A total of 129 cases were included in this study with 41 in RDD-CD group, 43 in RRD group, and 45 in TRD group. In RRD-CD group, there were 27 males and 14 females, with mean age of 52.24 ± 10.59 years. In RRD group, there were 38 males and 15 females, with mean age of 52.81 ± 13.13 years. In TRD group, there were 24 males and 21 females, with mean age of 53.64 ± 11.48 years. There was no significant difference in gender distribution (p = 0.34) and age (p = 0.56) among the three groups.
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The baseline characteristics of patients before the PPV surgery
In the affected eyes, the mean of AL in RRD-CD group was 24.46 ± 2.48 mm, which was similar to that in RRD group (25.43 ± 2.82 mm, p = 0.08), but longer than that in TRD group(23.16 ± 0.83 mm, p = 0.001).
In the fellow eyes, the mean of AL in RRD-CD group was 25.89 ± 2.78 mm, which was similar to that in RRD group (24.32 ± 5.43 mm, p = 0.08), but longer than that in TRD group (21.62 ± 5.90 mm, p < 0.001).
The median and IQR of AL difference between the affected eye and fellow eye was − 0.90 (2.15) mm in RRD-CD group, 0.07 (0.73) mm in RRD group, and − 0.04 (0.28) mm in TRD group respectively. The shorter AL of the affected eyes compared to fellow eyes was observed in RRD-CD group (p = 0.01), but not in RRD group (p = 0.17) or TRD group (p = 0.09). The variation of AL between two eyes of the same patient was greater in RRD-CD group than that in TRD group (p < 0.001), and RRD group (p = 0.01).
There were 12 patients (29.3%), 19 patients (35.8%), and none patient with PM in RRD-CD, the RRD, and TRD groups, respectively. The percentage of PM in RRD-CD group and RRD groups showed no significant difference (p = 0.71), but both are significantly higher than that in the TRD group (p < 0.001).
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The interval from PPV to SOR
The median and IQR of interval time between two surgeries was 154 (89) days in RRD-CD group, 159 (95) days in RRD group, and 201 (166) days in TRD group. There was no significant difference in the interval between two surgeries among the three groups (p = 0.32).
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The AL characteristics of patients before SOR surgery
In the affected eyes, the mean of AL before SOR in RRD-CD group was 25.72 ± 2.66 mm, which was similar to that in RRD group (25.75 ± 3.00 mm, p = 0.83), but significantly longer than that in TRD group (23.28 ± 0.95 mm, p = 0.001).
Similar to AL before the PPV surgery, in the unaffected eyes, the mean of pre-operative AL in RRD-CD group was 25.91 ± 2.81 mm, which was similar to that in RRD group (24.30 ± 5.47 mm, p = 0.06), but significantly longer than that in TRD group (21.59 ± 5.96 mm, p = 0.003).
The median and IQR of the difference of AL between the affected eye and fellow eye before SOR was − 0.04 (0.98) mm in RRD-CD group, 0.19 (0.98) mm in RRD group, and − 0.03 (0.29) mm in TRD group, respectively. AL of the affected eyes was shorter than that of the fellow eyes in RRD-CD group (p = 0.015). There was no significant difference in AL between the affected eyes and fellow eyes in RRD group (p = 0.17) or TRD group (p = 0.09). The difference of AL between the affected eye and fellow eye in RRD-CD group was not significantly different from that in RRD group (p = 0.11) or that in TRD group (p = 0.06). There were no significant changes of AL in the follow eye before PPV and before SOR in neither of the three groups (p = 0.96).
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The changes of AL from PPV to SOR (Fig. 1)
In RRD-CD group, AL measured before SOR was longer than that measured before PPV with a median (IQR) of 1.01 (1.42) mm (p = 0.02). There was no such significant difference in RRD group with a median of 0.15(0.38) mm (p = 0.58) or TRD group with a median of 0.07 (0.18) mm (p = 0.53). The variation of AL between the two surgeries in RRD-CD group was greater than that in RRD group (p < 0.001) and that in TRD group (p < 0.001).
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The changes of IOP of the affected eye from PPV to SOR (Fig. 2)
The mean IOP before PPV in RRD-CD group was 8.0 ± 2.7 mmHg, which was lower than that of RRD group (12.5 ± 4.3 mmHg, p < 0.001), and that of TRD group (12.7 ± 9.2 mmHg, p = 0.003).
There were 26 (73.4%) patients with a history of IOP > 30 mmHg in two consecutive follow-ups in RRD-CD group, similar with those in RRD group (23, 43.4%, p = 0.23), but more than those in TRD group (10, 22.2%, p < 0.001).
The mean IOP of the affected eye before SOR in RRD-CD group was 17.0 ± 5.7 mmHg, which was similar to both that of RRD group (17.4 ± 5.7 mmHg, p = 0.73), and that of TRD group (16.2 ± 6.6 mmHg, p = 0.58).
The increased IOP before SOR was observed in the three groups. The mean differences of IOP between PPV and SOR were 8.6 ± 6.4 (-3, 24) mmHg, 4.7 ± 6.2 (-6, 26) mmHg, and 3.5 ± 8.2 (-3.5, 13) mmHg in RRD-CD group, RRD group, and TRD group, respectively. The IOP before SOR was significantly higher than that before PPV in each group of patients (p < 0.001). The amplitude of the elevation of IOP from PPV to SOR was greater in RRD-CD group than that in RRD group (p = 0.002), and TRD group (p = 0.007).
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Factors that may be related to the variation of AL measured between two surgeries
It was reported that a 0.1 mm error in axial length is equivalent to an error of about 0.27D in the spectacle plane[14]. We divided the whole patients into two groups by whether the difference of AL measured before PPV and before SOR was greater than 1 mm in the binary logistic regression analysis. The greatest AIC was achieved in the final model. After adjusting the effect of the factors as the presence of PM (p = 0.45), IOP before PPV (p = 0.86), sustained elevation of IOP in postoperative follow-up (p = 0.51), RRD patients with CD was 11.42 times (3.54, 46.80) more likely to have axial elongation after PPV than patients with RRD (p < 0.001, AIC = 86.15). Patients with RRD-CD was 8.50 times (3.59, 24.87), more likely to have axial elongation than other patients without CD in the whole patients who underwent PPV (p < 0.001, AIC = 98.58).
We further investigated the relationship between AL changes and IOP changes. In linear regression analysis, the difference of AL measured before PPV and before SOR was related to the difference of IOP measured before PPV and before SOR in the group of RRD and RRD-CD. AL increased 0.06 mm when IOP measured before SOR was 1 mmHg greater than that measured before PPV (0.06, R2 = 0.11, p = 0.03) in RRD-CD group. AL increased 0.02 mm when IOP measured before SOR was 1 mmHg greater than that measured before PPV (0.02, R2 = 0.11, p = 0.01) in RRD group. The variation of AL measured between two surgeries was not related to the variation of IOP in the TRD group (p = 0.89)