Comparison of visual field tests in glaucoma patients with a central visual field defect

Comparison of visual field tests in glaucoma patients with a central visual field defect Hye-Young Shin, MD, PhD,* Hae-Young Lopilly Park, MD, PhD,y Chan Kee Park, MD, PhDy,1   ABSTRACT  RESUM E Objective: To compare the 24-2 and 10-2 visual fields (VFs) and investigate the degree of differences between the 2 tests in glaucomatous eyes with central VF defects. Design: Retrospective study. Participants: In all, 99 eyes of 99 glaucoma patients who underwent both the 24-2 VF and 10-2 VF tests within 6 months were enrolled. Methods: Glaucomatous eyes with damage involving a central VF defect were divided into 3 groups based on the average total deviation (TD) of 12 central points in the 24-2 VF test. The TD difference was calculated by subtracting the average TD of the 10-2 VF test from the average TD of 12 central points in the 24-2 VF test. The absolute central TD difference in each quadrant was defined as the absolute value of the TD value obtained by subtracting the average TD of 4 central points in the 10-2 VF test from the innermost TD in the 24-2 VF test in each quadrant. Results: The TD differences differed significantly between the severe group and the early and moderate groups ( p < 0.001). In the superonasal quadrant, the absolute central TD difference was significantly greater in the moderate group than in the early group ( p < 0.05). In the superotemporal quadrant, the absolute central TD difference was significantly greater in the severe group than in the other 2 groups ( p < 0.001). Conclusions: Our results indicate that the results of VF tests for different VFs can be inconsistent, depending on the degree of central defects and the VF quadrant. Objectif: Comparer les tests de champs visuels (CV) 24-2 et 10-2 et déterminer le degré de différence entre les 2 tests dans le glaucome s'accompagnant d'atteintes centrales du champ visuel. Nature: Étude rétrospective. Participants: Au total, 99 yeux de 99 patients glaucomateux qui ont subi les tests CV 24-2 et CV 10-2 dans un délai de 6 mois ont été admis à l’étude. Méthodes: Les yeux glaucomateux qui présentaient une atteinte centrale du champ visuel ont été divisés en 3 groupes, selon la déviation totale (DT) moyenne de 12 points centraux dans le test CV 24-2. La différence de la DT a été calculée en soustrayant la DT moyenne du test CV 10-2 de la DT moyenne de 12 points centraux du test CV 24-2. La différence centrale absolue de la DT dans chaque quadrant se définissait comme la valeur absolue de la DT obtenue en soustrayant la DT moyenne de 4 points centraux du test CV 10-2 de la DT la plus interne du test CV 24-2 dans chaque quadrant. Résultats: Les différences de la DT se démarquaient significativement selon qu'il s'agissait de patients du groupe glaucome grave ou de patients des groupes glaucome précoce ou modéré (p < 0,001). Dans le quadrant nasal supérieur, la différence de la DT centrale absolue était significativement plus élevée dans le groupe glaucome modéré que dans le groupe glaucome précoce (p < 0,05). Dans le quadrant temporal supérieur, la différence de la DT centrale absolue était significativement plus élevée dans le groupe glaucome grave que dans les deux autres groupes (p < 0,001). Conclusions: Selon notre étude, les résultats des tests pour différents champs visuels peuvent être variables, selon le degré d'atteintes centrales et le quadrant du CV.

Among various glaucomatous visual field (VF) defects, those involving the central VF are particularly concerning and have been a focus of research regardless of the stage of glaucoma because of the area’s proximity to the fixation point and its ability to affect daily life.17 According to the study by Curcio and Allen,8 the density of retinal ganglion cells is much greater central retina than peripheral retina. The 6° grid of points in the 24-2 VF test might be insufficient to accurately represent changes in the central macula. Weber and Dobek9 showed that the frequency of different scotoma detection between VF tests with different test grid was more than 10 times higher in the centre VF than in the periphery VF. Airaksinen and Heijl10 showed that small retinal nerve fibre layer (RNFL) defects might

be missed in VF test with coarse test points. Several previous studies have also suggested that if the perimetry test grid is inadequate, it may also contribute to intertest variability.1114 VF results can vary depending on test strategies, number and location of test points, and location of VF defects.9,11,12,14 In addition, other studies have reported higher detection rates in VF tests with locally condensed test points to detect or monitor glaucomatous damage compared with conventional stimulus arrangements.1518 According to more recent reports, paracentral scotoma may go undetected on standard automated perimetry using the standard 24-2 VF test, which examines a total of 52 points that are 6° apart, unlike the 10-2 VF test, which examines 68 points that are 2° apart in the central 10° VF.19,20

© 2018 Published by Elsevier Inc. on behalf of Canadian Ophthalmological Society. https://doi.org/10.1016/j.jcjo.2018.11.006 ISSN 0008-4182 CAN J OPHTHALMOL—VOL. 54, NO. 4, AUGUST 2019

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Comparison of visual field tests in glaucoma—Shin et al. Furthermore, Park et al.21 reported that the 10-2 VF test shows higher detection rates to the 24-2 VF test in detection of progression in glaucomatous eyes with initial parafoveal scotoma, and Nevalainen et al.17 demonstrated that applying locally condensed stimulus arrangements enhances the detection rate of glaucoma progression compared with conventional test grids. More recent studies have shown that 10-2 VFs show a stronger association with National Eye Institute Visual Function Questionnaire-25 score than do 24-2 VFs.22,23 Hood et al.24 recommend that that all patients with glaucoma, or suspected glaucoma, should undergo 10-2 VF. Nevertheless, until recently, the VF examination most commonly performed in clinical practice has been the Swedish Interactive Threshold Algorithm (SITA) 24-2 or 30-2 program. In addition, it may not be realistic to evaluate all patients using both the 24-2 VF and the 10-2 VF tests to detect or monitor glaucomatous VF defects because it is very time-consuming to perform both tests. Therefore, we guess roughly the degree of VF defects in the central 10° based on the retinal sensitivity values of the innermost test points in the 24-2 VF test for glaucoma patients with central VF defects. Other research has shown that the 10-2 VF test can be better than the 24-2 VF test in detecting glaucomatous scotoma in early glaucoma with central VF defects.19,20,24,25 In our previous report, we have shown that early glaucomatous eyes with any abnormal 24-2 VF points on the central 10° VF area should be further evaluated with a 10-2 VF examination26 and frequency doubling technology (FDT) 10-2 can be considered a useful tool to detect glaucomatous damage of the macula early.27 However, to the best of our knowledge, no study to date has compared the results of different VFs according to the quadrant of VF at the various stages of glaucoma. Therefore, knowledge about the performance of using 12 central points (central 10° VF area) in the 24-2 VF and 68 10-2 VF tests to evaluate central VF defects at various stages of glaucoma will help to determine which patients need further detailed 10-2 VF examination (Fig. 1). In the present study, we investigated the performance

of using central test points in the 24-2 VF test compared with the 10-2 VF test to evaluate central VF defects in glaucoma patients with VF defects involving the central 10° VF area.

TAGEDH1METHODSTAGEDEN Subjects

In this cross-sectional study, 99 eyes of 99 glaucoma patients who underwent both the 24-2 VF and 10-2 VF tests (Carl Zeiss Meditec, Dublin, CA) within 6 months were retrospectively enrolled from a clinical database at the glaucoma clinic of Seoul St. Mary’s Hospital, College of Medicine, Catholic University of Korea, between November 2012 and August 2014. We included only those patients with a visual acuity of 20/25 or better and a reliable VF. VF 10-2 was performed within 6 months after VF 24-2 test. All VF tests were performed by highly skilled operators. This study was conducted in accordance with the ethical standards stated in the Declaration of Helsinki and with the approval of the Institutional Review Board of Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea. Visual Field

Glaucomatous eyes were defined as having glaucomatous VF defects on the 24-2, as confirmed by at least 2 reliable VF tests with false-positive errors of <15%, false-negative errors of <15%, and fixation loss of <20%, and the presence of a compatible glaucomatous optic disc that showed diffuse or focal neural rim thinning, and/or RNFL defects. A glaucomatous VF defect was defined as a cluster of 3 or more points with a probability <5% on the pattern deviation map in at least one hemifield, including at least one point with a probability of <1%; or a result “outside normal limits” in the glaucoma hemifield test; or a pattern standard deviation (PSD) with a probability of <5%. Central VF defects were defined as glaucomatous defects that included at least one point with a probability <1% on the pattern deviation map within 12 points of a central 10°

Fig. 1—A, Total deviation (TD) plot in the 24-2 visual field (VF) test of the right eye. Twelve central test points within the central 10° of the VF are outlined with a bold line. The innermost test points in the superonasal (SN), superotemporal (ST), inferonasal (IN), and inferotemporal (IT) quadrants are filled by dots of different sizes, respectively. B, TD plot in the 10-2 VF test of the right eye. SN, ST, IN, and IT 4 test points within central 3° of VF are filled by dots of different sizes, respectively.

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Comparison of visual field tests in glaucoma—Shin et al. radius in the SITA 24-2 VF test. If both eyes were eligible for the study, one eye was selected randomly for inclusion. Total deviation (TD) plots of the 24-2 and 10-2 VF examinations were used to compare VF among the groups. The central TD was defined as the average of 12 central points in the 24-2 VF TD plot (Fig. 1A). Glaucomatous eyes involving a central VF defect were divided into 3 groups (terciles) based on the average TD of 12 central points in the 24-2 VF test (N = 33, in each group): the early group (tercile with the highest TD), the moderate group (intermediate TD), and the severe group (lowest TD). The total TD was defined as the average of a total of 68 points in the 10-2 VF TD plot (Fig. 1B). The TD difference was calculated by subtracting the total TD in the 10-2 VF test from the central TD in the 24-2 VF test. The TD difference was compared among the 3 groups to evaluate the differences in the central VF 108 radius between the 2 VF test results according to the degree of the central VF defects. The 4 quadrants were designated the superonasal (SN), superotemporal (ST), inferonasal (IN), and inferotemporal (IT) quadrants. SN, ST, IN, and IT innermost TD were

defined as the TD values of the innermost point of a central 3° radius of each quadrant in the 24-2 VF test (Fig. 1B). SN, ST, IN, and IT centre TD were defined as the average TD of 4 points within a central 38 radius in each quadrant in the 10-2 VF test (Fig. 1B). The absolute value was used because the TD difference in each quadrant was a positive or negative value (Fig. 2A). The absolute central TD difference in each quadrant was defined as the absolute value of the value obtained by subtracting the centre TD of the 10-2 VF test from the innermost TD of the 24-2 VF test in each quadrant. The absolute central TD difference was compared among the 3 groups to evaluate the differences within a central 3° radius between the 2 VF test results according to the degree of central VF defects. Statistical Analysis

Age, mean deviation (MD), PSD, VF index, and TD values of the VF tests were compared. One-way analysis of variance was used to assess the differences among the groups. The gender ratio was compared using the x2 test. All reported p values are 2-sided, and differences at a level of p < 0.05 were

Fig. 2—A-1, The moderate group results. The innermost TD in the superonasal (SN) quadrant was ¡32 dB in the 24-2 VF test but the SN centre TD was ¡14.5 dB in the 10-2 VF test. Therefore, the absolute central TD difference was 17.5. A-2, The moderate group results. The innermost TD in the superonasal (SN) quadrant was ¡8 dB in the 24-2 VF test but the SN centre TD was ¡26.5 dB in the 10-2 VF test. Therefore, the absolute central TD difference was 18.5. B, The severe group results. The innermost total deviation (TD) in the superotemporal (ST) quadrant was ¡30 dB in the 24-2 VF test but the ST centre TD was ¡10 dB in the 10-2 VF test. Therefore, the absolute central TD difference of the ST quadrant was 20. CAN J OPHTHALMOL—VOL. 54, NO. 4, AUGUST 2019

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Comparison of visual field tests in glaucoma—Shin et al. Table 1—Demographics Total Glaucoma Age, y Sex, M(F) 24-2 VF MD PSD VFI Central TD 10-2 VF MD PSD Total TD

Severe Group (N = 33)

p

Early Group (N = 33)

Moderate Group (N = 33)

50.52 § 13.83 20(13)

55.82 § 8.89 15(18)

57.97 § 14.90 13(20)

0.057* 0.207y

¡9.46 § 8.50 8.43 § 4.24 72.45 § 25.81 ¡10.42 § 8.49

¡2.51 § 1.97 4.46 § 3.01 93.42 § 4.37 ¡2.47 § 1.37

¡7.09 § 3.71 9.23 § 3.01 80.64 § 9.39 ¡8.13 § 2.60

¡18.76 § 7.66 11.59 § 3.13 43.30 § 23.13 ¡20.67 § 5.76

<0.001* <0.001* <0.001* <0.001*

¡10.10 § 7.59 9.43 § 4.50 ¡10.28 § 7.67

¡3.47 § 2.65 4.85 § 3.41 ¡3.51 § 2.59

¡8.19 § 3.35 10.32 § 3.23 ¡8.27 § 3.31

¡18.63 § 5.82 13.12 § 1.86 ¡19.06 § 5.62

<0.001* <0.001* <0.001*

54.77 § 13.06 48(51)

VF, visual field; MD, mean deviation; PSD, pattern standard deviation; VFI, visual field index; TD, total deviation. All data are expressed in mean § standard deviation. p-values <0.05 are noted in boldface. * One-way analysis of variance. y 2 x test.

Table 2—Comparison of total deviation values in each quadrant of 24-2 and 10-2 VF 24-2 VF SN innermost TD ST innermost TD IN innermost TD IT innermost TD 10-2 VF SN centre TD ST centre TD IN centre TD IT centre TD

p*

Early Group (N = 33)

Moderate Group (N = 33)

Severe Group (N = 33)

¡4.73 § 6.43 ¡0.94 § 2.83 ¡2.73 § 8.37 ¡0.06 § 1.75

¡17.00 § 14.66 ¡7.36 § 10.48 ¡6.67 § 9.83 ¡2.39 § 6.13

¡31.00 § 6.50 ¡25.12 § 11.97 ¡10.58 § 11.92 ¡5.33 § 7.43

<0.001 <0.001 0.009 0.001

¡4.91 § 6.18 ¡1.92 § 4.22 ¡2.27 § 4.46 ¡1.12 § 1.87

¡14.86 § 11.39 ¡7.26 § 8.38 ¡5.42 § 7.74 ¡2.59 § 5.52

¡29.06 § 6.72 ¡18.07 § 9.91 ¡9.10 § 10.68 ¡6.24 § 7.33

<0.001 <0.001 0.004 0.001

VF, visual field; TD, total deviation; SN, superonasal; ST, superotemporal; IN, inferonasal; IT, inferotemporal. All data are expressed in mean § standard deviation. p-values <0.05 are noted in boldface. * One-way analysis of variance.

Table 3—Comparison of difference of total deviation values between 24-2 and VF 10-2 VF Early Group (N = 33) TD Difference 1.04 § 2.14 Absolute Central TD Difference Superonasal 2.42 § 4.36 Superotemporal 1.57 § 1.86 Inferonasal 2.17 § 3.67 Inferotemporal 1.48 § 1.41

p*

Moderate Group (N = 33)

Severe Group (N = 33)

0.14 § 2.58

¡1.61 § 2.26

<0.001

Comparison Between Groups Severe Group > Early = Moderate Group

6.09 § 6.4 3.48 § 4.51 2.90 § 4.23 1.62 § 1.49

4.29 § 4.51 7.60 § 6.28 3.83 § 5.43 2.21 § 1.99

0.019 <0.001 0.332 0.168

Moderate Group > Early Group Severe Group > Early = Moderate Group

VF, visual field; TD, total deviation. All data are expressed in mean § standard deviation. p-values <0.05 are noted in boldface. *One-way analysis of variance.

considered to be statistically significant. The Statistical Package for the Social Sciences version 17.0 (SPSS Inc, Chicago, IL) was used for statistical analyses.

TAGEDH1RESULTSTAGEDEN The study demographics are summarized in Table 1. There were no significant differences in age or gender ratio among the 3 groups. The average VF MD in the 24-2 VF test was ¡9.46 § 8.50 dB in the total glaucoma group. The central TD and total TD in the 24-2 VF test in the total glaucoma group were ¡10.42 § 8.49 and ¡10.28 § 7.67 dB, respectively. By group, the central TD values were ¡2.47 § 1.37 dB, ¡8.13 § 2.60 dB, and ¡20.67 § 5.76 dB in groups 1, 2, and 3, respectively. The TD values by quadrant in each quadrant of the 24-2 and 10-2 VF tests are summarized in Table 2. There were significant differences among the 3 groups (all p < 0.001) in the innermost TD and centre TD of each quadrant.

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Compared with the total TD of the 10-2 VF test, the central TD of the 24-2 VF test was lower in the severe group but higher in the early and moderate groups (Table 1). The TD differences between the 2 VF tests are summarized in Table 3. The TD difference was significantly different between the severe group and the early and moderate groups (p < 0.001). Table 3 gives the absolute central TD differences for each quadrant. There were significant differences among the 3 groups in the SN and ST quadrants (p = 0.019 and p < 0.001, respectively), the TD being significantly greater in the SN quadrant for the moderate group than the early group, and in the ST quadrant for the severe group than in the other 2 groups. In the IN and IT quadrants, there were no big differences among the 3 groups.

TAGEDH1DISCUSSIONTAGEDEN Although recent studies have reported that the 10-2 VF test showed higher detection rates than that of the 24-2 VF test in

Comparison of visual field tests in glaucoma—Shin et al. detection of paracentral scotoma in early glaucoma,19,20 no study has compared the performance of the 24-2 VF and 10-2 VF tests as regards VF defects within the central 10° VF area at various stages of glaucoma. This is the first study to compare VF results between the central test points of the 24-2 VF and 10-2 VF tests at various stages of glaucoma. We also evaluated the performance of the 24-2 VF test in each quadrant compared with the 10-2 VF test. Our results indicate that the results of the 2 VF tests can be inconsistent depending on the degree of the central VF defect and the VF quadrant examined. The results of the analysis of TD differences suggest that in glaucoma patients with severe central VF defects the results of the 24-2 VF test were worse than those of the 10-2 VF test, whereas in glaucoma patients with mild central VF defects the results of the 10-2 VF test were worse than those of the 24-2 VF test for the central VF. When considering only the central 3° VF area, the 2 tests again showed significant differences in some quadrants according to the degree of central VF defects. In comparisons of TD values in the central 10° VF area, the TD difference in the severe group was negative, whereas those of groups 1 and 2 were positive values (Table 3). This suggests that the degree of VF defects in the 12 central points seems to be more severe in the 24-2 VF test than in the 10-2 VF test when central VF damage is severe, whereas the degree of VF defects in the 12 central points seems to be milder in the 24-2 VF test than in the 10-2 VF test when the central VF damage is not severe. Based on these findings, we suggest that the 24-2 VF test is not sufficient to evaluate VF defects properly within the central 10° VF area in earlier stages of functional damage. When considering absolute central TD differences by quadrant, there were significant differences between the tests for the central 3° VF area in the SN and ST quadrants (p = 0.019, p < 0.001, respectively) but not the IN and IT quadrants (Table 3). In the SN quadrant, the values were significantly greater in the moderate group than in the early group. In the ST quadrant, the values were significantly greater in the severe group than in the other 2 groups. These results suggest that the central test points of these quadrants are less reliable in the 242 VF test than in the 10-2 VF test, especially in patients with moderate to severe central VF defects. In the IN and IT quadrants, the absolute central TD difference did not differ significantly among the 3 groups. The values were lower in the IN and IT quadrants than in the SN and ST quadrants for all groups (Table 3), probably because VF defects in the inferior quadrants tend to be farther away from the fixation point in the inferior hemifield than in the superior hemifield,28 and central VF defects are less than in the superior quadrants. The quadrant with the largest absolute central TD difference value differed depending on the severity of the central VF defect (Table 3). In the moderate group, which included patients with moderate defects, the values were largest in the SN quadrant (Table 3). The VF defect was most severe in that area (Table 2). In these patients, various patterns and degrees of central VF defects can occur in the SN quadrant (Fig. 2A). Indeed, in the present study, in the moderate group, the TD

values of the innermost points of the SN quadrant of 3 patients in the 24-2 VF test (Fig. 2A) were ¡32 and ¡8 dB, respectively; the central TD values in the 10-2 VF tests were ¡14.5 and ¡26.5 dB, respectively. Therefore, the absolute central differences in the TD in this quadrant of these patients were 17.5 and 18.5, respectively (Fig. 2A-1,2). Despite the fact that the scotoma of case a-2 was closer to the fixation point than was that of a-1, the innermost TD values in the 24-2 VF test were contrary. This difference is probably the result of differences in the number of test points within the central 3° VF area between the 2 tests. The 10-2 VF test has a higher density of test points in this area. These results suggest that the innermost point used in the 24-2 VF test is insufficient to evaluate VF defects within the central 3° VF area. Therefore, in patients with moderate central VF defects in the SN quadrant, it is crucial to understand this limitation of the 24-2 VF examination and the higher detection rates of the 10-2 VF test in such cases. In the severe group, which included patients with severe defects, the values were largest in the ST quadrant. In the ST quadrant, the TD value of the innermost point of the SN quadrant in the 24-2 VF test tended to be more severe than the SN centre TD value in the 10-2 VF test (Fig. 2B). We think that the innermost point in the ST quadrant in the 24-2 VF test is not reliable to evaluate the degree of a VF defect in the central 3° VF area in patients with severe central VF defects because the ST quadrant contains the temporal island even in severe glaucoma patients.1,29 Unlike the moderate group, the absolute central TD difference in the SN quadrant was not the largest among the quadrants. We assumed that the difference in the SN quadrant between the 24-2 and 10-2 tests was not large because the SN quadrant is the most severely damaged among the 4 quadrants in patients with severe central VF defects (Table 2) and VF defects in the SN quadrant tend to be close to the fixation point in patients with advanced central VF defects (Fig. 2B). A limitation of our study is the relatively small number of cases in each subgroup. And VF is subject to fluctuation even in clinically stable glaucoma.11,30 Because this study was not performed with multiple VFs, fluctuation could have affected our findings. However, the paracentral test points are reported to have a lower test-retest variability than the peripheral test points.11,31 In addition, we included only patients with a visual acuity of 20/25 or better, but media opacity such as cataract could have affected our findings. However, this is the first study to compare the performance of these tests for the evaluation of central VF defects at various stages of glaucoma. We also analyzed and compared results by quadrant, taking into consideration the nature of the central VF damage. Because there are temporal islands in severely advanced glaucoma1,29 and inferior central VF defects tend to be farther from the fixation point than superior central VF defects,28 we should consider these features when interpreting 24-2 VF test results. In the present study, we showed that the degree of differences between the central points of the 24-2 VF and 10-2 VF tests may differ among quadrants according to the degree of central VF defects because of the nature of central VF damage. CAN J OPHTHALMOL—VOL. 54, NO. 4, AUGUST 2019

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Comparison of visual field tests in glaucoma—Shin et al. We showed that the central test points of SN and ST quadrants are less reliable in the 24-2 VF test than in the 10-2 VF test, especially in patients with moderate to severe central VF defects in the superior quadrants. Knowledge about these limitations of the 24-2 VF test will help clinicians to determine which patients need further detailed 10-2 VF examinations. We therefore recommend that clinicians should perform 10-2 VF test at least in these glaucoma patients if it is difficult to perform both VF tests in all glaucoma patients. In conclusion, there are significant differences in results for VF defects in the central 10° VF area in the 24-2 VF and 10-2 VF tests, depending on the severity of central VF defects. In addition, central VF results in the 24-2 VF test can differ from those in the 10-2 VF test in the central 3° VF area, depending on the severity of the defects and by quadrant. Therefore, the 24-2 VF examination should be interpreted with caution in patients with various central VF defects. TAGEDH1REFERENCESTAGEDEN 1. Zalta AH. Use of a central 10 degrees field and size V stimulus to evaluate and monitor small central islands of vision in end stage glaucoma. Br J Ophthalmol. 1991;75:151–4. 2. Zhang L, Drance SM, Douglas GR. Automated perimetry in detecting threats to fixation. Ophthalmology. 1997;104:1918–20. 3. Park SC, De Moraes CG, Teng CC, Tello C, Liebmann JM, Ritch R. Initial parafoveal versus peripheral scotomas in glaucoma: risk factors and visual field characteristics. Ophthalmology. 2011;118:1782–9. 4. Jung KI, Park HY, Park CK. Characteristics of optic disc morphology in glaucoma patients with parafoveal scotoma compared to peripheral scotoma. Invest Ophthalmol Vis Sci. 2012;53:4813–20. 5. Shin HY, Park HY, Jung KI, Choi JA, Park CK. Glaucoma diagnostic ability of ganglion cell-inner plexiform layer thickness differs according to the location of visual field loss. Ophthalmology. 2013;121:93–9. 6. Coeckelbergh TR, Brouwer WH, Cornelissen FW, Van Wolffelaar P, Kooijman AC. The effect of visual field defects on driving performance: a driving simulator study. Arch Ophthalmol. 2002;120:1509–16. 7. Fujita K, Yasuda N, Oda K, Yuzawa M. Reading performance in patients with central visual field disturbance due to glaucoma. Nihon Ganka Gakkai Zasshi. 2006;110:914–8. 8. Curcio CA, Allen KA. Topography of ganglion cells in human retina. J Comp Neurol. 1990;300:5–25. 9. Weber J, Dobek K. What is the most suitable grid for computer perimetry in glaucoma patients? Ophthalmologica. 1986;192:88–96. 10. Airaksinen PJ, Heijl A. Visual field and retinal nerve fibre layer in early glaucoma after optic disc haemorrhage. Acta Ophthalmol (Copenh). 1983;61:186–94. 11. Heijl A, Lindgren A, Lindgren G. Test-retest variability in glaucomatous visual fields. Am J Ophthalmol. 1989;108:130–5. 12. Artes PH, Iwase A, Ohno Y, Kitazawa Y, Chauhan BC. Properties of perimetric threshold estimates from Full Threshold, SITA Standard, and SITA Fast strategies. Invest Ophthalmol Vis Sci. 2002;43:2654–9. 13. Maddess T. The influence of sampling errors on test-retest variability in perimetry. Invest Ophthalmol Vis Sci. 2011;52:1014–22. 14. Maddess T. Modeling the relative influence of fixation and sampling errors on retest variability in perimetry. Graefes Arch Clin Exp Ophthalmol. 2014;252:1611–9. 15. Schiefer U, Malsam A, Flad M, et al. Evaluation of glaucomatous visual field loss with locally condensed grids using fundus-oriented perimetry (FOP). Eur J Ophthalmol. 2001;11(Suppl 2):S57–62. 16. Schiefer U, Flad M, Stumpp F, et al. Increased detection rate of glaucomatous visual field damage with locally condensed grids: a comparison

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Footnotes and Disclosure: The authors have no proprietary or commercial interest in any materials discussed in this article. This work was supported by the National Research Foundation of Korea grant funded by the Korea government (No. NRF2018R1D1A1B07047231). From the *Department of Ophthalmology, Uijeongbu St. Mary’s Hospital, College of Medicine, Catholic University of Korea, Seoul, Korea; yDepartment of Ophthalmology and Visual Science, Seoul St. Mary’s Hospital, College of Medicine, Catholic University of Korea, Seoul, Korea. Originally received Jan. 5, 2018. Final revision Oct. 5, 2018. Accepted Nov. 8, 2018. Correspondence to Chan Kee Park, MD, PhD, Department of Ophthalmology and Visual Science, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Seocho-ku, Seoul 137-701, Korea. [email protected]