Computer-animated model of accommodation and theory of reciprocal zonular action

The potential influence of the ligament of Wieger on the crystalline lens shape

This research uses mathematical modelling to evaluate the influence of the ligament of Wieger on the crystalline lens shape at rest, and during accommodation. An axisymmetric model of the anterior segment, including the ligament of Wieger, was created using the finite element method. Different conditions including variations of stiffness and positions of the ligament, with and without the ligament, were tested to see how they affected lens curvature and optical power. Adding the ligament of Wieger to the simulation had a noticeable impact on the optical power of the lens, particularly on the posterior surface power and total power. Ligament stiffness and width significant influenced the accommodative range of the eye by - 0.95D and - 2.39D for ligaments with the same and 3× the stiffness of the capsular bag, respectively. Ligament width and inner diameter had negligible effects on lens thickness but did have significant effects on posterior surface power and accommodation. In this simulation, we found that the ligament of Wieger can significantly affect the lens shape, both at rest and during accommodation, and may need to be considered in lens models.

Review of primary posterior capsulorhexis in cataract surgery

This article reviews the history and technique of primary posterior capsulorhexis with emphasis on anterior hyaloid membrane preservation and combined posterior optic capture of intraocular lenses into Berger's space for the purpose of lens stability and secondary cataract elimination among other potential advantages. Applications, variations, efficacy, and safety of the procedure are reviewed.

Classifications of Qualitative Characteristics on Angle Configurations via Ultrasound Biomicroscopy in Acute Primary Angle Closure

Purpose

To study the classifications of qualitative characteristics on the angle configurations in the acute primary angle closure (APAC) and fellow eyes by ultrasound biomicroscopy (UBM).

Methods

A total of 131 patients (262 eyes) were researched retrospectively. The qualitative parameters from UBM images were classified into iris form (IF), ciliary body configuration (CBC), basal iris thickness (BIT), iris convexity (IC), iris insert (II), iris angulation (IA), ciliary body size (CBS) and ciliary body position (CBP). Comparative analyses between the APAC (case group) and fellow (control group) eyes were performed.

Results

There were significant differences in IF, CBC, IC, II, CBS, CBP between the case group and control group in all quadrants (P<0.001). The IA of the case group and control group presented significant difference in all quadrants (P=0.001). However, there was not a significant difference in BIT between the case group and control group in all quadrants (P=0.495). The case group had fewer parallelogram-like and mushroom-like and more cone-like and hook-like CBCs than the control group (P<0.001).

Conclusion

Multiple ciliary body configurations can influence the stability of the lens and the anatomic configuration of the anterior chamber angle indirectly. New qualitative classification system of UBM may be more intuitionistic and refined to reflect the angle configurations to help clinical practice.

A Review of Intraocular Pressure (IOP) and Axial Myopia

The pathogenesis of myopia is driven by genetic and environmental risk factors. Accommodation not only alters the curvature and shape of the lens but also involves contraction of the ciliary and extraocular muscles, which influences intraocular pressure (IOP). Scleral matrix remodeling has been shown to contribute to the biomechanical susceptibility of the sclera to accommodation-induced IOP fluctuations, resulting in reduced scleral thickness, axial length (AL) elongation, and axial myopia. The rise in IOP can increase the burden of scleral stretching and cause axial lengthening. Although the accommodation and IOP hypotheses were proposed long ago, they have not been validated. This review provides a brief and updated overview on studies investigating the potential role of accommodation and IOP in myopia progression.

[Anatomical, morphological and biomechanical aspects of accommodation]

The article reviews the findings on the anatomy, morphological and biomechanical features of the accommodation apparatus. Modern methods of imaging and biometry confirm the validity of the Helmholtz lenticular theory of accommodation, according to which its mechanism involves three main components: the ciliary body, the zonular fibres and the lens capsule, the lens itself. Based on this, there is certain interest in studying the degree of participation of each of these components in the development of age-related changes in accommodation (presbyopia).

The action of ciliary muscle contraction on accommodation of the lens explored with a 3D model

The eye's accommodative mechanism changes optical power for near vision. In accommodation, ciliary muscle excursion relieves lens tension, allowing it to return to its more convex shape. Lens deformation alters its refractive properties, but the mechanics of ciliary muscle actions are difficult to intuit due to the complex architecture of the tissues involved. The muscle itself comprises three sections of dissimilarly oriented cells. These cells contract, transmitting forces through the zonule fibers and extralenticular structures. This study aims to create a finite element model (FEM) to predict how the action of the ciliary muscle sections leads to lens displacement. The FEM incorporates initialization of the disaccommodated lens state and ciliary muscle contraction, with three muscle sections capable of independent activation, to drive accommodative movement. Model inputs were calibrated to replicate experimentally measured disaccommodated lens and accommodated ciliary muscle shape changes. Additional imaging studies were used to validate model predictions of accommodative lens deformation. Models were analyzed to quantify mechanical actions of ciliary muscle sections in lens deformation and position modulation. Analyses revealed that ciliary muscle sections act synergistically: the circular section contributes most to increasing lens thickness, while longitudinal and radial sections can oppose this action. Conversely, longitudinal and radial sections act to translate the lens anteriorly with opposition from the circular section. This FEM demonstrates the complex interplay of the three sections of ciliary muscle in deforming and translating the lens during accommodation, providing a useful framework for future investigations of accommodative dysfunction that occurs with age in presbyopia.

Agreement between anterior segment parameters obtained by a new ultrasound biomicroscopy and a swept-source fourier-domain anterior segment optical coherence tomography

Purpose: To evaluate the agreement between anew UBM and an SS-OCT. Methods: The scans of the right eye of each volunteer were obtained using the two devices. Data were fitted and recorded including: central corneal thickness (CCT), aqueous depth (AQD) (the distance from endothelium to lens), angle-to-angle distance (ATA), lens thickness (LT), diameter of the lens in the horizontal direction (LDia^angle: distance between the sharp angles on both sides of the lens, LDia^arc: distance between the vertex of the circular arcs on both sides of the lens), anterior and posterior corneal radius (Rf and Rb). Results: 25 eyes were included in this study. It could be seen that the differences in CCT, LDia^angle, Rf measured by the two instruments were not statistically significant. Bland-Altman analysis plots of CCT, LDia^angle and Rf showed mean differences of 0.2 µm, 0.01mm and 0.0mm for the 2 devices, respectively. Conclusion: The values of CCT, LDia^angle and Rf obtained via two instruments were not clinically interchangeable and the AQD, ATA, LT, and Rb have poor agreement affected by accommodation. We can estimate the real lens diameter by subtracting 0.61 ± 0.43mm when the lens diameter can only be simulated with SS-OCT.

Vitreous Zonule and its Relation to Anterior Chamber Angle Characteristics in Primary Angle Closure

PRECIS

Primary angle-closure (PAC) eyes with no vitreous zonule (VZ) appear to have a narrower angle despite similar lens vault and iris configuration than eyes with visible VZ.

PURPOSE

To assess the clinical significance of the VZ in PAC.

METHODS

Medical records of 91 eyes of 91 participants with PAC or PAC glaucoma were retrospectively reviewed. Anterior segment parameters were measured using anterior segment optical coherence tomography; presence of the VZ was assessed with ultrasound biomicroscopy. Parameters were compared between eyes with vitreous zonule group (VZG) and no vitreous zonule group (NVZG). Factors associated with VZ presence were determined using logistic regression analysis.

RESULTS

The NVZG was more likely to have PAC glaucoma than PAC (51.4% vs. 25.0%; P=0.010) and use more glaucoma medications (0.77 vs. 0.36; P=0.004) than the VZG. The NVZG had a smaller anterior chamber area than the VZG (13.6 mm vs. 15.1 mm; P=0.020) but there were no significant between-group differences in anterior chamber depth (1.97 vs. 2.08 mm; P=0.119) and lens vault (1.21 vs. 1.13 mm; P=0.337). NVZG had a smaller scleral spur angle (11.5 vs. 17.4 degrees; P<0.001), angle opening distance at 500 μm (AOD500, 105 vs. 168 μm; P<0.001), and trabecular-ciliary process angle (75.7 vs. 81.9 degrees; P=0.029) than VZG. Older age [odds ratio (confidence interval), 1.087 (1.014-1.164); P=0.018], less AOD500 (0.984 (0.975-0.993); P<0.001), and less trabecular-ciliary process angle (0.938 (0.901-0.977); P=0.002) were independently associated with an absence of VZ.

CONCLUSIONS

PAC eyes with no VZ had a narrower angle and required more glaucoma medications than eyes with a VZ.

Agreement of Anterior Segment Parameters Obtained From Swept-Source Fourier-Domain and Time-Domain Anterior Segment Optical Coherence Tomography

Purpose

To assess the interdevice agreement between swept-source Fourier-domain and time-domain anterior segment optical coherence tomography (AS-OCT).

Methods

Fifty-three eyes from 41 subjects underwent CASIA2 and Visante OCT imaging. One hundred eighty–degree axis images were measured with the built-in two-dimensional analysis software for the swept-source Fourier-domain AS-OCT (CASIA2) and a customized program for the time-domain AS-OCT (Visante OCT). In both devices, we examined the angle opening distance (AOD), trabecular iris space area (TISA), angle recess area (ARA), anterior chamber depth (ACD), anterior chamber width (ACW), and lens vault (LV). Bland-Altman plots and intraclass correlation (ICC) were performed. Orthogonal linear regression assessed any proportional bias.

Results

ICC showed strong correlation for LV (0.925) and ACD (0.992) and moderate agreement for ACW (0.801). ICC suggested good agreement for all angle parameters (0.771–0.878) except temporal AOD500 (0.743) and ARA750 (nasal 0.481; temporal 0.481). There was a proportional bias in nasal ARA750 (slope 2.44, 95% confidence interval [CI]: 1.95–3.18), temporal ARA750 (slope 2.57, 95% CI: 2.04–3.40), and nasal TISA500 (slope 1.30, 95% CI: 1.12–1.54). Bland-Altman plots demonstrated in all measured parameters a minimal mean difference between the two devices (−0.089 to 0.063); however, evidence of constant bias was found in nasal AOD250, nasal AOD500, nasal AOD750, nasal ARA750, temporal AOD500, temporal AOD750, temporal ARA750, and ACD. Among the parameters with constant biases, CASIA2 tends to give the larger numbers.

Conclusions

Both devices had generally good agreement. However, there were proportional and constant biases in most angle parameters. Thus, it is not recommended that values be used interchangeably.

Real-Time Intraoperative Optical Coherence Tomography Imaging Confirms Older Concepts About the Berger Space

BACKGROUND

The presence of a space between the posterior capsule and the anterior vitreous was first reported in 1887, but difficulties inherent in examining this structure made it impossible to visualize this area in vivo until now. Estimation of the size of this space was considered to be impossible.

MATERIALS AND METHODS

We utilized an optical coherence tomography (OCT) system attached to the Zeiss Opmi Lumera 700/Rescan microscope (Zeiss Ltd., Jena, Germany) to provide real-time images of the Berger space, the anterior hyaloid and the ligament of Wieger.

RESULTS

Imaging in 3 patients provided beautiful, real-time OCT images of the Berger space and of the ligament of Wieger. In one highly myopic eye, there was even evidence of anterior vitreous detachment.

CONCLUSION

Previously unseen transparent structures of the eye can now be imaged intraoperatively using real-time OCT. This new technology seems very promising in achieving a better understanding of the anterior vitreous interface, more specifically of the anterior hyaloid and its posterior capsule attachment by the ligament of Wieger. Changes in the anterior hyaloid and its capsular attachment may contribute to a better understanding of the posterior segment complications after cataract surgery.