A study on correlation between the disc damage likelihood sc
作者：Xiao-Bo Xia, Xia Zhou, Si-Qi Xiong, Wei-Tao Song, Pei-Gang Huang
【摘要】 To determine the correlation between the disc damage likelihood scale and visual field damage in patients with open angle glaucoma(OAG),and study the method of early diagnosis of OAG. METHODS: Optic nerves of OAG (31 cases,58 eyes) and suspected glaucoma patients (29 cases,58 eyes) were photographed using a digital stereoscopic camera system (Discam, Marcher, Ltd, U.K.). Disc damage likelihood scale (DDLS) stages in a screen Vu stereoscope .A system of the Humphrey Field Analyzer (program 30-2,USA) was used to obtain the mean deviation(MD) and pattern standard deviation(PSD) values. The correlations between DDLS and the visual field parameters was evaluated. Findings were assessed by the Pearson correlation coefficients.RESULTS: 116 eyes are with moderate optic nerves(2-3mm).In 58 eyes with open angle glaucoma, the DDLS was significantly correlated with MD (Pearson，r =-0.664,P <0.01) and PSD (Pearson，r =0.554, P <0.01). There was no significant correlation of these parameters in suspectious glaucoma patients. CONCLUSION: DDLS is significantly correlated with the degree of glaucomatous visual field damage in patients with open angle glaucoma, and thus it is helpful in early diagnosis of open angle glaucoma.
【关键词】 disk damage likelihood scale; visual field damage; glaucoma; open angle
INTRODUCTION
Open angle glaucoma (OAG) with its most salient characteristic sneaking is one of the ophthalmic diseases which give rise to blindness. Commonly used diagnostic methods for OAG consist of optic disc morphologic examination，intraocular pressure measurement and visual field test. Research indicates that 50% of retinal nerve fiber layer (RNFL) defect affirmed by histopathological examination occurs when the RNFL defect can be detected by the human eye[1] , while detectable change of visual field is always five years later than the defect of optic nerve fiber. Since the impairment of visual function is irreversible, it is very important to monitor the extent of optic disc damage and the defect of RNFL for early diagnosis and management of OAG.
Cup/disk ratio(C/D ratio) which is related to visual field impairment, is the most commonly used method in clinical practice to measure the amount of optic disc damage. This method has its own shortcoming i.e. it is the individual observer's subjective assessment of the cop/disc ratio which may vary from one observer to another. If this can be assessed objectively, the extent of damage of optic disc (indirectly amount of RNFL damage) will be same by any observer. Consequently, a novel method which is sensitive and practical to evaluate and diagnose OAG should be put forward. Compared to C/D ratio ,disk damage likelihood scale(DDLS) depicted by Spaeth[2] is an objective and sensitive method to evaluate the degree of optic disc damage. However, reports using DDLS to diagnose OAG haven't come up with domestically until now. Our research adopted DDLS associated with visual field test to examine patients of OAG and persons in whom glaucoma was suspected, so as to explore correlation between DDLS and visual field impairment and its value in early diagnosis of OAG.
PATIENTS AND METHODS
Patients Sixty Patients(116 eyes) diagnosed as open-angle glaucoma (31 patients with 58 eyes , mean age 37.94±16.34, range 16-72 years) and suspected glaucoma(29 patients with 58 eyes , mean age 23.38±14.64, range 9-65 years) in the outpatient between May 2003 and May 2004 were included in the study. 37 patients ( 70 eyes )were male, while 23 ( 46 eyes )were female. All the cases included in the study met the following diagnostic criteria:(1)Open angle glaucoma : included normal tension glaucoma, primary open angle glaucoma and developemental glaucoma as per the criteria recommended by the Chinese Glaucoma Academic Group. Two normal tension glaucoma patients (4 eyes), nineteen primary open angle glaucoma patients (37 eyes) and ten developmental glaucoma patients (20 eyes) participated in our study. (2)Suspected glaucoma: a. Intraocular pressure greater than 21mmHg (at least measured twice by Goldmann tonometer) . b. Cup/disc ratio more than 0.6 or difference of C/D ratio between two eye greater than 0.2. c. Visual field impairment.or family history of glaucoma
A person was suspected with glaucoma if any of above three items manifest, excluding ocular hypertension, visual field damage from other diseases, blurred optic disc morphology arising from opacity in refractive media and any optic disc variability.
Instruments and Methods
Disc damage likelihood scale Pupil of patient was dilated to more than 5 mm diameter using 5% neosynephrin. Two clear stereo photographs of optic nerve (posterior pole of fundus 20°×20°, 512×512 pixels) were taken with digital stereoscopic camera system[3] (Discam, Marcher, Ltd. U.K.) and analyzed through Utilizing screen Vu stereoscope to confirm the radial width of the rim measured at its narrowest point compared to the vertical diameter of the disc. When there is no rim remaining, the circumferential extent of rim absence (0 rim/disc ratio) was measured in degrees. Average disc size is 2-3 mm; based on which DDLS staging was carried out to the patients included in our study (Figure 1) .
Figure 1 Drawing rim of optic disc and optic cup by utilizing screen Vu stereoscope based upon image of optic disc derived from digital stereoscopic camera system (Discam, Macher, Ltd. U.K.). Rim/disc ratio could be calculated automatically by computer. When it comes to no rim remaining , circumferential degree of rim absence will be displayed on the computer screen by shifting cursor, based on which DDLS stage could be obtained according to the following table 1
Method for visual field test and analysis A system of the Hemphrey Field Analyzer (HPA ，program 30-2) was used to obtain the mean deviation (MD) and pattern standard deviation (PSD) value. According to Johnson [5] six criteria are taken into consideration for the visual field loss: (1) PSD worse than the normal 1% level, (2) GHT outside normal limits, (3) one hemifield cluster worse than the normal 1% level, (4) two hemifield clusters worse than the normal 5% level,(5) four pattern deviation locations worse than the normal 5% level, and (6) five pattern deviation locations worse than the normal 5% level on the pattern deviation probability plot for two successive visual field examinations.
Excluding criteria for visual field analysis were fixation losses of more than 30% ,a false-positive and false-negative rate of greater than 20%.
Statistic methods Linear correlation and linear regression analysis between DDLS stage and both mean deviation and pattern standard deviation value were performed using SPSS11.0 software, while the correlation between the DDLS and Hemphrey Field Analyzer (HFA) visual field staging system was evaluated using the Spearman correlation test, from which the finding was assessed by the Pearson or spearman correlation coefficients.
RESULTS
A strong inverse correlation was found between DDLS and MD (Pearson,r =-0.664, P <0.01; Linear regression equation between DDLS and MD:DDLS=2.420+(-0.123MD) as shown in Figure 2, and a strong positive correlation was found between the DDLS stage and pattern standard deviation (Pearson, r =0.554, P <0.000).Linear regression equation between DDLS and PSD: DDLS=2.178+0.198PSD in glaucoma as shown in Figure 3), while no correlation of these parameters was found in suspected glaucoma. (Table 2).
Thirty seven percent of patients with open angle glaucoma (10/27) showed normal visual field compared to 90% (27/30) of patients with suspected glaucoma in DDLS stage 3, while 10%(3/30) of suspected glaucoma patients with visual field damage were in DDLS stage 3 to 7; indicating that the more optic nerve destroyed, the visual field damage was severe.
Figure 2 Scatterplot of relationship between mean deviations of the visual field and the DDLS. The horizontal axis shows the mean deviation of the Humphrey 30-2 field analyzer, and the vertical axis shows the DDLS stage
Figure 3 Scatterplot of relationship between pattern standard deviations of the visual field and the disk damage likelihood scale (DDLS). The horizontal axis shows the pattern standard deviation of the Humphrey 30-2 field analyzer and the vertical axis shows the DDLS stage
DISCUSSION
Besides visual field test and intraocular examination, optic disc morphologic examination is another important constitutional component which contribute greatly to diagnose glaucoma. At present, Armdy C/D ratio , a kind of optic disc morphologic examination associated with visual field damage, is a frequently- used method for diagnosing glaucoma in clinical practice[6]. Nevertheless , C/D ratio has the following three shortcomings[2]: (i) there is no direct description of actual damage extent occurring on the optic disc in glaucoma patient (focal rim thinning or notching and optic disc physiological variability), (ii) it does not consider the effects of optic disc size, which may affect the ability to detect glaucomatous damage, (iii) the reliability and the repeatability are not high. If C/D ratio is regarded as only diagnostic marker, larger discs and slope discs are more likely to have large C/D ratios and, as such, be classified as glaucomatous, while small disks are more likely to be classified as normal. Accordingly, the C/D ratio inadequately describe the critical feature of glaucomatous optic neuropathy. Latest study indicate that the neuroretinal rim area is an optic disk variable shown to be superior to the C/D ratio in its correlation with visual function and its ability to differentiate between normal eyes, eyes with suspected glaucoma, and eyes with early glaucoma. But, a disk having a normal neuroretinal rim area may have focal rim thinning or notching that causes underestimation of the severity of glaucomatous impairment. Disc damage likelihood scale is a classification scheme which not only take the optic disc size into consideration but also grade damage extent of the optic disks from no damage to progressive damage according to the radial width of the rim measured at its narrowest point compared to the diameter of the disc in the same axis (rim/disc ratio) or the circumferential amount of rim absence, for which shortcoming of C/D ratio and neuroretinal rim area is averted. Rudimentary research regarding to DDLS indicate that DDLS is a kind of new method which is reproducible, reliable and user-friendly in diagnosing patient with glaucoma[6]. Furthermore, DDLS is greater than both C/D ratio and neuroretinal rim area to estimate the amount of disc damage in patients with glaucoma.
Reliable morphological marker for diagnosing glaucoma should highly correlate with visual field damage[7]. Bayer [8] found correlation of DDLS with MD and PSD in patients with primary open angle glaucoma, low tension glaucoma and in whom glaucoma was suspected. When glaucoma patients and suspected glaucoma persons were evaluated separately, we discovered that DDLS highly correlated with MD,PSD in glaucoma group, whereas no correlation were found between DDLS and visual field indices (MD,PSD) in suspected glaucoma group ,which supposedly associated with large C/D ratio and mild visual filed damage.
In DDLS staging system, the ratio of radial width of the rim measured at its narrowest point compared to the diameter of the disc in the vertical axis (always no greater than 0.5), the large ratio indicate less optic nerve impairment. Stage 0 stand for no damage occurring in optic disc with ratio mentioned above between 0.5 to 0.4, stage 1 or 2 represent probable optic disc impairment with ratio varied from 0.3 to 0.2, while stage 3 to 7 indicate damage of optic disc certainly exists ,in which ratio is no more than 0.2 or no neurorim exist.In the fowllow-up we found that 37% patients with glaucoma (10/27) was manifested normal visual field compared to 90% (27/30) patients with suspected glaucoma in DDLS stage 3, while 10%(3/30) of suspected glaucoma patients with visual field damage,so DDLS is superior to visual field test for finding early damage of glaucoma . From DDLS stage 3 to 7, the more optic nerve destroyed, the severer is the visual field damage. Therefore, patients with DDLS stage 3 to 7 should receive appropriate treatment due to their severe retinal nerve fiber damage.
As a novel method to evaluate the amount of optic disc damage, DDLS stage with its accordance with visual field indices and Hemphrey Field Analyzer staging system's (HFASS) stage superior to both C/D ratio and neuroretinal rim area in offering the damage extent of optic disc. Consequently, substitution of DDLS for imperfect C/D ratio as a method for diagnosing open angle glaucoma could permit its detection more accurately rather than roughly. When retinal nerve fiber layer defect and neuroretinal rim area are analyzed by utilizing optic disc imaging system in clinical practice , DDLS should be applied as a test marker so as to enhance diagnostic rate of early open angle glaucoma. During the course of DDLS staging, caution must be taken to differentiate the actual absence of rim from sloping of the disc, for example, in some patients with myopia this can happen on the temporal side because a sloping disc is not an absent rim.
When you apply simple but strong non-contact slit lamp lens to measure vertical disk diameter, radial width of rim of narrowest point, and diameter of the disc in the same axis through slit beam[4], which is followed in DDLS staging, you will find that this is simple and economical. Therefore, this should be utilized in the government hospitals and in hospitals with less financial support for evaluating optic disc impairment in place of expensive instrument such as optic disc imaging system to diagnose glaucoma. If progression of DDLS stage were detected during the follow-up ,patients could receive prompt and suitable treatment to avoid further damage of the optic disc. We are confident that diagnostic rate of early open angle glaucoma would be enhanced dramatically, when DDLS is applied in association with intraocular pressure and visual field test rather than using it alone.
【】
1 Quigley HA, Addicks EM. Quantitative studies of retinal nerve fiber layer defects. Arch Ophthalmol ,1982;100:807-814
2 Spaeth GL, Henderer J, Liu C, Kesen M, Altangeral U, Bayer A, Katz LJ, Myers J, Rhee D, Steinmann W. The disc damage likelihood scale: reproducibility of a new method of estimating the amount of optic nerve damage caused by glaucoma. Trans Am Opthalmol Soc ,2002;100:181-186
3 Singer HW. Discam data offers early, objective way to study glaucoma. J Ophthalmic Nurs Technol ,2000;19:62-63
4 Henderer JD, Liu C, Kesen M, Altangeral U, Bayer A, Steinmann WG, Spaeth GL. Reliability of the disc likelihood scale. Am J Ophthalmol ,2003;135:44-48
5 Johnson CA, Sample PA, Cioffi GA, Liebmann JR, Weinreb RN. Structure and function evalution(SAFE):I Criteria for glaucomatous visual filed loss using standard automated perimetry (SAP) and short wavelength automated perimetry (SWAP). Am J Ophthalmol ,2002;134:177-185
6 Hoskins HD Jr, Gelber EC. Optic disk topography and visual field defects in patients with increased intraocular pressure. Am J Ophthalmol ,1975;80:284-290
7 Pan YZ, Li MY. The accordance of optic disc rim height in primary open angle glaucoma to visual field. Chin J Ophthalmol ,2000;36:275-277
8 Bayer A, Harasymowycz P, Henderer JD, Steinmann WG, Spaeth GL. Validity of a new disk grading scale for estimating glaucomatous damage: correlation with visual field damage. Am J Ophthalmol ,2002;133:758-763
