Comparison of the behavior of natural and refilled porcine lenses in a robotic lens stretcher

The mechanism by which the eye dynamically changes focal distance (accommodation), and the mechanism by which this ability is lost with age (presbyopia), are still contested. Due to inherent confounding factors in vivo, in vitro measurements have been undertaken using a robotic lens stretcher to examine these mechanisms as well as the efficacy of lens refilling - a proposed treatment for presbyopia. Dynamic forces, anterior and posterior curvatures, and lens thickness are all correlated for young natural and refilled porcine lenses. Comparisons are made to lenses refilled with a homogeneous polymer system. The amplitude of accommodation of the young porcine lens is very small such that it may be a suitable model for presbyopia. The behavior of refilled lenses was highly dependent on the refill volume. The volume could be tuned to maximize accommodative amplitude in the refilled lens.     

Changes in spherical aberration after lens refilling with a silicone oil

PURPOSE: It may be possible to restore accommodation to presbyopic human eyes by refilling the lens capsular bag with a soft polymer. In the present study, optical changes were measured that occurred in a pig eye model after the refilling of the capsular bag. METHODS: The optical power and spherical aberration in 10 isolated pig lenses were measured under different conditions. They were first determined by using a scanning laser ray-tracing technique over an effective pupil size of 6 mm. Second, the contours of the anterior and posterior lens surface were photographed, and a mathematical ray-tracing was performed by using a polynomial fit through the digitized surface contours, to determine optical power and spherical aberration. Third, the lenses were refilled with a silicone oil until their preoperative lens thickness was reached, and scanning laser ray-tracing, contour photography, and mathematical ray-tracing were repeated. Comparisons between the measurements were made to determine how the change from a gradient refractive index to a homogeneous refractive index influenced spherical aberration. The influence of the change in lens contour on spherical aberration after lens refilling was also studied. RESULTS: The natural lenses had a higher lens power than the refilled lenses (49.9 +/- 1.5 D vs. 36.8 +/- 1.5 D; P < 0.001). Moreover, there was a change in sign from negative spherical aberration before lens refilling (-3.6 D) to positive spherical aberration after lens refilling (7.9 D; P < 0.001). The comparison between scanning laser ray-tracing of the natural lens and mathematical ray-tracing of the photographed surface contours of the natural lens to determine the effect of refractive index substitution (i.e., replacement of a gradient refractive index by a homogeneous refractive index) showed a significant change in spherical aberration from -3.6 +/- 2.0 to 11.0 +/- 2.1 D (P < 0.001). The change in lens contour did not result in a significant change in spherical aberration (P = 0.08) before and after lens refilling with an equal refractive index. CONCLUSIONS: The lower lens power of refilled pig lenses compared to natural lenses was due to the lower refractive index of the refill material. Refilling pig lenses with the silicone oil used in this study resulted in an increase in spherical aberration. This increase was mainly caused by the change from a gradient refractive index to a homogeneous refractive index. The change in lens curvature after lens refilling did not result in an increase in spherical aberration. The influence of lens refilling on spherical aberration of human lenses must be determined in similar experiments in human eyes.     

Polymer refilling of presbyopic human lenses in vitro restores the ability to undergo accommodative changes

PURPOSE: Because presbyopia is thought to be accompanied by increased lens sclerosis this study was conducted to investigate whether refilling the capsule of the presbyopic human lens with a soft polymer would restore the ability of the lens to undergo accommodative changes. METHODS: Accommodative forces were applied to natural and refilled lenses by circumferential stretching through the ciliary body and zonular complex. Nine natural lenses and 10 refilled lenses from donors ranging in age from 17 to 60 years were studied. Two refill polymers with a different Young's modulus were used. The lens power was measured by a scanning laser ray-tracing technique, and lens diameter and lens thickness were measured simultaneously while the tension on the zonules was increased stepwise by outward pull on the ciliary body. RESULTS: In the natural lenses the older lenses were not able to undergo power changes with stretching of the ciliary body, whereas in the refilled lenses, all lenses showed power changes comparable to young, natural lenses. The refilled human lenses had a higher lens power than the age-matched natural lenses. The Young's modulus of the polymers influenced the lens power change when measured with the ciliary body diameter increased by 4 mm. CONCLUSIONS: Refilling presbyopic lenses with a soft polymer enabled restoration of lens power changes with mechanical stretching. Because sclerosis of the lens is an important factor in human presbyopia, refilling the lens during lens surgery for cataract could enable restoration of clear vision and accommodation in human presbyopia.     

Effect of infusion bottle height on lens power after lens refilling with and without a plug

PURPOSE: To evaluate the influence of intraoperative infusion bottle height on the power of refilled pig lenses. SETTING: Research Laboratory, Pharmacia Intraocular Lens Manufacturing Plant, Groningen, The Netherlands. METHODS: This study comprised 2 groups of pig eyes. In 1 group, the lens was refilled with silicone oil using a plug to close the capsulorhexis; in the other group, no plug was used. The anterior chamber depth, lens thickness, and vitreous chamber depth were measured by A-scan ultrasound. The total refraction was measured with a Hartinger refractometer. Measurements were performed with the infusion bottle at 0 cm, 25 cm, 50 cm, 75 cm, and 100 cm above eye level. Calculations using a model eye were performed to evaluate the change in lens power based on empirical data. RESULTS: The mean change in the power of refilled lenses caused by varying the height of the infusion bottle was 1.8 diopters. Lenses refilled with a plug had a thickness similar to that of natural lenses. Lenses refilled without a plug were significantly thinner (P<.05). The power of lenses refilled with a plug was significantly higher that of lenses refilled without a plug (P<.05). CONCLUSIONS: During lens refilling, infusion bottle height influenced the resulting lens power. Using a plug to close the capsulorhexis resulted in refilled lens dimensions similar to those of the natural lens.     

On- and off-eye spherical aberration of soft contact lenses and consequent changes of effective lens power.

BACKGROUND: Soft contact lenses produce a significant level of spherical aberration affecting their power on-eye. A simple model assuming that a thin soft contact lens aligns to the cornea predicts that these effects are similar on-eye and off-eye. METHODS: The wavefront aberration for 17 eyes and 33 soft contact lenses on-eye was measured with a Shack-Hartmann wavefront sensor. The Zernike coefficients describing the on-eye spherical aberration of the soft contact lens were compared with off-eye ray-tracing results. Paraxial and effective lens power changes were determined. RESULTS: The model predicts the on-eye spherical aberration of soft contact lenses closely. The resulting power change for a +/- 7.00 D spherical soft contact lens is +/- 0.5 D for a 6-mm pupil diameter and +/- 0.1 D for a 3-mm pupil diameter. Power change is negligible for soft contact lenses corrected for off-eye spherical aberration. CONCLUSIONS: For thin soft contact lenses, the level of spherical aberration and the consequent power change is similar on-eye and off-eye. Soft contact lenses corrected for spherical aberration in air will be expected to be aberration-free on-eye and produce only negligibly small power changes. For soft contact lenses without aberration correction, for higher levels of ametropia and large pupils, the soft contact lens power should be determined with trial lenses with their power and p value similar to the prescribed lens. The benefit of soft contact lenses corrected for spherical aberration depends on the level of ocular spherical aberration.     

动态检影法下近视患者反应性与刺激性AC/A

目的通过测量调节滞后量和眼位,研究在不同调节刺激下,患者反应性AC/A和刺激性AC/A的相关性。方法横断面研究。选择在校大学生29例,在全矫基础上,利用棱镜分离法测量被检者[平均年龄（23.3±3.8）岁,除近视外,无其他眼部及全身疾病]在5 m和40 cm处的隐斜量。在全矫度数的基础上添加+1.00、+1.50、-1.00、-2.00 D球镜,重新检查被检者在40 cm处的隐斜视,应用MEM动态检影法测量患者的调节滞后量。采用秩和检验对数据进行统计分析。结果在不同的调节刺激下,患者的调节滞后量、梯度法反应性AC/A及梯度法刺激性AC/A的差异均有统计学意义（x²=116.85、8.992、17.319,P<0.05）。基于梯度法得到的反应性AC/A与刺激性AC/A均呈正相关（+1.00 D：r=0.542,P<0.01;-1.00 D：r=0.789,P<0.01;-2.00 D：r=0.812,P<0.01）。基于计算法得到的反应性AC/A与刺激性AC/A也呈正相关（r=0.859,P<0.01）。结论附加负球镜时,调节滞后量更大。计算法求的反应性AC/A与刺激性AC/A的相关性最好。     

Accommodating intraocular lenses: a critical review of present and future concepts

Background Significant efforts have been made to develop lens implants or refilling procedures that restore accommodation. Even with monofocal implants, apparent or pseudoaccommodation may provide the patient with substantial though varying spectacle independence. True pseudophakic accommodation with a change of overall refractive power of the eye may be induced either by an anterior shift or a change in curvature of the lens optic. Materials and methods Passive-shift lenses were designed to move forward under ciliary muscle contraction. This is the only accommodative lens type currently marketed (43E/S by Morcher; 1CU by HumanOptics; AT-45 by Eyeonics). The working principle relies on various hypothetical assumptions regarding the mechanism of natural accommodation. Dual-optic lenses were designed to increase the dioptric impact of optic shift. They consist of a mobile front optic and a stationary rear optic which are interconnected with spring-type haptics. With active-shift lens systems the driving force is provided by repulsing mini-magnets. Lens refilling procedures replace the lens content by an elastic material and provide accommodation by an increase of surface curvature. Results Findings with passive-shift lenses have been contradictory. While uncorrected reading vision results were initially reported to be favorable with the 1CU, and excellent with the AT-45 lens, distant-corrected near vision did not exceed that with standard monofocal lenses in later studies. Mean axial shift from laser interferometric measurements under stimulation with pilocarpine showed a moderate anterior shift with the 1CU, while the AT-45 paradoxically exhibited a small posterior shift. With the 1CU, the shift-induced accommodative effect was calculated to be less than +0.5 D in most cases, while +1 D was achieved in a single case only. Ranges and standard deviations were very large in relation to the mean values. Under physiological near-point stimulation, however, no shift was seen at all. Prevention of capsule fibrosis by extensive capsule polishing did not enhance the functional performance. Dual optic lenses are under clinical investigation and are reported to provide a significant amount of accommodation. However, possible long-term formation of interlenticular opacifications remains to be excluded. Regarding magnet-driven active-shift lens systems, initial clinical experience has been promising. Prevention of fibrotic capsular contraction is crucial, and it has been effectively counteracted with a special capsular tension ring, or lens fixation technique, together with capsule polishing. Lens refilling has been extensively studied in the laboratory and in primates. Though it offers great potential for fully restoring accommodation, a variety of problems must be solved, such as achieving emmetropia in the relaxed state, adequate response to ciliary muscle contraction, satisfying image quality over the entire range of accommodation and sustained functioning. The key problem, however, is again after-cataract prevention. Conclusions As opposed to psychophysical evaluation techniques, laser interferometry measures what shift lenses are designed to provide: axial shift on accommodative effort. While under pilocarpine some movement was recorded, no movement at all was found under near-point stimulation with any of the lenses currently marketed. In contrast, magnetic-driven active-shift lens systems carry the potential of sufficiently topping up apparent accommodation to provide for clinically useful accommodation while using conventional lens designs with proven after-cataract performance. Dual optic implants significantly increase the impact of axial optic shift. The main potential problem, however, is delayed formation of interlenticular regenerates. Lens refilling procedures offer the potential of fully restoring accommodation due to the great impact of increase in surface curvature on refractive lens power. However, various problems remain to be solved before clinical use can be envisaged, above all, again, after-cataract prevention. The concept of passive single-optic shift lenses has failed. Concomitant poor capsular bag performance makes these lenses an unacceptable trade-off. Magnet-assisted systems potentially combine clinically useful accommodation with satisfactory after-cataract performance. Dual optic lenses theoretically offer substantial accommodative potential but may allow for interlenticular after-cataract formation. Lens refilling procedures have the greatest potential for fully restoring natural accommodation, but will again require years of extensive laboratory and animal investigations before they may function in the human eye. The author has no proprietary interest in any of the materials or equipment mentioned in this study.     

Comparison of pilocarpine-induced and stimulus-driven accommodation in phakic eyes

With the recent introduction of potentially accommodative intraocular lenses (IOL), there is a need for methods to evaluate their accommodative potential. In most studies assessing IOL movement, pilocarpine is used to stimulate contraction of the ciliary muscle. The aim of this study is to determine if pilocarpine-induced ciliary muscle contraction is comparable to physiological stimulus-driven accommodation in young and presbyopic subjects. Ten emmetropic young subjects (23-25 years) and 11 emmetropic presbyopic subjects (51-62 years) were included in this study. Anterior chamber depth (ACD) and lens thickness (LT) were assessed with partial coherence interferometry (PCI). A moveable stimulus was coupled to the PCI equipment for measurement of biometric lens changes. ACD was measured with the stimulus at infinity and then at the subjects individual nearpoint, and after application of two drops of 2% pilocarpine. In young subjects, there was no significant difference in lens change between nearpoint and pilocarpine stimulation. Presbyopic subjects showed no relevant lens change when accommodating at the nearpoint, however, under pharmacologically induced ciliary muscle contraction with pilocarpine, there was a significant forward shift of the anterior and posterior lens pole, leading to a translational forward lens shift of about 150 microm. This study demonstrates that pilocarpine acts "physiologically" in young phakic subjects, but is a "superstimulus" in presbyopic phakic subjects. Therefore, IOL movement may be overestimated when using pilocarpine to stimulate accommodation.     

Dynamic multi-arm radial lens stretcher: a robotic analog of the ciliary body

We developed a dynamic lens stretching device to quantitatively determine the relationships between force, equatorial displacement, and anterior curvature. A computer-controlled four-arm lens stretcher, equipped with real-time force transducers in each arm, was designed and constructed to obtain transient force measurements during lens stretching. The force-decay spectrum was fitted with a seven-parameter viscoelastic model characterized by three time constants. A corneal topography unit was used to measure the curvature of fresh porcine lenses ex vivo and in vitro in a four-arm lens stretcher at various equatorial displacements. The lens stretcher and corneal topography unit provided detailed information regarding the behavior of the porcine lens in vitro. For all lenses, the central portion of the anterior surface flattened as zonular force increased. Force increased nonlinearly with equatorial displacement. Relaxation time constants for accommodation were 34.5+/-12.2 ms, 310+/-122 ms, and 12,800+/-9490 ms. Time constants for disaccommodation were 34.9+/-4.7 ms, 291+/-79.1 ms, and 3400+/-775 ms, which were not statistically different from those measured for accommodation. The lens stretcher acts as a robotic analog of the ciliary body. This device allows direct, quantitative measurement of the forces and curvature changes relevant to accommodation. However, distortions were present due to the use of only four arms.     

A physiological model to measure effects of age on lenticular accommodation and spherical aberration in chickens.

PURPOSE: To assess physiological accommodative function of intact intraocular lenses, as measured by focal length changes, in chickens of various ages. METHODS: Eyes of white leghorn chickens, aged 0 days (hatchlings), 7 days, 14 days, 6 weeks, 1 year, and 2 years, were enucleated and the backs of the globes, except for the ciliary nerve and ganglion, were removed. The ciliary nerve and ganglion were suctioned into the tip of a suction electrode, and lenses were optically scanned before, during, and after accommodation. Accommodation was elicited by delivery of 30-Hz electrical pulses. RESULTS: For all age groups, lenticular focal lengths for stimulated eyes were significantly shorter than for relaxed eyes, indicating that accommodation had been induced. Lenticular accommodative amplitudes decreased significantly with age, with reduced function occurring between 0 and 7 days and again between 14 days and 1 year. Although accommodation was associated with an increased spherical aberration in all age groups, the increase was significant only in some age groups. CONCLUSIONS: Results showing reduction of lenticular accommodation concomitant with increasing age suggest that in spite of major differences in anatomy and physiology of the accommodative mechanism, chickens may become presbyopic. Results showing high amounts of nonmonotonic spherical aberration in hatchling lenses suggest inherently poor optics in these birds.     

Systematic measurement errors involved in over‐refraction using an autorefractor (Grand‐Seiko WV‐500): is measurement of accommodative lag through spectacle lenses valid?

PURPOSE: Lags of accommodation in ametropic children are often evaluated through spectacle lenses (over-refraction). This study investigated the validity of over-refraction when using an autorefractor. METHODS: Using an autorefractor (Shin-Nippon SRW-500/Grand-Seiko WV-500), refractive readings were obtained in 25 cyclopleged eyes (mean +/- S.D. refraction: -3.44 +/- 3.56 D, range: from -10.56 to +0.25 D) while placing spherical lenses of different power (from -5.00 to +5.00 D) in front of the eye at a vertex distance of 12 mm. Based on the refractive readings with and without the lens, and the lens power, measurement errors were estimated. Similarly, the measurement errors were estimated also in model eyes of -10.00, -4.75, 0.00 and +10.00 D. The results were compared with ray-tracing simulations based on the internal specifications of the autorefractor. RESULTS: Measurement errors were found unless the power of the spectacle lens was equal to the refractive error of the eye. When the spectacle lens power was greater (less myopic or more hyperopic) than the refraction of the eye, the measurement error was negative in sign and greater than -0.3 D. It follows that, when an accommodative response is measured in myopic subjects, the refractive reading usually becomes more myopic than the refraction of the eye including the accommodative response; hence, the accommodative response is overestimated, and the lag of accommodation is underestimated. CONCLUSIONS: The autorefraction through spectacle lenses involved systematic measurement errors. The extent of the errors is usually small but needs to be taken into account in a comparative study of accommodative responses among different refractive groups.     

Age-related changes in human ciliary muscle and lens: a magnetic resonance imaging study

PURPOSE: To use high-resolution magnetic resonance (MR) images of the eye to directly measure the relationship between ciliary muscle contraction and lens response with advancing age. METHODS: A General Electric, 1.5-Tesla MR imager and a custom-designed eye imaging coil were used to collect high-resolution MR images from 25 subjects, 22 through 83 years of age. A nonmagnetic binocular stimulus apparatus was used to induce both relaxed accommodation (0.1 diopter [D]) and strong accommodative effort (8.0 D). Measurements of the ciliary muscle ring diameter (based on the inner apex), lens equatorial diameter, and lens thickness were derived from the MR images. RESULTS: Muscle contraction is present in all subjects and reduces only slightly with advancing age. A decrease in the diameter of the unaccommodated ciliary muscle ring was highly correlated with advancing age. Lens equatorial diameter does not correlate with age for either accommodative state. Although unaccommodated lens thickness (i.e., lens minor axis length) increases with age, the thickness of the lens under accommodative effort is only modestly age-dependent. CONCLUSIONS: Ciliary muscle contractile activity remains active in all subjects. A decrease in the unaccommodated ciliary muscle diameter, along with the previously noted increase in lens thickness (the "lens paradox"), demonstrates the greatest correlation with advancing age. These results support the theory that presbyopia is actually the loss in ability to disaccommodate due to increases in lens thickness, the inward movement of the ciliary ring, or both.     

低度近视性屈光参差不同矫正方式的调节功能研究

目的:研究分别采用单焦框架眼镜与角膜塑形镜矫正低度近视性屈光参差的儿童单眼及双眼调节的差异。方法:回顾性研究。收集2019-11/2020-04于我院眼科门诊就诊的低度近视性屈光参差(1.0D≤双眼等效球镜差<2.5D)儿童47例94眼,其中配戴框架眼镜者27例54眼作为A组,配戴角膜塑形镜者20例40眼作为B组。分别记录并比较两组患儿矫正1mo后的矫正视力及调节参数[调节反应(AR)、调节灵活度(AF)、调节幅度(AMP)]的差异。结果:两组患儿AR测量值均为正值,表现为调节滞后,A组患儿屈光高度眼调节滞后量显著高于屈光低度眼(0.63±0.21D vs 0.25±0.34D,P<0.001),但B组患儿双眼调节滞后量无差异(P=0.104),且两组患儿屈光高度眼与屈光低度眼单眼矫正视力和单眼AMP均无差异(P>0.05)。A组患儿双眼AR差值高于B组(0.38±0.36D vs 0.10±0.26D,P=0.005),双眼AF低于B组(8.22±1.15c/min vs 9.95±0.89c/min,P<0.001),但两组患儿双眼AMP无明显差异(P=0.280)。结论:低度近视性屈光参差儿童配戴角膜塑形镜比单焦框架眼镜矫正可获得更高的双眼调节灵活度,降低双眼调节反应差值,从而维持更协调的双眼调节功能。     

Age-dependence of the optomechanical responses of ex vivo human lenses from India and the USA, and the force required to produce these in a lens stretcher: the similarity to in vivo disaccommodation

The purpose of this study was to study the age-dependence of the optomechanical properties of human lenses during simulated disaccommodation in a mechanical lens stretcher, designed to determine accommodative forces as a function of stretch distance, to compare the results with in vivo disaccommodation and to examine whether differences exist between eyes harvested in the USA and India.Postmortem human eyes obtained in the USA (n = 46, age = 6-83 years) and India (n = 91, age = 1 day-85 years) were mounted in an optomechanical lens stretching system and dissected to expose the lens complete with its accommodating framework, including zonules, ciliary body, anterior vitreous and a segmented rim of sclera. Disaccommodation was simulated through radial stretching of the sectioned globe by 2 mm in increments of 0.25 mm. The load, inner ciliary ring diameter, lens equatorial diameter, central thickness and power were measured at each step. Changes in these parameters were examined as a function of age, as were the dimension/load and power/load responses.Unstretched lens diameter and thickness increased over the whole age range examined and were indistinguishable from those of in vivo lenses as well as those of in vitro lenses freed from zonular attachments. Stretching increased the diameter and decreased the thickness in all lenses examined but the amount of change decreased with age. Unstretched lens power decreased with age and the accommodative amplitude decreased to zero by age 45-50. The load required to produce maximum stretch was independent of age (median 80 mN) whereas the change in lens diameter and power per unit load decreased significantly with age.The age related changes in the properties of human lenses, as observed in the lens stretching device, are similar to those observed in vivo and are consistent with the classical Helmholtz theory of accommodation. The response of lens diameter and power to disaccommodative (stretching) forces decreases with age, consistent with lens nuclear stiffening.     

不同非球面人工晶状体植入术后调节幅度的比较

目的 研究不同非球面单焦可折叠后房型人工晶状体（IOL）植入术后调节幅度的比较。方法 前瞻性病例对照研究。选取2010年8月至2011年8月在天津医科大学眼科医院行白内障超声乳化联合IOL植入术的年龄相关性白内障患者102例（102眼）,将其分为3组：Rayner组植入Rayner Superflex 920H型IOL（Rayner）,SN60WF组植入Acrysof IQ SN60WF型IOL（Alcon）,SN60AT组植入Acrysof NATURAL SN60AT型IOL（Alcon）。术后6个月检测患者裸眼远视力、最佳矫正远视力、最佳矫正远视力后的近视力;使用Hartmann-Shack波前像差仪（Wavefront）测量患者球差;使用综合验光仪调节尺测量患者主观调节幅度;使用WR-5100型全自动电脑验光仪（Grand Seiko）测量患者客观调节幅度。采用卡方检验和方差分析分别对计数资料和计量资料行统计学分析,采用Pearson相关分析检验参数相关性。结果 Rayner组、SN60WF组和SN60AT组患者主观调节幅度分别为（2.00±0.58）D、（2.26±0.60）D、（2.29±0.48）D,3组患者客观调节幅度分别为（0.87±0.37）D、（1.01±0.38）D、（1.04±0.37）D,3组患者比较差异均无统计学意义（F主观=2.662,P主观>0.05;F客观=1.925,P客观>0.05）。3组患者球差在瞳孔直径为3 mm时分别为（0.08±0.04）μm、（0.05±0.04）μm、（0.14±0.05）μm,3组比较差异有统计学意义（F=45.780,P<0.01）。球差与主、客观调节幅度均无相关性（r主观=0.056,P主观>0.05;r客观=0.095,P客观>0.05）。结论 植入Acrysof SN60WF型非球面IOL和Rayner Superflex 920H型非球面IOL与植入Acrysof SN60AT型球面IOL相比,对调节幅度没有明显影响。球面像差与人工晶状体眼调节幅度不相关。     

Edinger-Westphal and pharmacologically stimulated accommodative refractive changes and lens and ciliary process movements in rhesus monkeys

During accommodation, the refractive changes occur when the ciliary muscle contracts, releasing resting zonular tension and allowing the lens capsule to mold the lens into an accommodated form. This results in centripetal movement of the ciliary processes and lens edge. The goal of this study was to understand the relationship between accommodative refractive changes, ciliary process movements and lens edge movements during Edinger-Westphal (EW) and pharmacologically stimulated accommodation in adolescent rhesus monkeys. Experiments were performed on one eye each of three rhesus monkeys with permanent indwelling electrodes in the EW nucleus of the midbrain. EW stimulated accommodative refractive changes were measured with infrared photorefraction, and ciliary process and lens edge movements were measured with slit-lamp goniovideography on the temporal aspect of the eye. Images were recorded on the nasal aspect for one eye during EW stimulation. Image analysis was performed off-line at 30 Hz to determine refractive changes and ciliary body and lens edge movements during EW stimulated accommodation and after carbachol iontophoresis to determine drug induced accommodative movements. Maximum EW stimulated accommodation was 7.36+/-0.49 D and pharmacologically stimulated accommodation was 14.44+/-1.21 D. During EW stimulated accommodation, the ciliary processes and lens edge moved centripetally linearly by 0.030+/-0.001 mm/D and 0.027+/-0.001 mm/D, with a total movement of 0.219+/-0.034 mm and 0.189+/-0.023 mm, respectively. There was no significant nasal/temporal difference in ciliary process or lens edge movements. 30-40 min after pharmacologically stimulated accommodation, the ciliary processes moved centripetally a total of 0.411+/-0.048 mm, or 0.030+/-0.005 mm/D, and the lens edge moved centripetally 0.258+/-0.014 mm, or 0.019+/-0.003 mm/D. The peaks and valleys of the ciliary processes moved by similar amounts during both supramaximal EW and pharmacologically stimulated accommodation. In conclusion, this study shows, for the first time, that the ciliary processes and lens edge move centripetally, linearly with refraction during EW stimulated accommodation. During pharmacological stimulation, the ciliary processes move to a greater extent than the lens edge, confirming that in adolescent monkeys, lens movement limits the accommodative optical change in the eye.     

Pseudophakic accommodation with translation lenses – dual optic vs mono optic

PURPOSE: To investigate the pseudophakic accommodation effect in dual and mono optic translation accommodative intraocular lenses (AIOL) using linear matrix methods in the paraxial space. METHODS: Dual (anterior optic of power +32 D linked to a compensatory posterior optic of negative power) and mono lens power was determined in the non-accommodated state using linear geometric optics based on the Gullstrand model eye. The position of the AIOL was calculated from a regression formula. Pseudophakic accommodation was assessed with three systems: (1) forward shift of the mono optic lens, (2) anterior translation of the anterior optic in the dual optic lens system with an unchanged position of the posterior minus lens and (3) symmetrical anterior and posterior translation of the anterior and posterior lens. The Gullstrand model eye was modified by changing the axial length (and proportionally changing the phakic anterior chamber depth) to investigate the accommodative effect in myopic and hyperopic eyes. RESULTS: The dual optic lens system (2) yields a nearly constant accommodation amplitude of 2.4-2.5 D mm(-1) movement over the total range of axial lengths. The mono optic lens (1) provides a higher accommodative effect only in extremely short eyes (high refractive power of the lens), whereas for normal eyes (1.4-1.5 D mm(-1) movement) and for long (myopic) eyes the accommodative effect is much less than the dual optic lens. The dual optic lens system under condition (3) yields less accommodation amplitude compared with the dual optic system under condition (2) over the total range of axial length but provides higher accommodation amplitude compared with the mono optic lens system (1) with axial lengths greater than 22.3 mm (lens power 25.5 D). In the accommodated state, with lens translation of 1 mm, the absolute value of the lateral magnification increases with the refractive power of the mono optic lens (1) and decreases in both dual optic lens systems (under conditions 2 and 3). CONCLUSIONS: A mathematical strategy is presented for calculation of the accommodative effect of mono-optic and dual optic AIOL. The dual optic lens yielded a nearly constant accommodation amplitude of about 2.4-2.5 D mm(-1) translation, whereas the mono optic lens yielded an accommodative response of <2 D mm(-1) translation in long myopic or normal eyes. Only in extremely short eyes is the accommodative amplitude of the mono-optic lens higher than the dual optic lens.     

Lenticular accommodation in relation to ametropia: the chick model

Our goal was to determine whether experimentally induced ametropias have an effect on lenticular accommodation and spherical aberration. Form-deprivation myopia and hyperopia were induced in one eye of hatchling chicks by application of a translucent goggle and +15 D lens, respectively. After 7 days, eyes were enucleated and lenses were optically scanned prior to accommodation, during accommodation, and after accommodation. Accommodation was induced by electrical stimulation of the ciliary nerve. Lenticular focal lengths for form-deprived eyes were significantly shorter than for their controls and accommodation-associated changes in focal length were significantly smaller in myopic eyes compared to their controls. For eyes imposed with +15 D blur, focal lengths were longer than those for their controls and accommodative changes were greater. Spherical aberration of the lens increased with accommodation in both form-deprived and lens-treated birds, but induction of ametropia had no effect on lenticular spherical aberration in general. Nonmonotonicity from lenticular spherical aberration increased during accommodation but effects of refractive error were equivocal. The crystalline lens contributes to refractive error changes of the eye both in the case of myopia and hyperopia. These changes are likely attributable to global changes in the size and shape of the eye.     

Lens thickness with age and accommodation by optical coherence tomography

PURPOSE: To utilize time-domain optical coherence tomography (OCT) to measure changes in the crystalline lens with age and accommodation. METHODS: A cross-sectional study of pre-presbyopic and presbyopic subjects was conducted. Amplitude of accommodation was measured with the push-up test. Objective accommodation was measured with the Grand Seiko auto-refractor and a Badal lens system. Lens thickness was measured with the Zeiss Visante OCT and an internal optometer. The data were analysed using correlation coefficients, linear regression, and by calculating the average change in lens thickness per diopter change in objective accommodation. RESULTS: Twenty-two subjects between the ages of 36 and 50 years completed the study. Subjective amplitude of accommodation ranged from 2.17 to 6.38 D. Objective accommodation ranged from 0.22 to 4.56 D. The mean lens thickness was 4.05+/-0.20 mm. The mean change in lens thickness for up to a 5-D accommodative stimulus ranged from 0.01 to 0.26 mm. The correlation coefficients were: age and subjective accommodation, r= -0.74; age and objective accommodation, r= -0.84; change in lens thickness and age, r= -0.65; change in lens thickness and subjective accommodation, r=0.74; change in lens thickness and objective accommodation, r=0.64; objective and subjective accommodation, r=0.82 (all p<0.01). An increase in lens thickness of 21 microm per year of age was determined by linear regression. For the subjects who showed at least 1 D of accommodative response on the Grand Seiko auto-refractor, there was an increase of 51+/-19 microm per dioptre of accommodation. CONCLUSIONS: Optical coherence tomography is a non-invasive technique that can be used to quantify changes in the thickness of the crystalline lens. Subjective and objective measurements of accommodation, as well as age, were robustly correlated with the measured changes in lens thickness. Lens thickness changes with age and accommodation as measured with the Visante OCT compare well with previous findings using Scheimpflug photography and ultrasound.     

Evaluation of the performance of accommodating IOLs using a paraxial optics analysis

Purpose: We employed an analytical approach to evaluate the key parameters for the potential design optimisation of accommodating intra‐ocular lenses (AIOL) and to use these parameters to predict their accommodative performance. Methods: Paraxial thin‐lens equations to predict the accommodative performances of single‐element (1E) and two‐element (2E) AIOLs were developed. 2E‐AIOLs with either mobile front or back lens elements were analysed as well as 1E‐AIOL for their accommodative performance. A paraxial model including key ocular components (corneal surfaces, pupil and retina) as well as AIOL was used to evaluate the key control parameters and optimal design configurations. A range of variants of the model, representing varying powers of front and back optical elements and with either front or back optical element mobile was tested. Results: Optimal accommodative performance of 2E‐AIOL is governed by the power combinations of its optical elements; design variants with higher positive front element power produced greater accommodative efficacy, while mobility of the front element contributed more to the accommodative performance than the back element. The performance of 1E‐AIOL is primarily governed by the power of the AIOL; the higher the AIOL power, the better the accommodative performance. Conclusions: From an accommodative performance standpoint, the optimal design of 2E‐AIOL should comprise a high plus power front element. Considering the maximum potential amounts of element translation available clinically, 2E‐AIOLs are predicted to offer higher accommodative performance compared to 1E‐AIOL.