Weinreb Robert N, Bowd Christopher, Greenfield David S, Zangwill Linda M
Glaucoma Center, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0946, USA.
Arch Ophthalmol. 2002 Jul;120(7):901-6. doi: 10.1001/archopht.120.7.901.
Scanning laser polarimetry uses a polarization compensator to isolate corneal birefringence from the birefringence of the retinal nerve fiber layer. This compensator assumes a fixed corneal polarization magnitude (CPM) of 60 nm and a fixed corneal polarization axis (CPA) of 15 degrees in all subjects.
To measure the CPM and CPA with a scanning laser polarimeter and to determine if the assumed compensation values are representative of those observed in healthy and glaucomatous eyes.
The CPM and CPA were measured in 51 healthy eyes and 55 glaucomatous eyes using a modified scanning laser polarimeter (GDx Nerve Fiber Analyzer; Laser Diagnostic Technologies Inc, San Diego, Calif) with an experimental variable CPM and CPA compensator. The CPM and CPA distributions in healthy and glaucomatous eyes were compared, and the CPM and CPA relationships with age, corneal thickness, and corneal curvature were also investigated. Nasally upward CPA values (in degrees) were recorded as negative; nasally downward CPA values were recorded as positive.
The CPM and CPA measurements were normally distributed with many eyes having values different from those assumed by the GDx corneal compensator. For healthy and glaucomatous eyes combined, CPM measurements ranged from 7 nm to 91 nm (mean +/- SD, 40.0 +/- 15.7 nm). The CPA measurements ranged from -13 degrees to 73 degrees (mean +/- SD, 24.5 degrees +/- 17.4 degrees ). A significant effect of age on CPA was observed when all eyes were combined (R(2) = 0.10; P<.001). There were no differences in CPM or CPA between healthy and glaucomatous eyes after adjusting for age. No effects of corneal thickness on CPM (R(2) = 0.04; P =.05) or CPA (R(2) = 0.01; P =.24) or of corneal curvature on CPM (R(2) = 0.002; P =.67) or CPA (R(2) = 0.009; P =.34) were observed.
The range of CPM and CPA values observed in glaucomatous and healthy eyes suggests that the narrow-band corneal compensator used by the GDx scanning laser polarimeter is inappropriately compensating for anterior segment birefringence in many eyes.
扫描激光偏振仪使用偏振补偿器将角膜双折射与视网膜神经纤维层的双折射区分开来。该补偿器假定所有受试者的角膜偏振幅度（CPM）固定为60纳米，角膜偏振轴（CPA）固定为15度。
使用扫描激光偏振仪测量CPM和CPA，并确定假定的补偿值是否代表健康眼和青光眼眼中观察到的值。
使用具有实验性可变CPM和CPA补偿器的改良扫描激光偏振仪（GDx神经纤维分析仪；激光诊断技术公司，加利福尼亚州圣地亚哥），在51只健康眼和55只青光眼眼中测量CPM和CPA。比较健康眼和青光眼眼中CPM和CPA的分布，并研究CPM和CPA与年龄、角膜厚度和角膜曲率的关系。鼻向上的CPA值（以度为单位）记录为负值；鼻向下的CPA值记录为正值。
CPM和CPA测量值呈正态分布，许多眼睛的值与GDx角膜补偿器假定的值不同。对于健康眼和青光眼眼的总和，CPM测量值范围为7纳米至91纳米（平均值±标准差，40.0±15.7纳米）。CPA测量值范围为-13度至73度（平均值±标准差，24.5度±17.4度）。当所有眼睛合并时，观察到年龄对CPA有显著影响（R(2)=0.10；P<.001）。在调整年龄后，健康眼和青光眼眼之间的CPM或CPA没有差异。未观察到角膜厚度对CPM（R(2)=0.04；P=.05）或CPA（R(2)=0.01；P=.24）有影响，也未观察到角膜曲率对CPM（R(2)=0.002；P=.67）或CPA（R(2)=0.009；P=.34）有影响。
青光眼眼和健康眼中观察到的CPM和CPA值范围表明，GDx扫描激光偏振仪使用的窄带角膜补偿器在许多眼睛中对眼前节双折射的补偿不合适。
