一週，由國家動物實驗中心購得30隻6到8週，250公克Wistar品系雄性大白鼠，飼養於中山醫學大學動物實驗中心以腹腔注射，4%水合氯醛（chloral hydrate）方式麻醉大白鼠，並至於立體定位儀上，在解剖顯微鏡下將折成30度彎曲的27號針頭，自結膜後方1mm處插入將眼球睫狀體做180度睫狀體的離斷，並避免有任何大量出血的情形。並利用電子顯微鏡觀察處於低眼壓環境下兩週內，視網膜及視神經的變化。實驗結果中，視神經纖維外觀開始異常，神經纖維明顯膨大的現象產生，隨著低眼壓情形的持續一週後，腫大的程度也越來越明顯(P<0.05)，並且有空泡化的現象，另外，神經髓鞘由原本明顯緊密狀，也變得較為鬆散，有空泡在其中，二週後，軸突的分佈密度明顯減少(P<0.05)。而視網膜節細胞在低眼壓環境下，外觀在大小較對照組有明顯增大，並有許多凹凸面，相較對照組而言顯得較為粗糙，以及周圍軸突變短、變粗，且突觸周圍的髓鞘變的鬆散，內含有空泡化，使得軸突的完整性被破壞。因此，藉由我們的觀察透過動物實驗模式發現長期低眼壓下可引起視網膜結構上病理性的改變，造成組織的損傷，進而影響功能上的表現。
Low-tension Glaucoma was a progressive optic neuropathy with characteristic optic disc changes, retinal ganglion cell loss and progressive visual field defects; Clinical case report publicized that traumatic cyclodialysis would reduce intraocular pressures(IOP>30%), maculopathy and visual function degeneration. The present study was aimed to observe the cyclodialysis rat of model morphology change with transmission and scanning electro-microscopic approaches.
30 adult male Wistar rats(8~12wks/300g) IOP was measured in awake using a calibrated Tonopen XL- tonometer. in normal eyes resulted in an average 27 +/- 5%mmHg. Unilateral cyclodialysis used 28-gauge hypodermic needle and orienting the spatula hugging the sclera to strip the iris root attachment away from the sclera. After surgery, The animal model eye ball was been hypotony as average an intraocular pressure (IOP) at or below 5 mmHg. (Table. 2) and experience side IOP trimmed down more than 30%(4mmHg+/- 5%) and measured IOP at the same time every day.
The present results indicated that following 2 weeks unilateral cyclodialysis. We detected retina and optic nerve each three days in EM. After operation, the density of ganglion cell was lessen and axon were significantly less than in the control eyes.(control 63.1%+ 2.1%, exp 28.5%+3.4%, P<0.05) The optic nerve neuron to be abnormally enlarged and swollen , axon were characterized by accumulation of organelles, vacuole, cell shape was transformed.
Based on these histological findings, unilateral cyclodialysis drop off IOP for some time, affect the retina cell death and optic nerve degeneration in morphology that could influence the visual function loss.
