No significant differences in PIT and IC were observed between NSCACG and CPACG patients. However, we found that PIT and IC had high diagnosis power for malignant glaucoma in CPACG patients. Several mechanisms have been delineated to explain the cause of malignant glaucoma.
29–32 The key lies in the lack of forward movement of the aqueous due to the anterior rotation of the ciliary processes against the lens equator (ciliolenticular block) in phakic or the anterior hyaloid face (ciliovitreal) in aphakic or pseudophakic eyes, which leads to the difference of pressures in the posterior and anterior chambers.
32 By UBM studies, anterior rotation of the ciliary body has been identified as the main anatomic change in eyes with malignant glaucoma.
11,16 The pressure differential causes anterior convexity of the iris and shallowing of the anterior chamber. Huang et al.
33 reported that the thinned and floppy iris was more prone to positional changes influenced by aqueous currents. Our study firstly reported that PIT and IC had the diagnostic power for malignant glaucoma in CPACG patients, and the optimal thresholds for these two parameters were identified (PIT ≤ 0.29 mm, IC ≥ 0.33 mm). A disproportionately large lens in nanophthalmos leads to increased ciliolenticular apposition, which probably explains the higher malignant glaucoma tendency in these eyes.
34 Moreover, LV/ACD and LT/ACD could be used to identify malignant glaucoma in CPACG patients. For ruling in malignant glaucoma, the optimal LV/ACD threshold value of ≥ 0.55 had a sensitivity of 100% and specificity of 81%, and the optimal LT/ACD threshold value of ≥ 2.89 had a sensitivity of 100% and specificity of 87%. The PS Power and Sample Size Calculations V3.0 was used to detect the expected statistical power, presenting the probability that the tests correctly reject the null hypothesis when the alternative hypothesis is true.
35 The level of significance was set at 0.05. The powers to detect the association between IC, PIT, LV/ACD, LT/ACD, and the occurrence of malignant glaucoma were 0.899, 0.922, 0.878, and 0.868, respectively. All powers were over 0.80, which suggested the relative reliability of our study on addressing the associations between parameters and the occurrence of malignant glaucoma in CPACG patients. For NSCACG patients, although eyes with malignant glaucoma had relatively smaller AL, ACW, ACD, CCD, and relative larger LV compared to eyes without malignant glaucoma, no UBM parameters were observed to be associated with malignant glaucoma in NSCACG patients, resulting partly from the limited number of sample size. The modest anatomical differences in NSCACG patients could be studied by further large-scale cohort research.