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New Glaucoma Insights: Original Studies

Prediction of Central Visual Field Severity in Glaucoma

Chakravarti, Tutul MD*; Moghimi, Sasan MD; Weinreb, Robert N. MD

Author Information
doi: 10.1097/IJG.0000000000002031

Abstract

Current evidence suggests that in some glaucoma patients the initial visual field (VF) defect may be located centrally at or near fixation.1 Moreover, macular damage and central visual field defects (CVFDs) may be a clinical feature in the early stage of the disease.2–5 But central visual dysfunction often remains undetected by clinical assessment with standard 24-2 threshold testing in the early stage of glaucoma.6–8 This VF test has only 12 test locations within the central 10 degrees, the location of the majority of retinal ganglion cells.9 In contrast to these central locations, there are 42 other locations that correspond to more peripheral retinal areas, and they contain only 15% of the retinal ganglion cells.10 Therefore, it should not be surprising that glaucomatous damage to the macula or any abnormal point defect within the central 10 degrees may be missed in clinical practice if only 24-2 VF test is performed.6–8

In contrast to the 6 degrees grid with the 24-2 VF test pattern, some investigators have reported that the 10-2 VF test is more effective with 68 points, spaced 2 degrees apart, for detecting glaucomatous damage of the macula.6–8,11,12 These studies concluded that the 10-2 VF test should be considered for patient management to evaluate CVFDs in early glaucoma. However, other investigators have expressed reservations regarding the routine use of the 10-2 test as a general diagnostic test since it is often logistically difficult to obtain. It has also been proposed that the severity of 10-2 VF damage could be generally anticipated using results from 24-2 VF testing.13,14 Hence, they have opined that the additional information from 10-2 VF testing may be redundant for many patients.13 Yet, they have suggested 10-2 to 24-2 testing for detecting progressive paracentral field loss and functional progression, particularly in eyes with any abnormalities within the central 12 points on 24-2 VF.13,14

The value of detecting a CVFD (defined as the abnormalities within the central 12 points, in the central 10 degrees on 24-2 VF) and related parafoveal scotomas with a 10-2 VF test to document glaucomatous damage to the macula is well recognized.5,8,15 The macula, the central 8 degrees surrounding fixation, contains ∼40% of all retinal ganglion cells.10 Park et al11 offered clinical clues to predict the presence of parafoveal scotoma on 10-2 VF and their relationship to the abnormal central 12 points on a 24-2 VF in patients with early glaucoma. They divided those central 12 points into 2 groups: innermost central 4 points and paracentral 8 points. However, they did not report which factors led to those abnormal points influencing the severity of CVFD on a 24-2 VF and the related parafoveal scotoma on 10-2 VF.

In a recent study, we16 suggested that the severity of 10-2 VF could be predicted by measuring abnormal test points within the central-most 4 points (<1%) on 24-2 VF. However, we did not specify how perimetric parameters at the abnormal central-most 4 points would influence the paracentral 8 points on 24-2 VF and vice versa. The current study, undertaking a comparison of these two types of defects on 24-2 VF (central and paracentral points) and related 10-2 VF loss, may be helpful in understanding and predicting the nature of severity of CVFD on 24-2 VF.

METHODS

This cross-sectional, observational study was conducted at the glaucoma services at (1) Vivekananda Institute of Medical Sciences, an academic medical center; and (2) a private glaucoma clinic in Kolkata, India. Data were collected from March 2019 to November 2020 on 161 primary open angle glaucoma patients who completed 24-2 and 10-2 VF testing within six months. The Swedish interactive threshold algorithm standard SAP was performed with a Humphrey Field Analyzer II (Carl Zeiss Meditech, Dublin, CA) using programs 24-2 and 10-2 on all included eyes. On treatment, these glaucoma patients were at different stages of disease severities (mild, moderate, and severe) and regularly followed for at least 36 months. Of 161 glaucoma patients, 64 eyes of 56 patients were included who had a mean deviation (MD) better than −7 dB and a CVFD on a 24-2 VF test. Patients with either MD worse than −7 dB or without CFVDs on 24-2 VF were excluded. All patients enrolled in the study fulfilled the following additional criteria: (a) best-corrected visual acuity of 20/20, spherical refraction within±5.0 D, cylinder correction within ±3.0 D, and (b) open angles on gonioscopy. Excluding criteria were patients with an unreliable 10-2 and/or 24-2 VF (fixation loss >33% or false positive/negative rates >15%). Study participants were excluded if they had significant cataracts and history of intraocular surgery (except for uncomplicated cataracts). In this data set, there was no evidence of a uniformly depressed TD plot combined with a normal PD plot as would be expected in media opacification. Eyes with other conditions likely to impact VF testing (eg, corneal opacity, neuro-ophthalmic, or retinal disease) were also excluded.

We used the criteria set in the ADAGES for glaucoma diagnosis for this study.17 Glaucomatous optic neuropathy was defined as neuroretinal rim thinning (rim width reduced to ≤0.1) or notching, localized or diffuse retinal nerve fiber layer defect, or vertical cup-disc ratio asymmetry >0.2 between eyes (not explained by differences in disc size). Clinical assessment and disc stereo photographs closest to the date of the 24-2 and 10-2 VF testing were used to evaluate glaucomatous optic neuropathy. The methods and measures used in this study adhered to the Declaration of Helsinki. Informed consent was obtained from all participants. The study was approved by the Institutional Ethics Committee, Vivekananda Institute of Medical Sciences.

Criteria for Glaucomatous Damage on 24-2 VF

An abnormal 24-2 VF was defined as a pattern standard deviation (PSD) which had a P<5% or the Glaucomatous Hemifield Test was “outside normal limits.” Eyes with consistent glaucomatous VF loss had to be confirmed with additional 3 VF tests.

Criteria for Glaucomatous CVFD on 24-2 VF

CVFD was defined as abnormal VF points (in the central 10 degrees) in the central 12 points depressed <1% or <0.5% from the normal database on total or pattern deviation probability plot (TD/PD) on a 24-2 VF test. Any point involved in the central-most 4 points (innermost central 4 points) and the paracentral 8 points (2 points adjacent to central-most 4 points in each quadrant) was considered (Fig. 1).11 Two types of CVFDs were included: (1) Isolated Initial Parafoveal Scotoma (IPFS) or (2) VF with CVFDs extending beyond the central 10 degrees (Fig. 1). An isolated IPFS was defined as a glaucomatous VF defect either on TD or PD plot, in 1 hemifield within the central 10 degrees of fixation, with at least 1 point at P<1% lying at the 2 innermost paracentral points (Fig. 1A) and no VF abnormality outside the central 10 degrees.18 Glaucomatous defects beyond the central 10 degrees with CVFD were defined as CVFD associated with VF loss extended beyond the central 10 degrees either on TD or PD plot as shown in Figure 1B.

F1
FIGURE 1:
Representative cases of abnormal 24-2 visual field (VF) points within the central 12 points and related 10-2 VF defects. The central 12 points (orange circle) are constituted of the central-most 4 points (red circle) and paracentral 8 points (2 points adjacent to central 4 points in each quadrant, blue circle). A, An initial parafoveal scotoma (IPFS) in superior hemifield where central visual field defects (CVFDs) were within central 10 degrees. This IPFS had 1 abnormal point (<0.5%) within the central-most 4 and 1 inside the paracentral 8 points on 24-2 VF. The defect was severe at the abnormal central point: threshold sensitivity 0 dB and defect value −33 dB. The paracentral point’s defect was less severe. The 10-2 VF test displayed superior deep arcuate scotoma. B, A CVFD where glaucomatous defect extended beyond the central 10 degrees with severe defect at abnormal central-most point (<0.5%). Related 10-2 VF showed superior deep arcuate scotoma. C, This 24-2 VF had no abnormalities within the central-most 4 points but had 2 abnormal paracentral points. Paracentral defects were mild to moderate and 10-2 VF displayed superior shallow arcuate scotoma. D, This 24-2 VF had one abnormal point within the central-most 4 points and 3 abnormal paracentral points. Central and paracentral defects were mild and 10-2 VF displayed inferior partial arcuate scotoma. E, 24-2 VF had 2 central and 3 paracentral abnormal points; all were mild defects and 10-2 VF displayed cluster defect only.

Classifying 10-2 VF Defects

The cluster criteria and pattern defects were used to classify 10-2 VF defects in 64 eyes. A CVFD required a cluster of 3 contiguous abnormal points with P<5%, 5% and 1% or <5%, 2%, and 2% within a hemifield on either TD or PD plot. We developed modified criteria adapted from Hood et al,3 Traynis et al,8 Mee et al14 and Chakravarti et al16 for classifying pattern defects on 10-2 VF: (1) Deep arcuate scotoma: continuous, dense superior or inferior hemifield defect (P<1% on TD or PD plot) involving both nasal and temporal quadrants with very deep defect at test points and involving the central 5 degrees from the fixation of 10-2 VF (Figs. 1A and B); (2) Shallow arcuate scotoma: similar to a deep arcuate scotoma except not associated with very deep defect at test points and not involving the central 5 degrees from the fixation of 10-2 VF (Fig. 1C); (3) Partial arcuate scotoma: continuous but less dense (fewer abnormal points) than a shallow arcuate scotoma, superior or inferior hemifield defect (P<1%,<2% on TD or PD plot) and not involving the central 5 degrees from the fixation of 10-2 VF and may include both nasal and temporal quadrants (Fig. 1D); (4) Cluster defect: a cluster of 3 contiguous abnormal points with P<5%, 5% and 1% or <5%, 2%, and 2% within a hemifield on either TD or PD plot (Fig. 1E); (5) No CVFD: a VF that did not display any defect described above.

The deep and shallow arcuate scotomas were interpreted as the severe form of pattern defects and were grouped to form an arcuate defect group. Partial arcuate scotoma was considered a moderate form of pattern defects. Cluster defects and no CVFD were interpreted as mild defects and were merged as a minimal defect group.

Statistical Analysis

Only the 12 test locations within the central 10 degrees of the 24-2 test were included in the comparative analysis of the 24-2 and 10-2 tests. Our methods are similar to what we have reported previously.16 Abnormal VF points in the central 12 points (depressed either <1%, or <0.5% from the normal database on either TD or PD probability plot) on 24-2 VF tests were analyzed. For each abnormal test point, within the central-most 4 points and paracentral 8 points on 24-2 VF, we measured the test point’s threshold sensitivity value (dB) and deviated threshold sensitivity value (dB) on total deviation (TD) numerical plot and pattern deviation (PD) numerical plot separately. Deviated sensitivity value (dB) at abnormal test point on TD/PD numerical plots was termed as sensitivity loss or defect value of that abnormal point. The relative position and number of abnormal points in each hemifield on 24-2 VF were also analyzed. Using the Mann-Whitney U test, we compared perimetric parameters differences among 3 groups formed by the 10-2 VF pattern defects: arcuate, partial arcuate, and minimal defects. The association between threshold sensitivity and the magnitude of sensitivity loss (defect value on TD/PD) at abnormal test point on 24-2 VF and pattern defect on the 10-2 VF test was captured using the Pearson χ2 test. We also investigated the 24-2 VF characteristics that could predict the severity of an abnormal 10-2 VF result using binary logistic regression. The dependent variable was whether the 10-2 test was abnormal (based upon the cluster criteria and pattern defect described above) and the independent variable was the presence of abnormal central 24-2 VF points (defined based upon different perimetric defects: threshold sensitivity, defect value on TD/PD plots, relative position and the number of abnormal points). The statistical significance was tested at a 5% level. SPSS Version 26 (IBM Corp, Armonk, USA) was used for the statistical analysis. P-value was adjusted for pairwise multiple comparisons.

RESULTS

Patients’ demographic and ophthalmic measurements are shown in Table 1. Among 64 glaucomatous eyes, 15 eyes (23.4%) had CVFDs as isolated IPFS, and 49 (76.5%) eyes had CVFDs where VF defects extended beyond the central 10 degrees. Of 64 eyes, 26 eyes (40.6%) demonstrated arcuate scotoma on 10-2 VF test, 16 (25%) eyes displayed partial arcuate scotoma and 22 eyes (34.3%) displayed minimal defect either as cluster defect (18.7%) or no CVFDs (15.6%) on 10-2 VF test.

TABLE 1 - Patient Demographic and Clinical Characteristics
Mean±SD Minimum–Maximum
Patient characteristics (n=56)
Age, years 67.2±11.8 40–80
Sex, n (%)
Female 26 (46.4)
Male 30 (53.5)
Eye characteristics (n=64)
 Baseline IOP (mm Hg) 21.5±3.5 18–30
Glaucoma (based on 24-2 VF), n (%)
 Early (better than −6 dB) 54 (84.3)
 Moderate (worse than −6 dB and better than −7 dB) 10 (15.6)
Perimetric parameters at abnormal points in the central-most 4 points on 24-2 VF
Threshold sensitivity (dB) 21.9±8.5 <0–29
 Defect value* on TD plot (dB) −12.4±11.3 −5 to −35
 Defect value on PD plot (dB) −14.8±12.0 −5 to −35
Perimetric parameters at abnormal points in the paracentral 8 points on 24-2 VF
Threshold sensitivity dB 21.6±6.2 <0–28
 Defect value* on TD plot (dB) −12.9±9.7 −5 to −35
 Defect value on PD plot (dB) −13.0±10.1 −5 to −35
VFI% in 24-2 VF 90.8±4.9 81–99
Fovea sensitivity (dB) on 24-2 VF 35.4±2.5 32–40
 24-2 VF MD (dB) −3.8±1.9 −0.1 to −6.9
 10-2 VF MD (dB) −3.5±3.2 1.2 to −16.7
 24-2 VF PSD (dB) 4.9±2.7 1.7–14.6
 10-2 VF PSD (dB) 4.3±3.9 1.0–15.2
*Defect value on TD plot (dB)=deviated threshold sensitivity value at an abnormal point on total deviation numerical plot on 24-2 VF.
Defect value on PD plot (dB)=deviated threshold sensitivity value at an abnormal point on pattern deviation numerical plot on 24-2 VF.
dB indicates decibels; IOP, intraocular pressure; MD, mean deviation; PSD, pattern standard deviation; VF, visual field; VFI, visual field index.

With respect to severity, eyes with arcuate scotoma on 10-2 VF showed more substantial functional loss (worse MD and PSD) than partial arcuate [(MD=−5.9±3.6 vs. −2.9±1.1; P=0.001); (PSD=7.7±4.1 vs.2.8±1.7; P<0.001)] and minimal defect groups on 10-2 VF [(MD=−5.9±3.6 vs. −1.3±1.5; P<0.001); (PSD=7.7±4.1 vs. 1.5±0.8; P<0.001)] as in Table 2. The magnitude of sensitivity loss (defect value) on TD/PD plot at any abnormal central 12 points (<1%) on 24-2 VF and related parafoveal scotomas on 10-2 VF test are shown in Table 3. The presence of abnormal 24-2 VF points (<1%) within the central-most 4 points was significantly different between eyes with and without arcuate scotomas on 10-2 VF (P=0.002). The percentage of eyes without any abnormalities within the central-most 4 points on the PD plot on 24-2 VF was significantly higher in eyes without arcuate scotomas compared with eyes with arcuate scotomas on 10-2 VF test: (34% in arcuate vs. 68.7% in partial arcuate and 72.7% in minimal defect groups; P=0.015) (Table 3). This result indicated that there was a minimum difference between the 2 nonarcuate groups in number and percentage of eyes where the eyes had no abnormal points in the central-most 4 points. This finding may be a possible explanation of little differences of parameters in the analysis of central-most 4 points between the 2 nonarcuate groups in Table 2.

TABLE 2 - Comparison of Perimetric Parameters Between 24-2 Visual Field With Abnormal Central Points (<1%) and Related 10-2 Visual Fields With Pattern Defects
Related Parafoveal Scotomas on 10-2 VF
P*
Perimetric Parameters at Abnormal Central Points on 24-2 VF (n=64 eyes) Arcuate Defect, n=26 Partial Arcuate Defect, n=16 Minimal Defect, n=22 Arcuate vs. Partial Arcuate Defect Arcuate vs. Minimal Defect
Parameters in the central-most 4 points
Threshold sensitivity (dB) 19.1±10.5 24.7±4.7 24.3±7.2 0.14 0.15
 Defect value (TD) −17.5±13.1 −7.3±5.0 −7.2±6.3 0.024 0.019
 Defect value (PD) −18.5±13.3 −9.0±5.5 −9.2±8.2 0.23 0.20
Parameters in the paracentral 8 points
Threshold sensitivity (dB) 18.8±7.9 21.3±5.4 23.3±4.3 0.34 0.022
 Defect value (TD) −18.1±11.6 −9.7±5.1 −8.3±4.1 0.018 0.002
 Defect value (PD) −19.1±12.1 −10.6±5.2 −7.8±4.1 0.06 < 0.001
24-2 VF MD (dB) −4.3±1.8 −4.4±1.7 −3.2±1.8 0.93 0.044
10-2 VF MD (dB) −5.9±3.6 −2.9±1.1 −1.3±1.5 <0.001 <0.001
24-2 VF PSD (dB) 6.12±3.0 4.3±2.3 3.9±2.0 0.07 0.003
10-2 VF PSD (dB) 7.7±4.1 2.8±1.7 1.5±0.8 <0.001 <0.001
*Mann-Whitney U test was used.
Defect value (TD)=deviated threshold sensitivity value at an abnormal point on total deviation numerical plot on 24-2 VF
Defect value (PD)=deviated threshold sensitivity value at an abnormal point on pattern deviation numerical plot on 24-2 VF.
dB indicates decibels; MD, mean deviation; PSD, pattern standard deviation; VF, visual field.

TABLE 3 - Defect Value at Abnormal 24-2 Visual Field Points Depressed <1% in the Central 12 Points and Related Parafoveal Scotomas on 10-2 Visual Field
Defect Value at Abnormal Points Depressed <1% in the Central 12 Points on 24-2 Visual Field on TD/PD Plot (n=64 Eyes)
Defect Value Between −25 dB to −34 dB Defect Value Between −15 dB to −24 dB Defect Value Between −5 dB to −14 dB No Defect
Parafoveal Scotomas on 10-2 Visual Field Central 4 Paracentral 8 Central 4 Paracentral 8 Central 4 Paracentral 8 Central 4 Paracentral 8
Arcuate (n=26) 7 (27) 9 (34.6) TD 2 (7.6) TD 4 (15.3) TD10 (38.4) TD 13 (50) TD 7 (27) TD 0
PD 1 (3.8) PD 3 (11.5) PD 9 (34.6) PD 12 (46) PD 9 (34.6) PD 2 (7.6)
Partial arcuate (n=16) 0 0 1 (6.2) 3 (18.7) TD 8 (50) TD 12 (75) TD 7 (43.7) TD 1 (6.2)
PD 4 (25) PD 10 (62.5) PD 11 (68.7) PD 3 (18.7)
Minimal defect (n=22) 0 0 1 (4.5) 2 (9) TD 9 (41) TD 14 (63.6) TD 12 (54.5) TD 6 (27.2)
PD 5 (22.7) PD 17 (77.2) PD 16 (72.7) PD 3 (13.6)
P* 0.003 <0.001 0.93 0.66 TD: 0.75 TD: 0.25 TD: 0.14 TD: 0.008
PD: 0.62 PD: 0.08 PD: 0.015 PD: 0.56
Data are expressed in number (%) of eyes from each group.
*Pearson’s χ2 test.
When TD and PD values are the same, they are not mentioned separately.
dB indicates decibels; PD, pattern deviation numerical plot; TD, total deviation numerical plot.

As seen in Table 3, a high defect value (>−34 dB) at any abnormal central 12 points on TD/PD on 24-2 VF and arcuate scotoma on 10-2 VF were significantly related: 27% of eyes with arcuate defect had such severe sensitivity loss at an abnormal point within the central-most 4 points (P=0.003) and 35% eyes had within the paracentral 8 points (P<0.001). Similarly, an association between very low threshold sensitivity value (<0–10 dB) at any abnormal central 12 points on 24-2 VF and arcuate scotomas on 10-2 VF was also demonstrated (Table S1, Supplemental Digital Content 1, https://links.lww.com/IJG/A615). In contrast, eyes without having arcuate scotomas on 10-2 VF were not related to very low threshold sensitivity (<0–10 dB) and severe defect value (>−34 dB) at any abnormal central 12 points on 24-2 VF (except one in minimal defect group) (Table 3 and S1, Supplemental Digital Content 1, https://links.lww.com/IJG/A615).

We investigated the characteristics of the 24-2 VF result that predicted the presence of an arcuate scotoma on 10-2 VF testing (Table 4, Fig. 2). The severity of 10-2 VF significantly differed according to the variations of threshold sensitivity and defect value at any abnormal 24-2 VF points (<1% or <0.5%) and their location and number in the hemifield (Fig. 2). The presence of abnormal test point depressed <0.5% within the central-most 4 points on the PD plot was significantly associated with an arcuate scotoma on 10-2 VF [odds ratio (OR)=4.6; 95% confidence interval (CI): 1.5–13.7; P=0.004] (Fig. 2A). These effects were smaller in the presence of such abnormalities within the paracentral 8 points (OR=2.2; 95% CI: 0.4–12.1; P=0.3) (Fig. 2B). Having arcuate scotomas on a 10-2 VF test was more likely when such abnormal points’ threshold sensitivity was lower than 20 dB (OR=7.2; 95% CI: 1.7–30.1; P=0.002 and OR=5.1; 95% CI: 1.6–15.9; P=0.003 for the central 4 and paracentral 8 points, respectively) and defect value worse than −15 dB (OR=8.0; 95% CI: 1.5–41.6 and OR=5.6; 95% CI: 1.6–19.0 for the central 4 points and paracentral 8 points, respectively, both P=0.005) on 24-2 VF (Table 4, Figs. 2A and C). The severity of parafoveal scotomas on 10-2 VF was mild when abnormal central 24-2 VF points’ threshold sensitivity was higher than 20 dB and sensitivity loss was better than –15 dB (Fig. 2D). There were 10 eyes (15.6%) with abnormal 24-2 VF points (<1% to <0.5%) in the central 12 points, but without parafoveal scotomas on the 10-2 VF test as the defects were very mild at abnormal test points (Fig. 2E). Abnormal superior nasal defect in the central 5 degrees on 24-2 VF was significantly associated with an arcuate defect on 10-2 VF (OR=50.4; 95% CI: 5.9–425.9; P<0.001). However, the effect was much lower in the presence of such defect within paracentral 8 points (OR=2.7; 95% CI: 0.8–8.6; P=0.07).

TABLE 4 - Predictive Value of 24-2 Visual Field Abnormalities (Within the Central 12 Points) on Having an Arcuate Scotoma on 10-2 Visual Field
Abnormal Points in 24-2 Visual Field Within the Central 12 Points
Within the Central-most 4 Points Within the Paracentral 8 Points
OR 95% CI P OR 95% CI P
Presence of abnormal 24-2 VF points 4.6 1.5–13.7 0.004 2.2 0.4–12.1 0.33
Presence of abnormal 24-2 VF point with defect value worse than −15 dB 8.0 1.5–41.6 0.005 5.6 1.6–19.0 0.005
Presence of abnormal 24-2 VF point with threshold sensitivity lower than 20 dB 7.2 1.7–30.1 0.002 5.1 1.6–15.9 0.003
Presence of single abnormal point on 24-2 VF 7.7 2.2–25.9 <0.001 0.4 0.1–1.4 0.17
Presence of >1 abnormal points on 24-2 VF 1.1 0.2–5.4 0.89 5.1 1.6–15.6 0.003
Presence of abnormal 24-2 VF point at the superior nasal location 50.4 5.9–425.9 <0.001 2.7 0.8–8.6 0.07
Presence of abnormal 24-2 VF point at superior temporal location 1.1 0.2–5.4 0.89 2.0 0.7–5.5 0.17
The 24-2 abnormalities are defined based upon probabilities on pattern deviation plots. The dependent variable is the presence of parafoveal scotoma on the 10-2 test.
CI indicates confidence interval of the mean; OR, odds ratio; PD, pattern deviation numerical plot; TD, total deviation numerical plot; VF, visual field.

F2
FIGURE 2:
Examples of cases demonstrate the predictive value of 24-2 visual field (VF) abnormalities (within the central 12 points) on having arcuate scotoma on 10-2 VFs. A, This 24-2 VF had 1 abnormal point <0.5% within the central-most 4 and 2 abnormal points (<0.5% and <1%) within paracentral 8 points. Abnormal central and paracentral points had very low threshold sensitivity (0 dB) and worse defect value (−34 dB). Related 10-2 defect was arcuate scotoma. Figures B and C are comparable. Both the VFs had no abnormal central points and only abnormal paracentral points (<0.5%) on 24-2 VF. In (B), 2 abnormal test points’ defect was mild to moderate on 24-2 VF. Corresponding 10-2 VF was inferior partial arcuate scotoma. In (C), 24-2 VF had 3 abnormal paracentral points, and abnormal points’ defect was severe. One of those abnormal paracentral points had a worse defect value (−34 dB) and very low threshold sensitivity (<0 dB) and related parafoveal scotoma on 10-2 VF was an arcuate defect. D, This 24-2 VF had 2 abnormal central points (<0.5%) and 1 abnormal paracentral point (<1%) but the severity of the defect at all abnormal test points was very mild. Hence, the corresponding 10-2 VF demonstrated only cluster defects. E, This 24-2 VF had a single abnormal test point (<0.5%) within the central-most 4 points, but without any parafoveal scotoma or cluster defect on 10-2 VF test as the defect was very mild at abnormal test point.

A single abnormal 24-2 VF point with severe defect value and low threshold sensitivity within the central-most 4 points on the PD plot was significantly associated with arcuate scotoma on 10-2 VF (OR=7.7; 95% CI: 2.2–25.9; P<0.001). In contrast, no significant association was found between an arcuate scotoma on 10-2 VF and the presence of a single abnormal 24-2 VF point within the paracentral 8 points on the PD plot. However, the likelihood of having an arcuate scotoma on 10-2 VF was significantly higher (OR=5.1; 95% CI: 1.6–15.6; P=0.003) in the presence of multiple abnormal 24-2 VF points (<1% or <0.5%) within the paracentral 8 points on the PD plot.

DISCUSSION

The current study demonstrated that the clinical characteristics of 10-2 VF varied significantly depending on the variation of threshold sensitivity and magnitude of sensitivity loss at abnormal central 12 points depressed <1% or <0.5%, and also their location and number within the central-most 4 or paracentral 8 points on 24-2 VF. Eyes with an arcuate scotoma showed more functional loss than the aforementioned two groups without arcuate scotoma on 10-2 VF. A significant association was observed between threshold sensitivity lower than 20 dB and defect value worse than −15 dB at an abnormal central or paracentral test point on the 24-2 VF and arcuate scotoma on the 10-2 VF. These cutoff values are consistent with the cutoff values obtained from previous studies16 and there is also a close correspondence with the existing guideline for evaluating functional damage in glaucoma.19 Hence our results showed that the severity of 10-2 field loss was reasonably predictive based on the findings of the 24-2 VF test alone. These findings are consistent with previous studies.13,14

Glaucoma affects both central and midperipheral vision. Patients with CVFDs would have greater impairment in visual function than those with the preserved central VF.20 CVFDs at baseline demonstrate significant association with more rapid global progression of the field.21 These patients are at high risk and may need early detection, intensive follow-up, and aggressive treatment.21

Since the severity of 10-2 VF loss is expected to have a stronger relationship with an individual’s functional capability than the mere presence of 10-2 field loss, the main concern of our study was to determine the relationship between the severity of 10-2 VF loss and the presence of abnormal points’ defect within the central 12 points on a 24-2 VF. As the impact of an arcuate parafoveal scotoma on a patient’s quality of life is more severe than that of a cluster defect, a classification system for grading the clinical characteristics of parafoveal scotoma on a 10-2 VF test should be considered. Such quantification is also essential for a better follow-up of the progression of the disease. Classification of arcuate-like defects on 10-2 VFs has been used previously by other investigators3,8,14 based on the patterns of defects on 10-2 VF. Following their observations and our previous report,16 we proposed a modified classification system for grading parafoveal scotomas on 10-2 VF which primarily depend on perimetric defects of abnormal central 12 points on 24-2 VF.

The presence of a single abnormal point depressed <1% with low threshold sensitivity and high sensitivity loss within the central-most 4 points on 24-2 VF was strongly related to the incidence of arcuate-like parafoveal scotoma on 10-2 VF. In contrast, the relationship between the presence of such abnormal single point within paracentral 8 points on 24-2 VF and arcuate scotoma on the 10-2 VF was poor. However, the presence of multiple abnormal paracentral points (<1%) was associated with increased severity of CVFDs, even without any abnormalities within the central-most 4 points on 24-2 VF (Fig. 2C). Our results highlight some important points. First, abnormalities within the central-most 4 points were mostly associated (77%) with an arcuate defect on 10-2 VF. Second, a 10-2 VF could display arcuate parafoveal scotoma even without any abnormal points in the central-most 4 points, but in the presence of multiple abnormal paracentral points (<1%) on 24-2 VF. Third, the severity of 10-2 VF could be anticipated by assessing the threshold sensitivity and the magnitude of sensitivity loss at abnormal central 12 points depressed <1% or <0.5% on 24-2 VF.

We report 10 eyes (15.6%) with abnormal test points either within the central-most 4 points or paracentral 8 points depressed between <1% and <0.5% on 24-2VF, but without any parafoveal scotoma or cluster defect on 10-2 VF (Fig. 2E). Park et al11 found that 10% of eyes had abnormal points within the central-most 4 points and 30% eyes had within the paracentral 8 points depressed to <0.5% but without any parafoveal scotomas on 10-2 VF test. Overall, our findings concur well with results from a previous study and support the premise that abnormal 24-2 VF points depressed <1% or <0.5% within the central 10 degrees on the PD plot may not always be significantly related to parafoveal scotomas or even cluster defects on 10-2 VF test. Hence, we suggest that the severity of CVFDs may be evaluated by measuring perimetric factors at abnormal test points and not merely by the probability plot values. For example, in Figure 2A and D, both the VFs had abnormal points depressed <0.5% within the central-most 4 points and paracentral 8 points. Figure 2A showed very low threshold sensitivity and severe sensitivity loss at both central and paracentral points and a related 10-2 defect was arcuate scotoma. In contrast, in Figure 2D, abnormal central and paracentral points’ sensitivity loss was mild and threshold sensitivity was near normal. So, related 10-2 VF demonstrated only cluster defect. The typical range of normal threshold sensitivity in the central VF is slightly higher than 20 dB and a little under 40 dB.22

Our earlier study demonstrated that the severity of parafoveal scotoma on 10-2 VF was determined by measuring perimetric factors at abnormal test points (<1%, <0.5%) within the central-most 4 points on 24-2 VF.16 The present study departs from our previous study as we investigated here both abnormal central-most 4 points and paracentral 8 points on 24-2 VF and related parafoveal scotomas on 10-2 VF. But in the earlier report, observations were restricted to only abnormal central-most 4 points on 24-2 VF.16 Consequently, those findings have limited applications in clinical practice and might only be applicable to elucidate the severity of CVFDs within the central 5 degrees in early glaucoma. Overlooking abnormalities within the paracentral 8 points could be a considerable limitation to assessing the association between exposure to abnormal central 12 points’ defect on 24-2 VF and the outcome of having parafoveal scotomas on 10-2 VF.

There are some limitations to our study. For the sensitivity measurement at abnormal test points within the central 12 points, we did not convert a dB value to asb unit and did not apply any particular measure to evaluate the defect value of <0 dB at the abnormal test point. Another practical limitation is that we did not have good quality optical coherence tomography images. So, the correlation between VF loss and optical coherence tomography measurements was not done and was hard to determine whether those abnormalities were real or false positives. We put maximum importance on the arcuate-like severe parafoveal scotoma on 10-2 VF rather than to relatively less severe defects: partial arcuate and cluster defect. It may create a hindrance to the proper understanding of the severity of these two groups.

To conclude, threshold sensitivity and magnitude of sensitivity loss at abnormal central 12 points depressed <1% and their location and number within the central-most 4 or paracentral 8 points may determine the severity of CVFDs on 24-2 VF and related parafoveal scotomas on 10-2 VF in glaucomatous eyes. Further, a comparison between the 2 types of defects, central-most 4 and paracentral 8 points on 24-2 VF, provides invaluable information on the severity of CVFDs, thus enabling more accurate staging of the disease. In clinical practice, this study may improve early prediction of the severity of CVFDs by assessing threshold sensitivity and sensitivity loss at abnormal central 12 points (<1%) within the central 10 degrees on 24-2 VF in early glaucoma. Our results and recommendations are appropriate only for eyes without macula disease. These data do not minimize the importance of a 10-2 VF test especially in patients with a high risk of CVFDs. By using only 24-2 VF, one may miss glaucomatous damage of the macula that may occur before peripheral damage. Additional research is needed to optimize clinical testing and health care resource utilization for early detection of CVFDs and proper evaluation of the severity of CVFDs on 24-2 VF for glaucoma management.

ACKNOWLEDGMENTS

The authors acknowledged the help and infrastructural support from Eye & Glaucoma Care Trust, Kolkata, India.

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Keywords:

severity; central visual field defects; central-most 4 points; paracentral 8 points; threshold sensitivity

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