Presbyopia and the optical changes in the human crystalline lens with age

BCLA CLEAR presbyopia: Mechanism and optics

With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.

Perception and awareness of the public about presbyopia and its corrective approaches in Saudi Arabia: a population-based survey

BACKGROUND

This study investigated patients' awareness of presbyopia and its management approaches and their preferred methods for near vision correction.

METHODS

In Saudi Arabia, 785 participants (aged between 35 and 60 years) completed a structured survey online, consisting of hard copies and direct interviews. The survey consisted of twenty-eight items divided into three parts. It was designed to record participants' awareness of and preferences for presbyopia and its refractive corrections. Nonparametric tests and descriptive analyses were conducted to analyse participants' responses.

RESULT

Approximately half of the participants had difficulty with near vision activities, such as reading newspapers or using mobile phones. Among all the participants, 76% were not aware of presbyopia. The prevalence of uncorrected presbyopia was 48% of the 785. The majority (82%) felt that spectacles were acceptable for correction of presbyopia. Most reported that they did not experience social stigma when using reading spectacles (87% of participants). When asked if they were aware of management approaches other than spectacles, 72% responded with not at all. Most participants had no earlier knowledge of the use of multifocal contact lenses or eye drops for presbyopia correction (67% and 82%, respectively). In the present study, some tendencies to use corrective approaches to presbyopia other than spectacles were noted. Finally, participants' age, sex, region, education, and income had a statistically significant impact on essential parts of their responses (p < 0.05).

CONCLUSION

Presbyopia is a highly prevalent age-related ocular disorder, and a significant percentage of cases are uncorrected due to a lack of awareness or reluctance to wear spectacles. More efficient health education about presbyopia and its corrective alternatives is urgently needed.

Functional effects of the spatial-varying lens mechanical properties in accommodation

Lens biomechanical properties are critical for our eyes to accommodate. While it is well understood that lens mechanical properties change with age, different experimental techniques have been used over the years, with varying results on how the lens modulus changes. In this study, we developed a spatial-varying elasticity model to characterize the overall elastic modulus of the lens and establish its effect on accommodation. First, to validate the model, ex vivo porcine lenses underwent compression testing using biopsy punches of different diameters to change the percentage of nucleus within samples. Importantly, we found that, indeed, changing nucleus/cortex spatial ratio produces dramatic (∼7-fold) increase in overall sample modulus. Comparing the model with human lens spatial ratios, we demonstrate how changing spatial mechanics are more influential than peak modulus changes on overall elastic modulus. Next, in vivo clinical measurements of the spatial-varying lens modulus were used to generate a simplified mechanical-optical model of accommodation. We defined an ellipsoid lens with patient-derived modulus and geometry measurements, and a statics simulation and ray tracing analysis were performed through the deformed and undeformed lens. The resulting accommodation estimates agree with general accommodation expectations.

Wavefront Changes during a Sustained Reading Task in Presbyopic Eyes

The objective of this study was to assess the effect of sustained reading on the temporal changes in the wavefront error in the presbyopic eye. The wavefront aberration of the eyes was measured using an IRX3 Shack-Hartmann aberrometer before and after (immediately, 5 min, and 10 min after) a reading task. Temporal changes in C20, C40, and C3-1 coefficient values of the eyes were plotted, showing a predominant number of V-shaped patterns (for C40 and C3-1) and inverse V-shaped patterns (for C20) among the study group, and the percentages (between 27 and 73%) were reported. The median of the total RMS of aberrations and the RMS of HOA (higher-order aberrations), which included comatic (3rd order) and spherical-like aberrations (4th and 6th order), increased immediately after finishing the near-vision reading task and then decreased. The median of RMS of comatic aberrations had a similar pattern of variations, while the median of RMS of spherical-like aberrations displayed an opposite pattern. Simulating the aberration changes due to lens decentration caused by relaxed zonules during 4 D accommodation in an eye model demonstrated that the expected range of changes for the vertical coma and spherical aberrations are in the order of 0.001 and 0.01 μm, respectively, which could justify why the observed changes were not statistically significant. The observed dynamic changes in HOA might be linked to the biomechanical characteristics and alterations in the displacement of the crystalline lens following prolonged near-vision tasks in presbyopic people. Although some predominant patterns under some conditions were shown, they exhibit considerable inter-subject and inter-ocular variability. This might be due to slight misalignments while fixating on the internal extended object in the aberrometer.

Age and Type of Task-Based Impact of Mental Fatigue on Balance: Systematic Review and Meta-Analysis

The role of cognition in balance control suggests that mental fatigue may negatively affect balance. However, cognitive involvement in balance control varies with the type or difficulty of the balance task and age. Steady-state balance tasks, such as quiet standing, are well-learned tasks executed automatically through reflex activities controlled by the brainstem and spinal cord. In contrast, novel, and challenging balance tasks, such as proactively controlling balance while walking over rugged terrain or reacting to unexpected external perturbations, may require cognitive processing. Furthermore, individuals with preexisting balance impairments due to aging or pathology may rely on cognitive processes to control balance in most circumstances. This systematic review and meta-analysis investigated the effect of mental fatigue on different types of balance control tasks in young and older adults. A literature search was conducted in seven electronic databases and 12 studies met eligibility criteria. The results indicated that mental fatigue had a negative impact on both proactive (under increased cognitive load) and reactive balance in young adults. In older adults, mental fatigue affected steady-state and proactive balance. Therefore, mentally fatigued older individuals may be at increased risk of a loss of balance during steady-state balance task compared to their younger counterparts.

Defocus Curve and Satisfaction of Patients with Presbyopia After LASIK Using the Differential Modulation of Binocular Longitudinal Spherical Aberration

Purpose

To investigate the visual acuity and satisfaction of patients after Zhang & Zheng's corneal laser-enhanced accommodation refraction Q (ZZ-CLEAR-Q) surgery utilizing differential modulation of binocular longitudinal spherical aberration and determine its clinical significance.

Patients and Methods

This prospective observational study enrolled a consecutive cohort of patients with presbyopia who underwent ZZ-CLEAR-Q surgery between December 2020 and January 2023. The study assessed visual acuity, distance-corrected defocus curve, satisfaction, Q factor, manifest spherical equivalent, and primary spherical aberration, among others, at 3 months postoperatively. Additionally, the study conducted a binocular comparison to analyze the clinical significance of setting the different longitudinal spherical aberrations.

Results

A total of 232 eyes of 116 patients were included. The binocular uncorrected distance visual acuity was 20/20 for all patients. At 3 months postoperatively, the binocular uncorrected near visual acuity was Jaeger 1 for 96% of the patients and Jaeger 2 for 100% of the patients. Furthermore, 93.1% of the patients expressed satisfaction. The monocular distance-corrected defocus curve revealed that the dominant eyes had significantly better visual acuity at 0 D (P<0.001), while the non-dominant eyes had significantly better visual acuity across various defocus levels except 0 and -0.50 D (All P<0.05). At 3 months, there were no significant differences between the expected and achieved manifest spherical equivalents, corneal Q factor values, and ocular primary spherical aberration values of both groups.

Conclusion

Patients with presbyopia who underwent ZZ-CLEAR-Q surgery were likely to achieve normal uncorrected visual acuity and be satisfied. The increased depth of field has clinical significance for assisting near vision.

Mental fatigue does not affect static balance under both single and dual task conditions in young adults

The ability to control balance and prevent falls while carrying out daily life activities may require a predominantly controlled (cognitive) or automatic processing depending on the balance challenge, age, or other factors. Consequently, this process may be affected by mental fatigue which has been shown to impair cognitive abilities. Controlling static balance in young adults is a relatively easy task that may proceed automatically with minimal cognitive input making it insusceptible to mental fatigue. To investigate this hypothesis, static single and dual task (while concurrently counting backward by seven) balance was assessed in 60 young adults (25.2 ± 2.4 years) before and after 45 min of Stroop task (mental fatigue condition) and watching documentary (control), presented in a randomized counterbalanced order on separate days. Moreover, because mental fatigue can occur due to task underload or overload, participants carried out two different Stroop tasks (i.e., all congruent, and mainly incongruent trials) on separate days in the mental fatigue condition. Results of the study revealed a significantly higher feeling of mental fatigue after the mental fatigue conditions compared to control (p < 0.001). Similarly, the performance on congruent Stroop trials decreases with time indicating objective mental fatigue (p < 0.01). However, there was no difference in balance or concurrent task performance under both single and dual task assessments between the three conditions (p  > 0.05) indicating lack of effect of mental fatigue on static balance in this population. Therefore, future studies investigating this phenomenon in occupational or sport settings in similar population should consider using more challenging balance tasks.

Refractive development I: Biometric changes during emmetropisation

PURPOSE

Although there are many reports on ocular growth, these data are often fragmented into separate parameters or for limited age ranges. This work intends to create an overview of normal eye growth (i.e., in absence of myopisation) for the period before birth until 18 years of age.

METHODS

The data for this analysis were taken from a search of six literature databases using keywords such as "[Parameter] & [age group]", with [Parameter] the ocular parameter under study and [age group] an indication of age. This yielded 34,409 references that, after screening of title, abstract and text, left 294 references with usable data. Where possible, additional parameters were calculated, such as the Bennett crystalline lens power, whole eye power and axial power.

RESULTS

There were 3422 average values for 17 parameters, calculated over a combined total of 679,398 individually measured or calculated values. The age-related change in refractive error was best fitted by a sum of four exponentials (r²  = 0.58), while all other biometric parameters could be fitted well by a sum of two exponentials and a linear term ('bi-exponential function'; r² range: 0.64-0.99). The first exponential of the bi-exponential fits typically reached 95% of its end value before 18 months, suggesting that these reached genetically pre-programmed passive growth. The second exponentials reached this point between 4 years of age for the anterior curvature and well past adulthood for most lenticular dimensions, suggesting that this part represents the active control underlying emmetropisation. The ocular components each have different growth rates, but growth rate changes occur simultaneously at first and then act independently after birth.

CONCLUSIONS

Most biometric parameters grow according to a bi-exponential pattern associated with passive and actively modulated eye growth. This may form an interesting reference to understand myopisation.

Evaluating the effect of ocular aberrations on the simulated performance of a new refractive IOL design using adaptive optics

Adaptive optics (AO) visual simulators are excellent platforms for non-invasive simulation visual performance with new intraocular lens (IOL) designs, in combination with a subject own ocular aberrations and brain. We measured the through focus visual acuity in subjects through a new refractive IOL physically inserted in a cuvette and projected onto the eye's pupil, while aberrations were manipulated (corrected, or positive/negative spherical aberration added) using a deformable mirror (DM) in a custom-developed AO simulator. The IOL increased depth-of-focus (DOF) to 1.53 ± 0.21D, while maintaining high Visual Acuity (VA, -0.07 ± 0.05), averaged across subjects and conditions. Modifying the aberrations did not alter IOL performance on average.

Intraocular accommodative movements in monkeys; relationship to presbyopia

Our goal was to quantify the age-related changes in the dynamic accommodative movements of the vitreous and aqueous humor in iridic, aniridic, phakic and aphakic primate eyes. Six bilaterally iridic and four bilaterally iridectomized rhesus monkeys, ranging in age from 6 to 25 years, received a stimulating electrode in the midbrain Edinger-Westphal nucleus to induce accommodation, measured by a Hartinger coincidence refractometer. One of the four iridectomized monkeys underwent unilateral extracapsular and another monkey underwent intracapsular lens extraction. Eyes were imaged utilizing specialized techniques and contrast agents to resolve intraocular structures. During accommodation the anterior hyaloid membrane and the posterior lens capsule bowed backward. Central vitreous fluid and structures/strands moved posteriorly toward the optic nerve region as peripheral vitreous, attached to the vitreous zonule, was pulled forward by ciliary muscle contraction. Triamcinolone particles injected intravitreally were also observed in the anterior chamber and moved from the anterior chamber toward the cleft of the anterior hyaloid membrane and then further posteriorly into the vitreous-filled cleft between the vitreous zonule and the ciliary body pars plana. These accommodative movements occurred in all eyes, and declined with age. There are statistically significant accommodative movements of various intravitreal structures. The posterior/anterior fluid flow between the anterior chamber and the vitreous compartments during accommodation/disaccommodation represents fluid displacement to allow/facilitate lens thickening. The posterior accommodative movement of central vitreous fluid may result from centripetal compression of the anterior tips of the cistern-like structure attached to the vitreous zonule, and posterior displacement of the central trunk of the cistern during ciliary muscle contraction and centripetal muscle movement. The findings may have implications for presbyopia.

Visual and Refractive Outcomes Following Laser Blended Vision With Non-linear Aspheric Micro-anisometropia (PRESBYOND) in Myopic and Hyperopic Patients

PURPOSE

To report 6-month visual and refractive outcomes following PRESBYOND Laser Blended Vision (Carl Zeiss Meditec) treatment using non-linear aspheric micro-anisometropia laser in situ keratomileusis (LASIK) for the correction of myopic and hyperopic presbyopia.

METHODS

A retrospective, non-comparative study of 139 consecutive patients with a mean age of 53.13 ± 5.84 years (range: 42 to 70 years) treated with LASIK-induced micro-anisometropia using the MEL 90 excimer laser and VisuMax femtosecond laser (both Carl Zeiss Meditec). The target refraction was plano for distance eyes (dominant eye) and between -0.50 and -1.50 diopters (D) for near eyes. Patients were observed for 6 months.

RESULTS

A total of 278 eyes (78 myopic and 200 hyperopic) from 139 patients completed the study. Mean preoperative spherical equivalent (SE) was -3.40 ± 1.83 D (range: -0.50 to -8.25 D) for myopic eyes and +1.61 ± 0.98 D (range: -1.25 to +4.63 D) for hyperopic eyes. Mean postoperative SE refraction of distance eyes was +0.20 ± 0.35 D (range: -0.38 to +1.00 D) and -0.14 ± 0.42 D (range: -1.38 to +0.88 D) for myopic and hyperopic eyes, respectively. Mean postoperative SE refraction of near eyes was -0.90 ± 0.44 D (range: -0.13 to -2.25 D) and -1.21 ± 0.48 D (range: -0.13 to -2.25 D) for myopic and hyperopic eyes, respectively. Mean binocular uncorrected near visual acuity was 0.70 ± 0.28 logMAR (range: 0.32 to 1.00 logMAR) and 0.79 ± 0.27 logMAR (range: 0.25 to 1.00 logMAR) for myopic and hyperopic eyes, respectively. Mean binocular uncorrected distance visual acuity was 1.19 ± 0.18 logMAR (range: 0.63 to 1.25 logMAR) and 1.14 ± 0.26 logMAR (range: 0.40 to 1.25 logMAR) for myopic and hyperopic eyes, respectively. Stereoacuity was better than 100 seconds of arc in 79% of myopic eyes and 85% of hyperopic eyes and all vision quality scores were greater than 90 of 100. No eyes lost two or more lines.

CONCLUSIONS

The non-linear aspheric micro-anisometropia protocol resulted in safe and effective visual outcomes in patients with both myopic and hyperopic presbyopia. [J Refract Surg. 2022;38(5):288-297.].

Membrane elasticity modulated by cholesterol in model of porcine eye lens-lipid membrane

Experimental evidence shows that the eye lens loses its elasticity dramatically with age. It has also been reported that the cholesterol (Chol) content in the eye lens fiber cell plasma membrane increases significantly with age. High Chol content leads to the formation of cholesterol bilayer domains (CBDs) in the lens membrane. The role of high Chol associated with lens elasticity is unclear. The purpose of this research is to investigate the membrane elasticity of the model of porcine lens-lipid (MPLL) membrane with increasing Chol content to elucidate the role of high Chol in lens membrane elasticity. In this study, we used atomic force microscopy (AFM) to study the mechanical properties (breakthrough force and area compressibility modulus (K_A)) of the MPLL membrane with increasing Chol content where K_A is the measure of membrane elasticity. We varied Chol concentration in Chol/MPLL membrane from 0 to ∼71 mol%. Supported Chol/MPLL membranes were prepared by fusion of small unilamellar vesicles (SUVs) on top of a flat mica surface. SUVs of the Chol/MPLL lipid mixture were prepared with the rapid solvent exchange method followed by probe-tip sonication. For the Chol/MPLL mixing ratio of 0, AFM image showed the formation of two distinct phases of the membrane, i.e., liquid-disordered phase (l_d) and solid-ordered phase (s_o) membrane. However, with Chol/MPLL mixing ratio of 0.5 and above, only liquid-ordered phase (l_o) membrane was formed. Also, two distinct breakthrough forces corresponding to l_d and s_o were observed for Chol/MPLL mixing ratio of 0, whereas only one breakthrough force was observed for membranes with Chol/MPLL mixing ratio of 0.5 and above. No significant difference in the membrane surface roughness was measured with increasing Chol content for these membranes; however, breakthrough force and K_A for l_o membrane increased when Chol/MPLL mixing ratio was increased from 0.5 to 1. Interestingly above the Chol/MPLL mixing ratio of 1, both breakthrough force and K_A decreased, indicating the formation of CBDs. Furthermore, these results showed that membrane elasticity increases at high Chol content, suggesting that high Chol content in lens membrane might be responsible for maintaining lens membrane elasticity.

Rethinking presbyopia: results of bilateral refractive lens exchange with trifocal intraocular lenses in 17 603 patients

PURPOSE

To evaluate the safety and effectiveness of bilateral refractive lens exchange (RLE) with trifocal intraocular lens (IOL) as the surgical treatment of presbyopia.

SETTINGS

Memira AS. Norway, Sweden and Denmark.

DESIGN

Multicentric retrospective interventional case series.

METHODS

17 603 consecutive patients submitted to bilateral presbyopic RLE with trifocal IOLs from 2013 to 2019. The main outcomes were manifest refraction spherical equivalent (MRSE), uncorrected distance (UDVA) and near (UNVA) visual acuity, corrected distance visual acuity (CDVA), vision gain/loss, safety and efficacy indices, IOL power calculation accuracy and rate of excimer laser enhancements.

RESULTS

Three months postoperatively, the mean MRSE was 0.00±0.40 diopters (D), mean binocular UDVA was -0.03±0.09, with 14 470 patients (82.2%) with combined binocular UDVA and UNVA equal or better than 0.00 and Jaeger 3. Approximately 86% (n=30.124) of the eyes were within 0.50D of MRSE. Enhancement surgery was performed in 5810 eyes (16.5%). IOL power calculation refining improved accuracy and reduced enhancements rate from 20% in 2013 to 12% in 2019. Safety and efficacy indices were 0.98±0.11 and 0.85±0.18, respectively. Myopic eyes presented significant higher safety (1.00±0.19) and efficacy indices (0.87±0.19), with p<0.005. Approximately 0.38% (n=130) of the eyes lost two or more lines of CDVA, with cystoid macular oedema (n=53, 40.8%) and posterior capsular opacification (n=35, 26.9%) as the main causes. After proper care, the final incidence of two or more lines of vision loss was 0.08% (28 eyes).

CONCLUSIONS

Presbyopic RLE with trifocal IOL is a safe and effective modality of treatment for patients with presbyopia.

Effect of cognitive task complexity on dual task postural stability: a systematic review and meta-analysis

The dual task experimental paradigm is used to probe the attentional requirements of postural control. However, findings of dual task postural studies have been inconsistent with many studies even reporting improvement in postural stability during dual tasking and thus raising questions about cognitive involvement in postural control. A U-shaped non-linear relationship has been hypothesized between cognitive task complexity and dual task postural stability suggesting that the inconsistent results might have arisen from the use of cognitive tasks of varying complexities. To systematically review experimental studies that compared the effect of simple and complex cognitive tasks on postural stability during dual tasking, we searched seven electronic databases for relevant studies published between 1980 to September 2020. 33 studies involving a total of 1068 participants met the review's inclusion criteria, 17 of which were included in meta-analysis (healthy young adults: 15 studies, 281 participants; Stroke patients: 2 studies, 52 participants). Narrative synthesis of the findings in studies involving healthy old adults was carried out. Our result suggests that in healthy population, cognitive task complexity may not determine whether postural stability increases or decreases during dual tasking (effect of cognitive task complexity was not statistically significant; P > 0.1), and thus the U-shaped non-linear hypothesis is not supported. Rather, differential effect of dual tasking on postural stability was observed mainly based on the age of the participants and postural task challenge, implying that the involvement of cognitive resources or higher cortical functions in the control of postural stability may largely depends on these two factors.

Testing the efficacy of vision training for presbyopia: alternating-distance training does not facilitate vision improvement compared to fixed-distance training

PURPOSE

Current evidence demonstrates the effectiveness of vision training for presbyopia. We developed and examined a training program to test the effectiveness of alternating focal distances as a training method.

METHODS

We devised a sharpness discrimination task, in which participants judged whether the stimulus was a sine- or square-wave grating, and tested in two training groups and one control group. In the alternating-distance training group (N = 8, age 49-64), participants had to alternate the fixation between a near- and far-screen. In the fixed-distance training group (N=8, age 47-65), participants fixated on the same-distance target for the whole block. Before and after the 20 training sessions, we measured the near- and far-visual acuity (VA) using the Landolt C and Early Treatment Diabetic Retinopathy Study (ETDRS) tasks and contrast sensitivity using the qCSF procedure. The control group (N=8, age 49-65) participated only in the pre- and post-tests.

RESULTS

Both training groups showed a significant improvement between the pre- and post-tests in the Landolt C task, and the improvement sizes were not significantly different between the groups. In the ETDRS task, only the fixed-distance training group showed significant improvement, although there was no significant difference between the two groups. Neither group showed improvement in the contrast sensitivity task compared to the control group.

CONCLUSION

The novel sharpness discrimination task can be an effective training method for presbyopia to prevent the deterioration of VA; however, contrary to popular belief, the effect of alternating-distance training was comparable to or even weaker than that of fixed-distance training.

EphA2 Affects Development of the Eye Lens Nucleus and the Gradient of Refractive Index

Purpose

Our studies in mouse eye lenses demonstrate that ephrin-A5 and EphA2 are needed for normal epithelial cells and lens transparency. We sought to determine whether EphA2 and ephrin-A5 are important for lens morphometrics, nucleus formation, and refractive index.

Methods

We performed tissue morphometric measurements, electron microscopy, Western blots, and interferometric measurements using an X-ray synchrotron beam source to measure the gradient of refractive index (GRIN) to compare mouse lenses with genetic disruption of EphA2 or ephrin-A5.

Results

Morphometric analysis revealed that although there is no change in the overall lens volume, there is a change in lens shape in both EphA2-/- lenses and ephrin-A5-/- lenses. Surprisingly, EphA2-/- lenses had small and soft lens nuclei different from hard lens nuclei of control lenses. SEM images revealed changes in cell morphology of EphA2-/- fiber cells close to the center of the lens. Inner EphA2-/- lens fibers had more pronounced tongue-and-groove interdigitations and formed globular membrane morphology only in the deepest layers of the lens nucleus. We did not observe nuclear defects in ephrin-A5-/- lenses. There was an overall decrease in magnitude of refractive index across EphA2-/- lenses, which is most pronounced in the nucleus.

Conclusions

This work reveals that Eph-ephrin signaling plays a role in fiber cell maturation, nuclear compaction, and lens shape. Loss of EphA2 disrupts the nuclear compaction resulting in a small lens nucleus. Our data suggest that Eph-ephrin signaling may be required for fiber cell membrane reorganization and compaction and for establishing a normal GRIN.

Age-related changes of lens stiffness in wild-type and Cx46 knockout mice

We have investigated how connexin 46 (Cx46) regulates lens stiffness by studying different Cx46 knockout (Cx46KO) mice. A modified muscle lever system was used to determine the lens stiffness of wild-type (WT) and Cx46KO mice at the C57BL/6J (B6) and the 129SvJae (129) strain backgrounds according to total lens displacement at the point of maximum force when fresh lenses were compressed with a maximum of 2 mN of force. In comparison to B6-WT controls, young and old B6-Cx46KO lenses showed 23% and 28% reductions in lens displacement, respectively. Comparing to 129-WT controls, old 129-Cx46KO lenses showed 50% reduction in the lens displacement while young 129-Cx46KO lenses displayed similar displacement. Old B6-Cx46KO and old 129-Cx46KO lenses showed almost identical lens displacement, 128 μm versus 127 μm. Morphological data revealed unique changes of peripheral fiber cell shapes in young B6-WT lenses but not in young B6-Cx46KO, 129-WT and 129-Cx46KO lenses. This work reveals Cx46 deletion increases the lens stiffness in both young and old mice at B6 strain background but only in old mice at 129 strain background which contains intermediate filament CP49 gene deletion. Cx46 impairment increases old mouse lens stiffness and may contribute to the development of presbyopia.

Age-Dependent Changes in Total and Free Water Content of In Vivo Human Lenses Measured by Magnetic Resonance Imaging

Purpose

To use magnetic resonance imaging (MRI) to measure age-dependent changes in total and free water in human lenses in vivo.

Methods

Sixty-four healthy adults aged 18 to 86 years were recruited, fitted with a 32-channel head receiver coil, and placed in a 3 Tesla clinical MR scanner. Scans of the crystalline lens were obtained using a volumetric interpolated breath-hold examination sequence with dual flip angles, which were corrected for field inhomogeneity post-acquisition using a B1-map obtained using a turbo-FLASH sequence. The spatial distribution and content of corrected total (ρlens) and free (T1) water along the lens optical axis were extracted using custom-written code.

Results

Lens total water distribution and content did not change with age (all P > 0.05). In contrast to total water, a gradient in free water content that was highest in the periphery relative to the center was present in lenses across all ages. However, this initially parabolic free water gradient gradually developed an enhanced central plateau, as indicated by increasing profile shape parameter values (anterior: 0.067/y, P = 0.004; posterior: 0.050/y, P = 0.020) and central free water content (1.932 ms/y, P = 0.022) with age.

Conclusions

MRI can obtain repeatable total and free water measurements of in vivo human lenses. The observation that the lens steady-state free, but not total, water gradient is abolished with age raises the possibility that alterations in protein-water interactions are an underlying cause of the degradation in lens optics and overall vision observed with aging.

Recent advances in representation of monochromatic aberrations of human eyes

The field of aberrations of the human eye is moving rapidly, being driven by the desire to monitor and optimise vision following refractive surgery. In this paper, I discuss the different ways of representing aberrations of the human eye, the terminology used, how wave aberrations are used to determine refractions, the influence of pupil size on aberrations, how to compare right and left eye aberrations, how aberrations can be manipulated into different forms, how to make corrections for changes in wavelength, the appropriate ocular axis, and corneal and lenticular components of the aberrations.

Simulating Outcomes of Cataract Surgery: Important Advances in Ophthalmology

As the human eye ages, the crystalline lens stiffens (presbyopia) and opacifies (cataract), requiring its replacement with an artificial lens [intraocular lens (IOL)]. Cataract surgery is the most frequently performed surgical procedure in the world. The increase in IOL designs has not been paralleled in practice by a sophistication in IOL selection methods, which rely on limited anatomical measurements of the eye and the surgeon's interpretation of the patient's needs and expectations. We propose that the future of IOL selection will be guided by 3D quantitative imaging of the crystalline lens to map lens opacities, anticipate IOL position, and develop fully customized eye models for ray-tracing-based IOL selection. Conversely, visual simulators (in which IOL designs are programmed in active elements) allow patients to experience prospective vision before surgery and to make more informed decisions about which IOL to choose. Quantitative imaging and optical and visual simulations of postsurgery outcomes will allow optimal treatments to be selected for a patient undergoing modern cataract surgery.

Visual and Refractive Outcomes Following Laser Blended Vision Using Non-linear Aspheric Micro-monovision

PURPOSE

To report 1-year visual and refractive outcomes following PRESBYOND Laser Blended Vision using non-linear aspheric micro-monovision with the MEL 90 platform (Carl Zeiss Meditec GmbH).

METHODS

Data were collected retrospectively for all patients who underwent treatment for simultaneous correction of refractive error and presbyopia from June 2015 to June 2018. Only those patients who completed at least 6 months of follow-up were included in the study.

RESULTS

A total of 101 patients with a mean age of 51.05 ± 5.15 years (range: 40 to 65 years), of whom 38 patients had myopic and 63 patients had hyperopic refractive error with or without astigmatism, were included in the study. Mean preoperative spherical equivalent was -3.36 ± 1.86 diopters (D) in the myopia group and +1.75 ± 0.99 D in the hyperopia group. At 1 year, the mean spherical equivalent refraction was +0.13 ± 0.32 D in the distance eye and -1.42 ± 0.33 D (range: -0.88 to -2.50 D) in the near eye in the myopia group and -0.13 ± 0.24 D in the distance eye and -1.28 ± 0.31 D (range: -0.63 to -2.00 D) in the near eye in the hyperopia group. Two eyes in the hyperopia group underwent early enhancement for the near eye at 3 months. Ninety-seven percent of the patients in the myopia group and 96% in the hyperopia group were satisfied with their distance vision. Near vision satisfaction score was 95% for the myopia group and 89% for the hyperopia group.

CONCLUSIONS

At 1 year, the aspheric micro-monovision protocol resulted in satisfactory and fairly stable visual outcomes in both myopic and hyperopic individuals. [J Refract Surg. 2020;36(5):300-307.].

Age-Dependence of the Peripheral Defocus of the Isolated Human Crystalline Lens

Purpose

To characterize the peripheral defocus of isolated human crystalline lenses and its age dependence.

Methods

Data were acquired on 116 isolated lenses from 99 human eyes (age range, 0.03–61 years; postmortem time, 40.1 ± 21.4 hours). Lenses were placed in a custom-built combined laser ray tracing and optical coherence tomography system that measures the slopes of rays refracted through the lens for on-axis and off-axis incidence angles. Ray slopes were measured by recording spot patterns as a function of axial position with an imaging sensor mounted on a positioning stage below the tissue chamber. Delivery angles ranged from –30° to +30° in 5° increments using a 6 mm × 6 mm raster scan with 0.5-mm spacing. Lens power at each angle was calculated by finding the axial position that minimizes the root-mean-square size of the spot pattern formed by the 49 central rays, corresponding to a 3-mm zone on-axis. The age dependence of the on-axis and off-axis optical power and the relative peripheral defocus (difference between off-axis and on-axis power) of lenses were quantified.

Results

At all angles, lens power decreased significantly with age. Lens power increased with increasing delivery angle for all lenses, corresponding to a shift toward myopic peripheral defocus. There was a statistically significant decrease in the lens peripheral defocus with age.

Conclusions

The isolated human lens power increases with increasing field angle. The lens relative peripheral defocus decreases with age, which may contribute to the age-related changes of ocular peripheral defocus during refractive development.

Ageing and multisensory integration: A review of the evidence, and a computational perspective

The processing of multisensory signals is crucial for effective interaction with the environment, but our ability to perform this vital function changes as we age. In the first part of this review, we summarise existing research into the effects of healthy ageing on multisensory integration. We note that age differences vary substantially with the paradigms and stimuli used: older adults often receive at least as much benefit (to both accuracy and response times) as younger controls from congruent multisensory stimuli, but are also consistently more negatively impacted by the presence of intersensory conflict. In the second part, we outline a normative Bayesian framework that provides a principled and computationally informed perspective on the key ingredients involved in multisensory perception, and how these are affected by ageing. Applying this framework to the existing literature, we conclude that changes to sensory reliability, prior expectations (together with attentional control), and decisional strategies all contribute to the age differences observed. However, we find no compelling evidence of any age-related changes to the basic inference mechanisms involved in multisensory perception.

Polymeric Materials for Eye Surface and Intraocular Applications

Ocular applications of polymeric materials have been widely investigated for medical diagnostics, treatment, and vision improvement. The human eye is a vital organ that connects us to the outside world so when the eye is injured, infected, or impaired, it needs immediate medical treatment to maintain clear vision and quality of life. Moreover, several essential parts of the eye lose their functions upon aging, causing diminished vision. Modern polymer science and polymeric materials offer various alternatives, such as corneal and scleral implants, artificial ocular lenses, and vitreous substitutes, to replace the damaged parts of the eye. In addition to the use of polymers for medical treatment, polymeric contact lenses can provide not only vision correction, but they can also be used as wearable electronics. In this Review, we highlight the evolution of polymeric materials for specific ocular applications such as intraocular lenses and current state-of-the-art polymeric systems with unique properties for contact lens, corneal, scleral, and vitreous body applications. We organize this Review paper by following the path of light as it travels through the eye. Starting from the outside of the eye (contact lenses), we move onto the eye's surface (cornea and sclera) and conclude with intraocular applications (intraocular lens and vitreous body) of mostly synthetic polymers and several biopolymers. Initially, we briefly describe the anatomy and physiology of the eye as a reminder of the eye parts and their functions. The rest of the Review provides an overview of recent advancements in next-generation contact lenses and contact lens sensors, corneal and scleral implants, solid and injectable intraocular lenses, and artificial vitreous body. Current limitations for future improvements are also briefly discussed.

Deformations and Ruptures in Human Lenses With Cortical Cataract Subjected to Ex Vivo Simulated Accommodation

Purpose

Human cortical opacities are most commonly accompanied by changes in lens fiber structure in the equatorial region at the lens nucleus–cortex interface. Cortex and nucleus have different elastic properties, which change with age. We therefore subjected ex vivo lenses to simulated accommodation and studied the internal deformations to better understand the mechanism of cortical cataract formation.

Methods

Nine human donor lenses (33–88 years old) were tested using a bespoke radial stretching device for anterior eye segments. Seven of the lenses exhibited cortical cataracts. The other two lenses, without cataract, were used as controls. Frontal and cross-sectional images of the lens obtained during stretching facilitated measurements on equatorial lens diameter and central lens thickness in the stretched and unstretched states.

Results

Stretching caused the lens equatorial diameter to increase in all cases. Conversely, the lens central thickness showed no systematic variation during stretching. For four of the lenses with cortical cataract, ruptures were observed during stretching at the nucleus–cortex boundary adjacent to the cortical cataracts. Ruptures were not observed in the control lenses or in the three other lenses with cortical cataract.

Conclusions

Internal ruptures can occur in aged ex vivo lenses subjected to simulated disaccommodation. These ruptures occur at the nucleus–cortex interface; at this location, a significant stiffness discontinuity is expected to develop with age. It is hypothesized that ruptures occur in in vivo lenses during accommodation—or attempted accommodation.

Portable device for presbyopia correction with optoelectronic lenses driven by pupil response

A novel portable device has been developed and built to dynamically, and automatically, correct presbyopia by means of a couple of opto-electronics lenses driven by pupil tracking. The system is completely portable providing with a high range of defocus correction up to 10 D. The glasses are controlled and powered by a smartphone. To achieve a truly real-time response, image processing algorithms have been implemented in OpenCL and ran on the GPU of the smartphone. To validate the system, different visual experiments were carried out in presbyopic subjects. Visual acuity was maintained nearly constant for a range of distances from 5 m to 20 cm.

Presbyopic refractive lens exchange with trifocal intraocular lens implantation after corneal laser vision correction: Refractive results and biometry analysis

PURPOSE

To evaluate the refractive and biometry results of presbyopic refractive lens exchange (RLE) with trifocal intraocular lens (IOL) implantation in eyes with previous myopic or hyperopic corneal laser vision correction (LVC).

SETTINGS

Memira AS, Norway, Sweden, and Denmark.

DESIGN

Retrospective case series.

METHODS

The refractive results included the manifest refraction spherical equivalent, uncorrected near (UNVA) and distance (UDVA) visual acuities, corrected distance visual acuity, safety, efficacy, and precision. The biometry analysis included the refractive prediction error (RPE), median absolute error (MedAE), and percentage of eyes within a certain RPE range for the formulas from the American Society of Cataract and Refractive Surgery (ASCRS) online calculator.

RESULTS

The study comprised 241 eyes. Six months postoperatively, 60.0% of eyes were within ±0.25 diopter (D), 80.9% within ±0.50 D, and 97.9% within ±1.00 D of emmetropia. There were no statistical differences in the mean monocular UDVA (0.87 ± 0.20 [SD]), safety index (0.98 ± 0.09), or efficacy index (0.81 ± 0.18) between the myopic ablation group and hyperopic ablation group. Binocularly, 85% of patients had simultaneous UDVA and UNVA of 0.9 or better and Jaeger 3, respectively. The ASCRS online calculator formulas gave different performances for previous myopic and hyperopic ablation profiles. Using optimized constants and nomogram for correcting the mean RPE improved the MedAE.

CONCLUSIONS

Presbyopic RLE was safe and effective in selected cases with a history of LVC. The use of optimized IOL constants and nomograms can improve the refractive precision of lens-based refractive surgery.

The optomotor response of aging zebrafish reveals a complex relationship between visual motion characteristics and cholinergic system

Understanding the principles underlying age-related changes in motion perception is paramount for improving the quality of life and health of older adults. However, the mechanisms underlying age-related alterations in this aspect of vision, which is essential for survival in a dynamic world, still remain unclear. Using optomotor responses to drifting gratings, we investigated age-related changes in motion detection of adult zebrafish (wild-type/AB-strain and ache^sb55/+ mutants with decreased levels of acetylcholinesterase). Our results pointed out negative optomotor responses that significantly depend on the spatial frequency and contrast level of stimulation, providing supporting evidence for the visual motion-driven aspect of this behavior mainly exhibited by adult zebrafish. Although there were no significant main effects of age and genotype, we found a significant three-way interaction between contrast level, age, and genotype. In the contrast domain, the changes in optomotor responses and thus in the detection of motion direction were age- and genotype-specific. Accordingly, these behavioral findings suggest a strong but complicated relationship between visual motion characteristics and the cholinergic system during neural aging.

Age-Related Changes to the Three-Dimensional Full Shape of the Isolated Human Crystalline Lens

Purpose

Studying the full shape crystalline lens geometry is important to understand the changes undergone by the crystalline lens leading to presbyopia, cataract, or failure of emmetropization, and to aid in the design and selection of intraocular lenses and new strategies for correction. We used custom-developed three-dimensional (3-D) quantitative optical coherence tomography (OCT) to study age-related changes in the full shape of the isolated human crystalline lens.

Methods

A total of 103 ex vivo human isolated lenses from 87 subjects (age range, 0–56 years) were imaged using a 3-D spectral-domain OCT system. Lens models, constructed after segmentation of the surfaces and distortion correction, were used to automatically quantify central geometric parameters (lens thickness, radii of curvatures, and asphericities of anterior and posterior surfaces) and full shape parameters (lens volume, surface area, diameter, and equatorial plane position). Age-dependencies of these parameters were studied.

Results

Most of the measured parameters showed a biphasic behavior, statistically significantly increasing (radii of curvature, lens volume, surface area, diameter) or decreasing (asphericities, lens thickness) very fast in the first two decades of life, followed by a slow but significant increase after age 20 years (for all the parameters except for the posterior surface asphericity and the equatorial plane position, that remained constant).

Conclusions

Three-dimensional quantitative OCT allowed us to study the age-dependency of geometric parameters of the full isolated human crystalline lens. We found that most of the lens geometric parameters showed a biphasic behavior, changing rapidly before age 20 years and with a slower linear growth thereafter.

Comparison of the Visual Performance after Implantation of Three Aberration-correcting Aspherical Intraocular Lens

PURPOSE

To compare the visual performance after implantation of three aberration-correcting aspherical intraocular lens (IOL).

MATERIALS AND METHODS

Seventy-seven eyes of 77 cataract patients were divided into three groups: 26 eyes implanted with a non-constant aberration IOL (LUCIA 601P IOL, Zeiss Company, Germany); 26 eyes implanted with a spherical aberration -0.18μm IOL (CT ASPHINA 509M, Zeiss Company, Germany) and 27 eyes implanted with a spherical aberration -0.27μm IOL (AMO Tecnis ZCB00, Johnson & Johnson Surgical Vision, USA). Three months after operation, the distance visual acuity, wavefront aberrometry, contrast sensitivity, intraocular stray light, IOL decentration, and tilt were evaluated.

RESULTS

Three months postoperatively, no statistically significant differences were found in uncorrected distance visual acuity and corrected distance visual acuity (p≥.83). The RMS for total ocular coma was statistically significantly lower in the Lucia group (p=.03) and spherical aberration was statistically significantly lower in the Tecnis group (p<.01). No statistically significant differences were observed among the three lenses in higher order aberration (p=.85) and in contrast sensitivity under both photopic and mesopic lighting conditions (p≥.05). The intraocular stray light was statistically significantly better in the Lucia group (p=.04). No statistically significant differences were observed with respect to IOL decentration (p=.75) and tilt (p=.89).

CONCLUSIONS

Cataract surgery with non-constant aberration IOL resulted in lower coma and better intraocular stray light than with the spherical aberration -0.18μm and -0.27μm IOLs despite equivalent postoperative levels of visual acuity and contrast sensitivity.

Review of the application of the open-source software CilOCT for semi-automatic segmentation and analysis of the ciliary muscle in OCT images

Presbyopia and myopia research shows a growing interest in ciliary muscle biometry using optical coherence tomography (OCT). Until now, segmentation of the ciliary muscle is often performed manually using either custom-developed programs or image processing software. Here we present a novel software for semi-automatic segmentation of the ciliary muscle. It provides direct import of OCT images in DICOM format, a standardized procedure for segmentation, image distortion correction, the export of anatomical ciliary muscle landmarks, like ciliary muscle apex and scleral spur, as well as a continuous thickness profile of the ciliary muscle as a novel way of analysis. All processing steps are stored as XML files, fostering documentation and reproducibility of research through the possibility of replicating the analysis. Additionally, CilOCT supports batch processing for the automated analysis of large numbers of images and the respective data export to tabulated text files based on the stored XML files. CilOCT was successfully applied in several studies and their results will be summarized in this paper.

Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy

Assessing the biomechanical properties of the crystalline lens can provide crucial information for diagnosing disease and guiding precision therapeutic interventions. Existing noninvasive methods have been limited to global measurements. Here, we demonstrate the quantitative assessment of the elasticity of crystalline lens with a multimodal optical elastography technique, which combines dynamic wave-based optical coherence elastography (OCE) and Brillouin microscopy to overcome the drawbacks of individual modalities. OCE can provide direct measurements of tissue elasticity rapidly and quantitatively, but it is a challenge to image transparent samples such as the lens because this technique relies on backscattered light. On the other hand, Brillouin microscopy can map the longitudinal modulus with micro-scale resolution in transparent samples. However, the relationship between Brillouin-deduced modulus and Young's modulus is not straightforward and sample dependent. By combining these two techniques, we can calibrate Brillouin measurements with OCE, based on the same sample, allowing us to completely map the Young's modulus of the crystalline lens. The combined system was first validated with tissue-mimicking gelatin phantoms of varying elasticities (N = 9). The OCE data was used to calibrate the Brillouin shift measurements and subsequently map the Young's modulus of the phantoms. After validation, OCE and Brillouin measurements were performed on ex-vivo porcine lenses (N = 6), and the Young's modulus of the lenses was spatially mapped. The results show a strong correlation between Young's moduli measured by OCE and longitudinal moduli measured by Brillouin microscopy. The correlation coefficient R was 0.98 for the phantoms and 0.94 for the lenses, respectively. The mean Young's modulus of the anterior and posterior lens was 1.98 ± 0.74 kPa and 2.93 ± 1.13 kPa, respectively, and the Young's modulus of the lens nucleus was 11.90 ± 2.94 kPa. The results presented in this manuscript open a new way for truly quantitative biomechanical mapping of optically transparent (or low scattering) tissues in 3D.

Age-related changes in eye lens biomechanics, morphology, refractive index and transparency

Life-long eye lens function requires an appropriate gradient refractive index, biomechanical integrity and transparency. We conducted an extensive study of wild-type mouse lenses 1-30 months of age to define common age-related changes. Biomechanical testing and morphometrics revealed an increase in lens volume and stiffness with age. Lens capsule thickness and peripheral fiber cell widths increased between 2 to 4 months of age but not further, and thus, cannot account for significant age-dependent increases in lens stiffness after 4 months. In lenses from mice older than 12 months, we routinely observed cataracts due to changes in cell structure, with anterior cataracts due to incomplete suture closure and a cortical ring cataract corresponding to a zone of compaction in cortical lens fiber cells. Refractive index measurements showed a rapid growth in peak refractive index between 1 to 6 months of age, and the area of highest refractive index is correlated with increases in lens nucleus size with age. These data provide a comprehensive overview of age-related changes in murine lenses, including lens size, stiffness, nuclear fraction, refractive index, transparency, capsule thickness and cell structure. Our results suggest similarities between murine and primate lenses and provide a baseline for future lens aging studies.

Morphological changes of human crystalline lens in myopia

Ocular biometric parameters, including full shape crystalline lens, were assessed in myopes and emmetropes using 3-D optical coherence tomography. The anterior chamber depth, the radius of the curvature of the anterior cornea, anterior lens, and posterior lens, lens thickness, lens equatorial diameter, surface area, equatorial position, volume, and power, were evaluated as functions of refractive errors and axial lengths while controlling for age effects. The crystalline lens appears to change with myopia consistent with lens thinning, equatorial, and capsular stretching while keeping constant volume. Axial elongation appears counteracted by a crystalline lens power reduction, while corneal power remains unaffected.

Spatiotemporal changes in the human lens proteome: Critical insights into long-lived proteins

The ocular lens is a unique tissue that contains an age gradient of cells and proteins ranging from newly differentiated cells containing newly synthesized proteins to cells and proteins that are as old as the organism. Thus, the ocular lens is an excellent model for studying long-lived proteins (LLPs) and the effects of aging and post-translational modifications on protein structure and function. Given the architecture of the lens, with young fiber cells in the outer cortex and the oldest cells in the lens nucleus, spatially-resolved studies provide information on age-specific protein changes. In this review, experimental strategies and proteomic methods that have been used to examine age-related and cataract-specific changes to the human lens proteome are described. Measured spatio-temporal changes in the human lens proteome are summarized and reveal a highly consistent, time-dependent set of modifications observed in transparent human lenses. Such measurements have led to the discovery of cataract-specific modifications and the realization that many animal systems are unsuitable to study many of these modifications. Mechanisms of protein modifications such as deamidation, racemization, truncation, and protein-protein crosslinking are presented and the implications of such mechanisms for other long-lived proteins in other tissues are discussed in the context of age-related neurological diseases. A comprehensive understanding of LLP modifications will enhance our ability to develop new therapies for the delay, prevention or reversal of age-related diseases.

Changes in intraocular pressure during reading or writing on smartphones in patients with normal-tension glaucoma

BACKGROUND/AIMS

To investigate (1) the effect of reading or writing on a smartphone in terms of intraocular pressure (IOP) change in eyes with glaucoma, and (2) to determine whether previous glaucoma filtering surgery can affect IOP fluctuation during such work.

METHODS

Forty eyes of 40 medically well IOP-controlled normal-tension glaucoma (NTG) patients and 38 eyes of 38 NTG patients who had undergone successful trabeculectomy (TLE) were enrolled. The participants were instructed to read a sample text and to then type it on a smartphone under low-light [100 lux] conditions. Three IOP measurements were obtained: baseline; during smartphone work (5, 15 and 25 min); post-work (5 and 15 min).

RESULTS

Baseline IOP did not significantly differ between the two groups (medication group: 13.9±1.6 mm Hg; TLE group: 13.6±1.7 mm Hg; p=0.426). After 5 min of smartphone work, the medication group showed significantly elevated mean IOP (15.5±1.8 mm Hg;+11.5%; p<0.001), along with further increases over the course of 25 min (17.5±2.2 mm Hg;+25.9%; p<0.001). 5 min after halting work, IOP dropped below the baseline (13.1±1.7 mm Hg; p<0.001). For the TLE group, IOP also was elevated after 5 min (14.9±1.7 mm Hg;+9.4%; p<0.001); however, it did not show further increase over the course of 25 min of work (15.0±1.6 mm Hg;+10.3%). At 5 min after cessation of work, IOP had restored to the pre-work level (14.0±1.9 mm Hg;+2.8%; p=0.053).

CONCLUSION

Working on a smartphone under low-light condition can incur IOP elevation in treated NTG patients. However, among the participants in this study, IOP fluctuation was much smaller in those who had undergone TLE.

Lens Stretching Modulates Lens Epithelial Cell Proliferation via YAP Regulation

Purpose

The continuous growth of the lens throughout life may contribute to the onset of age-related conditions in the lens (i.e., presbyopia and cataract). Volumetric growth is the result of continuous proliferation of lens epithelial cells (LECs). The driving factors controlling LEC proliferation are not well understood. This study tested the hypothesis that mechanical stretching modulates LEC proliferation.

Methods

Biomechanical regulation of LEC proliferation was investigated by culturing whole porcine lenses and connective tissues ex vivo under varying physiologically relevant stretching conditions using a bespoke lens stretching device. Additionally, some lenses were treated with a YAP function inhibitor to determine the Hippo signaling pathway's role in regulating lens growth. Resulting changes in LEC labeling index were analyzed using EdU incorporation and flow cytometry for each lens.

Results

LEC proliferation was found to be modulated by mechanical strain. Increasing both the magnitude of static stretching and the stretching frequency in cyclic stretching resulted in a proportional increase in the labeling indices of the LECs. Additionally, treatment with the YAP function inhibitor effectively eliminated this relationship.

Conclusions

These data demonstrate that LEC proliferation is regulated in part, by the mechanotransduction of stresses induced in the lens capsule and that YAP plays an important role in mechanosensing. These results have important implications for understanding lens growth and morphogenesis. The model may also be used to identify and evaluate targets for modulating lens growth.

Older adults sacrifice response speed to preserve multisensory integration performance

Aging has been shown to impact multisensory perception, but the underlying computational mechanisms are unclear. For effective interactions with the environment, observers should integrate signals that share a common source, weighted by their reliabilities, and segregate those from separate sources. Observers are thought to accumulate evidence about the world's causal structure over time until a decisional threshold is reached. Combining psychophysics and Bayesian modeling, we investigated how aging affects audiovisual perception of spatial signals. Older and younger adults were comparable in their final localization and common-source judgment responses under both speeded and unspeeded conditions, but were disproportionately slower for audiovisually incongruent trials. Bayesian modeling showed that aging did not affect the ability to arbitrate between integration and segregation under either unspeeded or speeded conditions. However, modeling the within-trial dynamics of evidence accumulation under speeded conditions revealed that older observers accumulate noisier auditory representations for longer, set higher decisional thresholds, and have impaired motor speed. Older observers preserve audiovisual localization performance, despite noisier sensory representations, by sacrificing response speed.

Vision with different presbyopia corrections simulated with a portable binocular visual simulator

Presbyopes can choose today among different corrections to provide them with functional vision at far and near, and the outcomes and patient satisfaction depend on the selection. In this study, we present a binocular and portable vision simulator, based on temporal multiplexing of two synchronized tunable lenses allowing see-through and programmable visual simulations of presbyopic corrections. Seventeen binocular corrections were tested: 3 Monofocal (Far, Intermediate, Near), 4 Simultaneous Vision (bifocal, trifocal), 2 Monovision (far and near in either eye) and 8 Modified Monovision corrections (Simultaneous vision in one eye, Monofocal in the other eye). Perceived visual quality was assessed through the simulated corrections in 8 cyclopleged subjects who viewed a composite realistic visual scene with high contrast letters and a landscape at far (4 m) and a high contrast text at intermediate (66 cm) and near (33 cm) distances. Perceptual scores were obtained on a scale of 0 to 5 (low to high perceived quality). Perceptual preference was assessed by judging 36 random image pairs (6 repetitions) viewed through 9 binocular presbyopic corrections using two-interval forced choice procedures. The average score, across far and near distances, was the highest for Monovision (4.4±0.3), followed by Modified Monovision (3.4±0.1), Simultaneous Vision (3.0±0.1) and Monofocal corrections (2.9±0.2). However, the mean difference between far and near was lower for Simultaneous Vision and Monovision (0.4±0.1 PS) than Modified Monovision (1.8±0.7) or monofocal corrections (3.3±1.5). A strong significant correlation was found between the perceptual scores and the percentages of energy in focus, for each correction and distance (R = 0.64, p<0.0001). Multivariate ANOVA revealed significant influence of observation distances (p<10-9) and patients (p = 0.01) on Perceptual Score. In conclusion, we have developed a binocular portable vision simulator that can simulate rapidly and non-invasively different combinations of presbyopic corrections. This tool has applications in systematic clinical evaluation of presbyopia corrections.

A Modeling Approach for Investigating Opto-Mechanical Relationships in the Human Eye Lens

OBJECTIVE

The human visual system alters its focus by a shape change of the eye lens. The extent to which the lens can adjust ocular refractive power is dependent to a significant extent on its material properties. Yet, this fundamental link between the optics and mechanics of the lens has been relatively under-investigated. This study aims to investigate this opto-mechanical link within the eye lens to gain insight into the processes of shape alteration and their respective decline with age.

METHODS

Finite Element models based on biological lenses were developed for five ages: 16, 35, 40, 57, and 62 years by correlating in vivo measurements of the longitudinal modulus using Brillouin scattering with in vitro X-ray interferometric measurements of refractive index and taking into account various directions of zonular force.

RESULTS

A model with radial cortical Young's moduli provides the same amount of refractive power with less change in thickness than a model with uniform cortical Young's modulus with a uniform stress distribution and no discontinuities along the cortico-nuclear boundary. The direction of zonular angles can significantly influence curvature change regardless of the modulus distribution.

CONCLUSIONS

The present paper proposes a modelling approach for the human lens, coupling optical and mechanical properties, which shows the effect of parameter choice on model response.

SIGNIFICANCE

This advanced modelling approach, considering the important interplay between optical and mechanical properties, has potential for use in design of accommodating implant lenses and for investigating non-biological causes of pathological processes in the lens (e.g., cataract).

Corneal Curvature: the Influence of Corneal Accommodation and Biomechanics on Corneal Shape

Purpose

Variation in the presence and magnitude of corneal conformational changes during accommodation may predict postoperative ectasia following refractive surgery and assist in the early diagnosis of corneal ectatic disorders. The current study aimed to establish a baseline for corneal refractive changes during ocular accommodation and to clarify the role of biomechanical factors in predicting these changes in a population without corneal pathology.

Methods

GALILEI G2 corneal tomography was assessed in 63 participants in both the accommodated and unaccommodated states. Four diopters (D) of physiological accommodation were induced using near-acuity calibrated words viewed through an externally mounted beam splitter mounted on a three-dimensional-printed frame. Corneal biomechanical characteristics were assessed with the CorVis-ST instrument, and statistical analysis was completed in R software.

Results

Anterior chamber depth was reduced by 0.10 ± 0.07 mm with accommodation (P < 0.01). Areas of statistically significant change in corneal curvatures were seen in all participants with accommodation. Mean anterior instantaneous corneal power increased in the superior-nasal periphery (0.1 D, 95% confidence interval [CI] = 0.05–0.2 D) and decreased in the inferior-temporal periphery (0.1 D, 95% CI = −0.05 to −0.15 D). Corneal stiffness and the corneal deformation amplitude ratio predicted peripheral corneal curvature changes with accommodation (P < 0.05).

Conclusion

Corneal conformational changes occur during accommodation in normal subjects. Further studies are required to assess the magnitude of corneal changes during accommodation in patients with corneal ectasia.

Translational Relevance

An externally mounted beam splitter can be used to modify the visual target presented by clinical ocular imaging instruments. Corneal conformational changes during accommodation may be useful in the diagnosis of corneal ectasia.

The Science Behind Virtual Reality Displays

Virtual reality (VR) is becoming an increasingly important way to investigate sensory processing. The converse is also true: in order to build good VR technologies, one needs an intimate understanding of how our brain processes sensory information. One of the key advantages of studying perception with VR is that it allows an experimenter to probe perceptual processing in a more naturalistic way than has been possible previously. In VR, one is able to actively explore and interact with the environment, just as one would do in real life. In this article, we review the history of VR displays, including the philosophical origins of VR, before discussing some key challenges involved in generating good VR and how a sense of presence in a virtual environment can be measured. We discuss the importance of multisensory VR and evaluate the experimental tension that exists between artifice and realism when investigating sensory processing.

Accommodative insufficiency in a student population in Iran

PURPOSE

To determine the prevalence of accommodative insufficiency (AI) and its relation with age, gender, and refractive errors in a college-age student population in Iran.

METHODS

The present study was conducted cross-sectionally in 2017. All students had optometric tests including measurement of visual acuity, objective and subjective refraction, as well as binocular vision and accommodative examinations. Amplitude of accommodation was measured with the Donders' push-up method using the Royal Air Force (RAF) rule. Monocular accommodative facility was measured with ±2.00diopter flipper lenses. The accommodative response was tested using dynamic retinoscopy with the monocular estimation method (MEM).

RESULTS

The prevalence of AI in the studied population was 4.07% (95% CI: 2.61-5.52). The rate was 6.04% (95% CI: 3.58-8.50) in females and 2.01% (95% CI: 0.53-3.48) in males, and logistic regression showed a significantly higher odds of AI in females (OR=3.14, 95% CI: 1.33-7.45, p-value=0.009). The prevalence of AI was 2.59% (95% CI: 0.55-7.56) in the 18-19-year-old age group and 4.08% (95% CI: 0.09-8.07) in the 24-25-year-old group (p-value=0.848). The prevalence of AI among emmetropic, myopic, and hyperopic individuals was 3.74% (95% CI: 1.88-5.61), 4.44% (95% CI: 2.07-6.81), and 5.26% (95% CI: 4.79-16.32), respectively (p-value=0.869). In the multiple regression model, only gender showed significant relationship with AI (Odds ratio=3.14, 95% CI: 1.33-7.45; p-values=0.009).

CONCLUSION

The prevalence of AI in the present study is lower than the most prevalence rates reported in previous studies. In the present study, gender and AI showed a strong association, such that AI prevalence was significantly higher in females than males.

Comprehensive Evaluation of Retinal Image Quality in Comparing Different Aspheric to Spherical Intraocular Lens Implants

Purpose: To compare the visual and optical quality of eyes implanted with three aspheric versus two spherical intraocular lenses (IOL) after cataract surgery. Methods: This prospective comparative study included 349 eyes of 349 patients with age-related cataract and undergone uneventful phacoemulsification. Implanted posterior monofocal IOLs have an aspheric optic (Tecnis ZCB00 [Johnson & Johnson Vision], Acrysof IQ SN60WF [Alcon], Akreos AO [Bausch & Lomb]) or a spherical optic (Akreos [Bausch & Lomb], Sensar AR40e [Johnson & Johnson Vision]). Postoperatively, objective optical quality parameters were performed using an Optical Quality Analysis System II (Visiometrics), and wave-front aberrations were assessed using a KR-1W aberrometer (Topcon). Meanwhile, subjective visual acuity was performed using a logarithm of the minimum angle of resolution chart at 3 months after cataract surgery. Results: Statistical significant differences (P < .05) across all groups were found regarding intraocular and total ocular spherical aberration (SA) at 4.0 mm and 6.0 mm pupil diameter and total high-order aberration (tHOA) at 6.0 mm pupil diameter. Furthermore, differences among the evaluated groups were observed regarding several objective parameters such as objective scatter index (OSI), modulation transfer function cutoff (MTF cutoff), Strehl ratio (SR) at two dimensions and contrast visual acuity (OV) at three contrast levels. Conclusions: The present results reflect the optical characteristics of IOL in vivo. The scattering light and high-order aberration may be the main reasons for the degradation of retinal imaging quality in comparing different aspheric to spherical IOL implants.