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

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.
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Correlating of the visual field index with mean deviation and pattern standard deviation in glaucoma patientsJOURNAL OF MEDICAL RESEARCHCORRELATING OF THE VISUAL FIELD INDEX WITH MEANDEVIATION AND PATTERN STANDARD DEVIATION INGLAUCOMA PATIENTSBui Thi Huong Giang, Pham Thi Kim ThanhDepartment of Ophthamology , Hanoi Medical UniversityThe 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 in103 eyes of 58 patients with mild to severe glaucoma or ocular hypertension. The correlation of VFIto MD, PSD was evaluated with linear regression models, and the coefficient of determination (r) wascalculated. The result showed that the average values of VFI, MD and PSD were 78.76%, -10.22dB and 4.56 dB respectively. The VFI and the MD were linearly correlated with r = 0.984. For thepatients with VFIs below 90%, the correlation with the MD was better than for the patients with VFIs90% and above (r = 0.986 vs 0.571). There was no statistically significant difference in VFI valuebetween the group with cataract and the group without cataract (p > 0.05) but MD varied significantlybetween these two groups (p < 0.05). For the PSD, the correlation for the patients with VFIs 90% andabove 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. INTRODUCTIONIn management of glaucoma patients,the visual field (VF) is the most importanttool to determine the stage and progressionof the disease [1]. VF data is summarizedin global summary indices [2] . At this time,the mean deviation index (MD) and the patternstandard deviation (PSD) are the standardindices to evaluate for glaucomatousdamage [3]. The Visual Field Index (VFI) is aCorresponding author: Bui Thi Huong Giang, Department of Ophthamology, Hanoi Medical UniversityEmail: buihuonggiang@hmu.edu.vnReceived: 03 June 2017Accepted: 16 November 201768new index, introduced by Bengtsson B andHeijl A in 2008 [4]. The VFI expresses thevisual function as a percentage of normalage-corrected sensitivity. Therefore, the VFIof an eye with a completely normal visualfield is 100% and the VFI of a perimetricallyblind eye is 0%. The VFI was designed usingthe Humphrey 30 - 2 and 24 - 2 test pointpatterns, which are the most commonlyused patterns in glaucoma management [3].To avoid effects of cataract on the VFI, thepattern deviation probability map was usedto identify test points with normal sensitivity(100%), having absolute defect (0%), andJMR 111 E2 (2) - 2018JOURNAL OF MEDICAL RESEARCHthose demonstrating relative loss. Thesensitivity at these points were scored usingthe following formula:100 - [(total deviationI/age-correctednormal threshold) x 100] ,where |total deviation| is the absolutevalue of the numerical total deviation valueand age-corrected normal threshold isintercept - age coefficient x patient age.The VFI was also constructed to weighthe central points of the visual field moreheavily than peripheral points. The VFI isthe mean of all weighed scores in percent.The test point pattern was divided into fiveconcentric rings of increasing eccentricity.Cortical magnification of any given visualfield location is assumed to reflect bothganglion cell density and the number ofneurons in an area of the visual cortexresponsible for processing a stimulus of agiven size [5]. The weights of the test pointsdecreased with increasing eccentricity from3.29, 1.28, 0.79, and 0.57 to 0.45 at theoutermost ring. The VFI is automaticallycomputed using in the current ‘‘Statpacsoftware’’ of the Humphrey Field Analyzer(HFA II; Carl Zeiss Meditec, Inc., Dublin,California, USA) (Fig.1) [4].Figure 1. Visual field of a glaucomapatientMean Deviation (MD) is the average ofJMR 111 E2 (2) - 2018these deviations across all test locations.Mean defect expresses the differencebetween observed and expected meansensitivity. MD expresses the overallreduction in sensitivity, and is thereforedecreased not only by increasing glaucoma,but also by cataract [6]. Pattern standarddeviation (PSD), a depiction of focal defects,measures irregularity between the thresholdvalue for each point and the average visualfield sensitivity at each point . Thus, inpatients with severely damaged visual fieldsthe value of PSD is too low to be useful asan indicator of severity of disease [7].Glaucoma is an ocular disease, in whichcharacteristic visual field loss correspondsto the underlying anatomic arrangementof damagedretinalganglioncells.Glaucomatous visual field characterizedby loss is localized ...