Biometric indicators of Eyes with Occult Lens Subluxation inducing Secondary Acute Angle Closure

Results

There was a significant difference in the ocular axial length among the four groups of patients (P=0.000). A pair-wise comparison revealed that the patients with ASAC-LS had a longer ocular axial length than those with APAC and CPACG (P=0.002, 0.016, respectively). There were no significant differences in the axial length between the ASAC-LS group and the cataract group (P =0.902).

Table 1. Biometry parameters in groups

Corneal thickness was significantly different among the four groups (0.002). Corneal thickness in the ASAC-LS group was not significantly different from that in the APAC group, but was significantly different from those in the CPACG and cataract groups (Table 1).

There was a significant difference in anterior chamber depth and aqeous depth (AD) among the four groups (P=0.000 both). The APAC group had the smallest anterior chamber depth among the four groups, while the ASAC-LS group had the smallest AD among the four groups. The ASAC-LS group exhibited significantly shallower anterior chamber depth than the other three groups (P=0.000). (Figure1).

The ASAC-LS group had the largest lens thickness, followed by the APAC group; however, the difference between these two groups was not statistically significant. Compared with the other two groups, lens thickness in the ASAC-LS group was significantly different (P=0.000). There was a statistical difference among the four groups in terms of each of the above-mentioned indices. The ASAC-LS group had the smallest value for each of the above-mentioned indices, which are significantly different from other three groups. The factors in APAC and CPACG had no statistical differences【P=0.323(LP), 0.058 (CLP), 0.678 (RLP)】，while other groups did have. (Table2).

The range of lens zonula dehiscence were recorded during subsequent surgery, with the average of 5 ± 2.24 o’clock lens zonula dehiscence. The AD correlated with the range of lens zonula dehiscence (P=0.034).

Discussion

The main mechanism of PACG is considered as pupillary block. Increased resistance of aqueous humor flow between the iris and anterior lens surface leads to angle closure. A short axial length (AL) of the globe, thicker lens, anteriorly placed lens, are the main dangerous factors[13].

Traumatic or spontaneous lens dislocation can cause acute angle closure. The features of zonular instability include iridodonesis, decentration of the nucleus, phacodonesis, the lens equator exposure, and vitreous prolapse in the AC. In clinic, due to the risk of iatrogenic angle-narrowing and elevated intraocular pressure, angle-closed eyes usually do not undergo pharmacologic pupil dilation[14]. Due to relaxation or lens zonula dehiscence, the anterior capsule of the lens can attach or adhere to the posterior surface of the iris [1]. The lens and/or vitreous hernia can cause pupil block, leading to an increase in posterior chamber pressure; consequently, the iris is pushed against and closes the anterior angle, resulting in increased IOP. Its clinical manifestations are very similar to those of APAC and, thus, is prone to misdiagnosis. The literature also suggested that the major form of the secondary glaucoma associated with lens subluxation was the open-angle type[15].

We analyzed the clinical features of a group of patients with acute secondary angle closure due to lens dislocation, monocular onset, and acute anterior chamber shallowing (AD<1.25 mm). Compared with the APAC, CPACG, and cataract groups, the anterior chamber depth of patients with acute angle closure due to lens dislocation was significantly smaller, even less than 0.66mm. Therefore, whenever small anterior chamber depth is observed during clinical diagnosis of patients with APAC, it is necessary to devote attention to acute secondary angle closure caused by lens factors. It has been reported that the anterior chamber depth is significantly different between the involved eye and the contralateral eye in patients with acute angle closure due to LS16. In this study, data from the contralateral eyes were incomplete; therefore, anterior chamber depth was not compared between the two eyes.

Patients with angle-closure glaucoma usually exhibit a shorter ocular axial length. However, the ocular axial length in the group of patients with acute angle closure caused by ASAC-LS was not significantly different from that in the cataract group, but was longer than that in the APAC and CPACG groups. It has been reported that LS patients have the longest ocular axial length among the population with acute angle closure. Other causes of acute angle closure include iris bombe, pupil block, and plateau iris [17-18].

Among the four groups of patients, lens thickness in the ASAC-LS group was the greatest, and was significantly different from that in the cataract and the CPACG groups; therefore, lens thickness was not sufficient to diagnose the four diseases. As a result, the parameter of lens position (LP) (defined as the sum of anterior chamber depth and 1⁄2 lens thickness) was introduced in this study. Calculations indicated that there was significant difference between any two groups. Some studies18 in the literature used lens vault (defined as the perpendicular distance between the anterior lens pole and the horizontal line joining the two scleral spurs) measured using UBM as an indicator of lens morphology and found that lens vault increases in patients with unstable suspensory ligaments of the lens.

When the lens is subluxated, the lens zonule dehisence has a large effect on the position of the lens. In this group, the dehisence was recorded during surgery and was found to correlate with AD. Therefore, for occult LS, which does not have clear clinical manifestations and does not have a very high UBM diagnosis rate, AD can be used as one of the indirect determinant indicators.

In summary, we retrospectively analyzed biometric characteristics of the anterior segment of patients with acute angle closure secondary to occult LS. Several points should be addressed during diagnosis and treatment. For younger patients with acute angle-closure glaucoma, it is necessary to exclude lens zonula relaxation caused by abnormal lens development; otherwise, the patients would be misdiagnosed with APAC rather than acute secondary angle-closure glaucoma due to lens dislocation and undergo peripheral iridotomy or glaucoma filtering surgery, which not only increases the risk for complications, such as intraoperative vitreous herniation, postoperative shallow anterior chamber and even malignant glaucoma, but also reduces the success rate of the operation. When applicable, UBM should be used to observe whether the suspensory ligament of the lens is severed or simply relaxed. The anterior chamber depth should be measured: a short depth (< 1.25 mm) is highly indicative of abnormality in the lens zonula dehiscence or relaxation, and the depth should be compared with that of the contralateral eye. Lens thickness should be measured and, if it is > 5.13 mm, abnormal suspensory ligament of the lens should be suspected. Meanwhile, LP and CLP can be calculated for differential diagnosis.

Limitations of the present study include the absence of a biometric comparison of the lateral eyes in each group of patients. LS900 can only be used to measure the patients with no serious opacity of cataracts.

Conclusions

For younger patients with acute angle-closure glaucoma, it is necessary to exclude lens zonula relaxation. A short depth (< 1.25 mm) and a thick lens thickness (> 5.13 mm) are crisis of lens subluxation in our data. LP and CLP can be helpful for differential diagnosis.

Declarations

Ethics approval and consent to participate

This research followed the tenets of the Declaration of Helsinki, informed consent was obtained from the subjects after explanation of the nature and possible consequences of the study and proof of publication. This study was approved by the ethics committee of Tianjin Medical University Eye Hospital.

Consent for publication

Written consent for publication was obtained from the participants.

Availability of data and material

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

This work was supported by grants from Natural Science Foundation of Tianjin Medical University (2016KYZM16), Scientific and Clinical ResearchFund of Ophthalmology Institute of Tianjin Medical University Eye Hospital (15YKYJS001).

Authors' contributions

X.X.L. designed and supervised the study; H.L.Y. analyzed data; L.W.and L.Y.J. drafted the manuscript; L.A.H. performed research; all authors read and approved the final manuscript.

Acknowledgements

Not applicable.

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Table 2

Table 2: Comparison of biometry parameters in different groups

CATA: cataract