中国人前房深度、van Herick比率和前房角镜的关系
眼视光学杂志 1999年第1期第1卷 专稿
作者：Yap MKH,Brown B
关键词：前房深度；前房角镜；中国人；van；Herick比率
The relationship between the anterior chamber depth,van Herick ratio and the gonioscopic angle: findings in the Chinese eye
Yap MKH1, Brown B2
Abstract The van Herick test is widely used to estimate the width of the anterior angle.Recent studies suggest that the peripheral corneal radius may be smaller in Chinese eyes than in Caucasian eyes.If this is the case,then the established relationship between the van Herick test and gonioscopy which has been shown for Caucasian eyes may not be applicable to Chinese eyes. In this study,we graded the anterior angles in 101 Chinese subjects using the van Herick test and gonioscopy .Our results suggest that the van Herick test over-estimates angle width compared to gonioscopy .
Key words The anterior chamber depth The gonioscopic angle The chinese van Herick ratio
摘 要 目的： van Herick介绍了一种用来评估前房角的方法，该方法为评价前房角的非侵犯性方法，它无需表面麻醉或特殊设计的接触镜，将裂隙光束投到角膜和巩膜之间，通过比较角巩缘光束和虹膜投影宽度来估算前房角宽度。假如虹膜投影光带宽度比角膜宽度小25%以上，该眼就有房角关闭的危险，需要用前房角镜观察。van Herick试验一直被广泛使用至今。van Herick等曾表示该试验与前房角镜所见有着很高的符合率。最近的研究表明，中国人的眼睛前段特点与白色人种相比，有些不同，尤其是角膜周边曲率较陡，角膜直径较小。如果事实如此，则基于白色人种而得出的van Herick试验与前房角镜的关系就有可能不适用于中国人，为此需作进一步的临床验证。方法：①检测对象为101例中国人，年龄19～75岁(平均：51.9±15.7岁)，女性59例，男性42例。健康状态良好，并排除眼部异常和疾病。②采用摄影法评价van Herick比率。使用van Herick 等所述的可摄影裂隙灯显微镜，用透明胶片(Ektachrome 200)拍摄右眼角膜的鼻侧和颞侧照片。将透明片投影到屏幕上，通过测量角膜光带宽度和角膜后表面到虹膜的距离，由此推算出van Herick比率。③采用Haag Streit双平面镜前房角镜方法观察右眼前房角，按照Scheie描述的分级标准将前房角进行分级；④采用A超(日本Nidek Echoscan US-2000)检测右眼各组成成分之间的距离。并检测视力、屈光不正、瞳孔大小、角膜曲率和眼压等。结果 ：van Herick比率与前房角镜所见的结果相关性为：鼻侧0.53(P＜0.01)，颞侧0.50(P＜0.01)。van Herick法观察到的前房角宽度比用前房角镜观察到的宽，如果前房角镜法被认为是“金标准”，van Herick法所得的前房角结果偏宽。前房深度与各van Herick法各区域的分级无显著差异。当将年龄和屈光不正稳定控制好时，鼻侧和颞侧的van Herick比率和前房角镜观测结果、IOP、前房深度等方面男女性别之间并无差别。眼内压与角膜曲率、前房深度和暗环境的瞳孔直径轻度相关。结论 ：在评价前房角宽度时，采用van Herick法和前房角镜法，所得结果相关。然而，这些相关性仅能说明和解释与测量有关的28%和25%变异。van Herick法所得的结果比用前房角镜法所得的结果大。因此提醒临床医师要注意 van Herick法的结果的误差倾向，如出现 van Herick法的结果值得怀疑时，则有必要作前房角镜检查。(翻译：俞阿勇)
van Herick et al. described a non-invasive procedure which enables the examiner to assess the anterior angle without the need for topical anaesthesia or specially designed contact lenses. The angle width is estimated by comparing the width of the corneal section at the limbus with the width of the shadow cast by the illumination slit beam between the cornea and iris. van Herick et al. suggested that if the width of this shadow is less 25% of the width of the cornea, the eye may be at risk from angle closure and gonioscopic examination is indicated. This test is now widely referred to as the van Herick test. van Herick et al. suggested this test agreed closely with gonioscopic findings but did not present any data to support this claim［1］.
Recent studies suggest that the anterior segment characteristics of the Chinese eye may be slightly different from those of the Caucasian eyes.In particular,the radius of the peripheral cornea may be steeper and the corneal diameter smaller in Chinese eye than in Caucasian eyes［2,3］.The anterior chamber may also be shallower in Chinese eyes［4］.Although Oh et al［5］found no difference between the angle width of Caucasian, Afro-Americans and Asians, they noted that the iris joins the scleral wall more anteriorly in Asians, slightly more posteriorly in Afro-Americans,and most posteriorly in Caucasians.This may explain why primary angle closure glaucoma is more commonly found in the Chinese eye, compared to the Caucasian eye［5］.
With these factors in mind,we sought to establish the relationship between the gonioscopic appearance of the anterior angle,the van Herick ratio, anterior chamber depth and corneal radius in the Chinese eye.We also examined how these parameters relate to the intraocular pressure.
1 Subjects and Methods
1.1 Subjects One hundred and one subjects, aged between 19 and 75 years (Mean:51.9 years SD 15.7 years) participated in this study after informed consent had been obtained.There were 59 females and 42 males in the study. Subjects who were recruited were in good health and free from known ocular abnormalities or disease. Subjects were either students at the Hong Kong Polytechnic or patients who had attended the Optometry Clinic at the Hong Kong Polytechnic University.
1.2 Procedure For each subject, the following data and parameters were recorded from the right eye only:
1 From the department of Optometry %26 Vision Science
The University of Auckland.Auckland，New Zealand
2 From the department of Optometry %26 Radiography
Hong Kong Polytechnic University,Hong Kong
1.2.1 Refractive error data were obtained from the most recent clinical records. In all cases, these records were less than 12 months old.
1.2.2 Visual acuity was checked using the Bailey-Lovie chart.
1.2.3 To assess pupil size, we photographed the subject's right eye in the light(mean illuminance:105 lux)and in total darkness using Ektachrome 200 film.The transparencies were projected on a screen and the apparent pupil diameter measured using a millimeter ruler. This value was then adjusted for magnification to derive the true pupil diameter. A period of at least ten minutes was allowed betweed photographs to allow the pupil to return to the natural state for the prevailing room light level.
1.2.4 Corneal radius was measured using the SUN SK-2000 topographical keratometer(SUN Instruments,Japan).Three readings were recorded from the right eye and averaged to give the corneal radius.
1.2.5 Intraocular pressure was measured using an American Optical non-contact tonometer.Three readings were taken from the right eye and averaged to give the IOP value.
1.2.6 The van Herick ratio was assessed using a photographic method. With the photo slit-lamp biomicroscope set up as described by van Herick et al.［1］photographs were taken of the nasal and temporal sectors of the right cornea using transparency film(Ektachrome 200).The transparency was projected on a screen and the van Herick ratio derived by measuring the width of the corneal section and the distance between the posterior cornea to the surface of the iris. Each ratio was based on at least three measurements.The classification described by van Herick et al. was used to grade the ratios［1］.
1.2.7 A-scan ultrasonography(Nidek Echoscan US-2000,Nidek, Japan)was used to measure the distances between ocular components of the right eye.A local anaesthetic(1 drop,0.4% Benoxinate) was instilled before measurements commenced. The subject lay supine and was instructed to fixate a target directly overhead with the left eye. The handheld A-scan probe was gently placed on the cornea. Readings were automatically accepted by the A-scan system when the reflected echos were within the range expected by the machine. Five measurements were averaged for the right eye.From these measurements, we were able to derive the anterior chamber depth ,crystalline lens thickness, and vitreous for each eye.
1.2.8 Gonioscopy was performed on the right eye using a Haag Streit 2 mirror goniolens.A local anaesthetic was instilled on the eye (1 drop,0.4% Benoxinate)before the goniolens was placed on the cornea. Celluvisc(Allergan)was used as a lubricant between the goniolens and cornea.The angle was graded according to the classification described by Scheie［6］.Grades were established nasally, temporally,superiorly and inferiorly.All observations were performed by the same observer and were recorded on videotape for additional analysis and confirmation of the grading.
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