Method to reduce undesired multiple fundus scattering effects in double-pass systems.

Double-pass systems rely on backscattering of light by the human ocular fundus to assess the optical quality of the eye. In this work, we present a method to reduce double-pass image degradation caused by undesired multiple scattering effects in the eye fundus. The reduction is based on combined data processing of simultaneous measurements using two different configurations: one symmetric with equal entrance and exit pupils and another asymmetric with unequal entrance and exit pupils. Under certain conditions, such scattering effects may be effectively suppressed. Measurements of human eyes show that, although multiple fundus scattering imposes a shift on the estimations, double-pass systems can be used to predict the optical quality of the eye within a population.

Stimulus Unpredictability in Time, Magnitude, and Direction on Accommodation.

SIGNIFICANCE: The effect of predictability in changes of time, magnitude, and direction of the accommodation demand on the accommodation response latency and its magnitude are insignificant, which suggests that repetitive accommodative tasks such as the clinical accommodative facility test may not be influenced by potential anticipation effects. PURPOSE: The purpose of this study was to investigate the effect of stimulus' time, magnitude, and direction predictability, as well as their interactions, on accommodation latency and response magnitude. METHODS: Monocular accommodative response and latency were measured in 12 young subjects for nine different conditions where the stimulus accommodative demand changed several times in a steplike fashion for a period of 120 seconds. Each change in accommodative demand could have different time duration (i.e., 1, 2, or 3 seconds), magnitude (1, 2, or 3 diopters), and/or direction (i.e., accommodation or disaccommodation). All conditions were created permuting the factors of time, magnitude, and direction with two levels each: random and not random. The baseline condition was a step signal from 0 to 2 diopters persisting for 2 seconds in both accommodative demands. After each condition, subjects were asked to provide a score from 1 to 5 in their perceived predictability. RESULTS: Friedman test conducted on the perceived predictability of each condition resulted in statistically significant differences between the nine conditions (χ = 56.57, P < .01). However, repeated-measures analysis of variance applied to latency and accommodative response magnitude did not show significant differences (P > .05). In addition, no correlation was found between the perceived predictability scores and both latency and accommodative response magnitudes between the most predictable and the most unpredictable conditions. CONCLUSIONS: Subjects were able to perceptually notice whether the stimulus was predictable or not, although our results indicate no significant effect of stimuli predictability on either the accommodation latency or its magnitude.

Validation of a gonio-hyperspectral imaging system based on light-emitting diodes for the spectral and colorimetric analysis of automotive coatings.

In this study, a novel gonio-hyperspectral imaging system based on light-emitting diodes for the analysis of automotive coatings was validated colorimetrically and spectrally from 368 to 1309 nm. A total of 30 pearlescent, 30 metallic, and 30 solid real automotive coatings were evaluated with this system, the BYK-mac and X-Rite MA98 gonio-spectrophotometers, and also with the SPECTRO 320 spectrometer for further comparison. The results showed very precise correlations, especially in the visible range. In conclusion, this new system provides a deeper assessment of goniochromatic pigments than current approaches due to the expansion of the spectral range to the infrared.

Effect of Experimental Conditions in the Accommodation Response in Myopia.

SIGNIFICANCE: The accommodative response is more affected by the type of refractive error than the method of stimulation, field of view (FOV), or stimulus depth. PURPOSE: This study aims to analyze the effect of stimulation method, stimulus depth, and FOV on the accommodation response (AR) for emmetropes (EMM), late-onset myopes (LOM), and early-onset myopes (EOM). METHODS: Monocular AR was measured in 26 young observers (n = 9 EMM, n = 8 LOM, n = 9 EOM) under 60 different viewing conditions that were the result of permuting the following factors: (1) stimulation method (free space or Badal lens viewing), (2) stimulus depth (flat or volumetric), (3) FOV (2.5, 4, 8, 10, and 30°), and (4) accommodative stimulus (AS: 0.17, 2.50, and 5.00 diopters [D]). RESULTS: Mixed analysis of variance for 2.50 D of AS resulted in a significant effect of refractive group (F = 6.77, P < .01) and FOV (F = 1.26, P = .04). There was also a significant interaction between stimulus depth and FOV (F = 2.73, P = .03) and among stimulation method, FOV, and refractive group (F = 2.42, P = .02). For AS of 5.00 D, there was a significant effect of refractive group (F = 13.88, P < .01) and stimulation method (F = 5.16, P = .03). There was also a significant interaction of stimulation method, stimulus depth, and refractive group (F = 4.08, P = .03). When controlling for all interactions, LOM showed larger lags than EMM and EOM; the AR did not significantly change for fields of 8, 10, and 30°, and it did not significantly differ for different stimulation methods or stimulus depth. CONCLUSIONS: Previously reported differences in AR when using lens-based methods compared with free space viewing may be explained by the effect of other factors such as the FOV or the depth of the stimulus. Targets with an FOV of 8 or 10° may be optimal for accurate ARs.

Does the Badal optometer stimulate accommodation accurately?

PURPOSE: To study whether the accommodation response to Badal optometer is equivalent to the response for real space targets. METHODS: Accommodative responses were measured for 28 young eyes with the WAM-5500 autorefractometer in eight configurations for 0.17 D, 2.0 D and 5.0 D accommodation stimuli. Parameters that might contribute to differences in response were systematically isolated: stimulation method (real space vs Badal targets), field of view, instrument's cover proximity, the looming effect, and the peripheral interposition of objects in depth. RESULTS: Mean accommodative response differences between a natural view configuration and a configuration with a Badal Optometer were 0.50 ± 0.43 D and 0.58 ± 0.53 D for 2.0 D and 5.0 D stimulation, respectively (p < 0.001), with accommodation lags for the latter condition. Of the isolated parameters that might contribute to these differences, varying the interposition of objects in depth affected accommodation response more markedly. CONCLUSIONS: It is likely that Badal optometers affect accommodation through a combination of some or all of the studied parameters. We conclude that accommodation response to closed-view Badal optometers is not equivalent to real space target response.

Response for light scattered in the ocular fundus from double-pass and Hartmann-Shack estimations.

Double-pass (DP) and Hartmann-Shack (HS) are complementary techniques based on reflections of light in the ocular fundus that may be used to estimate the optical properties of the human eye. Under conventional data processing, both of these assessment modes provide information on aberrations. In addition, DP data contain the effects of scattering. In the ocular fundus, this phenomenon may arise from the interaction of light with not only the retina, but also deeper layers up to which certain wavelengths may penetrate. In this work, we estimate the response of the ocular fundus to incident light by fitting the deviations between DP and HS estimations using an exponential model. In measurements with negligible intraocular scattering, such differences may be related to the lateral spreading of light that occurs in the ocular fundus due to the diffusive properties of the media at the working wavelength. The proposed model was applied in young healthy eyes to evaluate the performance of scattering in such a population. Besides giving a parameter with information on the ocular fundus, the model contributes to the understanding of the differences between DP and HS estimations.

Repeatability of aberrometric measurements with a new instrument for vision analysis based on adaptive optics.

PURPOSE: To evaluate intersession and intrasession repeatability of aberration data obtained with a new visual simulator based on adaptive optics, which includes a Hartmann-Shack aberrometer (Adaptive Optics Vision Analyzer; Voptica S.L., Murcia, Spain). METHODS: Thirty-one healthy right eyes were included in the study. To evaluate intrasession repeatability, three consecutive measurements without repositioning the patient or realigning the eye were obtained. Intersession repeatability was evaluated in three sessions. Aberrometric data computed from the second to the fifth order for a 4-mm pupil were used. Statistical analysis included the repeated measures analysis of variance (or the Wilcoxon signed rank test), the coefficient of repeatability, the Bland-Altman method, and the intraclass correlation coefficient. RESULTS: No significant differences in the intrasession and intersession repeatability analysis for any of the parameters (P > .05) were found, suggesting a consistent variability of the instrument over time. Similar coefficient of repeatability values were obtained in the three sessions. The Bland-Altman analysis confirmed differences close to zero and the variations were independent of the mean within and between sessions. The intersession intraclass correlation coefficient values were generally above 0.75, suggesting moderate to high repeatability. However, some exceptions were found in the intrasession analysis. CONCLUSIONS: The findings suggest that the new instrument provides consistent and repeatable aberrometric data. It is therefore a suitable tool to perform consistent and repeatable visual simulations.

Binocular open-view system to perform estimations of aberrations and scattering in the human eye.

We present a system that integrates a double-pass (DP) instrument and a Hartmann-Shack (HS) wavefront sensor to provide information not only on aberrations, but also on the scattering that occurs in the human eye. A binocular open-view design permits evaluations to be made under normal viewing conditions. Furthermore, the system is able to compensate for both the spherical and astigmatic refractive errors that occur during measurements by using devices with configurable optical power. The DP and HS techniques provide comparable data after estimating wavefront slopes with respect to the intersections of an ideal grid and compensating for residual errors caused by the optical defects of the measuring system. Once comparable data is obtained, it is possible to use this combined manner of assessment to provide information on scattering. Measurements in an artificial eye suggest that the characteristics of the ocular fundus may induce deviations of DP with respect to the HS data. These differences were quantified in terms of the modulation transfer function in young, healthy eyes measured in infrared light to demonstrate the potential use of the system in visual optics studies.

Comparing Autorefractors for Measurement of Accommodation.

PURPOSE: To compare the static and dynamic accommodative responses measured with the WAM-5500 and the PowerRef-II autorefractors. METHODS: The dynamic and static monocular accommodative responses were measured with the WAM-5500 and the PowerRef-II instruments in 30 pre-presbyopic patients (23.66 [±3.19] years). The spherical equivalent was measured at 0.00, 2.50, and 5.00 diopters (D) of accommodative stimulation for the static measurements. The subjective refraction was also determined. Dynamic accommodation was measured for abrupt changes of stimulus vergence of 2.00 D. Mean and peak velocities of accommodation and disaccommodation were evaluated. For the PowerRef-II, dynamic measurements were calculated for sampling frequencies of 5 and 25 Hz. RESULTS: For far distance static results, the differences between subjective and WAM-5500 measurements were 0.07 (±0.21) D (p = 0.093) and those between subjective and PowerRef-II measurements were 0.70 (±0.47) D (p = 0.001). The difference in the response measured with both instruments was 0.08 (±0.32) D (p = 0.194) for 2.50 D and -0.32 (±0.48) D (p = 0.001) for 5.00 D of stimulation. For the dynamic mode, the PowerRef-II at 25 Hz measured faster mean and peak velocities of accommodation and disaccommodation than the WAM-5500, with statistically significant (p < 0.05) differences of 0.68 (±1.01), 0.67 (±0.98), 1.26 (±1.19), and 1.42 (±1.53) D/s, respectively. With a sampling frequency of 5 Hz for the PowerRef-II, these differences, which were statistically significant (p < 0.05), were reduced to 0.52 (±0.90), 0.49 (±0.91), 0.83 (±1.07), and 0.83 (±1.31) D/s, respectively. CONCLUSIONS: There is good agreement between subjective refraction and WAM-5500 measurements. In contrast, the PowerRef-II produced more hyperopic results. There were no differences among instruments at 2.50 D of static stimulation; however, differences were found at 5.00 D. In the dynamic measurements, the PowerRef-II measured faster velocities, partly attributed to the difference in the sampling frequency.

Portable multispectral imaging system based on light-emitting diodes for spectral recovery from 370 to 1630 nm.

To expand and investigate the potential of spectral imaging, we developed a portable multispectral system using light-emitting diodes. This system recovers spectral information from the UV to the near IR over a large area using two different image sensors synchronized with 23 bands of illumination. The system was assessed for spectral reconstruction through simulations and experimental measurements by means of two methods of spectral reconstruction and three different evaluation metrics. The results over a Macbeth ColorChecker chart and other samples, including pigments usually employed in art paintings, are compared and discussed. The portable multispectral system using LEDs constitutes a cost-effective and versatile method for spectral imaging.

Age-related changes in accommodation measured with a double-pass system.

PURPOSE: To measure the accommodative response in a wide age range population using the retinal image quality assessments provided by a double-pass system. METHODS: The accommodative response was measured using a custom-built double-pass setup in 84 patients from 15 to 55 years of age. Patients were classified in four groups (A: 15-25 year old; B: 26-35; C: 36-45; D: 46-55). Accommodation was stimulated from 0 to 5 dioptres (D) with the push up method using an open field fixation test. The total accommodative response in the stimulated range, the accommodative stimulus-response curve, the slope and the progression of optical quality with accommodation were measured. RESULTS: The total accommodation obtained in groups A and B was high, with a mean value of 4 D or higher, whereas values in older individuals were significantly lower. The accommodative stimulus-response curve and the slope were also high with a sudden decrease in patients over 35 years of age. The optical quality of the eye during accommodation did not change significantly. CONCLUSIONS: Participants aged 15-35 years showed a good accommodative response. Thereafter, a significant decrease of the response in the total accommodation, stimulus response curve and slope was observed. The younger groups showed a larger accommodative response than previously published.

Feasibility of measuring fusional vergence amplitudes objectively.

Two tests to measure fusional vergence amplitudes objectively were developed and validated against the two conventional clinical tests. Forty-nine adults participated in the study. Participants' negative (BI, base in) and positive (BO, base out) fusional vergence amplitudes at near were measured objectively in an haploscopic set-up by recording eye movements with an EyeLink 1000 Plus (SR Research). Stimulus disparity changed in steps or smoothly mimicking a prim bar and a Risley prism, respectively. Break and recovery points were determined offline using a custom Matlab algorithm for the analysis of eye movements. Fusional vergence amplitudes were also measured with two clinical tests using a Risley prism and a prism bar. A better agreement between tests was found for the measurement of BI than for BO fusional vergence amplitudes. The means ± SD of the differences between the BI break and recovery points measured with the two objective tests were -1.74 ± 3.35 PD and -1.97 ± 2.60 PD, respectively, which were comparable to those obtained for the subjective tests. For the BO break and recovery points, although the means of the differences between the two objective tests were small, high variability between subjects was found (0.31 ± 6.44 PD and -2.84 ± 7.01 PD, respectively). This study showed the feasibility to measure fusional vergence amplitudes objectively and overcome limitations of the conventional subjective tests. However, these tests cannot be used interchangeably due to their poor agreement.

Influence of power and the time of application of fogging lenses on accommodation.

Fogging is a non-invasive technique based on the use of positive spherical power lenses to relax accommodation during refraction that is commonly used as an alternative to cycloplegic drugs. Although the mechanism of the fogging technique has been described, some aspects of its methodology remain unclear. The main purpose of this work was to determine which lens power and time of application are more suitable for achieving a successful relaxation of accommodation by analyzing the changes in accommodation when fogging lenses of different powers were placed in front of the participants' eye for a certain timespan. The results of this analysis showed, in general, that low-power lenses and timespans of less than half a minute provided the highest relaxation of accommodation. However, high inter-subject variability was found in the two variables (power and time).

Comparison between an objective and a psychophysical method for the evaluation of intraocular light scattering.

In this study we present the comparison of the performance of two systems to measure intraocular scattering. Measurements were made by using a psychophysical system based on a brightness comparison method that provides a glare index and a physical system based on the double-pass technique, which gives an objective scatter index by measuring the optical quality of the eye. Three external diffuser filters that simulated different grades of intraocular scattering were used in subjects with normal vision. The two measured indexes showed a graded rise with increasing level of scattering. The discrimination ability obtained for both systems showed that they were able to distinguish among conditions ranging from normal to early cataracts.

Reflectance evaluation of eye fundus structures with a visible and near-infrared multispectral camera.

We examined the spectral reflectance of fundus structures in the visible and near-infrared (400-1300 nm) range for contributing to the medical diagnosis of fundus diseases. Spectral images of healthy eye fundus and other ocular diseases were acquired using a novel multispectral fundus camera. Reflectance metrics were computed based on contrast to analyze the spectral features. Significant differences were observed among the structures in healthy and diseased eye fundus. Specifically, near-infrared analysis allows imaging of deeper layers, such as the choroid, which, to date, has not been retrieved using traditional color fundus cameras. Pathological structures, which were hardly observable in color fundus images owing to metamerism, were also revealed by the developed multispectral fundus camera.

Implementation of the Frequency Scatter Index in Clinical Commercially Available Double-pass Systems.

A previous work has reported a methodology to quantify intraocular scattering using a high sensitivity double-pass instrument with a robust index, the frequency scatter index. The purpose of our study was to evaluate an adaptation of the frequency scatter index for use in clinical double-pass systems. A prospective observational study was carried out in a group of patients with nuclear cataracts (n = 52) and in a control group (n = 11) using conventional double-pass systems. The frequency scatter index and the objective scatter index were used to assess the scattering. The Spearman coefficient was calculated to assess the correlation between both indexes, obtained from the double-pass images. Simultaneous measurements were performed with a double-pass and with a Hartmann-Shack wavefront sensor in the control group. The root-mean-square wavefront error and the full width at half maximum of the double-pass image were used to quantify the residual aberrations introduced by the variations in pupil size and retinal eccentricity. Measurement in eyes with different grades of cataracts shows a strong correlation (ρ = 0.929, p < .0001) between the frequency scatter index and the objective scatter index. A certain degree of correlation was observed between the objective scatter index and the root-mean-square and between the objective scatter index and the full width at half maximum, both for measurements with a different pupillary diameter and with a different retinal eccentricity (p < .05). No relationship was observed between the frequency scatter index and the root-mean-square or between the frequency scatter index and the full width at half maximum (p > .05). We have introduced and evaluated an adaptation of a methodology proposed recently for the measurement of intraocular scattering using the double-pass technique with a robust index, which is less affected by ocular aberrations. The frequency scatter index can be applied to conventional double-pass instruments available in clinical environments.

Characteristics of saccades during the near point of convergence test.

The near point of convergence test is widely used to evaluate binocular vision. It assesses the ability of the eyes to converge at short distances. Although the test consists of a pure symmetrical vergence task, small involuntary saccades occur concurrently. The main goal of this study was to analyze saccadic characteristics as a function of vergence demand when testing the near point of convergence. To this purpose, the eye movements of 11 participants were registered with an eye-tracker while they performed the near point of convergence test by following a target that traveled forward and backward on a motorized bench. Saccade amplitude increased and, on average, saccade rate decreased with vergence demand. In general, the direction of the concurrent vergence movement had no significant effect on saccade characteristics. However, each individual subject showed idiosyncratic behavior. Most saccades tended to be corrective in terms of both binocular disparity and individual fixation position errors. In particular, most participants tended to correct the fixation position error of the dominant eye.

Whole anterior segment and retinal swept source OCT for comprehensive ocular screening.

Whole eye visualization and morphometry are of high relevance in clinical practice. However, most standard ophthalmic OCT instruments are dedicated either to retinal or to anterior segment imaging. We demonstrate a swept source optical coherence tomography system (SS-OCT) that images both the whole anterior segment and the retina alternately using a single source and detector. A pilot population was imaged with the proof of concept prototype. We demonstrate the clinical potential of whole eye OCT screening for the description and early detection of relevant clinical features in the anterior segment and retina of several patients.

Intra- and intersession repeatability of a double-pass instrument.

PURPOSE: To evaluate the intra- and intersession repeatability of the optical quality parameters provided by the Optical Quality Analysis System (OQAS), which is based on the double-pass technique. METHODS: We performed optical quality measurements using the OQAS on 20 eyes of 10 healthy subjects who had best spectacle-corrected visual acuity of 20/20 or better. Measurements were performed by the same examiner in three different sessions that were separated by 10-min intervals. The subject's eye was realigned at the beginning of each session. During each session, three consecutive measurements were taken without realignment. The following optical quality parameters were analyzed: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl ratio, the OQAS values (OV) at contrasts of 100%, 20%, and 9%, and the objective scatter index (OSI). RESULTS: The mean coefficients of repeatability obtained for the first session were 4.51 (MTFcutoff), 0.049 (Strehl ratio), 0.15 (OV 100%), 0.21 (OV 20%), 0.28 (OV 9%), and 0.11 (OSI), which were similar to those found in the second and third sessions. The confidence limits in the Bland and Altman charts when the intrasession repeatability was assessed (in a comparison of the first and second measurements of the first session) ranged from -3.16 to 3.94 (MTFcutoff), -0.060 to 0.069 (Strehl ratio), -0.12 to 0.18 (OV 100%), -0.20 to 0.23 (OV 20%), -0.29 to 0.27 (OV 9%), and -0.12 to 0.13 (OSI). The same limits when the intersession repeatability was assessed (in a comparison of the first and second sessions) ranged from -5.30 to 5.49 (MTFcutoff), -0.054 to 0.050 (Strehl ratio), -0.17 to 0.17 (OV 100%), -0.22 to 0.19 (OV 20%), -0.26 to 0.29 (OV 9%), and -0.12 to 0.13 (OSI). CONCLUSIONS: Our findings showed that OQAS is a clinical instrument with a good intra- and intersession repeatability and that the realignment of the eye does not introduce any additional variability in the measurements.

Optical quality one month after verisyse and Veriflex phakic IOL implantation and Zeiss MEL 80 LASIK for myopia from 5.00 to 16.50 diopters.

PURPOSE: To evaluate the eye's optical quality after phakic intraocular lens (IOL) implantation and LASIK for moderate to high myopia. METHODS: The retinal image quality of 45 patients was evaluated after undergoing one of three surgical procedures (9 patients with Verisyse IOL [AMO] implants, 11 patients with Veriflex IOL [AMO] implants, and 25 patients who underwent LASIK). Patients were aged <40 years, had at least 5.00 diopters of myopia, and had preoperative best spectacle-corrected visual acuity and postoperative uncorrected visual acuity better than 20/30. The eye's optical quality was measured using the Optical Quality Analysis System (OQAS, Visiometrics S.L.), which is an instrument based on the double-pass technique. Measurements were performed before surgery and 1 day and 1 month after surgery. RESULTS: Optical quality worsened noticeably 1 day after surgery with the Verisyse IOL with a 50% to 60% loss, most likely due to the large incision and the presence of sutures in most eyes. The LASIK technique and Veriflex IOL implant did not cause as remarkable a decrease in optical quality (20% to 25% loss). One month after surgery, the optical quality of patients with IOL implants was high, although some surgically induced astigmatism remained, especially in the Verisyse patients. Conversely, LASIK patients had slightly lower optical quality, with optical parameters that represented 90% of their initial value. CONCLUSIONS: Verisyse and Veriflex phakic IOL implantation and LASIK are both safe and effective in correcting moderate to high myopia, but they involve different processes of optical quality recovery. One day after surgery, the Verisyse IOL implantation significantly reduced the eye's optical quality, mainly due to the larger incision required and the higher number of sutures used. This reduction was not as remarkable with the other two techniques. However, 1 month after surgery, patients with IOL implants recovered more optical quality than LASIK patients.