Zoumalan Christopher I, Agarwal Madhu, Sadun Alfredo A
Doheny Eye Institute and the Department of Ophthalmology, Keck School of Medicine, University of Southern California, 1355 San Pablo St, DVRC 311, Los Angeles, CA 90033, USA.
Graefes Arch Clin Exp Ophthalmol. 2005 May;243(5):410-6. doi: 10.1007/s00417-004-1053-1. Epub 2004 Nov 23.
To map and identify the pattern, in vivo, of axonal degeneration in ethambutol-induced optic neuropathy using optical coherence tomography (OCT). Ethambutol is an antimycobacterial agent often used to treat tuberculosis. A serious complication of ethambutol is an optic neuropathy that impairs visual acuity, contrast sensitivity, and color vision. However, early on, when the toxic optic neuropathy is mild and partly reversible, the funduscopic findings are often subtle and easy to miss.
Three subjects with a history of ethambutol (EMB)-induced optic neuropathy of short-, intermediate-, and long-term visual deficits were administered a full neuro-ophthalmologic examination including visual acuity, color vision, contrast sensitivity, and fundus examination. In addition, OCT (OCT 3000, Humphrey-Zeiss, Dublin, CA) was performed on both eyes of each subject using the retinal nerve fiber layer (RNFL) analysis protocol. OCT interpolates data from 100 points around the optic nerve to effectively map out the RNFL.
The results were compared to the calculated average RNFL of normal eyes accumulated from four prior studies using OCT, n=661. In all subjects with history of EMB-induced optic neuropathy, there was a mean loss of 72% nerve fiber layer thickness in the temporal quadrant (patient A, with eventual recovery of visual acuity and fields, 58% loss; patient B, with intermediate visual deficits, 68% loss; patient C, with chronic visual deficits, 90% loss), with an average mean optic nerve thickness of 26+/-16 microm. There was a combined mean loss of 46% of fibers from the superior, inferior, and nasal quadrants in the (six) eyes of all three subjects (mean average thickness of 55+/-29 microm). In both sets (four) of eyes of the subjects with persistent visual deficits (patients B and C), there was an average loss of 79% of nerve fiber thickness in the temporal quadrant.
The OCT results in these patients with EMB-induced optic neuropathy show considerable loss especially of the temporal fibers. This is consistent with prior histopathological studies that show predominant loss of parvo-cellular axons (or small-caliber axons) within the papillo-macular bundle in toxic or hereditary optic neuropathies. OCT can be a valuable tool in the quantitative analysis of optic neuropathies. Additionally, in terms of management of EMB-induced optic neuropathy, it is important to properly manage ethambutol dosing in patients with renal impairment and to achieve proper transition to a maintenance dose once an appropriate loading dose has been reached.
使用光学相干断层扫描（OCT）绘制并识别乙胺丁醇所致视神经病变中轴突变性的模式及体内情况。乙胺丁醇是一种常用于治疗结核病的抗分枝杆菌药物。乙胺丁醇的一个严重并发症是视神经病变，会损害视力、对比敏感度和色觉。然而，在早期，当毒性视神经病变较轻且部分可逆时，眼底检查结果往往很细微，容易被忽视。
对三名有乙胺丁醇（EMB）所致视神经病变病史、分别有短期、中期和长期视力缺陷的受试者进行了全面的神经眼科检查，包括视力、色觉、对比敏感度和眼底检查。此外，使用视网膜神经纤维层（RNFL）分析方案，对每位受试者的双眼进行了OCT（OCT 3000，Humphrey-Zeiss，加利福尼亚州都柏林）检查。OCT对来自视神经周围100个点的数据进行插值，以有效绘制出RNFL。
将结果与之前四项使用OCT的研究（n = 661）中积累的正常眼睛的计算平均RNFL进行比较。在所有有EMB所致视神经病变病史的受试者中，颞侧象限神经纤维层厚度平均损失72%（患者A，视力和视野最终恢复，损失58%；患者B，有中期视力缺陷，损失68%；患者C，有慢性视力缺陷，损失90%），平均视神经厚度为26±16微米。所有三名受试者的（六只）眼睛中，上、下和鼻侧象限的纤维平均联合损失46%（平均厚度为55±29微米）。在有持续性视力缺陷的受试者（患者B和C）的两组（四只）眼睛中，颞侧象限神经纤维厚度平均损失79%。
这些EMB所致视神经病变患者的OCT结果显示有相当程度的损失，尤其是颞侧纤维。这与之前的组织病理学研究一致，该研究表明在毒性或遗传性视神经病变中，乳头黄斑束内小细胞轴突（或小口径轴突）主要损失。OCT可成为视神经病变定量分析的有价值工具。此外，就EMB所致视神经病变的管理而言，重要的是对肾功能损害患者正确管理乙胺丁醇剂量，并在达到适当的负荷剂量后正确过渡到维持剂量。
