Comparative analysis of OCT-defined parapapillary beta and gamma zones between primary open-angle glaucoma and primary angle-closure glaucoma

Demographics

The study included 172 patients with primary glaucoma. Among them, 12 patients were excluded for incomplete data and 9 patients were excluded for poor image quality. 73 eyes of 73 PACG patients and 78 eyes of 78 POAG patients were finally analyzed. After propensity score matching, 60 pairs of patients matched to two variables 1:1 (age and MD value) were generated. Overall, mean age was 55.43 ± 13.93 years (range 20–80 years), mean axial length was 23.84 ± 1.66 mm (range 20.45–28 .77 mm) and the mean MD value was -14.52 ± 8.96 (range -1.51 to −32.03 dB). All eyes were phakic.

The demographic and clinical characteristics of the patients in the PACG group and the POAG group before and after matching are presented in Table 1. The two groups did not vary significantly in terms of DM value and cpRNFL thickness. Compared with the POAG group, the mean axial length was significantly shorter (PPP= 0.017), the mean age was significantly higher (P= 0.02), and the mean area of ​​the beta zone was significantly larger (P= 0.031) in the PACG group. After matching the propensity score for age and MD value, the mean area of ​​the beta zone no longer showed a significant difference between the PACG and POAG groups (P= 0.493).

Table 1 Demographic and clinical characteristics of patients before and after PSM in the PACG and POAG groups.

Factors associated with the parapapillary beta zone and the gamma zone

Among all patients included, parapapillary beta zone (mean area 0.76 ± 0.69 mm2range from 0.18 to 4.84 mm2) was present in 135 eyes, including 66 (90.4%) eyes in the PACG group and 69 (88.5%) eyes in the POAG group (Figs. 1, 2). Parapapillary gamma zone (average area 0.19 ± 0.30 mm2range 0.06-1.42mm2) was present in 54 eyes, including 16 (21.9%) eyes in the PACG group and 38 (48.1%) eyes in the POAG group.

Figure 1

Illustration of measurement of parapapillary beta and gamma zones in bilateral eyes of patients with glaucoma. (A,B) The size of the parapapillary beta zone (orange shadow) and the parapapillary gamma zone (blue shadow) was similar between the severe right eye and the moderate left eye in a POAG patient. (VS,D) The severe right eye showed a concentric shape of the parapapillary beta zone in a PACG patient, while the moderate left eye showed a relatively smaller parapapillary beta zone. Red arrow/line: optic disc margin; Blue arrow/line: the end of Bruch’s membrane; Orange arrow/line: the end of the RPE.

Figure 2
Figure 2

Distribution of parapapillary beta zone area in POAG and PACG groups.

To investigate the factors associated with the parapapillary beta zone, we first performed univariate and multivariate linear regression on the beta zone in the entire study group. In univariate analysis, a larger beta zone was significantly associated with older age (PP= 0.041) and gender (P= 0.043). Model construction for the multivariate analysis began with the list of independent parameters including age, gender, axial length, IOP, DM, cpRNFL thickness, and type of glaucoma. Non-significant parameters were removed step by step from this complete model. In the final model, a larger beta zone was associated with older age (PP= 0.002) and a longer axial length (P= 0.029) (Table 2).

Table 2 Linear regression analysis of variables associated with parapapillary beta zone area in the entire study group.

We then performed the univariate and multivariate linear regression on the beta zone in the PACG group and the POAG group, respectively. In the multivariate model, the beta zone in the POAG group was ultimately associated with age (P= 0.007), whereas in the PACG group it was ultimately associated with age (P= 0.005) and the MD value (P= 0.009) (Table 3). We further performed a paired sample t-test in eyes with bilateral POAG in 45 patients whose MD value differed by more than 2 dB. The results also showed that there was no significant difference on the beta zone between severe eyes and mild eyes with POAG (P= 0.576).

Table 3 Multivariate regression analysis of variables associated with parapapillary beta zone area in PACG and POAG groups.

Multivariate linear regression analyzes were also performed to investigate factors related to the parapapillary gamma zone. In the multivariate analysis model for gamma zone, parameters include beta zone (P=0.099), MD value (P=0.825), age (P=0.817), IOP (P=0.630), type of glaucoma (P = 0.592), and mean cpRNFL thickness (P = 0.563). In the final model, a larger gamma zone was only associated with axial length (P

Beta zone subtype according to angular extent

Among 135 glaucomatous eyes with beta parapapillary zone, the mean angular extent was 196.0 ± 112.5° (range 60–360°). Among them, 90 eyes were classified into the temporal shape group and 45 eyes into the concentric shape group. The proportions of different shape of the parapapillary beta zone showed no significant difference between eyes with PACG and POAG (P> 0.05, Table 1). Compared to the concentric shape group, the temporal shape group showed a significantly younger age (PPP= 0.039), while IOP, MD value, cpRNFL and gamma area showed no significant difference (P> 0.05). In multivariate logistic analysis of the whole group, the factors associated with the concentric or temporal shape were age (OR = 1.081, P= 0.001) and the MD value (OR = 1.064, P= 0.034) (Table 4).

Table 4 Logistic regression analysis of variables associated with the concentric/temporal shape of the parapapillary beta zone.

The variables were then compared between the temporal and concentric shape of the beta zone in the PACG group and the POAG group, respectively. In the PACG group, the temporal beta-zone eye shape showed a significantly younger age (P= 0.003), mild MD value (P= 0.048); while in the POAG group, the temporal beta-zone eye shape showed a significantly younger age (P= 0.004) and a longer axial length (P= 0.004).

Since the parapapillary gamma zone may not appear simultaneously with the beta zone, the distribution of beta+gamma zone type versus beta zone type only among the concentric/temporal shape of the parapapillary beta zone was also analyzed. Among eyes with temporal form of beta zone (n=90), 56.5% of eyes (26/46) had a parapapillary gamma zone in the POAG group, 13.6% of eyes (6/44) had a parapapillary gamma zone in the PACG group (Pversus. 24.17±0.99mm, P

Table 5 The distribution of the beta/gamma zone combination among the concentric/temporal form of the parapapillary beta zone.

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