Hayreh Sohan Singh, Zimmerman M Bridget, Kimura Alan, Sanon Ashish
Department of Ophthalmology and Visual Sciences, College of Medicine, University Hospitals and Clinics, University of Iowa, 200 Hawkins Drive, Iowa City, IA 55242-1091, USA.
Exp Eye Res. 2004 Mar;78(3):723-36. doi: 10.1016/s0014-4835(03)00214-8.
To investigate the retinal survival time following central retinal artery occlusion (CRAO).
In 38 elderly, atherosclerotic and hypertensive rhesus monkeys, transient CRAO (varying from 97 to 240 min) was produced by temporarily clamping the CRA at its site of entry into the optic nerve. Stereoscopic color fundus photography, fluorescein fundus angiography, electroretinography (ERG), and visual evoked potential (VEP) recording were performed before and during CRA clamping, after unclamping, and serially thereafter. After unclamping of the CRA, the animals were followed for variable lengths of time (median duration 8.14 weeks). Finally, the eyes and optic nerves were examined histologically. The data on ERG changes were analyzed in the following four time frames: (1) baseline before CRA clamping, (2) during CRA clamping, (3) immediately after unclamping, and (4) at the end of follow-up. Duration of CRAO was divided into four groups: 97, 105-120, 150-165, and > or = 180 min.
A 'negative ERG' appeared during CRA clamping. With removal of the CRA clamp, there was b-wave recovery, with differential rates of recovery of ERG-eyes with shorter CRAO recovered sooner than those with longer occlusion. On removal of clamp, recovery was seen in scotopic 24 dB b-wave, photopic 0 dB single flash b-wave and 30 Hz flicker, with the b/a ratio of the combined rod and cone response and selective rod response showing statistically significant differences amongst the shorter and longer periods of CRAO. A delayed normalization of the depressed b/a ratio immediately after CRA reperfusion may indicate high-grade ischemic damage. At the final follow-up test session, no clear-cut derangement of any ERG parameter was seen for any group, with subtotal b-wave amplitude recovery for all groups. Longer CRAO produced incomplete VEP recovery. On histology, in the macular retina, eyes with CRAO for 97 min showed practically no damage, but duration of CRAO was found to be significantly associated with the amount of damage in the ganglion cell layer (p = 0.009) and inner nuclear layer (p = 0.017). Outer nuclear and plexiform layers and photoreceptors showed no damage at all with CRAO. There was no significant association of the ERG measures and histologic changes with any of the residual retinal circulation variables.
Our electrophysiologic, histopathologic and morphometric studies showed that the retina of old, atherosclerotic, hypertensive rhesus monkeys suffers no detectable damage with CRAO of 97 min but above that level, the longer the CRAO, the more extensive the irreversible damage. The study suggests that CRAO lasting for about 240 min results in massive irreversible retinal damage.
研究视网膜中央动脉阻塞（CRAO）后的视网膜存活时间。
在38只患有动脉粥样硬化和高血压的老年恒河猴中，通过在视网膜中央动脉进入视神经处临时夹闭该动脉，造成短暂性CRAO（持续时间从97分钟至240分钟不等）。在夹闭CRA之前、夹闭期间、松开夹闭后以及之后连续进行立体彩色眼底摄影、荧光素眼底血管造影、视网膜电图（ERG）和视觉诱发电位（VEP）记录。松开CRA夹闭后，对动物进行不同时长的随访（中位持续时间8.14周）。最后，对眼睛和视神经进行组织学检查。对ERG变化数据在以下四个时间框架内进行分析：（1）CRA夹闭前的基线水平；（2）CRA夹闭期间；（3）松开夹闭后即刻；（4）随访结束时。CRAO持续时间分为四组：97分钟、105 - 120分钟、150 - 165分钟以及≥180分钟。
在CRA夹闭期间出现“负性ERG”。随着CRA夹闭的解除，b波恢复，CRAO持续时间较短的ERG眼恢复速度比持续时间较长的眼更快。夹闭解除后，在暗视24dB b波、明视0dB单次闪光b波及30Hz闪烁光下可见恢复，CRAO持续时间较短和较长的组之间，视杆和视锥联合反应以及选择性视杆反应的b/a比值显示出统计学上的显著差异。CRA再灌注后即刻，抑郁的b/a比值延迟恢复正常可能表明存在高度缺血性损伤。在最后一次随访测试时，所有组均未发现任何ERG参数有明显紊乱，所有组的b波振幅均有部分恢复。CRAO持续时间较长导致VEP恢复不完全。组织学检查显示，在黄斑视网膜中，CRAO持续97分钟的眼睛几乎没有损伤，但发现CRAO持续时间与神经节细胞层（p = 0.009）和内核层（p = 0.017）的损伤程度显著相关。外核层、神经丛层和光感受器在CRAO时未显示任何损伤。ERG测量值和组织学变化与任何残余视网膜循环变量均无显著相关性。
我们的电生理、组织病理学和形态学研究表明，患有动脉粥样硬化和高血压的老年恒河猴视网膜在CRAO持续97分钟时未出现可检测到的损伤，但超过该水平后，CRAO持续时间越长，不可逆损伤越广泛。该研究表明，CRAO持续约240分钟会导致大量不可逆的视网膜损伤。
