Correlating of the visual field index with mean deviation and pattern standard deviation in glaucoma patients

Nội dung text: Correlating of the visual field index with mean deviation and pattern standard deviation in glaucoma patients

1. JOURNAL OF MEDICAL RESEARCH CORRELATING OF THE VISUAL FIELD INDEX WITH MEAN DEVIATION AND PATTERN STANDARD DEVIATION IN GLAUCOMA PATIENTS Bui Thi Huong Giang, Pham Thi Kim Thanh Department of Ophthamology , Hanoi Medical University The purpose of our study was to evaluate the correlation between the new index - visual field index (VFI) and mean deviation index (MD) and pattern standard deviation (PSD) in patients with glaucoma. MD, PSD and VFI were calculated in data about 103 eyes obtained from a cross-sectional study in 103 eyes of 58 patients with mild to severe glaucoma or ocular hypertension. The correlation of VFI to MD, PSD was evaluated with linear regression models, and the coefficient of determination (r) was calculated. The result showed that the average values of VFI, MD and PSD were 78.76%, -10.22 dB and 4.56 dB respectively. The VFI and the MD were linearly correlated with r = 0.984. For the patients with VFIs below 90%, the correlation with the MD was better than for the patients with VFIs 90% and above (r = 0.986 vs 0.571). There was no statistically significant difference in VFI value between the group with cataract and the group without cataract (p > 0.05) but MD varied significantly between these two groups (p < 0.05). For the PSD, the correlation for the patients with VFIs 90% and above was greater than for the patients with VFIs below 90% (r = -0.982 vs -0.196). In conclusion, VFI was linearly correlated with MD and PSD. VFI seems to be less affected by cataract than MD. Keywords: VFI, MD, PSD, visual field. I. INTRODUCTION In management of glaucoma patients, new index, introduced by Bengtsson B and the visual field (VF) is the most important Heijl A in 2008 [4]. The VFI expresses the tool to determine the stage and progression visual function as a percentage of normal of the disease [1]. VF data is summarized age-corrected sensitivity. Therefore, the VFI in global summary indices [2] . At this time, of an eye with a completely normal visual the mean deviation index (MD) and the pattern field is 100% and the VFI of a perimetrically standard deviation (PSD) are the standard blind eye is 0%. The VFI was designed using indices to evaluate for glaucomatous the Humphrey 30 - 2 and 24 - 2 test point damage [3]. The Visual Field Index (VFI) is a patterns, which are the most commonly used patterns in glaucoma management [3]. Corresponding author: Bui Thi Huong Giang, Depart- To avoid effects of cataract on the VFI, the ment of Ophthamology, Hanoi Medical University pattern deviation probability map was used Email: buihuonggiang@hmu.edu.vn to identify test points with normal sensitivity Received: 03 June 2017 (100%), having absolute defect (0%), and Accepted: 16 November 2017 68 JMR 111 E2 (2) - 2018
2. JOURNAL OF MEDICAL RESEARCH those demonstrating relative loss. The these deviations across all test locations. sensitivity at these points were scored using Mean defect expresses the difference the following formula: between observed and expected mean 100 - [(total deviationI/age-corrected sensitivity. MD expresses the overall normal threshold) x 100] , reduction in sensitivity, and is therefore where |total deviation| is the absolute decreased not only by increasing glaucoma, value of the numerical total deviation value but also by cataract [6]. Pattern standard and age-corrected normal threshold is deviation (PSD), a depiction of focal defects, intercept - age coefficient x patient age. measures irregularity between the threshold The VFI was also constructed to weigh value for each point and the average visual the central points of the visual field more field sensitivity at each point . Thus, in heavily than peripheral points. The VFI is patients with severely damaged visual fields the mean of all weighed scores in percent. the value of PSD is too low to be useful as The test point pattern was divided into five an indicator of severity of disease [7]. concentric rings of increasing eccentricity. Glaucoma is an ocular disease, in which Cortical magnification of any given visual characteristic visual field loss corresponds field location is assumed to reflect both to the underlying anatomic arrangement ganglion cell density and the number of of damaged retinal ganglion cells. neurons in an area of the visual cortex Glaucomatous visual field characterized responsible for processing a stimulus of a by loss is localized defects [8]. To stage given size [5]. The weights of the test points glaucoma, most classification systems use decreased with increasing eccentricity from MD, PSD, and the number of defective 3.29, 1.28, 0.79, and 0.57 to 0.45 at the points in the visual field test. However, the outermost ring. The VFI is automatically MD is affected by both glaucoma and media computed using in the current ‘‘Statpac opacities. Thus, cataract or media opacities software’’ of the Humphrey Field Analyzer can falsely inflate glaucoma severity. (HFA II; Carl Zeiss Meditec, Inc., Dublin, Bengtsson B and Heijl A used the pattern California, USA) (Fig.1) [4]. deviation probability maps in the visual field test to make the VFI test as resistant as possible to the effects of media opacities, while clearly depicting localized loss [4]. There are many studies concerning the VFI in the world [9;10]. The relationship between VFI and other visual field indices has not been studied in Vietnam. The objective of this study was Figure 1. Visual field of a glaucoma to evaluate the correlation between VFI patient and other visual field indices (MD, PSD) in Mean Deviation (MD) is the average of glaucoma patients. JMR 111 E2 (2) - 2018 69
3. JOURNAL OF MEDICAL RESEARCH II. SUBJECTS AND METHODS mean of the total deviation values, and the weight assigned to each location was 1. Subjects the inverse of the variance in the healthy Glaucoma patients who agreed to reference group. The PSD was determined participate were examined. Patients by comparing the differences between performed the 24 - 2 threshold test adjacent points [2]. The VFI was calculated (Humphrey SITA standard). The VF tests as described by Bengtsson and Heijl. At with reliability indices (Fixation losses, each location, the measured sensitivity was False positives, False negatives) > 20% expressed as a percentage of the sensitivity were excluded. expected in a healthy observer of the same Inclusion criteria included a clinical age, and the VFI was calculated as the diagnosis of primary glaucoma or ocular weighted mean of all locations with pattern hypertension and absence of other retinal deviation probability outside normal limits disease. They had a best corrected visual (< 5%) [11]. acuity (VA) equal to or better than 20/60 and The relationship between VFI, MD, and refractive error within ± 5.00 D sphere and ± PSD was described with linear regression 3.00 D astigmatism. analysis. VFI was treated as the dependent 2. Methods variable; MD and PSD were treated as This cross-sectional study was performed independent variables in all regressions. To between December 2015 and April 2016 at evaluate the relationship between variables Glaucoma department, Vietnam National from a single patient, the correlation Institute of Ophthalmology. coefficient (r) was calculated by SPSS 20.0 To calculate the sample size of this cross- Statistics. sectional study, we assumed that the rate of 3. Ethics visual field loss in glaucoma patients was Research subjects were informed 85% [6]. The following formula was used: about the goals of the study and voluntarily N = [(Z 1-α/2)2 p.q] / d2. To achieve 95% agreed to participate. The study was confidence intervals (CIs) and 7% error, 103 approved by Vietnam National Institute of eyes from 58 patients were examined. Ophthalmology. The MD was calculated as the weighted III. RESULTS A total of 77 eyes with glaucoma and 26 eyes with ocular hypertension were studied. The VFI ranged from 100% (normal visual field) to 1%. The MD showed the overall depression ranged from - 33.56 dB to - 0.93 dB. PSD ranged from 1.03 to 13.35 dB. 70 JMR 111 E2 (2) - 2018
4. JOURNAL OF MEDICAL RESEARCH Table 1. Average visual field indices VFI (%) MD (dB) PSD (dB) Average ± SD 78.76 ± 28.75 - 10.22 ± 8.71 4.56 ± 3.45 Min - max 1 – 100 (- 33.56) – (- 0.93) 1.03 – 13.35 Chart 1. Comparison of MD and VFI Correlation coefficient (r) is 0.984 The two tailed P value is < 0.0001 In single visual fields, there was a close relationship between MD and VFI. A significant correlation between MD and VFI was shown in all eyes (r = 0.984, P < 0.0001) which was positive linear. This relationship was described by the equation: VFI = 111.4 + 3.2 x MD (%). This model predicts VFIs of 92%, 73%, and 47% for visual fields with MDs of − 6, − 12, and − 20 dB, with prediction intervals of approximately ± 8%. Chart 2. Comparison of PSD and VFI Correlation coefficient(r) is -0.667 The two tailed P value is < 0.0001 Chart 2 showed the linear regression between VFI and PSD with r = - 0.667, p < 0.0001. JMR 111 E2 (2) - 2018 71
5. JOURNAL OF MEDICAL RESEARCH Table 2. The correlation between VFI and MD, PSD in the patients with VFI ≥ 90% and VFI < 90% VFI (≥ 90%) - MD VFI (< 90%) - MD VFI (≥ 90%) - PSD VFI (< 90%) - PSD p 0.05 R 0.986 0.571 - 0.982 - 0.196 The VFI was more closely correlated with MD than it was with PSD. PSD was significantly correlated observations of VFI ≥ 90%, but not with observations where VFI < 90% Table 3. MD and VFI average patients without glaucomatous defects in visual field test Cataract VF index MD (dB) VFI (%) No cataract - 3.22 ± 1.28 (26) 98.73 ± 0.96 (26) Cataract - 5.34 ± 2.63 (12) 98.83 ± 0.72 (12) p 0.014 0.09 In 50 eyes with MD > - 6dB, 38 eyes had no glaucomatous defects in visual field test (stage 0 – classification Hodapp, Parish and Anderson - 1993) [12]. We compare the average MD and average VFI between the group with cataract and the group without cataract. There was no significant difference in the VFI between two the groups (p > 0.05) but was significant difference in the MD between two the groups (p < 0.05). IV. DISCUSSION with the correlation coefficient is 0.984 and Global indices of VFs have always -0.667. played an important role in summarizing The increase in the variability of MD the severity of glaucoma. MD and PSD are observed in damaged visual fields is the two most popular global indices used consistent with previous reports [13,14]. in clinical practice. However, both of them Our analysis suggests also an equation have limitations. MD is affected by media for estimating VFI from MD. opacities and by other causes of generalized In this study, we compared the MD and depression of visual function in addition to the VFI in the patients without glaucomatous glaucoma. PSD is less affected by media defects in visual field test. So that, MD opacities, but has the disadvantage that decreased only by cataract or by media it falsely improves as the severity of VF opacities. There was no statistical difference loss increases. VFI was meant to address in the VFI between group with cataract and some of the limitations of MD and PSD [13]. group without cataract. These findings are The results of our study show that a linear similar to those of previous studies on visual regression between VFI and MD, and PSD fields [15,16]. This result demonstrated that 72 JMR 111 E2 (2) - 2018
6. JOURNAL OF MEDICAL RESEARCH VFI seems less affected by cataract than the correlation between MD and VFI is less MD. Bengtsson B and Heijl A used the strict. This result confirmed that VFI seems pattern deviation probability maps of the less affected by media opacities. standard Statpac program of the Humphrey V. CONCLUSION perimeter to make the VFI as resistant as possible to the effects of media opacities. In conclusion , VFI had linear correlation They realized that MDI is only very weakly with both MD and with PSD. This correlation center weighted, and therefore is not as well was stronger in patients with high VFI correlated to patient visual function as may values. VFI seems to be less affected by be desired [4]. The pattern deviation concept cataract than MD. Our study suggest that has been widely accepted and applied to VFI may become a useful and simple tool perimetric analysis and is used as a way of for accurately determining glaucomatous reducing the effects of developing cataract. visual field defects, especially in patients The pattern deviation was only used as a that have both glaucoma and cetaracts. tool for identifying abnormal test points. The Acknowlegements extent of the field loss at those locations, We would like to express our sincere then, is based on total deviation values. thanks to the doctors and medical staff In addition, locations in the center of the at the Glaucoma department at Vietnam visual field are more heavily weighted and National Institute of Ophthalmology for their therefore make a greater contribution to the support during this study. VFI than do those in the periphery [4,15,17]. For the patients with VFIs 90% and REFERENCES above, the correlation with the MD and with 1. Paul N Shacknow andJohn R the PSD was better than for the patients Samples (2010), The Glaucoma Book: with VFIs below 90% (r = 0.986 vs. 0.571). a practical, evidence-based approach to The stronger correlation of higher VFI patient care, chủ biên, Springer Science & values with higher MD may reflect differing Business Media,. 253 - 257. patterns of local and diffuse VF loss of 2. Heijl A, Lindgren G, Olsson Jet al glaucoma. In group with VFI below 90%, the (1992), "On weighted visual field indices", patients had more severe glaucoma. These Graefes Arch Clin Exp Ophthalmo. 230, eyes were often accompanied by cataract 397 – 400. (due to intraocular hyertension). The MD on 3. Advanced Glaucoma Intervention these eyes were higher than the “true value” Study. 2. (1994), Visual field test scoring reflecting the glaucoma stage due to MD and reliability, ed, Vol. 101, Ophthalmology. that reflect localized defects of glaucoma but 4. Bengtsson B andHeijl A (2008), "A also reflects diffuse defects due to cataract. visual field index for calculation of glaucoma While the VFI only reflects localized defects rate of progression", Am J Ophthalmol. 145, due to glaucoma [15]. This explains that 343 – 353. JMR 111 E2 (2) - 2018 73
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