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PurposePersonal mobile devices such as smartphones are proving their usefulness in ever more applications in tele-eyecare. An inconvenience and potential source of error in these past approaches stemmed from the requirement for the subjects to situate their devices at a distance. The present study aims to clinically validate best corrected visual acuity (BCVA) measures carried out by a novel smartphone application "vision.app" (VisionApp Solutions S.L.) using comparative statistics against clinical measurements.Materials and methodsBCVA was measured in both eyes of 40 subjects using vision.app which displayed a black Landolt-C optotype with crowding on a white background, and utilized a 4 forced-choice procedure for the subjects to find (by means of swiping in either of four directions) the smallest optotype size they could resolve. Results were compared to BCVA measurements taken using a standard Snellen chart placed at 20 feet (6 m).ResultsThe t-test revealed no significant differences between the app- and clinically-measured VA (p = 0.478 (OD) and 0.608 (OS)), with a mean difference between clinical and app measurements of less than one line of the eye chart (-0.009 logMAR (OD) and -0.005 logMAR (OS)). A limit of agreement for a 95% confidence interval of ± 0.08 logMAR for OD and OS was found.ConclusionsThe results show the potential use of a smartphone to measure BCVA at a handheld distance. The newly validated study results can hold major future advancements in tele-eyecare and provide eye care professionals with a reliable and accessible method to measure BCVA.

INTRODUCTION: A periodical self-monitoring of spherical refraction using smartphones may potentially allow a quicker intervention by eye care professionals to reduce myopia progression. Unfortunately, at low levels of myopia, the far point (FP) can be located far away from the eye which can make interactions with the device difficult. To partially remedy this issue, a novel method is proposed and tested wherein the longitudinal chromatic aberration (LCA) of blue light is leveraged to optically bring the FP closer to the eye. METHODS: Firstly, LCA was obtained by measuring spherical refraction subjectively using blue pixels in stimuli shown on organic light-emitting diode (OLED) screens and also grey stimuli with matching luminance. Secondly, the visual acuity (VA) measured with a smartphone located at 1.0 m and 1.5 m and displaying blue optotypes was compared with that obtained clinically standard measurements. Finally, the spherical over refraction obtained in blue light with a smartphone was compared with clinical over-refraction with black and white (B&W) optotypes placed at 6 m. RESULTS: Mean LCA of blue OLED smartphone screens was -0.67 ± 0.11 D. No significant differences (p > 0.05) were found between the VA measured with blue optotypes on a smartphone screen and an eye chart. Mean difference between spherical over-refraction measured subjectively by experienced subjects with smartphones and the one obtained clinically was 0.08 ± 0.34 D. CONCLUSIONS: Smartphones using blue light can be used as a tool to detect changes in visual acuity and spherical refraction and facilitate monitoring of myopia progression.

Monocular polyplopia (ghost or multiple images) is a serious visual impediment for some people who report seeing two (diplopia), three (triplopia) or even more images. Polyplopia is expected to appear if the point spread function (PSF) has multiple intensity cores (a dense concentration of a large portion of the radiant flux contained in the PSF) relatively separated from each other, each of which contributes to a distinct image. We present a theory that assigns these multiple PSF cores to specific features of aberrated wavefronts, thereby accounting optically for the perceptual phenomenon of monocular polyplopia. The theory provides two major conclusions. First, the most likely event giving rise to multiple PSF cores is the presence of hyperbolic, or less probably elliptical, umbilic caustics (using the terminology of catastrophe optics). Second, those umbilic caustics formed on the retinal surface are associated with certain points of the wave aberration function, called cusps of Gauss, where the gradient of a curvature function vanishes. However, not all cusps of Gauss generate those umbilic caustics. We also provide necessary conditions for those cusps of Gauss to be fertile. To show the potential of this theoretical framework for understanding the nature and origin of polyplopia, we provide specific examples of ocular wave aberration functions that induce diplopia and triplopia. The polyplopia effects in these examples are illustrated by depicting the multi-core PSFs and the convolved retinal images for clinical letter charts, both through computer simulations and through experimental recording using an adaptive optics set-up. The number and location of cores in the PSF is thus a potentially useful metric for the existence and severity of polyplopia in spatial vision. These examples also help explain why physiological pupil constriction might reduce the incidence of ghosting and multiple images of daily objects that affect vision with dilated pupils. This mecha

PURPOSE: Multifocal contact lenses have been growing in popularity as a modality to correct presbyopic eyes, although visual side effects such as disability glare have been reported. The objective of this study was to investigate the effect of multifocal contact lenses on disability glare by means of ocular straylight.METHODS: A prospective randomized, comparative study was performed that included 16 subjects free of ocular pathology. Straylight was measured using a commercial straylight meter with the natural and dilated pupil. Participants were fitted with Proclear Multifocal (Distance/Near), ACUVUE Oasys for Presbyopia, and Air Optix Aqua Multifocal randomized to the left or right eye. Straylight measurements were repeated with the contact lens in situ after the pupil dilation. Results obtained with the dilated pupil without contact lens acted as a control.RESULTS: Diameter of the natural and dilated pupil was 2.87 ± 0.40 mm and 7.45 ± 0.86 mm, respectively (P < .001). After pupil dilation, straylight increased from 0.92 ± 0.13 log(s) to 1.04 ± 0.11 log(s) (P < .001). Of the four studied lenses, a significant difference was only found between Air Optix and the control group (P = .006). The latter showed also slightly increased light scatter.CONCLUSIONS: A difference in measured straylight was found between the studied multifocal lenses. The observed variability and the straylight-pupil size dependency should be taken into account to avoid elevated straylight in multifocal contact lens wearers. The reason for the observed differences in straylight must be the subject of future studies.

A psychophysical approach has been designed to measure straylight from intraocular lenses (IOLs) in vitro. This approach uses a clinical straylight meter (C-Quant) and an observer's eye as optical detector. Based on this, we introduced a method for study of straylight-wavelength dependency for IOLs. This dependency can be used to distinguish between 2 types of scattering particles (small and large) as defined by Mie theory. Validation was performed using a turbidity standard and scattering filters. Several IOLs were analyzed to identify potential scattering sources. Large particles were found to predominate in scattering from the studied lenses. This was confirmed by straylight-angular dependency found in these IOLs.

A psychophysical approach has been designed to measure straylight from intraocular lenses (IOLs) in vitro. This approach uses a clinical straylight meter (C-Quant) and an observer's eye as optical detector. Based on this, we introduced a method for study of straylight-wavelength dependency for IOLs. This dependency can be used to distinguish between 2 types of scattering particles (small and large) as defined by Mie theory. Validation was performed using a turbidity standard and scattering filters. Several IOLs were analyzed to identify potential scattering sources. Large particles were found to predominate in scattering from the studied lenses. This was confirmed by straylight-angular dependency found in these IOLs.

PURPOSE: Multifocal contact lenses have been growing in popularity as a modality to correct presbyopic eyes, although visual side effects such as disability glare have been reported. The objective of this study was to investigate the effect of multifocal contact lenses on disability glare by means of ocular straylight.METHODS: A prospective randomized, comparative study was performed that included 16 subjects free of ocular pathology. Straylight was measured using a commercial straylight meter with the natural and dilated pupil. Participants were fitted with Proclear Multifocal (Distance/Near), ACUVUE Oasys for Presbyopia, and Air Optix Aqua Multifocal randomized to the left or right eye. Straylight measurements were repeated with the contact lens in situ after the pupil dilation. Results obtained with the dilated pupil without contact lens acted as a control.RESULTS: Diameter of the natural and dilated pupil was 2.87 ± 0.40 mm and 7.45 ± 0.86 mm, respectively (P < .001). After pupil dilation, straylight increased from 0.92 ± 0.13 log(s) to 1.04 ± 0.11 log(s) (P < .001). Of the four studied lenses, a significant difference was only found between Air Optix and the control group (P = .006). The latter showed also slightly increased light scatter.CONCLUSIONS: A difference in measured straylight was found between the studied multifocal lenses. The observed variability and the straylight-pupil size dependency should be taken into account to avoid elevated straylight in multifocal contact lens wearers. The reason for the observed differences in straylight must be the subject of future studies.

Human crystalline lens has a layered, shell-like structure with the refractive index increasing from cortex to nucleus (gradient index or GRIN structure). Moreover, every iso-indicial layer has a certain curvature which also varies from cortex to nucleus, with a gradient of curvature (G). In the present manuscript, the role of G on the lens power is investigated along with its implications regarding the lens paradox (change of lens power with age) and intra-capsular accommodation mechanism (larger than expected changes of lens power during accommodation compared to a homogenous lens). To this end, a simplified formulation of paraxial lens power based on thin lens approximation is developed and applied to the anterior and posterior parts of the lens. The main theoretical result is that the power of both anterior and posterior lens is given by the sum of the power of a lens with a homogeneous refractive index equal to that of the nucleus and power associated with the contribution of the internal GRIN structure, which depends on G. This general result suggests that the sign of G is fundamental in increasing or decreasing the lens power. We found that the curvature gradient has a strong impact on lens power, helping to explain both the lens paradox and intra-capsular accommodation mechanism.

We evaluated the possible effect of orthokeratology on accommodative response. Using optical modelling we computed the negative half of the depth-of-field (DoFi) for the range of target vengeances from –1.00 D to –3.00 D, of two eye models designed to mimic the levels of primary and secondary spherical aberration found in 24 patients before and after undergoing orthokeratology (ortho-k). Five trained observers were subjected to a resolution task to identify the negative threshold of the depth-of-field of these model eyes by viewing a set of computed images representative of the model eyes trough focus retinal image quality for five target vengeances (TV), from –1.00 to – 3.00 D. The differences in the DoFi estimated by the five observers were maximum for a –3.00 D TV (0.21 D), with the post ortho-k model presenting a higher DoFi compared to the pre ortho-k model. Differences were consistent for all five observers and all TV’s. In conclusion, the increase in spherical aberration after ortho-k seems to contribute to a small increase in the DoFi. Although small, the benefits might be sufficient to improve retinal image quality in eyes with high accommodative lag.

A method to analyse the effect of the curvature gradient of the internal structure of the lens on the lens power was developed and validated. This method was then applied to estimate the impact of the curvature gradient of the iso-indicial surfaces on both the power and accommodation of the crystalline lens.

The goal of this work was to objectively characterize the external morphology, topography, and optics of the cornea after orthokeratology (ortho-k). A number of 24 patients between the ages of 17 and 30 years (median=24 yearsmedian=24 years) were fitted with Corneal Refractive Therapy® contact lenses to correct myopia between −2.00−2.00 and −5.00−5.00 diopters (D) (median=−3.41 Dmedian=−3.41 D). A classification algorithm was applied to conduct an automatic segmentation based on the mean local curvature. As a result, three zones (optical zone, transition zone, and peripheral zone) were delimited. Topographical analysis was provided through global and zonal fit to a general ellipsoid. Ray trace on partially customized eye models provided wave aberrations and retinal image quality. Monozone topographic description of the ortho-k cornea loses accuracy when compared with zonal description. Primary (C04C40) and secondary (C06C60) spherical aberration (SA) coefficients for a 5-mm pupil increased 3.68 and 19 times, respectively, after the treatments. The OZ area showed a strong correlation with C04C40 (r=−0.49r=−0.49, p<0.05p<0.05) and a very strong correlation with C06C60 (r=0.78r=0.78, p<0.01p<0.01). The OZ, as well as the TZ, areas did not correlate with baseline refraction. The increase in the eye’s positive SA after ortho-k is the major factor responsible for the decreased retinal optical quality of the unaccommodated eye.

Ocular straylight has been measured by means of psychophysical methods over the years. This approach gives a functional parameter yielding a straight comparison with optically defined light scattering, and the point-spread-function. This is of particular importance when the effect of intraocular lenses (IOLs) on postoperative straylight is sought. An optical system for straylight measurements of IOLs was adapted to a commercial device (C-Quant, Oculus), which employs such psychophysical method. The proposed modifications were validated using light-scattering filters and some sample IOLs. The measurements were performed by 3 observers to prove that results are independent from straylight of the eye. Other applications will be discussed.

Ocular straylight has been measured by means of psychophysical methods over the years. This approach gives a functional parameter yielding a straight comparison with optically defined light scattering, and the point-spread-function. This is of particular importance when the effect of intraocular lenses (IOLs) on postoperative straylight is sought. An optical system for straylight measurements of IOLs was adapted to a commercial device (C-Quant, Oculus), which employs such psychophysical method. The proposed modifications were validated using light-scattering filters and some sample IOLs. The measurements were performed by 3 observers to prove that results are independent from straylight of the eye. Other applications will be discussed.

[Puropse]: In some eyes, aberrometric measurements of the refractive error can differ by more than 1 diopter from standard subjective refraction. We aim to understand the reasons for these discrepancies and to study the role of both amplitude (irregular or inhomogeneous pupil transmission) and phase (aberrations) of the wavefront. [Methods]: The spherical equivalent was measured by different subjective, objective, and aberrometric methods in a population of 177 eyes. We first analyzed the degree of correlation between the outcomes of the different methods. Then we analyzed cases showing the highest discrepancies (>1 diopter) between subjective and aberrometric spherical equivalent. The refractive error sensing method was generalized and applied here to include the effect of inhomogeneous pupil transmittance (Stiles-Crawford effect) and irregular pupil shapes on refractive error. [Results]: Objective and aberrometric methods showed a strong correlation with subjective methods (R2 > 0.89 in all cases). However, individual data points may show large discrepancies. Several eyes with discrepancies of 1 D or even 2 D usually presented higher values of higher-order aberration (mainly coma and/or spherical aberration) than average, which may cause these eyes to have a natural bifocal (or even multifocal) optical performance. Refractive error sensing analysis suggests that this multifocal performance could explain the high objective-subjective discrepancies found in these eyes. Nevertheless, the Stiles-Crawford effect (or irregular pupils) can substantially modify the energy distribution, tending to minimize multifocal effects, thus minimizing discrepancies between aberrometric and subjective refraction. [Conclusions]: Discrepancies between aberrometric and subjective refraction may appear in aberrated eyes when aberrometric methods ignore the impact of the wavefront amplitude (inhomogeneous or irregular pupil transmittance.) The generalized refractive error sensing proposed

Several examples of eyes with multifocal wavefronts are analyzed by comparing subjective and aberrometric refraction. These multifo-cal eyes are analyzed using a generalized refractive error sensing method. Our results suggest an important effect on the refraction caused by inhomogeneous pupil transmittance (SCE or vignetting.). [Introduction]: In some eyes subjective refraction may differ more than 1 D from objective refraction obtained by aberrometry or autorrefracto-metry. Usually these eyes present wavefront errors larger than ave-rage (in particular coma and/or spherical aberration). Here, our goal was to assess the hypothesis that these important discrepancies in these highly aberrated eyes might be explained by their multifocal properties. In normal eyes, the prevalence of these cases is not high. We identified 8 out of 178 eyes (~5%) from a previous study. However the prevalence in post-surgical eyes is expected to be much higher. The analysis was based on refractive error sensing, which was generalized to account for multifocal wavefronts, as well as to include the effect of possible irregular and/or non-uniform transmission pupils (Stiles-Crawford effect, etc.)., [Discussion]: The study was focused on the above mentioned 8 eyes, which sho-wed differences greater than 1 D between subjective and objective equivalent sphere, Se. Se was obtained subjectively by standard subjective refraction and also by a more precise custom Badal system. For the objective refraction we used retinoscopy, autorefracto-meter (Canon T1000) and aberrometer (irx3, Imagine Eyes). In what follows we present one example of bifocal eye, which showed the maximum discrepancy of nearly 2.5 D between subjective and ob-jective refraction. This case is especially interesting, since there are two different possible explanations for such a large difference. The left panel of Fig. 1 shows the distribution of equivalent sphere across a 4.9 mm pupil diameter, showing values ranging from -5 to -9 D. The right panel shows the frequency histogram of that distribution under three hypothetical situations. Red line corresponds to the histogram of the plain aberrometric measure which implicitly assumes a perfect circular pupil with uniform transmission. This histogram shows two peaks separated by more than 2.5 D, which is indicative of a bifocal wavefront. Nevertheless, the peak on the right is domi-nant as it shows Se = -5.8 D. The blue histogram simulates the effect of pupil vignetting by the upper eye lid. This simulation was inclu-ded, since this phenomenon was actually observed in this subject. For that purpose we assumed that the area of the pupil above the das-hed line was blocked by the eye lid. The resulting (blue) histogram is totally different, now showing a single peak, which is much closer to the value of the subjective refraction (Se=-8.2 D). The green histogram represents a second possible explanation. It was computed by weighting the data points according to the Stiles-Crawford effect (SCE). Here we used standard nominal values, ex-cept for the fact that we shifted the SCE peak downwards (its positi-on is indicated by the cross on the left panel.). As expe, [Conclusions]: A small percentage of normal eyes show bifocal wavefronts, with power differences greater than 1 D (or even 2.5 D in some cases), which are typically associated to high values of HOA. These bifocal eyes often show important discrepancies between subjective and objective refraction. Our results suggest that these discrepancies may appear because aberrometric methods ignore the inhomogene-ous effective pupil transmittance. The generalization of refractive error sensing proposed here seems suitable to obtain the refraction in these multifocal eyes. It may be especially relevant for postsurgi-cal eyes, which often present high levels of HOA, and hence may show multifocal wavefronts.

Photopolymers are considered today one of the most promising recording materials for holographyc because with them it is possible to achieve high diffraction efficiencies and low signal-to-noise ratios, while working in real time. Moreover, they are self-developing materials. In this paper we propose a non-linear model that, using the accepted mechanism of most photopolymerization reactions as a starting point, justifies the non-linear response of the diffraction efficiency curve, when these recording materials are analysed in real time.

Photopolymers are considered today one of the most promising recording materials for holographyc because with them it is possible to achieve high diffraction efficiencies and low signal-to-noise ratios, while working in real time. Moreover, they are self-developing materials. In this paper we propose a non-linear model that, using the accepted mechanism of most photopolymerization reactions as a starting point, justifies the non-linear response of the diffraction efficiency curve, when these recording materials are analysed in real time.