Effects of accommodation on geometrical parameters of human lens: A systematic review and meta-analysis

Purpose

To investigate the effects of accommodation on the geometrical parameters of human lens.

Methods

Eight databases from inception to November 2023 were used for the literature search: CNKI, CBM, VIP, Wan-Fang, PubMed, Web of Science, EMBASE, and the Cochrane Library. The Methodological Index for Non-randomized Studies was used to assess the risk of bias. The PRISMA were followed and the following outcomes were taken into consideration: lens diameter (LD), lens thickness (LT), anterior curvature radius (ACR), posterior curvature radius (PCR), lens center position (LCP), and total cross-sectional area (TCSA). This systematic review was registered on an international platform for registered systematic reviews and meta-analysis (INPLASY202260085).

Results

A total of 19 studies were included. LT increased by 0.04 mm/D (18 studies; 95% confidence interval [CI], 0.03-0.06; I2 = 96.6%; P < 0.001). At the same time, LD, ACR, and PCR decreased by 0.06 mm/D (6 studies; 95%CI, -0.07-0.05; I2 = 50.1%; P < 0.001), 0.53 mm/D (8 studies; 95%CI, -0.64-0.41; I2 = 96.5%; P < 0.001), and 0.14 mm/D (9 studies; 95%CI, -0.19-0.09; I2 = 94.7%; P < 0.001) during accommodation, respectively. Moreover, LCP shifted forward by 0.01 mm/D (3 studies; 95%CI, -0.02-0.00; I2 = 0.0%; P < 0.001), and TCSA by 0.58 mm2/D (2 studies; 95%CI, 0.41-1.57; I2 = 97.0%; P = 0.457) during accommodation.

Conclusions

Changes in LT, LD, ACR, PCR and LCP supported Helmholtz's theory. Different apparatuses or measurement methods influenced the measurement of lens geometrical parameters.

Novel diagnostic indicators for acute angle closure secondary to lens subluxation based on anterior segment and lens parameters

Purpose: To explore stable and sensitive indicators for clinical diagnosis of acute angle closure (AAC) secondary to lens subluxation (LS) through quantitative analysis of CASIA 2 imaging.Design: A prospective cross-sectional study.

Methods

Setting: Clinical practice.Participants: 23 patients with unilateral acute angle closure secondary to lens subluxation and 23 cataract patients without lens subluxation were recruited. Lens subluxation was confirmed by ultrasound biomicroscope diagnosis. The contralateral eyes without LS served as fellow control group. The cataract eyes without LS were enrolled in blank control group.Intervention: Participants underwent ophthalmologic examinations including slit-lamp biomicroscope, best corrected visual acuity, intraocular pressure, central corneal thickness measurement, axial length, gonioscopy, ultrasound biomicroscope and 360-degree anterior chamber and crystalline lens scan protocols of CASIA 2 system.Main outcome measures: Automated circumferential anterior segment and lens morphological parameters under anterior segment optical coherence tomography were analyzed via three-dimensional analysis.

Results

Significant differences were found in the front and back radius of the lens, the front and back radius of steep curvature of the lens, lens thickness, lens decentration, lens diameter, iris-trabecular contact (ITC) index, ITC area, anterior chamber depth (ACD), lens vault (LV), and iris volume between LS and controls. Among these parameters, LV, the anterior radius of steep curvature of the lens and ACD demonstrated the highest prediction power (AUC = 0.87, 0.89, and 0.86, respectively). The prediction power of tilt/axis was much higher in the Gaussian Naive Bayes model (AUCs = 0.90) than in the logistic model (AUCs = 0.74). Combination of LV_mean, LV_std, tilt and tilt axis in Gaussian Naive Bayes model presented as most stable and excellent diagnostic markers for AAC secondary to LS (AUCs = 0.98).

Conclusions

The combination of markers including lens tilt and lens vault in the mathematic model facilitate clinical work as it not only provides novel diagnostic indications and possible prompt treatment for AAC secondary to lens subluxations, but also enhances our understanding of the pathogenic role of zonulopathy in angle closure glaucoma.

Alterations in Lens Free Water Distribution Are Associated with Shape Deformation in Accommodation

Objective

To investigate whether a redistribution of water within the crystalline lens is associated with the shape deformation that occurs during accommodation.

Design

Observational, cross sectional study.

Subjects

Eleven young adults without presbyopia (aged 18-39 years) and 9 middle-aged adults with presbyopia (aged 40-55 years).

Methods

Magnetic resonance imaging (MRI) scans of the lens were acquired on a 3 Tesla clinical MRI scanner, without and with the presentation of a 3 Diopter accommodative stimulus. The MRIs were postprocessed using established methods to extract the geometric dimensions and spatial maps of water distribution of the lens.

Main Outcome Measures

Accommodative changes in the full 3-dimensional description of lens shape, the lens total-water distribution profile, and the lens free-water distribution profile.

Results

Viewing of an accommodative stimulus by young subjects elicited an elastic shape deformation of the lens consistent with accommodation that was associated with an elevated, smoother free-water distribution, primarily in the anterior region of the lens. In contrast, viewing of an accommodative stimulus by presbyopic subjects produced an atypical shape deformation of the lens that was instead associated with a lowered free-water distribution, primarily in the anterior region of the lens. No discernible changes to the lens total-water distribution were observed in response to the accommodative stimulus in either subject cohort.

Conclusions

The present study suggests that protein-mediated alterations in the free-water distribution of the anterior region of the lens influence the shape deformation in accommodation, presenting pharmacological modulation of free-water distribution as an attractive novel approach for treating presbyopia.

Financial Disclosures

The authors have no proprietary or commercial interest in any materials discussed in this article.

Interocular difference in crystalline lens morphology in children and adolescents with unilateral high myopia

PURPOSE

To investigate the between-eye differences of the crystalline lens in subjects with unilateral high myopia and assess its contribution to the interocular refractive error disparity.

METHODS

Children and adolescents with unilateral high myopia, defined as cycloplegic spherical equivalent (SE) ≤ -5D in one eye and ≥ -3D in the other eye, were recruited. Ocular biometric parameters, including axial length (AL) and lens thickness (LT), were measured by IOLMaster 700. Other lens-related parameters, including anterior lens radius of curvature (ALR) and posterior lens radius of curvature (PLR), were measured by CASIA2 swept-source optical coherence tomography. Lens power (LP) was calculated using Bennett's formula. Paired t-test was used to assess the between-eye difference in biometric parameters, and multiple regression analysis was used to assess factors associated with the between-eye SE difference.

RESULTS

Ninety-one participants (6-18 years of age; 52.75% girls) were included. The highly myopic eyes showed significantly lower LP (P < 0.001) and smaller ALR (P < 0.001) than the contralateral eyes, while no significant difference was found in central LT. In both eyes, ALR was significantly related to SE (P = 0.001 and P = 0.006, respectively); while LT was not associated with SE (P = 0.051 and P = 0.052, respectively). Paired-eye analysis showed that the between-eye difference in ALR was the only lenticular parameter significantly associated with the between-eye difference in SE (P = 0.005).

CONCLUSION

In highly myopic eyes, the crystalline lens reduced total power but morphologically changed to a more curved shape without significant lens thinning, suggesting that the LP loss is mainly achieved by reducing its internal power in high myopes.

Age-related changes in geometry and transparency of human crystalline lens revealed by optical signal discontinuity zones in swept-source OCT images

BACKGROUND

The shape and microstructure of the human crystalline lens alter with ageing, and this has an effect on the optical properties of the eye. The aim of this study was to characterise the age-related differences in the morphology and transparency of the eye lenses of healthy subjects through the optical signal discontinuity (OSD) zones in optical coherence tomography (OCT) images. We also investigated the association of those changes with the optical quality of the eye and visual function.

METHODS

OCT images of the anterior segment of 49 eyes of subjects (9-78 years) were acquired, and the OSD zones (nucleus, C1-C4 cortical zones) were identified. Central thickness, curvature and optical density were measured. The eye's optical quality was evaluated by the objective scatter index (OSI). Contrast sensitivity and visual acuity tests were performed. The correlation between extracted parameters and age was assessed.

RESULTS

The increase in lens thickness with age was dominated by the thickening of the cortical zone C3 (0.0146 mm/year). The curvature radii of the anterior lens surface and both anterior and posterior nucleo-cortical interfaces decreased with age (- 0.053 mm/year, - 0.013 mm/year and - 0.006 mm/year, respectively), and no change was observed for the posterior lens radius. OCT-based densitometry revealed significant correlations with age for all zones except for C1β, and the highest increase in density was in the C2-C4 zones (R = 0.45, 0.74, 0.56, respectively, P < 0.001). Increase in OSI was associated with the degradation of visual function.

CONCLUSIONS

OCT enables the identification of OSD zones of the crystalline lens. The most significant age-related changes occur in the C3 zone as it thickens with age at a faster rate and becomes more opaque than other OSD zones. The changes are associated with optical quality deterioration and reduction of visual performance. These findings contribute to a better understanding of the structure-function relationship of the ageing lens and offer insights into both pathological and aging alterations.

The evolution of mechanism of accommodation and a novel hypothesis

Myopia and presbyopia are two major optometry problems facing the whole society. The mechanism of accommodation is strongly related to the treatments of myopia and presbyopia. However, the key mechanism of accommodation has puzzled us for over 400 years and is still not clear at present, leading to the stagnation of prevention and treatment of myopia and presbyopia. With the continued development of experimental technologies and equipment, the approaches to elucidate accommodation's intricacies have become more methodological and sophisticated. Fortunately, some significant progress has been made. This article is to review the evolution of the mechanism of accommodation. Helmholtz proposed a classical theory of "zonules relax during accommodation." In contrast, Schachar put forward a theory of "zonules taut during accommodation." Those hypotheses are relatively complete, but either do not fully explain everything about the accommodation mechanism or lack sufficient experimental and clinical evidence to support them. Then, some contentious issues are discussed in detail to find the truth. Finally, we proposed our hypothesis about accommodation based on the anatomy of the accommodative apparatus.

Congenital anomalies of lens shape

The crystalline lens is an important structure in the eye that starts to develop as early as the 22nd day of gestation, with further differentiation that continues after the induction. Congenital anomalies of the lens may involve the size, shape, and position of the lens. They may sometimes be associated with anterior segment dysgenesis or persistence of the tunica vasculosa lentis and hyperplastic vitreous and hyaloid system. Manifestations of anomalies of the lens shape are usually seen in early or late childhood however may sometimes be delayed into adulthood based on the level of visual impairment or the presence or absence of any syndromic associations. While lens coloboma has more often been reported in isolation, the more commonly implicated genes include the PAX6 gene, lenticonus in particular anterior is often part of Alport syndrome with extra-ocular manifestations in the kidneys and hearing abnormalities due to mutations in the alpha 5 chain of the Type IV collagen gene. Recognition of these manifestations and obtaining a genetic diagnosis is an important step in the management. The level of visual impairment and amblyopia dictates the outcomes in patients managed either conservatively with optical correction as well as surgically where deemed necessary. This review discusses the various anomalies of the lens shape with its related genetics and the management involved in these conditions.

Review on age-related differences in non-visual effects of light: melatonin suppression, circadian phase shift and pupillary light reflex in children to older adults

Physiological effects of light exposure in humans are diverse. Among them, the circadian rhythm phase shift effect in order to maintain a 24-h cycle of the biological clock is referred to as non-visual effects of light collectively with melatonin suppression and pupillary light reflex. The non-visual effects of light may differ depending on age, and clarifying age-related differences in the non-visual effects of light is important for providing appropriate light environments for people of different ages. Therefore, in various research fields, including physiological anthropology, many studies on the effects of age on non-visual functions have been carried out in older people, children and adolescents by comparing the effects with young adults. However, whether the non-visual effects of light vary depending on age and, if so, what factors contribute to the differences have remained unclear. In this review, results of past and recent studies on age-related differences in the non-visual effects of light are presented and discussed in order to provide clues for answering the question of whether non-visual effects of light actually vary depending on age. Some studies, especially studies focusing on older people, have shown age-related differences in non-visual functions including differences in melatonin suppression, circadian phase shift and pupillary light reflex, while other studies have shown no differences. Studies showing age-related differences in the non-visual effects of light have suspected senile constriction and crystalline lens opacity as factors contributing to the differences, while studies showing no age-related differences have suspected the presence of a compensatory mechanism. Some studies in children and adolescents have shown that children's non-visual functions may be highly sensitive to light, but the studies comparing with other age groups seem to have been limited. In order to study age-related differences in non-visual effects in detail, comparative studies should be conducted using subjects having a wide range of ages and with as much control as possible for intensity, wavelength component, duration, circadian timing, illumination method of light exposure, and other factors (mydriasis or non-mydriasis, cataracts or not in the older adults, etc.).

Research progress of lens zonules

Background

The lens zonule, a circumferential system of fibres connecting the ciliary body to the lens, is responsible for centration of the lens. The structural, functional, and positional abnormalities of the zonular apparatus can lead to the abnormality of the intraocular structure, presenting a significant challenge to cataract surgery.

Main text

The lens zonule is the elaborate system of extracellular fibers, which not only centers the lens in the eye but also plays an important role in accommodation and lens immunity, maintains the shape of the lens, and corrects spherical aberration. The zonules may directly participate in the formation of cataract via the immune mechanism. Abnormal zonular fibers that affect the position and shape of the lens may play an important role in the pathogenesis of angle closure disease and increase the complexity of the surgery. Capsular tension rings and related endocapsular devices are used to provide sufficient capsular bag stabilization and ensure the safety of cataract surgery procedures. Better preoperative and intraoperative evaluation methods for zonules are needed for clinicians.

Conclusions

The microstructure, biomechanical properties, and physiological functions of the lens zonules help us to better understand the pathogenesis of cataract and glaucoma, facilitating the development of safer surgical procedures for cataract. Further studies are needed to carefully analyze the structure-function relationship of the zonular apparatus to explore new treatment strategies for cataract and glaucoma.

New technology using crystalline lens autofluorescence for presbyopia and cataract grading

PURPOSE

To investigate  whether fundus autofluorescence (FAF) obtained using an ultra-wide field (UWF) fundus camera with an artificial opacity pattern can grade the degree of presbyopia and nuclear cataract.

METHODS

Sixty eyes of 30 patients were enrolled in this prospective diagnostic study. The nuclear cataract (nuclear color/opalescence (NC/NO)) was graded according to the Lens Opacity Classification System III. The monocular near point of accommodation (NPA) was measured in eyes with NC3/NO3 or less. The mean gray value difference between the central 8 artificial opacity lesions and peripheral 8 artificial opacity lesions in the retinal AF was measured. The correlation between the mean gray value difference, NPA, and nuclear cataract grade was analyzed.

RESULTS

The mean nuclear cataract grade of 60 eyes was 3.2 ± 1.6 and mean NPA of 37 eyes was 45.3 ± 16.1 cm. The mean gray value differences increased with increasing nuclear cataract grade (eyes with NC/NO grade 1, 53.3 ± 11.4; 2, 78.3 ± 13.6; 3, 95.2 ± 12.2; 4, 101.6 ± 11.9; 5, 109.0 ± 22.9; and 6, 121.1 ± 12.0; p < 0.001). The mean gray value difference was positively correlated with both the monocular NPA (R² = 0.637; β coefficient = 1.009; 95% CI, 0.748 to 1.271; p < 0.001) and nuclear cataract grade (R² = 0.661; β coefficient = 12.437; 95% CI, 10.097 to 14.778; p < 0.001).

CONCLUSIONS

The FAF camera with an artificial opacity pattern attached can be used to effectively diagnose the degree of presbyopia and nuclear cataract.

Refractive and biometrical characteristics of children with retinopathy of prematurity who received laser photocoagulation or intravitreal ranibizumab injection

PURPOSE

To investigate the refractive and biometrical developments of children with retinopathy of prematurity (ROP) who received laser photocoagulation (LP) or intravitreal ranibizumab injection as treatment.

METHODS

This case-control study involved cases with Zone II Stage 3 ROP. Fourteen children (28 eyes) who received single LP were included in the laser group, and 14 children (27 eyes) who received single intravitreal ranibizumab injection were included in the injection group. The mean age at operation was 37.00±1.72 and 36.36±1.66 weeks for the laser and injection groups, respectively (P=0.161), and refraction measurements and biometry were performed at the mean age of 5.00±1.63 and 5.00±0.94 years for the laser and injection groups, respectively (P=1.000). Spherical equivalent (SE) after mydriatic refraction and best corrected visual acuity (BCVA) were measured by refraction test. Central corneal thickness (CCT), anterior corneal surface curvature and curvature radius, anterior chamber depth (ACD), lens thickness (LT) and axial length (AL) were measured by biometry using the IOL Master700 biometric instrument (Carl Zeiss Meditec AG). The biometrical images were reanalysed using a self-developed program in MATLAB (R2016a, MathWorks, Inc.) to obtain additional eye parameters, including the curvatures of the posterior cornea and the anterior and posterior surfaces of the lens. SPSS (V.23.0) was used for statistical analysis. Independent sample t test was used to compare the eyeball biological and refractive state measures of the two groups, and Pearson correlation coefficient was used to evaluate the correlation between SE and the biological parameters.

RESULTS

1. (1) Cornea-related parameters: CCT (0.54±0.04mm vs 0.55±0.02mm, P>0.05), anterior corneal surface curvature radius (7.56±0.26 mm vs 7.67±0.43mm, P>0.05) and posterior corneal surface curvature radius (6.82±0.27mm vs 6.79±0.42mm, P>0.05). (2) ACD (3.21 ± 0.25mm vs 3.22 ± 0.19mm, P>0.05). (3) Lens-related parameters: anterior lens surface curvature radius (10.04±0.89mm vs 9.82±1.08mm, P>0.05), posterior lens surface curvature radius (5.49±0.55mm vs 5.92±0.73mm, P<0.05) and LT (3.80±0.14mm vs 3.59±0.16mm, P<0.05). (4) AL (21.82±1.07 vs 22.68±1.61, P<0.05). (5) Parameters related to refractive state: SE (-2.43±3.56 vs -0.53±3.12, P<0.05) and BCVA (log MAR, 0.17±0.14 vs 0.21±0.18, P>0.05). 2. (1) The SE of children in the laser group was positively correlated with LT (r=0.438, P<0.05), negatively correlated with ACD (r=-0.437, P<0.05) and had no significant correlation with other eyeball biological indicators (P>0.05). (2) The SE of children in the injection group was negatively correlated with AL (r=-0.537, P<0.05), positively correlated with CCT (r=0.455, P<0.05) and had no significant correlation with other eyeball biological indicators (P>0.05).

CONCLUSION

LP and intravitreal ranibizumab injection as ROP treatments produce myopic refraction with increased degree of myopia in children who received LP than in children who received ranibizumab injection. The increased myopia after LP is due to the increases in LT and posterior lens curvature and a shallow ACD.

Changes in ocular parameters the crystalline lens after implantation of a collamer lens

CLINICAL RELEVANCE

Understanding changes in ocular anatomical parameters after intraocular lens implantation will allow a more accurate determination of dioptric power prior to surgery.

BACKGROUND

The crystalline lens position might change due to the implantation and removal of an implantable collamer lens (ICL) or toric implantable collamer lens (TICL). This study aimed to assess the effect of ICL implantation on position of the crystalline lens.

METHODS

This retrospective study was conducted on patients who underwent V4c ICL or V4c TICL implantation between March and September, 2018. Preoperative and post-operative (2 weeks, 3 months and 6 months) axial length, central corneal thickness, crystalline lens position, crystalline lens thickness and vault height were analysed. Multivariable linear regression was used to determine the variables associated with 6-month changes in lens position.

RESULTS

This study included 117 eyes of 117 patients. There were decreases in all vertical distance measures from the central corneal endothelium to the anterior and posterior crystalline lens capsule (all p > 0.05). The amount of reduction was related to the crystalline lens position before the operation and crystalline lens thickness after the operation (all p < 0.01). An error in anterior chamber depth and lens thickness may appear when the ICL/TICL is close to the crystalline lens.

CONCLUSION

Phakic intraocular lens implantation resulted in lens thickening and forward movement on day 1 post-operatively, which becomes stable within 6 months. Preoperative lens position and post-operative lens thickness were related to the amount of movement.

Functional integration of eye tissues and refractive eye development: Mechanisms and pathways

Refractive eye development is a tightly coordinated developmental process. The general layout of the eye and its various components are established during embryonic development, which involves a complex cross-tissue signaling. The eye then undergoes a refinement process during the postnatal emmetropization process, which relies heavily on the integration of environmental and genetic factors and is controlled by an elaborate genetic network. This genetic network encodes a multilayered signaling cascade, which converts visual stimuli into molecular signals that guide the postnatal growth of the eye. The signaling cascade underlying refractive eye development spans across all ocular tissues and comprises multiple signaling pathways. Notably, tissue-tissue interaction plays a key role in both embryonic eye development and postnatal eye emmetropization. Recent advances in eye biometry, physiological optics and systems genetics of refractive error have significantly advanced our understanding of the biological processes involved in refractive eye development and provided a framework for the development of new treatment options for myopia. In this review, we summarize the recent data on the mechanisms and signaling pathways underlying refractive eye development and discuss new evidence suggesting a wide-spread signal integration across different tissues and ocular components involved in visually guided eye growth.

Relationship of the cornea and globe dimensions to the changes in adult human crystalline lens diameter, thickness and power with age

It is well known that human crystalline lens shape, dimensions and optical properties change throughout life and influence whole eye refraction. However, it is not clear if lens properties are associated with other ocular parameters. The purpose of the present study was to investigate the relationship of corneal and external globe dimensions with adult lens diameter (LD), lens thickness (LT) and lens power (LP) in order to determine if external factors influence lens properties. Postmortem human eyes (n = 66, age = 20-78 years) were obtained from the Ramayamma International Eye Bank, Hyderabad, India. Globe antero-posterior length (GAPL) and mean (average of horizontal and vertical) diameters of cornea (MCD) and globe (MGD) were measured using digital calipers. Eyes were dissected to produce ocular structures that contain the lens maintained in its accommodating framework, including intact zonules, ciliary body and sections of sclera. Specimens were mounted in a mechanical lens stretching system. LD, LT and LP were measured using high magnification retro-illumination photography, slit illumination photography and Scheiner principle-based optical system respectively in the unstretched (accommodated) state. Relationships between external globe and corneal dimensions and LD, LT or LP were assessed by multiple regression analysis. Age (0.012 ± 0.003 mm/year; p<0.001) and GAPL (0.185 ± 0.045 mm/mm; p<0.001) were significant (p<0.0001) predictors of LD. After adjusting for age-related increases, LD appears to be positively correlated with GAPL. Age (0.010 ± 0.004 mm/year; p = 0.009) and GAPL (-0.143 ± 0.060 mm/mm; p = 0.02) were significant (p = 0.001) predictors of LT. After adjusting for the age-related increase, LT appears to be negatively correlated with GAPL. Only age was a significant predictor of LP (-0.26 ± 0.04 D/year; p<0.001). The results suggest that, apart from aging, lens diameter and thickness are dependent on the anteroposterior length of the eye globe. Lens power is not influenced by globe dimensions.

Isolated human crystalline lens three-dimensional shape: A comparison between Indian and European populations

There have been many studies on lens properties in specific populations (e.g. in China, Europe, Singapore, etc.) some of which suggest there may be differences between populations. Differences could be caused by ethnic or environmental influences or experimental procedures. The purpose of this study is to evaluate if any differences exist between Indian and European populations in the central geometric and full shape properties of human lenses. Two custom-developed spectral domain optical coherence tomography systems were used to acquire the crystalline lens geometry: one in India (69 lenses from 59 donors) and the other in Spain (24 lenses from 19 donors). The steps for obtaining accurate 3-D models from optical coherence tomography raw images comprised of image segmentation, fan and optical distortion correction, tilt removal and registration. The outcome variables were lens equatorial diameter, lens thickness, anterior and posterior lens thicknesses and their ratio, central radius of curvature of the anterior and posterior lens surfaces, lens volume and lens surface area. A mixed effects model by maximum likelihood estimation was used to evaluate the effect of age, population and their interaction (age*population) on lens parameters. After adjusting for age, there were no population differences observed in anterior and posterior radii of curvature, equatorial diameter, lens thickness, anterior and posterior lens thicknesses and their ratio, volume and surface area (all p ≥ 0.08). There was also no effect of the interaction term on anterior and posterior radii of curvature, equatorial diameter, lens thickness, anterior and posterior lens thicknesses and their ratio, volume and surface area (all p ≥ 0.06). All central geometric and full shape parameters appeared to be comparable between the European and Indian populations. This is the first study to compare geometric and full shape lens parameters between different populations in vitro.

Lens regeneration in humans: using regenerative potential for tissue repairing

The crystalline lens is an important optic element in human eyes. It is transparent and biconvex, refracting light and accommodating to form a clear retinal image. The lens originates from the embryonic ectoderm. The epithelial cells at the lens equator proliferate, elongate and differentiate into highly aligned lens fiber cells, which are the structural basis for maintaining the transparency of the lens. Cataract refers to the opacity of the lens. Currently, the treatment of cataract is to remove the opaque lens and implant an intraocular lens (IOL). This strategy is inappropriate for children younger than 2 years, because a developing eyeball is prone to have severe complications such as inflammatory proliferation and secondary glaucoma. On the other hand, the absence of the crystalline lens greatly affects visual function rehabilitation. The researchers found that mammalian lenses possess regenerative potential. We identified lens stem cells through linear tracking experiments and designed a minimally invasive lens-content removal surgery (MILS) to remove the opaque lens material while preserving the lens capsule, stem cells and microenvironment. In infants with congenital cataract, functional lens regeneration in situ can be observed after MILS, and the prognosis of visual function is better than that of traditional surgery. Because of insufficient regenerative ability in humans, the morphology and volume of the regenerated lens cannot reach the level of a normal lens. The activation, proliferation and differentiation of lens stem cells and the alignment of lens fibers are regulated by epigenetic factors, growth factors, transcription factors, immune system and other signals and their interactions. The construction of appropriate microenvironment can accelerate lens regeneration and improve its morphology. The therapeutic concept of MILS combined with microenvironment manipulation to activate endogenous stem cells for functional regeneration of organs in situ can be extended to other tissues and organs with strong self-renewal and repair ability.

Comparison of radius of anterior lens surface curvature measurements in vivo using the anterior segment optical coherence tomography and Scheimpflug imaging

Background

To assess the radius of anterior lens surface curvature (RAL) measurements with anterior segment optical coherence tomography (AS-OCT) in comparison with Scheimpflug imaging.

Methods

This prospective, cross-sectional study was carried out at Zhongshan Ophthalmic Center, Guangzhou, China. We enrolled 59 eyes, including 30 eyes from 30 cataractous volunteers (59 to 87 years) and 29 eyes from 29 young participants (19 to 49 years). After mydriasis, the RAL was measured automatically by the built-in software in the AS-OCT (CASIA 2). The Scheimpflug images were measured with the build-in caliper tool of the Scheimpflug camera (Pentacam), and RAL were further calculated with the principle of best-fitted circle. Intraobserver and interobserver reproducibility of RAL measurement using Scheimpflug camera were evaluated with limit of agreement (LoA) and intraclass correlation coefficient (ICC). Consistency between RAL measurement of Scheimpflug camera and AS-OCT were assessed with LoA, correlation analysis and linear regression.

Results

For all subjects, intraobserver (LoA: −0.25 to 0.23 mm, ICC: 0.996) and interobserver reproducibility (LoA: −0.85 to 0.92 mm, ICC: 0.947) of RAL were good using Scheimpflug imaging. Both AS-OCT and Scheimpflug imaging found that the age-related cataract participants had smaller RAL (P=0.010, P=0.001 respectively). LoA of RAL measurement between AS-OCT and Scheimpflug imaging was −3.83 to −0.79 mm, and the Pearson correlation efficient was 0.909 (P<0.001). The RAL values measured by AS-OCT were significantly greater than that by Scheimpflug camera with a mean difference of 2.31 mm for all participants (P<0.001). The RAL measurement could be converted using the equation: Y_{CASIA 2} =1.155 × X_Pentacam + 1.060.

Conclusions

Both Scheimpflug camera system with internal caliper tool and the AS-OCT are fast and non-contact tools that could measure RAL successfully. The two measurement results are highly correlated and interchangeable through linear regression equation.

Transient crystalline lens deposits following the insertion of a phakic sulcus-fixated collamer intraocular lens in a hyperopic eye

Purpose

The purpose of this study was to report crystalline lens deposit formation following ICL implantation for the correction of hyperopia.

Observations

A 23-year-old male presented at the American University of Beirut Medical Center in 2008 seeking refractive surgery for hyperopia. His cycloplegic refraction was +7–1.25 × 115° and +7–1.00 × 115° in the right and left eyes, respectively, yielding a vision of 20/20 bilaterally. The patient underwent right eye insertion of a non-toric phakic sulcus-fixated collamer lens 2 weeks after undergoing peripheral iridotomies. The early postoperative course was complicated by anterior chamber inflammation and the appearance of diffuse whitish precipitates on the anterior surface of the crystalline lens, hypotony, and a mid-dilated mildly reactive pupil. With the prompt administration of topical and systemic steroids, the anterior chamber reaction subsided, and the anterior capsular deposits gradually resolved peripherally with some remaining centrally over the course of several weeks. The patient's visual acuity at 6 months was 20/20.

Conclusionsand importance

Adequate viscoelastic removal and minimal iris stimulation seem to be essential to avoid this condition in hyperopic implants that lack a central port. Additionally, prompt treatment can minimize visual impairment and hasten visual recovery.

Iatrogenic crystalline lens injury during intravitreal injection of triamcinolone acetonide: A report of two cases

BACKGROUND

Intravitreal injection has become an efficient approach for delivering drugs at therapeutic levels to the posterior segment in retinal diseases. However, the increased frequency and number of intravitreal injections have raised concerns about their side effects. As manipulation during surgery is relatively simple, details of the procedure are easily overlooked. Iatrogenic crystalline lens injury is a rare complication caused by improper manipulation during surgical procedures. We report two cases of crystalline lens injury during intravitreal injection of triamcinolone acetonide (TA) with the hope of providing an insight into this treatment.

CASE SUMMARY

Case 1 was a 62-year-old woman with macular edema caused by central retinal vein occlusion in her right eye, and Case 2 was a 65-year-old man with macular edema caused by branch retinal vein occlusion in his right eye. In view of the patients’ condition and economic constraints, an intravitreal injection of TA was administered. Due to inappropriate manipulation during surgery, the lens was injured. The site of lens injury and clinical manifestations were different in the two cases. Symptomatic treatment and continuous follow-up were carried out. The therapeutic effect following phacoemulsification of the cataract was satisfactory.

CONCLUSION

Well-defined surgical incision under proper anesthesia, sufficient patient information and proficient anatomical skills of the physician are mandatory to prevent this rare adverse event. Careful and meticulous phacoemulsification of the cataract is suggested.

Hydrotropic function of ATP in the crystalline lens

The hypothesis proposed herein is presented to explain the unexpectedly high concentration of ATP and provide evidence to support its hydrotropic function in the crystalline lens determined using ³¹P NMR. The lens, historically considered to be a metabolically quiescent organ, has the requisite machinery to synthesize ATP, such that the homeostatic level is maintained at about 3 mM. This relatively high concentration of ATP has been found to be consistent among multiple mammalian species including humans. This millimolar quantity is many times greater than the micromolar amounts required for the other known functions of ATP. The recent postulation that ATP at millimolar concentrations functions as a hydrotrope in various cell/tissue homogenates preventing protein aggregation coupled with observations presented herein, provide support for extending the hypothesis that ATP functions as a hydrotrope not only in homogenates but in an intact functioning organ, the crystalline lens. Concentrations of ATP of this magnitude are hypothesized to be required to maintain protein solubility and effectively prevent protein aggregation. This concept is important considering protein aggregation is the etiology for age-related cataractogenesis. ATP is a common ubiquitous intracellular molecule possessing the requisite hydrotropic properties for maintaining intracellular proteins in a fluid, non-aggregated state. It is proposed that the amphiphilic ATP molecule shields the hydrophobic regions on intralenticular fiber cell protein molecules and provides a hydrophilic interfacial surface comprised of the ATP negatively charged triphosphate side chain. Evidence is presented that this side chain is exposed to and has been reported to organize intracellular interstitial water to form an interfacial rheologically dynamic water layer. Such organization of water is substantiated with the effect of deuterium oxide (heavy water) on ATP line widths of the side chain phosphates measured ex vivo by ³¹P NMR. A novel model is presented to propose how this water layer separates adjacent lens fiber cell proteins, keeping them from aggregating. This hypothesis proposes that ATP can prevent protein aggregation in normal intact lenses, and with declining concentrations can be related to the disease process in age-related cataractogenesis, an affliction that affects every older human being.

Angular dependence of shielding effect of radiation protective eyewear for radiation protection of crystalline lens

Radiation protective (RP) eyewear effectively protects crystalline lenses from radiation exposure. A drawback of RP eyewear is the angular dependence of the shielding effect, which results from the design of the eyewear. In this study, 21 models of RP eyewear with different designs and lead equivalences were assessed. Each piece of RP eyewear was hung on a Styrofoam phantom that imitated the head, and a 0.125-cc ionization chamber dosimeter was placed at the position of the crystalline lens. The differences in angular dependence of the shielding effect were evaluated by changing the irradiation angle, and parameters that improved the angular dependence of the shielding effect-sufficient lead equivalence, large coverage design, and minimum gap between the crystalline lens and the RP eyewear-were identified. Thus, the findings highlight the importance of selecting RP eyewear according to the angular distribution and the nature of radiation exposure in the workplace for radiation workers.

The Effect of Cycloplegia on the Ocular Biometric and Anterior Segment Parameters: A Cross-Sectional Study

Introduction

To evaluate the effects of cycloplegia on the biometric components and anterior segment parameters of the eye.

Methods

In this cross-sectional study, changes to axial length (AL), anterior chamber depth (ACD) lens thickness, anterior chamber angle (ACA) and volume, corneal thickness in the pupil center (PC), corneal curvature (CC) and white-to-white (WTW) following cycloplegia induced by tropicamide 1% in 42 eyes of patients aged 23–58 years were assessed. Biometric components and anterior segment parameters were measured using an IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany) and a Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany), respectively.

Results

Significant statistical changes in ACD (increased by 0.06 ± 0.05 mm; p < 0.001), anterior chamber volume (increased by 15.19 ± 10.32 mm³; p < 0.001), ACA (decreased by 2.18 ± 10.20°; p = 0.029) and lens thickness (decreased by 0.02 ± 0.03 mm; p < 0.001) were observed post-cycloplegia, while the changes in CC, corneal thickness in the PC, WTW and AL were not statistically different (p > 0.05). Also, a significant inferior displacement of the PC along the vertical axes was seen (p = 0.020).

Conclusion

Cycloplegia resulted in a deeper ACD and thinner lens thickness. These changes should be considered in determining intraocular lens (IOL) power to prevent refractive surprises in cataract surgery and also in the phakic IOL implantation.

Visualization of adult fish lens fiber cells

The crystalline lens of a vertebrate eye is a gradient-index lens and grows throughout life by addition of new lens fiber cells in the periphery. In fish, the growing ball-shaped lens maintains sophisticated optical properties throughout life by maintaining the distribution of refractive index relative to the increasing radius of the lens. During this process, the central fibers must increase refractive index by increasing the cytosolic concentration of crystallin proteins. However, only the youngest, most peripheral lens fiber cells have the ability to synthesize proteins. Unfortunately, the hardness of fish lenses makes investigation of the cellular anatomy impossible with traditional histological methods. We have developed a method for visualizing lens fiber cells across the diameter of the lens in adult fish. The method relies on sectioning embedded lenses with a high-speed power saw and observing the cut surface with a scanning electron microscope (SEM). The combination of SEM and image analysis allowed for precise tracking of the positions of individual cell fiber cells. As an application of the method, we present a cell thickness profile, i.e. the distribution of cells thicknesses and their relative positions along the lens's radius. Combined with detailed optical studies, which by mathematical reasons only are possible on ball-shaped lenses, our method can lead to new insights into the mechanism governing the functional and cellular development of vertebrate lenses.

Noninvasive assessment of age-related stiffness of crystalline lenses in a rabbit model using ultrasound elastography

Background

The pathological or physiological changes of a crystalline lens directly affect the eye accommodation and transmittance, and then they increase the risk of presbyopia and cataracts for people in the middle and old age groups. There is no universally accepted quantitative method to measure the lens' mechanical properties in vivo so far. This study aims to investigate the possibility of assessing the age-related stiffness change of crystalline lens by acoustic-radiation-force-based ultrasound elastography (ARF-USE) in a rabbit model in vivo.

Methods

There were 13 New Zealand white rabbits that were divided into four groups and fed normally until they were 60 (n = 4), 90 (n = 2), 120 (n = 4), and 150 (n = 3) days old, respectively. An ARF-USE platform was built based on the Verasonics™ Vantage 256 system. The shear waves were excited and traced in the lens by a linear ultrasound probe after a rabbit was anaesthetized.

Results

The average group velocities were 1.38 ± 0.2 m/s, 2.06 ± 0.3 m/s, 2.07 ± 0.29 m/s, and 2.30 ± 0.28 m/s, respectively, for the four groups of rabbits. The results shows that the group velocity has a strong correlation with the day age (r = 0.84, p < 1 × 10⁻⁷) and the weight (r = 0.83, p < 1×10⁻⁷) of the rabbits while the maximum displacement has no correlations with the day age (r = 0.27, p > 0.1) and the weight (r = 0.32, p > 0.1).

Conclusion

This study demonstrated that the group velocity measured by ARF-USE had a strong correlation with age-related stiffness in a rabbit model, suggesting that group velocity is a good biomarker to characterize the stiffness of a crystalline lens. This study also demonstrated the feasibility of using this USE technique to assess the mechanical properties of the lens in vivo for clinical or research purposes.

Semiautomatic procedure to assess changes in the eye accommodative system

PURPOSE

The aim of this pilot study was to evaluate a new semiautomatic procedure to assess in vivo changes in the crystalline lens and ciliary muscle during accommodation.

METHODS

A total of 14 subjects were divided into two groups, young (aged between 20 and 25 years) and adult (aged between 35 and 40 years), and measured with an anterior segment optical coherence tomography. A semiautomatic procedure was implemented to measure the central lens thickness (CLT), anterior lens radius (ALR) and the ciliary muscle area (CMA) for the unaccommodated eye and for a vergence of - 3.00 D.

RESULTS

The CLT increase for each population group was smaller than 5%, and the dispersion of each group was similar between them. Contrariwise, the reduction in the ALR was about 30% for both groups, although the young one showed the largest variability. The CMA increase was smaller than 30% for both groups, and the dispersion was similar between them. For each metric, differences between both groups were not statistically significant.

CONCLUSIONS

The semiautomatic procedure seems to be useful for the in vivo analysis of the accommodative system. Additionally, the results obtained showed that changes in the CLT were much smaller compared to those obtained for the ALR or CMA.

Dysfunctional lens syndrome

PURPOSE

To report the pre- and post-operative findings of a case with dysfunctional lens syndrome.

METHODS

An adult patient was evaluated using iTrace aberrometer, Tomey topographer and slitlamp biomicroscopy to confirm dysfunctional lens syndrome.

RESULTS

A 45-year-old male patient presented with the chief complaint of poor visual quality; uncorrected visual acuity 20/40 in the right eye, best spectacle corrected visual acuity 20/25 in the right eye with refraction Plano/-1.50 × 80 (SE = -0.75D). Pre- and post-operative root-mean-square (RMS) of total higherorder aberrations in the entire eye, the internal optics and the cornea were 0.350 & 0.257, 0.311 & 0.236 and 0.214 & 0.191 micron (μ), respectively. Also, the magnitude of preoperative total, internal and corneal coma was 0.254 μ × 222°, 0.274μ×242° and 0.097μ × 131° and postoperative values were 0.170 μ × 162°, 0.131 μ × 177°, 0.054 μ × 125°, respectively.

CONCLUSION

These results show that sometime the HOAs of the internal optics, mainly crystalline lens, are not compensated by the cornea and this may cause visual discomfort in the absence of any significant cataract, this situation is known as dysfunctional lens syndrome (DLS).

Off-axis astigmatism in the isolated chicken crystalline lens

The chicken eye was previously found to have little off-axis astigmatism which is not explained by its special corneal shape but rather by the optical properties of the crystalline lens. To learn more about lens design, we studied off-axis astigmatism in the chicken lens in situ and compared it to a glass lens of similar power but with homogenous refractive index. After euthanasia, enucleated eye balls were cut in the equatorial plane right behind the scleral ossicles. The anterior segment was placed in a water-filled chamber. Several thin laser beams were projected in two perpendicular meridians through the lens under various eccentricities and the focal lengths were determined. Off-axis astigmatism across the horizontal visual field was determined as the differences in power in the two meridians. The same procedure was used for the glass lens. On-axis, the chicken crystalline lens had slightly more power in the vertical than in the horizontal meridian (-2.8±0.7D (SEM)). Astigmatism flipped sign and increased with eccentricity to reach +6.1±2.1D (SEM) at 33.5deg off-axis, as expected from off-axis astigmatism. Even though this value appears high, it was still 2.5 times lower than in the glass lens. A ZEMAX model of a lens with a homogeneous index and with surface profiles taken of the natural chicken lens revealed even higher levels of off-axis astigmatism. Obviously, the natural chicken lens displays much less off-axis astigmatism than a glass lens with similar power. Since its shape does not explain the low off-axis astigmatism, it must be due to a refined internal refractive index structure.

Jellyfish sign for intraoperative identification of posterior lenticonus

Posterior lenticonus is a rare progressive disease characterized by protrusion of posterior lens capsule along with lens cortex into the vitreous cavity. It may be associated with local thinning or absence of posterior lens capsule. It generally occurs sporadically, but familial cases have also been reported. If visually significant or if amblyopia is present, lens removal is indicated. Treatment consists of clear or cataractous lens extraction, optical correction along with prompt amblyopia therapy. In this case, we propose a "jellyfish sign" seen intraoperatively, which is referred to the characteristic movement of the posterior capsular cataractous material on injection of balanced salt solution in the capsular bag.

Solar ultraviolet radiation cataract

Despite being a treatable disease, cataract is still the leading cause for blindness in the world. Solar ultraviolet radiation is epidemiologically linked to cataract development, while animal and in vitro studies prove a causal relationship. However, the pathogenetic pathways for the disease are not fully understood and there is still no perfect model for human age related cataract. This non-comprehensive overview focus on recent developments regarding effects of solar UV radiation wavebands on the lens. A smaller number of fundamental papers are also included to provide a backdrop for the overview. Future studies are expected to further clarify the cellular and subcellular mechanisms for UV radiation-induced cataract and especially the isolated or combined temporal and spatial effects of UVA and UVB in the pathogenesis of human cataract. Regardless of the cause for cataract, there is a need for advances in pharmaceutical or other treatment modalities that do not require surgical replacement of the lens.

[Epidemiologic and etiological characteristics of congenital cataract: study of 59 cases over 10 years]

OBJECTIVE

The goal of this study was to analyze the epidemiology and maternal, prenatal and perinatal risk factors for congenital cataracts.

MATERIALS AND METHODS

We conducted a retrospective study of all consecutive cases of congenital cataracts diagnosed and managed at hôpital Nord Marseille, France. We describe demographic, personal, maternal and familial characteristics of these patients.

RESULTS

We identified 59 children with congenital cataract. The group consists of 31 girls (53%) and 28 boys (47%). Cataract was bilateral in 71% of cases and unilateral in 29% of cases. This group is first divided according to etiological forms. Idiopathic cataract accounts for 63% of patients. Genetic and infectious cataract accounts for 34% and 3%, respectively. According to the clinical presentation, congenital cataract was an isolated finding in 51% of cases. It was associated with ocular abnormalities in 27% of cases and with systemic abnormalities in 22% of cases. The diagnosis was made upon routine screening in 41% of cases. Leucoria and strabismus led to the diagnosis in 24% and 19%, respectively. The average age of diagnosis was 19.7 months.

CONCLUSION

Congenital cataract is a relatively rare condition. The description of a series of 59 cases is important as well as the comparison of our results to large epidemiological data previously published. The elucidation of novel risk factors requires consideration at a national or even global scale.

Lenticonus diagnosis in Alport's syndrome: Anterior capsule apical angle calculation using Scheimpflug imagery

OBJECTIVE

We describe a simplified method to detect anterior lenticonus. Three eyes of 2 patients with anterior lenticonus, plus 16 eyes from 16 healthy controls underwent Scheimpflug imaging of their anterior segment with Pentacam. The anterior capsule apex angle was manually identified and automatically measured by AutoCAD.

RESULTS

The mean angle was 173.06° (SD: 1.91) in healthy subjects, and 158.33° (SD: 3.05) in anterior lenticonus eyes. The angle obtained from patients was more than 3 SD steeper than those from healthy subjects.

CONCLUSIONS

The apical angle calculation method seems to discriminate well between normal eyes and eyes suspected of having anterior lenticonus.

Protective effect of catechin on apoptosis of the lens epithelium in rats with N-methyl-N-nitrosourea-induced cataracts

Purpose

To investigate the effect of catechin on apoptotic cell death in the lens epithelium of rats with cataract.

Methods

Cataract was induced by intraperitoneal injection of 100 mg/kg N-methyl-N-nitrosourea (MNU) to ten day-old Sprague-Dawley rats. The neonatal rats were randomly divided into five groups (n=15 in each group): a control group, and four cataract-induction groups, treated with either 0, 50, 100, 200 mg/kg catechin. We performed slit-lamp biomicroscopic analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, Western-blot for Bcl-2 and Bax, and immunohistochemistry for caspase-3.

Results

Apoptotic cell death in lens epithelial cells that increased following cataract formation in rats was suppressed by cathechin.

Conclusions

Catechin inhibited cataract-induced apoptotic cell death in the lens epithelium and may prove useful for the prevention of cataract progression.