Antonio J. Del Águila-Carrasco

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.

Corneal changes with accommodation using dual Scheimpflug photography.

Purpose To assess whether corneal parameters and aberrations are affected by accommodation. Setting Optics Department, University of Valencia, Valencia, Spain. Design Prospective cross‐sectional study. Methods The Galilei G4 dual Scheimpflug device was used to obtain data on the anterior and posterior axial curvatures, total corneal power (TCP), and corneal pachymetry from 3 corneal zones (central: 0.0 up to 4.0 mm; paracentral or mid: 4.0 up to 7.0 mm; peripheral: 7.0 up to 10.0 mm) in young emmetropic eyes in the unaccommodated and 4 accommodated states (from −1.0 to −4.0 diopters [D] in 1.0 D steps). The 2nd‐, 3rd‐, and 4th‐order aberrations as well as the root mean square (RMS) were also determined for the entire cornea at the same accommodative demands. Results The study evaluated 7 subjects (12 eyes). No significant changes in any measured parameter were found during accommodation for any corneal zone (P > .05). Statistically significant differences were found in the various corneal zones when it was assumed they were constant with accommodation (P < .01). A stable linear trend with accommodation was also found for corneal aberrations, although individual variations existed because of the high standard deviation values. Conclusion Different parameters in various zones of the cornea as well as corneal aberrations were stable during accommodation. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Measurements of anterior chamber depth, white-to-white distance, anterior chamber angle, and pupil diameter using two Scheimpflug imaging devices

PURPOSE To compare the ocular anterior chamber depth, white-to-white distance, anterior chamber angle, and pupil diameter, as measured with two different Scheimpflug imaging devices. METHODS This transversal study included 80 right eyes from 80 subjects aged from 20 to 40 years. Their spherical equivalents ranged from -4.25 to +1.00 diopters (D). Each eyes anterior chamber depth, white-to-white distance, anterior chamber angle, and pupil diameter, were measured for far vision using both the Galilei G4 (double Scheimpflug camera) and the Pentacam HR (single Scheimpflug camera) systems. RESULTS Mean anterior chamber depths were calculated as 3.12 ± 0.23 mm and 3.19 ± 0.24 mm when measured with the Galilei G4 and the Pentacam HR, respectively. The mean white-to-white distance measured was 11.84 ± 0.31 mm and 11.90 ± 0.43 mm when measured with the Galilei G4 and the Pentacam HR, respectively. Mean pupil diameters were measured as 3.22 ± 0.58 mm and 3.22 ± 0.52 mm when measured with the Galilei G4 and the Pentacam HR, respectively. Finally, the mean anterior chamber angle was 34.30 ± 2.86 degrees when it was measured with the Galilei G4, and 39.26 ± 2.85 degrees when measured with the Pentacam HR. A comparative analysis revealed that the Galilei G4 yielded a significantly lower (P<0.05) measurement for the anterior chamber depth, anterior chamber angle, and pupil diameter, than the Pentacam HR system. Comparable values (P>0.05) for both devices were obtained for the white-to-white distance measurements. CONCLUSION The Galilei G4 and Pentacam HR Scheimpflug systems cannot be used interchangeably because they produce significant measurement differences.

Changes in the anterior chamber during accommodation assessed with a Scheimpflug system

Purpose To study changes in the anterior chamber depth (ACD), anterior chamber angle, and pupil diameter with accommodation. Setting University of Valencia, Valencia, Spain. Design Evaluation of diagnostic technology. Methods A rotating Scheimpflug camera (Pentacam HR) was used to measure changes in the ACD, anterior chamber angle, and pupil diameter with accommodation. Peripheral ACD was measured at the corneal center and 2.0 mm away from it in the nasal, superior, temporal, and inferior directions. The anterior chamber angle was computed as the mean anterior chamber angle of the entire eye. All measurements were obtained with accommodation stimuli ranging from +1.0 to −4.0 diopters (D) in 1.0 D steps. Results Eighty subjects (80 eyes) aged 22 to 30 years were evaluated. The ACD did not vary significantly with accommodation in any location. The relative change was 3.67%, 3.65%, 3.67%, 5.66%, and 6.22% in the central, nasal, temporal, superior, and inferior locations, respectively. The central ACD values were significantly higher than the nasal, temporal, superior, and inferior values. The nasal ACD was significantly less than the central, temporal, and inferior ACD. Temporal versus inferior ACD and nasal versus superior ACD yielded similar values. No significant accommodation‐related changes occurred in the anterior chamber angle or pupil diameter. Conclusions Although the ACD and anterior chamber angle remained stable with accommodation, the pupil diameter varied. Regarding location‐dependent ACD variability, the nasal–superior areas were significantly shallower than the temporal–inferior areas. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Human eyes do not need monochromatic aberrations for dynamic accommodation

To determine if human accommodation uses the eyes own monochromatic aberrations to track dynamic accommodative stimuli.

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 patients visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome.

Dynamic accommodation without feedback does not respond to isolated blur cues

&NA; 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 21–40 years were recruited. Four different aberration patterns were used as stimuli to induce blur with (1) the eyes 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 0.2 Hz. Dynamic images were observed through a 0.8 mm pinhole placed at a plane conjugated with the eyes 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. HighlightsA new methodology is used to study a potential cue for dynamic accommodation.We show that human accommodation is not driven correctly by defocus alone.Accommodation is most efficient using changes in stimulus vergence with feedback.

Assessing the in vitro optical quality of presbyopic solutions based on the axial modulation transfer function

Purpose To present a metric for assessing the in vitro optical quality of rotationally symmetrical optical elements based on volume calculation under the surface defined by the axial modulation transfer function (MTF). Setting University of Valencia, Valencia, Spain. Design Experimental study. Methods The metric volume under the axial MTF was used to assess the optical quality of 2 rotationally symmetrical multifocal intraocular lenses (IOLs) within various defocus intervals (0.50 diopter [D], 0.75 D, and 1.00 D) and at various spatial frequency intervals (7.5 cycles per degree [cpd], 15.0 cpd, and 30.0 cpd). Results The far focus of the bifocal IOL yielded higher volume values at all spatial frequencies and defocus intervals than the trifocal IOL. The results for the near focus were similar for both IOLs. In addition, the trifocal IOL provided a distinct focus for intermediate vision. Conclusions The volume under the axial MTF proved to be a useful tool for objective evaluation of multifocal IOLs. Moreover, it can be applied to evaluate the optical quality of every rotationally symmetrical IOL or optical element. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

In vitro optical quality comparison of 2 trifocal intraocular lenses and 1 progressive multifocal intraocular lens

Purpose To evaluate the optical quality of 3 multifocal intraocular lenses (IOLs): the Mini Well Ready progressive multifocal aspheric IOL, the AT LISA trifocal diffractive IOL, and the Finevision full diffractive trifocal IOL. Setting University of Valencia, Valencia, Spain. Design Experimental study. Methods An instrument designed for measuring real‐time modulation transfer function (MTF) and IOL power was used to measure the optical quality of each IOL for 3.0 mm and 4.5 mm apertures. This instrument measures both sagittal and tangential MTFs. The optical quality of each IOL was evaluated with the MTF, through‐focus MTF, defocus tolerance, Strehl ratio MTF, and relative percentage of light in each focus. These metrics were evaluated at best focus for each IOL. Results Through‐focus graphs corresponding to trifocal IOLs showed 3 mean peaks. Nevertheless, the progressive multifocal aspheric IOL showed 2 main areas, 1 corresponding to distance vision focus and the other including both intermediate and near vision foci. Conclusions The results obtained in the present study suggest that the progressive multifocal aspheric IOL might be considered for cataract surgery. Financial Disclosure None of the authors has a financial or proprietary interest in any method or material mentioned.

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.