Characteristics of Anterior Segment in Congenital Ectopia Lentis: An SS-OCT Study

Purpose To investigate the characteristics of anterior chamber angle parameters in congenital ectopia lentis (CEL) patients and to evaluate the sensitivity and specificity of anterior segment parameters in distinguishing CEL from healthy controls. Setting. Zhongshan Ophthalmic Center, Guangzhou, China. Design Cross-sectional study. Methods 35 CEL patients and 35 age- and sex-matched healthy controls were recruited. Axial length (AL) and anterior segment parameters including anterior chamber width (ACW), angle open distance (AOD), angle recess area (ARA), trabecular-iris space area (TISA), and trabecular-iris angle (TIA) were measured. All the above parameters and the ratio index of angle parameters, which was defined as the angle parameter value of the narrower side to that of the contralateral side, were compared between CEL and controls. Receiver operating characteristic (ROC) curves were also plotted to evaluate the diagnostic performance of anterior chamber angle parameters in CEL patients. Results All angle parameters of the contralateral side to the dislocated lens side were significantly smaller than those of the dislocated lens side in CEL (all P < 0.05). For the diagnostic performance of anterior chamber angle parameters, the ratio index of TIAr500 combined with TIAr750 had the best diagnostic performance for CEL screening (AUC = 0.798), and TIAr500 of 0.887 and TIAr750 of 0.917 were detected to be the optimal cut-off points, representing a sensitivity of 89.8% and specificity of 68.7%. Conclusion The contralateral side to the dislocated lens side in the CEL had a narrower anterior chamber angle. TIAr500 combined with TIAr750 is the optimal combination strategy for ectopia lentis screening.


Introduction
Congenital ectopia lentis (CEL) is a rare disease in which the lens dislocates from its normal position; it is a hereditary connective tissue disease [1]. CEL can not only lead to ocular symptoms such as severe refractive errors and amblyopia but also be associated with systemic diseases, such as such as Marfan's syndrome (MFS), homocystinuria, Weill-Marchesani syndrome, and sulfite oxidase deficiency syndrome [2].
For eyes with ectopia lentis, it has been reported that the dislocated lens can shallow the anterior chamber angle (ACA) and even cause acute secondary angle closure [3]. Zhang et al. [4] reported that CEL accounts for 2.4% of all causes of secondary glaucoma. However, little is known about the anterior segment characteristics of CEL patients, which hinders our understanding of the disease. While the slit lamp biomicroscope has been widely used for diagnosing ectopia lentis, this examination method may not detect early mild lesions without obvious signs; hence, objective and accurate diagnosis strategies for lens dislocation are needed.
In this study, we aimed to use the latest anterior segment swept-source optical coherence tomography (SS-OCT), a noncontact instrument with high-resolution imaging [5], to investigate the anterior segment parameters of patients with CEL and to evaluate the sensitivity and specificity of anterior segment parameters in distinguishing ectopia lentis from healthy controls.

Methods
is cross-sectional study was conducted in accordance with the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Zhongshan Ophthalmic Center.
e CEL patients and the healthy controls were consecutively recruited from January 2021 to August 2021 in Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. e included CEL patients were diagnosed according to the Ghent-2 criteria with genetic testing [6]. Exclusion criteria were as follows: (1) patients with ocular surgery history; (2) with other ocular diseases such as corneal diseases which would affect the measurement of anterior segment parameters. Age-and sex-matched individuals without ocular disease other than refractive error were included as the healthy controls. Written informed consent was obtained from all participants before enrolling.

Swept-Source Anterior Segment Optical
Coherence Tomography Examination e Casia SS-1000OCT (Tomey, Nagoya, Japan) is a commercially available swept-source OCT system with a sweptsource laser wavelength of 1310 nm, using a monochromatic, tunable, fast scanning laser source and a photodetector to detect wavelength-resolved interference signals. During the examination, all the participants were asked to fixate on an internal fixation target during the scan. All images were obtained in a dark environment by the same observer before the participants received any pupil dilation or constriction medications. For the patients with mild subluxation, we also performed SS-OCTscanning both under nonmydriatic pupil (to collect the angle parameters) and mydriatic pupil (to confirm the direction of lens dislocation). To avoid lid artifact, participants were instructed to pull down the lower lid against the lower orbital rim to expose the lower limbus while the technician elevated the upper lid against the upper orbital rim to expose the upper limbus. All images with lid or motion artifacts were excluded from the analysis.
Anterior segment parameters of different axes were obtained from each participant. For CEL patients, the scans were performed on the dislocated lens axis (Figure 1). For healthy controls, the scans were performed on the horizontal axis (0-180 degrees) and vertical axis (90-270 degrees). For each image, the scleral spur (SS) and angle recess (AR) were both marked by the SS-OCT system first and then manually corrected to complete anterior chamber measurements by the same experienced ophthalmologist (Liu ZZ). e scanned images were analyzed using custom software, and the obtained parameters included the following: anterior chamber dimension parameters (anterior chamber width (ACW)), angle parameters (angle opening distance (AOD), angle recess area (ARA), trabecular-iris space area (TISA), and trabecular-iris angle (TIA)). AOD, ARA, TISA, and TIA were all assessed at 250 μm, 500 μm, and 750 μm from the scleral spur. All SS-OCT anterior chamber parameters are shown in Supplemental Figure 1. Of the above parameters, ACW was defined as the distance between the two scleral spurs. Angle opening distances at 250, 500, and 750 μm (AOD250, AOD500, and AOD750) were defined as the distance between the posterior corneal surface and the anterior iris surface on a line perpendicular to the trabecular meshwork 250 μm, 500 μm, and 750 μm from the scleral spur, respectively. Angle recess areas at 250, 500, and 750 μm (ARA250, ARA500, and ARA750) were defined as the area of the angle recess bounded anteriorly by the AOD250, AOD500, and AOD750. Trabecular-iris space areas at 250, 500, and 750 μm (TISA250, TISA500, and TISA750) were defined as the area bounded anteriorly by AOD250, AOD500, and AOD750 as determined posteriorly by a line drawn from the scleral spur vertical to the plane of the inner scleral wall to the iris, superiorly by the inner corneoscleral wall, and inferiorly by the iris surface. Trabecular-iris angles at 250, 500, and 750 μm (TIA250, TIA500, and TIA750) were defined as an angle measured with the apex in the iris recess and the arms of the angle passing through a point on the trabecular meshwork 250 μm, 500 μm and 750 μm from the scleral spur and the point on the iris perpendicularly. For the CEL patients and healthy controls, the ratio index of angle parameters, defined as the angle parameter value of the narrower side to that of the contralateral side, was also introduced as AODr, ARAr, TISAr, and TIAr in this study. e angle parameters are shown in Figure 1

Statistical Analysis
All statistical analysis was performed using Stata MP 15.1 (Stata Corp LP, College Station, Texas, USA). Mean values with 95% confidence intervals (95% CI) were provided for normally distributed data. All data were tested for normality. Normally distributed parameters were compared between the CEL and healthy controls using the student's t test, while the rank sum test was used for nonnormal distribution data. e receiver operating characteristics (ROC) curve was plotted to evaluate the diagnostic value of each SS-OCT parameter in the differential diagnosis of CEL patients from healthy controls. A value of P < 0.05 was considered statistically significant unless otherwise specified.

Results
A total of 35 eyes from 35 CEL patients were recruited, of which 18 were male (51.43%) and 17 were female (48.57%). Meanwhile, 35 eyes from age-and sex-matched healthy controls were recruited, of which 17 were male (48.57%) and 18 were female (51.43%). e mean age of the CEL patients was 13.57 ± 8.37 years, and the healthy control group age was 11.11 ± 2.99 years. e mean AL was 25.01 ± 2.76 mm in the CEL and 25.01 ± 2.76 mm in the healthy controls, with no significant difference between the two groups were detected. Demographics and ocular biometric characteristics of participants are shown in Table 1.
e angle parameters (AOD, ARA, TISA, and TIA) at 250 μm, 500 μm, 500 μm, and 750 μm of the dislocated lens side, the contralateral side to the dislocated lens side in the CEL patients, and those of the horizontal axis (0 degree and 180 degrees) and vertical axis (90 degree and 270 degrees) in the healthy controls are reported in Table 2. All angle parameters of the contralateral side to the dislocated lens side were significantly smaller than those of the dislocated lens side in the CEL patients and those of the horizontal axis (0-180 degrees) and vertical axis (90-270 degrees) in the healthy controls (all P < 0.05). As shown in Table 3, there were significant differences for all ratio indexes of angle parameters between the CEL patients and the healthy controls. To evaluate the sensitivity and specificity of the anterior segment parameters in distinguishing ectopia lentis from healthy controls, we calculated the area under the receiving operating characteristics curve (AUROC), which is presented in Figures 2 and 3. e ROC curve indicated that TIAr250, TIAr500, and TIAr750 had good discriminative performance (AUC � 0.720; AUC � 0.794; AUC � 0.741, respectively) for CEL. Meanwhile, the ratio index of TIAr500 combined with TIAr750 had the best diagnostic performance for CEL (AUC � 0.798); and TIAr500 of 0.887 and TIAr750 of 0.917 were found to be the optimal cut-offs.
Among the included CEL patients, FBN1 mutations account for more than 90% of the detected mutations. ere was no statistical difference of anterior segment parameters among patients with different mutations.

Discussion
For CEL patients, the zonule of the lens is partially or completely slack or even broken, and the lens is often pushed forward to the iris which can change the anterior chamber angle structure. Until now, little is known about the characteristics of the anterior segment in CEL patients. Although changes in the anterior chamber depth can be easily detected in patients with severe lens dislocation, it is difficult to detect lens dislocation with traditional equipment such as a slitlamp biomicroscope for patients with mild lens dislocation, and new detection strategies are needed for these patients.
At present, SS-OCT serves as a noncontact, easy-to-use, and quantitative evaluation of the anterior chamber device [7,8] that utilizes much more data of the whole anterior chamber than can be obtained by the commonly used UBM. In addition, the noncontact nature of SS-OCT makes it more advantageous in pediatric patients with CEL. With the advancement of OCT technology, the current ultrahigh resolution of OCT can obtain very clear imaging of various structures in the anterior segment of the eye, and AS-OCT has been successfully used in the diagnosis of a variety of  anterior segment diseases [9][10][11]. Ma et al. [12] reported that SS-OCTshowed excellent diagnostic ability in distinguishing primary angle closure disease (PACD) from the healthy population and showed moderate diagnostic performance in distinguishing primary angle closure/primary angle closure glaucoma (PAC/PACG) from primary angle closure suspect (PACS). However, the use of SS-OCT in the diagnosis of CEL patients has not been reported by far.
In this study, we detected that all angle parameters of the contralateral side to the dislocated lens side in CEL patients were significantly smaller than those of the healthy controls (P < 0.05). Specifically, the angle parameters of the contralateral side to the dislocated lens side in the CEL patients were statistically smaller than those of the opposite side (P < 0.05). e explanation of our results may lie in the fact that the dislocated lens could cause mechanical compression of the ACA, hence affecting the angle parameters. Previous studies have reported that angle parameters were significantly associated with angle closure [13][14][15][16]. Previous reports by Henriquez et al. [17] identified that TISA500 < 0.009 was risk factor for developing phacomorphic angle closure, and narrower angle width was an independent predictive factor for the development of angle closure after ten years [18]. Additionally, the smaller AOD, angle open distance; ARA, angle recess area; TISA, trabecular-iris space area; TIA, trabecular-iris angle; * t-test for comparison of means with angle parameters of contralateral side to dislocated lens side in CEL patients.  Journal of Ophthalmology AOD750 was also identified to be strongly associated with the development of incident angle closure in a previous study [19]. Due to the angle characteristics of the CEL patients, much more attention should be paid to the changes in angle parameters, and regular follow-up is recommended.
In this study, we also introduced a series ratio index of the angle parameters such as TIAr, AODr, ARAr, and TISAr.
ere was a significant difference between the CEL patients and the healthy controls for all angle parameter ratio indexes, of which the ratio indexes in CEL patients were smaller compared to the healthy controls. To explore the potential value of angle parameters in the differential diagnosis of lens dislocation, ROCs were plotted, and the results showed that TIAr had a higher power of discrimination compared with AODr, ARAr, and TISAr (all P < 0.05). e TIA is a parameter that represents the angle width, which has been commonly used in the evaluation of the ACA [20,21]. In order to improve the diagnostic efficiency of the ratio parameters, TIAr250, TIAr500, and TIAr750 were combined, and the results showed that TIAr500 combined TIAr750 (AUC � 0.798) had a promising diagnostic performance for lens dislocation. is suggests  that TIAr500 combined with TIAr750 could serve as a screening tool for lens dislocation.
ere are several limitations to this study. First, not all the cross-sectional images were analyzed, and the accuracy may be affected to some extent. Second, the scleral spur and angle recess required manual labeling. Although the investigator in this study had been well trained before the study, bias may still exist. Finally, since our participants were all from a single eye center, the generalization of our conclusion may be limited and further studies are needed. However, the value of our study is in the use of advanced SS-AS-OCT technology to evaluate the anterior segment characteristics of CEL patients and investigate the possibility of utilizing anterior angle parameters to differentiate and diagnose ectopia lentis patients from healthy controls, which could be a significant contribution to disease management.
In conclusion, the ACA of the contralateral side to the dislocated lens in CEL patients was significantly narrower than that of the healthy controls. We recommend that clinicians remain attentive to these changes in values, and regular followup is recommended for these patients. For the differential diagnosis of ectopia lentis, TIAr500 combined with TIAr750 could serve as a screening tool in clinical practice.

Data Availability
e data used to support the findings of this study are included within the article.

Additional Points
What Was Known. (i) For eyes with ectopia lentis, the dislocated lens can squeeze the anterior chamber angle and even cause acute secondary angle closure, but little is known about the anterior segment characteristics of CEL patients. What is Paper Adds. (i) e anterior chamber angle of the contralateral side to the dislocated lens in congenital ectopia lentis was significantly narrower than that of the healthy controls. (ii) TIAr500 combined with TIAr750 could serve as a screening tool in differential diagnosis of ectopia lentis form healthy population.

Disclosure
Haotian Qi and Guangming Jin are co-first authors.

Conflicts of Interest
e authors declare that there are no conflicts of interest.