Optical and clinical simulated performance of a new refractive extended depth of focus intraocular lens.

OBJECTIVES: The purpose of this study is to evaluate the optical and expected clinical performance of a new refractive Extended Depth of Focus (EDF) intraocular lens (IOL) designed to maintain a monofocal-like dysphotopsia profile. METHODS: Simulated visual acuity (sVA) with varying defocus was calculated using the area under the Modulation Transfer Function measured in an average eye model and from computer simulations in eye models with corneal higher-order aberrations. Tolerance to defocus was evaluated using computer simulations of the uncorrected distance sVA under defocus. To evaluate the dysphotopsia profile, halo pictures obtained using an IOL-telescope, as well as simulated images in a realistic eye model under defocus were assessed. The results of the refractive EDF were compared to those of a diffractive EDF of the same platform. RESULTS: The refractive EDF IOL provides similar range of vision to the diffractive EDF IOL with the same distance, and similar intermediate and near sVA. The refractive EDF IOL provides the same tolerance to hyperopia as the diffractive EDF but more tolerance to myopia. Halo pictures and simulations showed that the refractive EDF provides comparable dysphotopsia profile to the monofocal IOL and better than the diffractive EDF. CONCLUSIONS: The results of this preclinical study in clinically relevant conditions show that the new refractive EDF IOL is expected to provide similar range of vision to the diffractive IOL of the same platform and higher tolerance to refractive errors. The refractive EDF provides a dysphotopsia profile that is better than the diffractive EDF and comparable to that of the monofocal IOL, also in the presence of residual refractive errors.

Influence of decentration and tilt of Tecnis ZCB00 on visual acuity and higher order aberrations.

BACKGROUND/OBJECTIVES: To determine the influence of decentration and tilt of a pseudophakic aspheric intraocular lens (IOL) on visual acuity (VA) and higher-order aberrations (HOAs), and to analyze the agreement between pupil center/axis and iridocorneal angles center/axis when assessing IOL decentration and tilt. SUBJECTS/METHODS: A prospective interventional case series study including thirty-three patients undergoing Tecnis ZCB00 (Abbott Medical Optics) implantation. IOL decentration and tilt with respect to two reference systems (pupil and iridocorneal angles centers/axes), in cartesian (X,Y) and polar (radius/tilt, polar angle/azimuth) coordinates, were assessed with optical coherence tomography. VA and internal and ocular HOAs were evaluated. Multiple linear regression models and intraclass correlation coefficient (ICC) were computed. RESULTS: IOL decentration only showed a significant effect on internal HOAs for [Formula: see text] (R2 = 0.20, P = 0.04). IOL decentration with respect to the pupil center showed a significant effect on ocular [Formula: see text] (R2 = 0.18, P = 0.05), [Formula: see text] (R2 = 0.36, P = 0.001) and [Formula: see text] (R2 = 0.24, P = 0.02); and with respect to the center of iridocorneal angles, on ocular [Formula: see text] (R2 = 0.21, P = 0.03), [Formula: see text] (R2 = 0.32, P = 0.003), primary coma (R2 = 0.41, P < 0.001), and coma-like (R2 = 0.40, P = 0.001). Poor agreement between both reference systems was found for IOL decentration measurements (ICC ≤ 0.41), except for the polar angle coordinate (ICC = 0.83). Tilt measurements showed good agreement (ICC ≥ 0.75). CONCLUSIONS: Tecnis ZCB00 decentration and tilt values after uneventful implantation appear not to have influence on VA, and their effect on HOAs are not high enough to clinically affect quality of vision. Pupil and iridocorneal angles used as reference systems may be interchangeable for IOL tilt measurements, but not for decentration.

The Effect of Retinal Illuminance on the Subjective Amplitude of Accommodation.

SIGNIFICANCE: We show that the amplitude of accommodation decreases with retinal illumination even under photopic reading conditions and a constant pupil size. This result provides a basis for clinical approaches that are not based on an optical explanation. PURPOSE: We investigated the effect of retinal illuminance on the amplitude of accommodation while the pupil of the eye remained constant. METHODS: The amplitudes of accommodation of 10 young subjects (from 20 to 38 years of age) and that of 10 presbyopic subjects (from 45 to 54 years of age) were measured subjectively through an artificial pupil of 5 mm using a Badal optometer and for four values of retinal illuminance: 222, 821, 2138, and 5074 trolands. Phenylephrine was instilled to all the subjects to ensure that their natural pupil was greater than the artificial one in all experimental runs. Linear mixed-effects model for repeated measures with age and log luminance as covariates were used to check whether changes in amplitude of accommodation with retinal illumination were statistically significant. RESULTS: In the range of illuminances tested, the amplitude of accommodation decreased on average from 6.34 to 4.35 D in the young subjects and from 1.69 to 1.04 D in the presbyopic subjects. Illuminance was associated with the amplitude of accommodation in both young and presbyopic groups, with P < .01. CONCLUSIONS: The reduction in the amplitude of accommodation with target illumination (a phenomenon named night presbyopia) under photopic light conditions is not only due to a reduction in the depth of focus as a consequence of pupil dilation; it is strongly affected by the decrease of retinal illumination.

Aberrations and accommodation.

Modern methods of measuring the refractive state of the eye include wavefront sensors which make it possible to monitor both static and dynamic changes of the ocular wavefront while the eye observes a target positioned at different distances away from the eye. In addition to monitoring the ocular aberrations, wavefront refraction methods allow measurement of the accommodative response while viewing with the eye's habitual chromatic and monochromatic aberrations present, with these aberrations removed, and with specific aberrations added or removed. A large number of experiments describing the effects of accommodation on aberrations and vice versa are reviewed, pointing out the implications for fundamental questions related to the mechanism of accommodation.

Effect of phenylephrine on static and dynamic accommodation / Efecto de la fenilefrina sobre la acomodación estática y dinámica

Purpose: We tested the hypothesis that changes in accommodation after instillation of Phenylephrine Hydrochloride (PHCl) observed in some studies could be caused by changes in optics. Methods: We performed two experiments to test the effects of PHCl on static and on dynamic accommodation in 8 and 6 subjects, respectively. Objective wavefront measurements were recorded of the static accommodation response to a stimulus at different distances or dynamic accommodation response to a sinusoidally moving stimulus (between 1 and 3 D of accommodative demand at 0.2 Hz). The responses were characterized using two methods: one that takes into account the mydriatic optical effects on the accommodation produced by higher-order aberrations of the eye and another that takes into account only power changes paraxially due to the action of the ciliary muscle and regardless of the pupil size. Results: When mydriatic optical effects were taken into account, differences in responses before and after PHCl instillation were 0.51 ± 0.53 D, and 0.12 ± 0.15, for static and dynamic accommodation, respectively, and were statistically significant (p < 0.039). When mydriatic optical effects were not taken into account, the differences in responses before and after PHCl instillation were -0.20 ± 0.51 D, and -0.05 ± 0.14, for static and dynamic accommodation, respectively, and were not statistically significant (p > 0.313). Conclusions: The mydriatic effect of the PHCl causes optical changes in the eye that can reduce the objective and subjective measurement of accommodation

Objetivo: Probamos la hipótesis de que los cambios de la acomodación tras la instilación de Hidrocloruro de Fenilefrina (PHCl) observados en algunos estudios podrían estar originados por los cambios en la óptica. Métodos: Realizamos dos experimentos para probar los efectos de PHCl sobre la acomodación estática y dinámica en 8 y 6 sujetos, respectivamente. Se registraron las mediciones objetivas de frente de onda de la respuesta acomodativa estática a un estímulo a diferentes distancias, o la respuesta acomodativa dinámica a un estímulo con movimiento sinusoidal (entre 1 y 3 D de demanda acomodativa a 0,2Hz). Las respuestas se caracterizaron utilizando dos métodos: uno que tiene en cuenta los efectos ópticos midriáticos sobre la acomodación producida por aberraciones de alto orden, y otro que considera únicamente los cambios de potencia paraxialmente, debido a la acción del músculo ciliar, independientemente del tamaño de la pupila. Resultados: Al tenerse en cuenta los efectos ópticos midriáticos, las diferencias de las respuestas antes y después de la instilación de PHCl fueron de 0,51 ± 0,53 D, y 0,12 ± 0,15, para la acomodación estática y dinámica, respectivamente, siendo estadísticamente significativas (p < 0,039). Al no considerarse los efectos ópticos midriáticos, las diferencias en cuanto a las respuestas antes y después de la instilación de PHCl fueron de -0,2 ± 0,51 D, y -0,05 ± 0,14, para la acomodación estática y dinámica, respectivamente, no siendo estadísticamente significativas (p > 0,313). Conclusiones: El efecto midriático de PHCl origina cambios ópticos en el ojo que pueden reducir la medición objetiva y subjetiva de la acomodación

Effect of phenylephrine on static and dynamic accommodation.

PURPOSE: We tested the hypothesis that changes in accommodation after instillation of Phenylephrine Hydrochloride (PHCl) observed in some studies could be caused by changes in optics. METHODS: We performed two experiments to test the effects of PHCl on static and on dynamic accommodation in 8 and 6 subjects, respectively. Objective wavefront measurements were recorded of the static accommodation response to a stimulus at different distances or dynamic accommodation response to a sinusoidally moving stimulus (between 1 and 3 D of accommodative demand at 0.2Hz). The responses were characterized using two methods: one that takes into account the mydriatic optical effects on the accommodation produced by higher-order aberrations of the eye and another that takes into account only power changes paraxially due to the action of the ciliary muscle and regardless of the pupil size. RESULTS: When mydriatic optical effects were taken into account, differences in responses before and after PHCl instillation were 0.51±0.53 D, and 0.12±0.15, for static and dynamic accommodation, respectively, and were statistically significant (p<0.039). When mydriatic optical effects were not taken into account, the differences in responses before and after PHCl instillation were -0.20±0.51 D, and -0.05±0.14, for static and dynamic accommodation, respectively, and were not statistically significant (p>0.313). CONCLUSIONS: The mydriatic effect of the PHCl causes optical changes in the eye that can reduce the objective and subjective measurement of accommodation.

Amplitude, Latency, and Peak Velocity in Accommodation and Disaccommodation Dynamics.

The aim of this work was to ascertain whether there are differences in amplitude, latency, and peak velocity of accommodation and disaccommodation responses when different analysis strategies are used to compute them, such as fitting different functions to the responses or for smoothing them prior to computing the parameters. Accommodation and disaccommodation responses from four subjects to pulse changes in demand were recorded by means of aberrometry. Three different strategies were followed to analyze such responses: fitting an exponential function to the experimental data; fitting a Boltzmann sigmoid function to the data; and smoothing the data. Amplitude, latency, and peak velocity of the responses were extracted. Significant differences were found between the peak velocity in accommodation computed by fitting an exponential function and smoothing the experimental data (mean difference 2.36 D/s). Regarding disaccommodation, significant differences were found between latency and peak velocity, calculated with the two same strategies (mean difference of 0.15 s and -3.56 D/s, resp.). The strategy used to analyze accommodation and disaccommodation responses seems to affect the parameters that describe accommodation and disaccommodation dynamics. These results highlight the importance of choosing the most adequate analysis strategy in each individual to obtain the parameters that characterize accommodation and disaccommodation dynamics.

Evaluation of the iridocorneal angle with accommodation using optical coherence tomography.

The changes in the iridocorneal angle structure during accommodation are assessed by means of anterior segment optical coherence tomography. Thirteen right eyes were included in the study. The device used for the measurement was the Visante®omni system. The stimuli were set up at different vergences (0.0 D, -1.5 D, and -3.0 D). The angle opening distance 500 and 750, the trabecular iris space area 500 and 750, and the scleral spur angle parameters were assessed at the nasal and temporal regions. The results in the iridotrabecular angle comparing the three accommodative states of the eye did not yield any statistically significant difference at nasal or temporal angle sections. In light of our results and in the conditions of our study, the structures of the iridocorneal angle are not significantly changed with accommodation.

Effect of even and odd-order aberrations on the accommodation response.

AIM: To investigate the potential effect that odd and even-order monochromatic aberrations may have on the accommodation response of the human eye. METHODS: Eight healthy subjects with astigmatism below 1 D, best corrected visual acuity 20/20 or better and normal findings in an ophthalmic examination were enrolled. An adaptive optics system was used in order to measure the accommodation response of the subjects' eyes under different conditions: with the natural aberrations being present, and with the odd and even-order aberrations being corrected. Three measurements of accommodation response were monocularly acquired at accommodation demands ranging from 0 to 4 D (0.5 D step). RESULTS: The accommodative lag was greater for the accommodative demands of 1.5, 3, 3.5 and 4 D for the condition in which the even-order aberrations were corrected, in comparison to that obtained for the natural aberrations and corrected odd-order aberrations for the same accommodation demands. No statistically significant differences were found between the accommodation responses under the three conditions. CONCLUSION: The odd and even-order aberrations are not helping the visual system to accommodate, because their partial correction do not affect the accommodation performance.

Human eyes do not need monochromatic aberrations for dynamic accommodation.

PURPOSE: To determine if human accommodation uses the eye's own monochromatic aberrations to track dynamic accommodative stimuli. METHODS: Wavefront aberrations were measured while subjects monocularly viewed a monochromatic Maltese cross moving sinusoidally around 2D of accommodative demand with 1D amplitude at 0.2 Hz. The amplitude and phase (delay) of the accommodation response were compared to the actual vergence of the stimulus to obtain gain and temporal phase, calculated from wavefront aberrations recorded over time during experimental trials. The tested conditions were as follows: Correction of all the subject's aberrations except defocus (C); Correction of all the subject's aberrations except defocus and habitual second-order astigmatism (AS); Correction of all the subject's aberrations except defocus and odd higher-order aberrations (HOAs); Correction of all the subject's aberrations except defocus and even HOAs (E); Natural aberrations of the subject's eye, i.e., the adaptive-optics system only corrected the optical system's aberrations (N); Correction of all the subject's aberrations except defocus and fourth-order spherical aberration (SA). The correction was performed at 20 Hz and each condition was repeated six times in randomised order. RESULTS: Average gain (±2 standard errors of the mean) varied little across conditions; between 0.55 ± 0.06 (SA), and 0.62 ± 0.06 (AS). Average phase (±2 standard errors of the mean) also varied little; between 0.41 ± 0.02 s (E), and 0.47 ± 0.02 s (O). After Bonferroni correction, no statistically significant differences in gain or phase were found in the presence of specific monochromatic aberrations or in their absence. CONCLUSIONS: These results show that the eye's monochromatic aberrations are not necessary for accommodation to track dynamic accommodative stimuli.

Dynamic accommodation without feedback does not respond to isolated blur cues.

The aim of this study was to determine whether dynamic accommodation responds to isolated blur cues without feedback, and without changes in the distance of the object. Nine healthy subjects aged 21-40years were recruited. Four different aberration patterns were used as stimuli to induce blur with (1) the eye's natural, uncorrected, optical aberrations, (2) all aberrations corrected, (3) spherical aberration only, or (4) astigmatism only. The stimulus was a video animation based on computer-generated images of a monochromatic Maltese cross. Each individual video was generated for each subject off-line, after measuring individual aberrations at different accommodation levels. The video simulated sinusoidal changes in defocus at 0.2Hz. Dynamic images were observed through a 0.8mm pinhole placed at a plane conjugated with the eye's pupil, thus effectively removing potential feedback stemming from accommodation changes. Accommodation responses were measured with a Hartmann-Shack aberrometer for the four different aberration patterns. The results showed that seven out of nine subjects did not respond to any stimuli, whereas the response of the other two subjects was erratic and they seemed to be searching rather than following the stimulus. A significant reduction in average accommodative gain (from 0.52 to 0.11) was obtained when the dioptric demand cue was removed. No statistically significant differences were found among the experimental conditions used. We conclude that aberration related blur does not drive the accommodation response in the absence of feedback from accommodation.

Optical quality of rotationally symmetrical contact lenses derived from their power profiles.

PURPOSE: To present a methodology for evaluating the optical quality of rotationally symmetrical contact lenses (CLs) from a single power profile. METHODS: Simulated rotationally symmetrical power profiles corresponding to different CLs designs (monofocal, two-zone center-near bifocal, and four-zone center-distance bifocal) were used to calculate the wavefront error profile by means of numerical integration. Then, each lens wavefront error profile was spun around the center to obtain the lens wavefront error surface. From the surface, monochromatic optical transfer functions (OTF), simulated images and the visual Strehl ratio based on the OTF (VSOTF) were obtained for different distances and pupil sizes (3 and 5.5mm) after performing a through-focus. RESULTS: VSOTF variations, taking into account both vergence and pupil size, were presented for the three CLs designs. The monofocal design showed excellent optical quality only for far vision, whereas the bifocal designs exhibited good optical quality for far and near vision. Modulation transfer function (MTF) from each lens design, pupil size, and work distance agreed with the previous results. CONCLUSIONS: The methodology presented here allows for a rapid and thorough assessment of the optical quality of rotationally symmetrical CLs by means of optical quality metrics, with a special interest in simultaneous image contact lenses. This methodology may be useful for choosing the most suitable lens for each subject's visual demands.

Non-invasive measurements of the dynamic changes in the ciliary muscle, crystalline lens morphology, and anterior chamber during accommodation with a high-resolution OCT.

PURPOSE: The purpose of the study was to assess non-invasively the changes in the anterior chamber eye, crystalline lens morphology, and ciliary muscle during accommodation by means of an anterior chamber optical coherence tomographer (OCT), and correlate them with vergence. METHODS: Twenty-five eyes of twenty-five healthy subjects, whose mean age was 29.9±7.1 years, were included and measured with an anterior chamber OCT. The central corneal thickness (CCT), anterior chamber depth (ACD), anterior crystalline lens radius of curvature (ALRC), crystalline lens thickness (CLT), and ciliary muscle area (CMA) were measured for each participant at 0, -1, -2, and -3 D of target vergence. A linear model was used to assess the correlation of each eye parameter with the vergence demand. RESULTS: The mean CCT showed no change for all the accommodative stimuli. The mean ACD and ALRC decreased with the vergence, about 4.5 and 30 % at -3 D, respectively. On the contrary, the CLT and CMA showed an opposite tendency, where the mean CLT was increased by 4.0 % and the mean CMA was done by 26% at -3 D. Statistical significant differences (p < 0.001) were obtained among all vergences for each eye metric, except for the CCT (p = 0.76). CONCLUSION: The ACD and ALRC decreased about 2 and 10 % per dioptre of accommodation, respectively; whereas the CLT and CMA increased about 2 and 9 %, respectively. These results add knowledge regarding the understanding of accommodation and give new perspectives for biomechanics and biometry.

Accommodation Responds to Optical Vergence and Not Defocus Blur Alone.

Purpose: To determine whether changes in wavefront spherical curvature (optical vergence) are a directional cue for accommodation. Methods: Nine subjects participated in this experiment. The accommodation response to a monochromatic target was measured continuously with a custom-made adaptive optics system while astigmatism and higher-order aberrations were corrected in real time. There were two experimental open-loop conditions: vergence-driven condition, where the deformable mirror provided sinusoidal changes in defocus at the retina between -1 and +1 diopters (D) at 0.2 Hz; and blur-driven condition, in which the level of defocus at the retina was always 0 D, but a sinusoidal defocus blur between -1 and +1 D at 0.2 Hz was simulated in the target. Right before the beginning of each trial, the target was moved to an accommodative demand of 2 D. Results: Eight out of nine subjects showed sinusoidal responses for the vergence-driven condition but not for the blur-driven condition. Their average (±SD) gain for the vergence-driven condition was 0.50 (±0.28). For the blur-driven condition, average gain was much smaller at 0.07 (±0.03). The ninth subject showed little to no response for both conditions, with average gain <0.08. Vergence-driven condition gain was significantly different from blur-driven condition gain (P = 0.004). Conclusions: Accommodation responds to optical vergence, even without feedback, and not to changes in defocus blur alone. These results suggest the presence of a retinal mechanism that provides a directional cue for accommodation from optical vergence.

Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses.

AIM: To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses. METHODS: Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device (LAMBDA-X, Belgium). Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance (far, intermediate, and near) and pupil size was also analyzed. RESULTS: The power distribution of the lenses was affected by pupil size differently. One of the lenses showed a significant spread in refractive power distribution, from about -3 D to 0 D. Generally, the power distribution of the lenses expanded as the pupil diameter became greater. The surface of the lens dedicated for each distance varied substantially with the design of the lens. CONCLUSION: In an experimental basis, our results show how the lenses power distribution is affected by the pupil size and underlined the necessity of careful evaluation of the patient's visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome.

Temporal multiplexing with adaptive optics for simultaneous vision.

We present and test a methodology for generating simultaneous vision with a deformable mirror that changed shape at 50 Hz between two vergences: 0 D (far vision) and -2.5 D (near vision). Different bifocal designs, including toric and combinations of spherical aberration, were simulated and assessed objectively. We found that typical corneal aberrations of a 60-year-old subject changes the shape of objective through-focus curves of a perfect bifocal lens. This methodology can be used to investigate subjective visual performance for different multifocal contact or intraocular lens designs.