Anterior shift of zonular insertion onto the anterior surface of human crystalline lens with age

The Effect of Lens Shape, Zonular Insertion and Finite Element Model on Simulated Shape Change of the Eye Lens

The process of lens shape change in the eye to alter focussing (accommodation) is still not fully understood. Modelling approaches have been used to complement experimental findings in order to determine how constituents in the accommodative process influence the shape change of the lens. An unexplored factor in modelling is the role of the modelling software on the results of simulated shape change. Finite element models were constructed in both Abaqus and Ansys software using biological parameters from measurements of shape and refractive index of two 35-year-old lenses. The effect of zonular insertion on simulated shape change was tested on both 35-year-old lens models and with both types of software. Comparative analysis of shape change, optical power, and stress distributions showed that lens shape and zonular insertion positions affect the results of simulated shape change and that Abaqus and Ansys show differences in their respective models. The effect of the software package used needs to be taken into account when constructing finite element models and deriving conclusions.

The major influence of anterior and equatorial zonular fibres on the far-to-near accommodation revealed by a 3D pre-stressed model of the anterior eye

PURPOSE

To explore the synergistic function of the ligaments in eye, the zonular fibres, that mediate change in eye lens shape to allow for focussing over different distances.

METHODS

A set of 3D Finite Element models of the anterior eye together with a custom developed pre-stress modelling approach was proposed to simulate vision for distant objects (the unaccommodated state) to vision for near objects (accommodation). One of the five zonular groups was cut off in sequence creating five models with different zonular arrangements, the contribution of each zonular group was analysed by comparing results of each specific zonular-cut model with those from the all-zonules model in terms of lens shape and zonular tensions.

RESULTS

In the all-zonular model, the anterior and equatorial zonules carry the highest tensions. In the anterior zonular-cut model, the equatorial zonular tension increases while the posterior zonular tension decreases, resulting in an increase in the change in Central Optical Power (COP). In the equatorial zonular-cut model, both the anterior and posterior zonular tensions increase, causing a decreasing change in COP. The change in COP decreases only slightly in the other models. For vitreous zonular-cut models, little change was seen in either the zonular tension or the change in COP.

CONCLUSIONS

The anterior and the equatorial zonular fibres have the major influence on the change in lens optical power, with the anterior zonules having a negative effect and the equatorial zonules contributing a positive effect. The contribution to variations in optical power by the equatorial zonules is much larger than by the posterior zonules.

Finite element analysis of zonular forces

To determine the effect of zonular forces on lens capsule topography, a finite element (FE) analyses of lens capsules with no lens stroma and constant and variable thickness with anterior capsulotomies of 1.5 mm-6.5 mm were evaluated when subjected to equatorial (Ez), anterior (Az) and posterior (Pz) zonular forces. The lens capsule was considered in the unaccommodated state when the total initial zonular force was 0.00075 N or 0.3 N. From the total 0.00075 N zonular force, the Ez force was increased in 0.000125 N steps for a maximum force of 0.03 N and simultaneously the Az plus Pz force was reduced in 0.000125 N steps to zero. In addition, the force of all the zonules was reduced from 0.00075 N and separately from 0.3 N in 0.000125 N steps to zero. Only when Ez force was increased as Az and Pz force was reduced did the capsule topography simulate in vivo observations with the posterior capsule pole bowing posteriorly. The posterior bowing was directly related to Ez force and capsulotomy size. Whether the total force of all the zonules in the unaccommodated state was 0.00075 N or 0.3 N and reduced in steps to zero, the lens capsule topography did not emulate the in vivo observations. The FE analysis demonstrated that Ez tension increases while the Az and Pz tension decreases and that all the zonules do not relax during ciliary muscle contraction.

Long Anterior Zonules and Angle Closure Disease

PRCIS

Angle closure disease was present in 59.3% of eyes with long anterior zonules (LAZ). The cause is multifactorial including a thick anteriorly positioned crystalline lens, shorter axial length, and increased lens thickness to axial length factor.

PURPOSE

To study the profile of eyes with LAZ presenting in a glaucoma clinic in a tertiary eye care centre and understand the pathogenesis of angle closure disease in these eyes.

METHODS

This was a retrospective cross-sectional study.All patients with LAZ seen from January 2014 to December 2018 were included. Demographic and clinical characteristics were noted. LAZ eyes (177 eyes of 177 patients) were compared with an equal number of age and sex-matched controls. LAZ was defined as radially oriented zonular fibers (both pigmented and nonpigmented), extending central to the normal zonular termination zone on the anterior lens surface >1 mm beyond their usual insertion of 1.42±0.24 mm from the lens equator onto the mid peripheral zone or central to it, as seen on slit-lamp examination, following pupillary dilation by a single examiner. Glaucoma was defined according to the International Society for Geographical and Epidemiological Ophthalmology classification. The following biometric parameters were compared: anterior chamber depth (ACD), axial length (AXL), lens thickness (LT), lens position (LP=ACD+0.5×LT), relative lens position (RLP=LP/AXL); lens thickness to axial length factor (LAF=(LT/AXL)×10). LAZ eyes without angle closure disease were also compared with controls.

RESULTS

Mean age of patients with LAZ was 64.8±8.1 years. Of these, 63.3% were females. Angle closure disease was present in 59.3% (105/177) patients. Majority of these eyes were primary angle closure suspects (PACS) (53.3%, n=56). Significant differences were found between LAZ eyes and controls for LT (4.8±0.38 mm vs. 4.49±0.40 mm, P<0.0001), ACD (2.68±0.39 mm vs. 3.0±0.32 mm, P<0.0001), AXL (22.37±0.79 mm vs. 22.94±1.1, P<0.0001), LAF (2.14±0.19 vs. 1.96±0.21, P<0.0001), and LP (5.07±0.37 vs. 5.3±0.25, P<0.0001).

CONCLUSIONS

Angle closure was present in more than half the eyes with LAZ. Majority of these eyes were PACS or had primary angle closure. LAZ eyes had a thicker lens, shallow AC, a shorter axial length and an increased LAF as compared with age and sex matched normal controls. The presence of LAZ may be an indicator of increased risk for angle closure.

Phacoemulsification in eyes with long anterior zonules

PURPOSE

To study the safety of phacoemulsification in eyes with long anterior zonules (LAZs).

SETTING

Institute.

DESIGN

Retrospective interventional case series.

METHODS

All patients with clinically proven LAZs who had undergone phacoemulsification by a single surgeon from January 2014 to December 2018 were included. All cases of LAZs with cataract extraction by procedures other than phacoemulsification or combined with any other ocular surgery were excluded. Sixty-five eyes of 52 patients were analyzed. Phacoemulsification with capsulorhexis that involves sacrificing the LAZs was performed. The primary outcome measures were the incidence of capsulorhexis extension or the need to rescue intraoperatively and the rate of intraoperative complications. Secondary outcomes assessed were the percentage of eyes within ±0.5 diopters (D) and ±1 D of the target refraction.

RESULTS

Sixty-five eyes (52 patients) were analyzed; the mean age of patients was 67.3 ± 7.4 years. The successful completion of an adequately sized capsulorhexis without extension or rescue was seen in 100% of cases. The incidence of intraoperative complications was 1.5% (posterior capsular rupture in 1 eye). The mean postoperative corrected distance visual acuity was 0.05 ± 0.1 (logarithm of the minimum angle of resolution) at a mean of 26.8 ± 7.6 days. The mean spherical equivalent was -0.15 ± 0.7 D. Eyes within ±0.5 D and ±1.00 D of the target refraction were 77% and 94%, respectively.

CONCLUSIONS

Phacoemulsification in eyes with LAZs can be safely performed through an adequately sized capsulorhexis by sacrificing, ie, cutting or breaking, the anteriorly inserted zonules 360 degrees without significant intraoperative complications.

The importance of parameter choice in modelling dynamics of the eye lens

The lens provides refractive power to the eye and is capable of altering ocular focus in response to visual demand. This capacity diminishes with age. Current biomedical technologies, which seek to design an implant lens capable of replicating the function of the biological lens, are unable as yet to provide such an implant with the requisite optical quality or ability to change the focussing power of the eye. This is because the mechanism of altering focus, termed accommodation, is not fully understood and seemingly conflicting theories require experimental support which is difficult to obtain from the living eye. This investigation presents finite element models of the eye lens based on data from human lenses aged 16 and 35 years that consider the influence of various modelling parameters, including material properties, a wide range of angles of force application and capsular thickness. Results from axisymmetric models show that the anterior and posterior zonules may have a greater impact on shape change than the equatorial zonule and that choice of capsular thickness values can influence the results from modelled simulations.

Evaluating relaxed ciliary muscle tone in presbyopic eyes

PURPOSE

Studies of age-related changes in ciliary muscle (CM) morphology and contractility have variously reported that CM weakens or strengthens with age. In response, the aim of this study was to evaluate relaxed CM tone in vivo in pre-presbyopic and presbyopic patients using a predictor value (P_CM).

METHODS

Two groups of eyes-40 eyes of 40 healthy volunteers with a mean age of 28.1 ± 5.8 years and 40 eyes of 40 healthy volunteers with a mean age of 56.6 ± 7.3 years-formed the sample for this prospective, observational cross-sectional study. Used to evaluate relaxed CM tone, P_CM was calculated as the difference between the change in mean anterior chamber depth (ACD) and lens thickness (LT) before and after cycloplegia, as measured with swept-source optical biometry.

RESULTS

The P_CM for relaxed CM tone was 0.04 ± 0.04 mm in pre-presbyopic participants, 0.06 ± 0.03 mm in presbyopic ones, and significantly greater in presbyopic patients (p = .018).

CONCLUSION

The statistical significance of P_CM between pre-presbyopic and presbyopic eyes might not signify clinical significance, since the difference was close to the repeatability limits for swept-source optical biometry. When relaxed, CM tone does not diminish with presbyopia according to changes in anterior chamber parameters due to cycloplegia.

Anterior zonulotomy: Rescue technique for capsulorhexis tear-out

An anterior zonulotomy technique to rescue a capsulorhexis tear-out is described. The technique uses microsurgical instruments that are capable of performing microprocedures within the confines of the anterior chamber. The anterior zonulotomy releases the tractional impediment caused by the anterior zonular fibers, enabling the surgeon to use conventional rescue methods to redirect the CCC centrally. The technique demonstrates how microsurgical instruments can be used to safely perform an anterior zonulotomy for radial tear-outs that have become lodged in the zonular fibers.

FINANCIAL DISCLOSURE

The author has no financial or proprietary interest in any material or method mentioned.

Remnants of the anterior tunica vasculosa lentis and long anterior lens zonules

PURPOSE

To investigate presence of remnants of the tunica vasculosa lentis, a possible indication of anterior segment dysgenesis, in subjects with the long anterior zonule (LAZ) trait.

METHODS

Retroillumination photographs of the pupil region had been collected in earlier study of the LAZ trait in African Americans. Secondary image analysis was performed to assess the frequency of intact persistent pupillary membrane iris strands (PPMIS).

RESULTS

The analysis included 148 subjects, comprised of 74 LAZ subjects (median age=70 y; range, 50 to 91 y; 64 females) and 74 controls (68 y; 50 to 83 y; 64 females). While controlling for age and sex, analysis showed that LAZ subjects were 3.1 times more likely than controls (odds ratio=3.1; 95% confidence interval, 1.4-6.7; P=0.004) to exhibit PPMIS in at least one of their eyes.

CONCLUSION

The LAZ trait, which is being studied as a potential risk factor for glaucoma, was associated with presence of PPMIS in our study population.

Correlation between ocular biometry and amplitude of accommodation in early presbyopia

PURPOSE

To determine the correlation between ocular biometric parameters and the amplitude of accommodation in early presbyopic eyes.

METHODS

This cross-sectional study was performed on 62 eyes of 62 subjects aged from 40 to 49 years. All participants were emmetropic (spherical equivalent refractive error within 0.50 D of emmetropia with astigmatism less than 0.75 D) and best spectacle-corrected visual acuity was 20/20. Only the right eyes of all subjects were included for analysis. In all subjects a complete ophthalmologic examination was performed and the amplitude of accommodation (AA) was measured by two methods: method of spheres and push-up test. Optical biometry was performed using Lenstar® (Haag-Streit AG, Koeniz, Switzerland) and keratometry (KR), anterior chamber depth (corneal epithelium to lens) (ACD), lens thickness (LT), vitreous length (VL), and axial length (AL) were measured before and after cycloplegia.

RESULTS

Mean age of the study participants was 44 ± 2 years and 36 subjects (58%) were men. Mean AA was 3.29 ± 1.36 D. There were statistically significant differences between ACD, LT, and AL values measured before and after cycloplegia. There was no significant correlation between AA and any biometric parameter measured by Lenstar using univariate and multivariate analysis.

CONCLUSIONS

According to this study, there seems to be no correlation between KR, ACD, LT, VL, and AL with AA in early presbyopic eyes.

Clinical outcomes of cataract surgery in very elderly adults

OBJECTIVES

To investigate the clinical outcomes of cataract surgery elderly adults.

DESIGN

Retrospective cohort study.

SETTING

Two clustered hospitals.

PARTICIPANTS

Two hundred seven individuals aged 90 and older who underwent cataract surgery for primary senile cataracts.

MEASUREMENTS

Best-corrected preoperative and postoperative Snellen visual acuity, type of cataract, surgical techniques, preoperative systemic or ocular comorbidities, and intraoperative and postoperative complications were assessed. Improvement of visual acuity was defined as a decrease in logMAR acuity of 0.1. Factors associated with visual outcome within 6 months after surgery were identified using logistic regression modeling. The duration of postoperative survival was calculated.

RESULTS

In the 207 participants (mean age 92.0 ± 2.1), 79.7% achieved visual improvement after cataract surgery. Forty-eight percent (mean age 97.4 ± 2.8) were alive on December 31, 2012. The most common systemic comorbidities were hypertension (66.2%), diabetes mellitus (25.1%), and myocardial infarction (19.8%). Age-related macular degeneration (AMRD) (15.9%), glaucoma (10.6%), and myopic degeneration (5.3%) were the three most common ocular comorbidities. Uncomplicated cataract surgery was performed in 87.0% cases. The most common complications were vitreous loss (8.2%), posterior capsular rupture (7.2%), and zonular rupture (4.8%). Participants with AMRD (P = .001, odds ratio (OR) = 4.77, 95% confidence interval (CI) = 1.86-12.26) and vitreous loss (P = .001, OR = 12.86, 95% CI = 2.71-61.10) were less likely to achieve postoperative visual improvement.

CONCLUSION

Despite a high prevalence of systemic and ocular comorbidities in very elderly adults, good clinical outcomes of cataract surgery were attainable. ARMD and vitreous loss were associated with a lower chance of postoperative visual improvement.

Matrix metalloproteinase-2 degrades fibrillin-1 and fibrillin-2 of oxytalan fibers in the human eye and periodontal ligaments in vitro

Oxytalan fibers are distributed in the eye and periodontal ligaments (PDL). The ciliary zonule, known as Zinn’s zonule, in the eye is composed of oxytalan fibers, which are bundles of microfibrils consisting mainly of fibrillin-1 and fibrillin-2. As turnover of oxytalan fibers is slow during life, their degradation mechanism remains unclarified. This study was performed to examine degradation pattern of fibrillin-1 and fibrillin-2 by experimental MMP activation. We cultured human non-pigmented ciliary epithelial cells (HNPCEC) and PDL fibroblasts for 7 days, then treated them with concanavalin A to activate matrix metalloproteinase (MMP)-2, and examined the degradation of fibrillin-1 and fibrillin-2 for 72 hr using immunofluorescence. At 7 days of HNPCEC culture, fibrillin-1-positive fibers were observed, some of which merged with fibrillin-2. After MMP-2 activation, fibrillin-1-positive fibers became thin and disappeared by 72 hr, while fibrillin-2-positive fibers disappeared almost completely within 24 hr. At 7 days of PDL fibroblast culture, fibrillin-1-positive fibers were mostly merged with fibrillin-2. After MMP-2 activation, fibrillin-1-positive fibers became thin by 24 hr and had almost disappeared by 48 hr, while fibrillin-2-positive fibers decreased constantly after 24 hr. A MMP-2 inhibitor completely suppressed these degradations. These results suggest that the patterns of fibrillin-1 and fibrillin-2 degradation differ between the eye and the PDL, possibly reflecting the sensitivity of fibrillin-1 and fibrillin-2 of each type of oxytalan fiber against MMP-2.

The characterization of retinal phenotype in a family with C1QTNF5-related late-onset retinal degeneration

PURPOSE

To describe the clinical, spectral-domain optical coherence tomography and electrophysiological features of C1QTNF5-associated late-onset retinal degeneration in a molecularly confirmed pedigree.

METHODS

Five members of a family participated, and affected individuals (n = 4) underwent detailed ophthalmologic evaluation including fundus autofluorescence and spectral-domain optical coherence tomography imaging and electroretinography. Electrooculography was performed in three individuals.

RESULTS

The visual acuity was initially normal and worsened with time. Anterior segment abnormalities included peripupillary iris atrophy and long anterior insertion of zonules. Peripapillary atrophy, drusenoid deposition, and scalloped sectorial chorioretinal atrophy were observed in all older individuals (n = 3). Fundus autofluorescence demonstrated hypofluorescent areas corresponding to regions of chorioretinal atrophy. The spectral-domain optical coherence tomography demonstrated multiple areas of retinal pigment epithelium-Bruch membrane separation with intervening homogeneous deposition that corresponded to the drusenoid lesions and areas of chorioretinal atrophy. Electrooculography was normal in one individual and showed abnormally low dark trough measures in older individuals (n = 2). Electroretinography was normal in early stages (n = 1), but showed marked abnormalities in the rod system (n = 3), which was predominantly inner retinal (n = 2) in late stages.

CONCLUSION

Late-onset retinal degeneration is a progressive degeneration, and anterior segment abnormalities present early. The widespread sub-retinal pigment epithelium deposition seen on spectral-domain optical coherence tomography in older individuals appears to be a characteristic in late stages. Electrooculography demonstrates abnormalities only in late stages of the disease.

Spatial analysis of human lens aquaporin-0 post-translational modifications by MALDI mass spectrometry tissue profiling

Aquaporin-0 (AQP0), the major integral membrane protein in lens fiber cells, becomes highly modified with increasing age. The functional consequences of these modifications are being revealed, and the next step is to determine how these modifications affect the ocular lens, which is directly related to their abundances and spatial distributions. The aim of this study was to utilize matrix-assisted laser desorption ionization (MALDI) direct tissue profiling methods, which produce spatially-resolved protein profiles, to map and quantify AQP0 post-translational modifications (PTMs). Direct tissue profiling was performed using frozen, equatorial human lens sections of various ages prepared by conditions optimized for MALDI mass spectrometry profiling of membrane proteins. Modified forms of AQP0 were identified and further investigated using liquid chromatography tandem mass spectrometry (LC-MS/MS). The distributions of unmodified, truncated, and oleoylated forms of AQP0 were examined with a maximum spatial resolution of 500 μm. Direct tissue profiling of intact human lens sections provided high quality, spatially-resolved, relative quantitative information of AQP0 and its modified forms indicating that 50% of AQP0 is truncated at a fiber cell age of 24 ± 1 year in all lenses examined. Furthermore, direct tissue profiling also revealed previously unidentified AQP0 modifications including N-terminal acetylation and carbamylation. N-terminal acetylation appears to provide a protective effect against N-terminal truncation.

A geometric model of ocular accommodation

An exoteric geometric mechanics model of ocular accommodation is detailed to elucidate the main ideas of various ongoing modeling efforts. The present study derives solutions for the stretched state of the ocular lens as it might appear during accommodation by using simple geometric arguments and a volume constraint, rather than the more mathematically intensive theory of elasticity. Results show that geometric shapes similar to the lens will deform in a similar fashion. This implies that, while the true lens geometry is somewhat more complex, it should also follow these qualitative behaviors.

Zonular fibers, multimolecular composition as related to function (elasticity) and pathology

Zonular fibers (ZF) play an important role in accommodation. With the rapid increase over the last decade of the oldest part of the population in industrialized countries, age-dependent loss of accommodation became an increasingly important problem. It appeared therefore interesting to review old and recent literature on ZF, their composition, structure and pathological alterations. By comparing former and recent reports it appeared to us, that several previous reports were not sufficiently taken in consideration for the understanding of the rheological properties of ZF. Elastin and proteoglycans-glycosaminoglycans were reported previously as constituents of ZF. Their presence besides fibrillin, the major constituent, helps to explain the rheological properties of these fibers, and especially their elasticity and its age- and pathology-dependent decline. Our review points also to some of the major problems, which remain to be addressed by future experiments.

The plateau iris component of primary angle closure glaucoma: developmental or acquired

Primary angle closure glaucoma has been called the most common form of glaucoma in the world, and the leading cause of bilateral blindness. Pupillary block is felt to be the main mechanism of outflow obstruction in this condition. Recent advances in morphologic assessment of angle closure, specifically by means of ultrasound biomicroscopy, have revealed that plateau iris in eyes with angle closure glaucoma is more common than had previously been thought. The most characteristic finding in this disease is thicker and more anteriorly positioned lens. This induces the pupillary block that relives by laser iridotomy. Residual angle closure after laser iridotomy is due to the plateau iris. Peripheral iridoplasty, the standard treatment of plateau iris, tights the peripheral iris and opens the angle but has no effect on the ciliary processes configuration. The ciliary processes are positioned posteriorly after lens extraction but dose not disappears completely. Considering these facts we hypothesized that the plateau iris in primary angle closure glaucoma is a developmental entity that reaches to a critical stage with aging owing to the thickening and forward movement of the lens. Cataract surgery deeps the anterior chamber, widens the irido-corneal angle and reposits the ciliary processes posteriorly, so it can prevents synechia formation and progressive lens-induced angle narrowing and plateau iris progression, the acquired component, with aging.

Sensitivity study of human crystalline lens accommodation

A nonlinear axisymmetric finite element method (FEM) analysis was employed to determine the critical geometric and material properties that affect human accommodation. In this model, commencing at zero, zonular traction on all lens profiles resulted in central lenticular surface steepening and peripheral surface flattening, with a simultaneous increase in central lens thickness and central optical power. An age-related decline in maximum zonular tension appears to be the most likely etiology for the decrease in accommodative amplitude with age.

[The aging lens--new concepts for lens aging]

Epidemiological changes within the next decades will lead to an increase in the world population and to life expectancy. These changes will in turn lead to an increase in age correlated lens opacities and cataracts. Intensive research on cataract formation therefore becomes more and more important for socioeconomic reasons. In addition to the known risk factors, increased attention is currently being paid to oxidative processes. Typically, changes in the old lens are caused by the failure of protective systems and an accumulation of metabolic end-products and their influence on light transmission. Advanced glycation end-products and their potential inhibition seem to play a key role.

Insights into the age-related decline in the amplitude of accommodation of the human lens using a non-linear finite-element model

AIM

To understand the effect of the geometric and material properties of the lens on the age-related decline in accommodative amplitude.

METHODS

Using a non-linear finite-element model, a parametric assessment was carried out to determine the effect of stiffness of the cortex, nucleus, capsule and zonules, and that of thickness of the capsule and lens, on the change in central optical power (COP) associated with zonular traction. Convergence was required for all solutions.

RESULTS

Increasing either capsular stiffness or capsular thickness was associated with an increase in the change in COP for any specific amount of zonular traction. Weakening the attachment between the capsule and its underlying cortex increased the magnitude of the change in COP. When the hardness of the total lens stroma, cortex or nucleus was increased, there was a reduction in the amount of change in COP associated with a fixed amount of zonular traction.

CONCLUSIONS

Increasing lens hardness reduces accommodative amplitude; however, as hardness of the lens does not occur until after the fourth decade of life, the age-related decline in accommodative amplitude must be due to another mechanism. One explanation is a progressive decline in the magnitude of the maximum force exerted by the zonules with ageing.

Growth patterns of fresh human crystalline lenses measured by in vitro photographic biometry

The purpose of the study was to demonstrate and evaluate the use of digital-image photography to measure the central thickness and equatorial diameter of whole fresh human crystalline lenses free of all zonular attachments. Forty-one human donor postmortem intact clear crystalline lenses, with a mean age of 28.5 +/- 16.4 years, were obtained by the contributing eye banks. The lenses were removed by the eye bank and shipped in Optisol-GS, a physiologic preservative storage medium, at 7 degrees C. The lenses were stored at the same temperature and in the same preservative throughout this study. This medium has been demonstrated to maintain the morphometric characteristics of epithelial cells. After freeing the lenses of all residual zonular attachments, digital photographs were obtained within an average of 20.9 +/- 13.4 h after death. The digital images were used to determine the central thickness and equatorial diameter of the crystalline lenses. By carefully calibrating the digital images and maintaining the lenses in physiological storage medium, reliable dimensional measurements were obtained. The dimensions for central thickness for each lens were compared to published, age-matched lenses, measured in vivo, and were found to duplicate these in vivo measurements reliably.

Clinical outcome following cataract surgery in very elderly patients

PURPOSE

The number of very elderly patients waiting for cataract surgery is predicted to increase. The aim of our study was to determine the clinical outcome following cataract surgery in this age group.

METHODS

In this retrospective study, patients aged 96 years and above, who underwent cataract surgery between June 1993 and January 2001, were identified. Clinical data were retrieved from their medical records. Living patients were further invited for clinical examination.

RESULTS

In all, 34 eyes of 21 patients (20 females) were identified. Six patients were deceased. In total, 30/34 eyes had phacoemulsification and four had extracapsular extraction. Preoperative vision was <or=6/36 in 24/34 eyes (70.59%) and <or=CF in 16/34 eyes (47.06%). Postoperative vision was >or=6/60 in 25/34 eyes (73.53%), >or=6/18 in 21/34 eyes (61.76%), and >or=6/9 in 10/34 eyes (29.41%). Visual acuity improved in 24/34 eyes (70.59%) and remained the same in 6/34 eyes. Complications included anterior capsule tear (three), zonular dialysis with vitreous loss (one), posterior capsule rupture with vitreous loss (one), incarceration of iris to paracentesis wound (two), postoperative uveitis (two), and posterior capsular opacification (19). In all, 7/34 eyes had undergone YAG capsulotomy.

CONCLUSION

Surgeons should not be deterred from offering cataract surgery to the very elderly as successful visual rehabilitation is the norm. A further prospective multicentre study is required to confirm the benefits and assess the risks of cataract surgery in this age group.

Long anterior zonules and pigment dispersion

PURPOSE

To describe pigment dispersion associated with long anterior zonules.

DESIGN

Multicenter observational case series.

METHODS

Fifteen patients, seven of whom were treated for glaucoma or ocular hypertension, were identified with long anterior zonules and pigment dispersion. Transmission electron microscopy was performed on one anterior capsule specimen.

RESULTS

All patients had anterior zonules that inserted centrally on the lens capsule. Signs of pigment dispersion included corneal endothelial pigmentation, loss of the pupillary ruff, and variable trabecular meshwork pigmentation. Ultrasound biomicroscopy verified the lack of posterior iris insertion and concavity. There was no exfoliation material. Transmission electron microscopy showed zonular lamellae with adherent pigment granules, and no exfoliation material.

CONCLUSIONS

Long anterior zonules inserted onto the central lens capsule may cause mechanical disruption of the pigment epithelium at the pupillary ruff and central iris leading to pigment dispersion.

Indocyanine green staining of anteriorly placed zonules

The anatomy of the capsules and zonules varies with each patient, particularly in the zonule-free zone. We present a case in which indocyanine green dye highlighted the anterior lens capsule and centrally encroaching zonular fibers within a 2.0 mm zonule-free zone. We suggest technique modifications to reduce the risk for capsule extensions and related complications.

Iridociliary apposition in plateau iris syndrome persists after cataract extraction

PURPOSE

To evaluate the ultrasound biomicroscopic appearance of the anterior segment before and after cataract extraction in eyes with plateau iris syndrome and to determine the effect of postoperative zonular relaxation on ciliary body position.

DESIGN

Interventional case series.

METHODS

Eyes with plateau iris syndrome scanned before and after cataract extraction between January 1994 and September 2001 were enrolled. The iridociliary relationship and the anterior chamber depth at a distance of 3 mm from the scleral spur were assessed.

RESULTS

We examined six eyes of six patients. Mean patient age was 74.2 +/- 6.4 years (standard deviation [SD]) (range, 65-81 years). Mean refractive error was + 1.0 +/- 3.9 diopters [D] (range, -5.75-+5.50), and mean axial length was 21.85 +/- 0.77 mm (range, 20.90-22.95 mm). All eyes had undergone laser iridotomy and argon laser peripheral iridoplasty before cataract extraction. Ultrasound biomicroscopy examination revealed a narrow angle and absence of a ciliary body sulcus in all eyes with focal areas of iridotrabecular apposition in three eyes. Following cataract extraction, the anterior chamber depth increased (P =.0006, paired t test), while the iridociliary contact remained unchanged.

CONCLUSIONS

Iridociliary apposition persists after cataract extraction in plateau iris syndrome. Whether the cause is congenital or acquired, or both, remains to be determined.

Accommodation dynamics as a function of age

Experiments are described in which the dynamic accommodation response to a stimulus whose vergence was varying sinusoidally with time between 1.33 and 2.38 D was measured as a function of frequency for 19 subjects, with ages distributed between 18 and 49 years. Response to abrupt stimulus change between the same levels was also measured. The results showed that at any age, for the sinusoidal stimuli, gain fell with frequency and phase lag increased: at fixed frequency, gain fell with age and phase lag increased. Neither reaction nor response times for step stimuli changed with age. Analysis of the sinusoidal data suggests the possible existence of a cut-off frequency of about 2 Hz, which varies little with age and above which the system cannot respond. The phase data is compatible with the existence of a frequency-independent time delay, which increases with age from about 0.17 s at 20 years to 0.48 s at 40 years. The results are discussed in terms of current knowledge of the factors contributing to the development of presbyopia.

Spontaneous posterior dislocation of intraocular lenses fixated in the capsular bag

We report 4 cases of complete posterior dislocation of an intraocular lens (IOL) in the capsular bag occurring a mean of 5.5 years after uneventful cataract surgery. In all 4 cases, posterior chamber IOLs were fixated within the capsulorhexis. The patients experienced sudden loss of vision without an episode of trauma or ocular disease. Using a 3-port pars plana vitrectomy, the IOLs were explanted through a limbal incision and a new IOL was sutured to the ciliary sulcus. Histological examination indicated that zonular fibers were severed at the site of insertion in the capsule.

Mechanism of human accommodation as analyzed by nonlinear finite element analysis

Results of nonlinear finite element analysis support the Schachar theory of accommodation and demonstrate that the long-held Helmholtz theory of accommodation is impossible.

Presbyopia, accommodation, and the mature catenary

OBJECTIVE

To demonstrate a plausible explanation of aging changes and to reduce the controversy relative to accommodation by using a mechanical model of the catenary theory of lens change. MECHANICAL MODELING: A mechanical model was used to simulate a human lens in both the accommodated and unaccommodated state to demonstrate changes in the mechanism of accommodation with age.

METHODS

Fluid-filled latex balloons were supported by a plastic wrap hammock to form a catenary that models the human lens. Increasing volumes were used to simulate that of the aging lens, and variations in curvature were measured.

MAIN OUTCOME MEASURES

The degree of curvature of a simulated anterior lens surface was measured and compared with mathematical modeling of its optical surface based on the catenary hydraulic suspension theory.

RESULTS

The measurements showed that accommodative loss and other features such as mass displacement, reproducible lens surfaces, and zonule support are consistent with the catenary theory of accommodation and an increasing lens volume with age.

CONCLUSIONS

The catenary theory of accommodation provides a basis for evaluating age changes of the human lens. Variable results with surgical procedures for presbyopia are also predictable with the model. These results can be used to provide a basis for intraocular lens design.

Theoretical basis for the scleral expansion band procedure for surgical reversal of presbyopia [SRP]

A new technique, the scleral expansion band procedure, has been developed for the surgical reversal of presbyopia. An understanding of demonstrable clinical effects of the scleral expansion band procedure, based on Schachar's theory, requires a revision of historically held views concerning the mechanism of accommodation.

Pediatric cataracts

There have been major changes over the past 5 to 10 years in our understanding of both the chemical basis for and the surgical treatment of cataract in infants and children. Important questions that remain to be answered include the appropriate power and design selection criteria for intraocular lens implantation, as well as management of the posterior capsule and long-term refractive sequelae. In the past 10 years, there have been radical changes in the management of visually significant cataract in the infant and child. Whereas lens removal, subtotal posterior capsulectomy, vitrectomy, and aphakia were once the standard of care, many physicians now feel that small incisions, phacoemulsification technology, and intraocular lenses (IOLs) are best for these patients. Work is continuing to accumulate a significant body of evidence to evaluate results of these changes in technique and to develop optimal IOL designs and selection criteria for these specialized cataract patients.