Evaluation of objective and subjective binocular ocular refraction with looking in type.

BACKGROUND: This study aimed to compare the results of the Chronos binocular/monocular refraction system, that measures objective and subjective ocular refraction in one unit, to objective findings obtained from a conventional autorefractometer and a conventional subjective ocular refraction using a trial-frame in real space. METHODS: Twenty-eight healthy volunteers (21.2 ± 1.5 years old) were included in this study. Objective ocular refraction was measured using two tests: the Chronos binocular/monocular refraction system under binocular conditions and a conventional autorefractometer under monocular conditions. Subjective ocular refraction was measured using three tests: Chronos binocular/monocular refraction system under binocular, monocular conditions, and trial-frame in the real space under monocular conditions. The measurement distance was set to 5.0 m for each test. All ocular refractions were converted into spherical equivalents (SEs). RESULTS: The objective SE was significantly more negative with Chronos binocular/monocular refraction system under binocular condition (- 4.08 ± 2.76 D) than with the conventional autorefractometer under monocular condition (- 3.85 ± 2.66 D) (P = 0.002). Although, the subjective SE was significantly more negative with Chronos binocular/monocular refraction system under binocular condition (- 3.55 ± 2.67 D) than with the trial-frame in the real space under monocular condition (- 3.33 ± 2.75 D) (P = 0.002), Chronos binocular/monocular refraction system under monocular condition (- 3.17 ± 2.57 D) was not significantly different from that in trial-frame in real space under monocular condition (P = 0.33). CONCLUSION: These findings suggest that the Chronos binocular/monocular refraction system, which can complete both objective and subjective ocular refraction tests in a single unit, is suitable for screening ocular refraction, although it produces slightly more myopic results. Furthermore, subjective ocular refraction testing accuracy in Chronos binocular/monocular refraction system can be equivalent to trial-frame in real-space testing by switching from binocular to monocular condition.

Objective evaluation of visual fatigue in patients with intermittent exotropia.

PURPOSE: The purpose of this study was to evaluate the degree of visual fatigue in patients with intermittent exotropia (IXT) using the binocular fusion maintenance (BFM) test. METHODS: Fourteen patients with IXT (32.1 ± 16.4 years) and 15 age-matched healthy volunteers (31.2 ± 9.3 years) participated in the study. BFM was assessed by measuring the transmittance of liquid crystals placed in front of the subject's nondominant eye at the instance when binocular fusion was broken and vergence eye movement was induced. A questionnaire on subjective symptoms was administered to the subjects before and after the visual task. The visual task consisted of a reciprocal movement between 67 and 40 cm. RESULTS: The change [post-pre] of BFM was significantly lower in the IXT group (-0.185 ± 0.187) than in the control group (-0.030 ± 0.070) (P = 0.010). The change of total subjective eye symptom score was significantly greater in the IXT group (2.28 ± 1.43) than in the control group (0.93 ± 1.27) (P = 0.018). The reduction in BFM rate with increasing total subjective eye symptom score was significantly greater in the IXT group (-0.106 ± 0.017) than in the control group (-0.030 ± 0.013) (P = 0.006). CONCLUSION: The present findings objectively showed that patients with IXT are at a greater risk of visual fatigue in comparison with healthy individuals.

Comparison of visual fatigue caused by head-mounted display for virtual reality and two-dimensional display using objective and subjective evaluation.

This study aimed to evaluate objective and subjective visual fatigue experienced before and after performing a visual task while using a head-mounted display for virtual reality (VR-HMD) and two-dimensional (2D) display. Binocular fusion maintenance (BFM) was measured using a binocular open-view Shack-Hartmann wavefront aberrometer equipped with liquid crystal shutters. Twelve healthy subjects performed the BFM test and completed a questionnaire regarding subjective symptoms before and after performing a visual task that induces low visually induced motion sickness (VIMS). BFM (p = .87) and total subjective eye symptom scores (p = .38) were not significantly different between both groups, although these values were significantly lower after the visual task than before the task within both groups (p < .05). These findings suggest that visual fatigue after using a VR-HMD is not significantly different from that after using a 2D display in the presence of low-VIMS VR content. Practitioner summary: Objective and subjective evaluation of visual fatigue were not significantly different with the use of a head-mounted display for virtual reality (VR-HMD) and two-dimensional display. These results should be valuable not only to engineers developing VR content but also to researchers involved in the evaluation of visual fatigue using VR-HMD. Abbreviations: VR: virtual reality; VR-HMD: head-mounted display for virtual reality; BFM: binocular fusion maintenance; BWFA: binocular open-view Shack-Hartmann wavefront aberrometer.

Objective Evaluation of Visual Fatigue Using Binocular Fusion Maintenance.

PURPOSE: In this study, we investigated whether an individual's visual fatigue can be evaluated objectively and quantitatively from their ability to maintain binocular fusion. METHODS: Binocular fusion maintenance (BFM) was measured using a custom-made binocular open-view Shack-Hartmann wavefront aberrometer equipped with liquid crystal shutters, wherein eye movements and wavefront aberrations were measured simultaneously. Transmittance in the liquid crystal shutter in front of the subject's nondominant eye was reduced linearly, and BFM was determined from the transmittance at the point when binocular fusion was broken and vergence eye movement was induced. In total, 40 healthy subjects underwent the BFM test and completed a questionnaire regarding subjective symptoms before and after a visual task lasting 30 minutes. RESULTS: BFM was significantly reduced after the visual task (P < 0.001) and was negatively correlated with the total subjective eye symptom score (adjusted R2 = 0.752, P < 0.001). Furthermore, the diagnostic accuracy for visual fatigue was significantly higher in BFM than in the conventional test results (aggregated fusional vergence range, near point of convergence, and the high-frequency component of accommodative microfluctuations; P = 0.007). CONCLUSIONS: These results suggest that BFM can be used as an indicator for evaluating visual fatigue. TRANSLATIONAL RELEVANCE: BFM can be used to evaluate the visual fatigue caused by the new visual devices, such as head-mount display, objectively.

Differences of Longitudinal Chromatic Aberration (LCA) between Eyes with Intraocular Lenses from Different Manufacturers.

Several researchers have studied the longitudinal chromatic aberration (LCA) of eyes implanted with an intraocular lens (IOL). We investigated the LCA of eyes implanted with yellow-colored IOLs from three different manufacturers: Alcon Inc., HOYA Corp., and AMO Inc. The number of subjects was 11, 16, and 16, respectively. The LCA of eyes implanted with SN60WF and SN60AT (Alcon Inc.), and with XY-1 (HOYA Corp.), was the same as that of phakic eyes. The LCA of eyes with ZCB00V (AMO Inc.) was smaller than that of phakic eyes. The LCA of eyes implanted with Alcon's and HOYA's IOLs, but not the LCA of eyes implanted with AMO's IOLs, was positively correlated with the powers of the IOLs. We also performed simulations to verify the impacts of LCA on visual performance for 4-mm pupil diameter; the simulations were a polychromatic modulation transfer function (MTF) and a visual Strehl ratio computed on the basis of an optical transfer function (VSOTF). We concluded that the differences between the LCA of different manufacturers do not affect visual performances when some extent of higher-order aberration (HOA) exists. The smaller HOA of AMO IOLs may enhance visual performance.

Verification of the lack of correlation between age and longitudinal chromatic aberrations of the human eye from the visible to the infrared.

Several researchers studied the longitudinal chromatic aberration (LCA) of the human eye and observed that it does not change due to age. We measured the LCA of 45 subjects' normal right eyes at three distinct wavelengths (561, 690, and 840 nm) using a Hartmann-Shack wavefront aberrometer (HSWA) while consecutively switching between three light sources for wavefront sensing. We confirmed that the LCA of the human eye does not change due to age between 22 and 57 years.

Asymmetric wavefront aberrations and pupillary shapes induced by electrical stimulation of ciliary nerve in cats measured with compact wavefront aberrometer.

To investigate the changes in the wavefront aberrations and pupillary shape in response to electrical stimulation of the branches of the ciliary nerves in cats. Seven eyes of seven cats were studied under general anesthesia. Trains of monophasic pulses (current, 0.1 to 1.0 mA; duration, 0.5 ms/phase; frequency, 5 to 40 Hz) were applied to the lateral or medial branch of the short ciliary nerve near the posterior pole of the eye. A pair of electrodes was hooked onto one or both branch of the short ciliary nerve. The electrodes were placed about 5 mm from the scleral surface. The wavefront aberrations were recorded continuously for 2 seconds before, 8 seconds during, and for 20 seconds after the electrical stimulation. The pupillary images were simultaneously recorded during the stimulation period. Both the wavefront aberrations and the pupillary images were obtained 10 times/sec with a custom-built wavefront aberrometer. The maximum accommodative amplitude was 1.19 diopters (D) produced by electrical stimulation of the short ciliary nerves. The latency of the accommodative changes was very short, and the accommodative level gradually increased up to 4 seconds and reached a plateau. When only one branch of the ciliary nerve was stimulated, the pupil dilated asymmetrically, and the oblique astigmatism and one of the asymmetrical wavefront terms was also altered. Our results showed that the wavefront aberrations and pupillary dilations can be measured simultaneously and serially with a compact wavefront aberrometer. The asymmetric pupil dilation and asymmetric changes of the wavefront aberrations suggest that each branch of the ciliary nerve innervates specific segments of the ciliary muscle and dilator muscle of the pupil.

Evaluation of electrochemically treated bulk electrodes for a retinal prosthesis by examination of retinal intrinsic signals in cats.

PURPOSE: Our goal was to determine the feasibility of using electrochemically treated bulk platinum electrodes with large charge injection capacity for a retinal prosthesis. METHODS: Seven eyes of seven cats were studied. Small retinal areas were focally stimulated with electrochemically treated bulk electrodes (φ = 500 µm) placed in a scleral pocket. Fundus images with near-infrared (800-880 nm) light were recorded, and a 2D map of the reflectance changes elicited by the electrical currents was constructed by subtracting the images taken before stimulation from those taken after stimulation. The impedance of each electrode was measured at 1 kHz. The degree of retinal elevation by the electrode was measured by optical coherence tomography. Scleral thickness where the electrode array was inserted was measured in histologic sections. RESULTS: The diameter of reflectance changes (full width at half maximum) was 0.42 ± 0.22 mm [mean ± standard deviation (SD)] in minor axes and 1.46 ± 0.82 mm in major axes. The threshold current decreased with a reduction in the residual scleral thickness (R (2) = 0.9215; P = 0.0002); it also decreased with an increase in retinal elevation (R (2) = 0.6259; P = 0.0111).The threshold current also decreased with an increase in electrode impedance (R (2) = 0.2554; P = 0.0147). CONCLUSIONS: Electrochemically treated porous platinum electrodes can stimulate localized retinal areas. The threshold current necessary to stimulate the retina was influenced by residual scleral thickness and the electrode tightness of fit against the sclera.

Characteristics of retinal reflectance changes induced by transcorneal electrical stimulation in cat eyes.

Transcorneal electrical stimulation (TES) activates retinal neurons leading to visual sensations. How the retinal cells are activated by TES has not been definitively determined. Investigating the reflectance changes of the retina is an established technique and has been used to determine the mechanism of retinal activation. The purpose of this study was to evaluate the reflectance changes elicited by TES in cat eyes. Eight eyes of Eight cats were studied under general anesthesia. Biphasic electrical pulses were delivered transcornealy. The fundus images observed with near-infrared light (800-880 nm) were recorded every 25 ms for 26 s. To improve the signal-to-noise ratio, the images of 10 consecutive recordings were averaged. Two-dimensional topographic maps of the reflective changes were constructed by subtracting images before from those after the TES. The effects of different stimulus parameters, e.g., current intensity, pulse duration, frequency, and stimulus duration, on the reflective changes were studied. Our results showed that after TES, the reflective changes appeared on the retinal vessels and optic disc. The intensity of reflectance changes increased as the current intensity, pulse duration, and stimulation duration increased (P<0.05 for all). The maximum intensity of the reflective change was obtained when the stimulus frequency was 20 Hz. The time course of the reflectance changes was also altered by the stimulation parameters. The response started earlier and returned to the baseline later with higher current intensities, longer pulse durations, but the time of the peak of the response was not changed. These results showed that the reflective changes were due to the activation of retinal neurons by TES and might involve the vascular changes induced by an activation of the retinal neurons.

Four discriminant models for detecting keratoconus pattern using Zernike coefficients of corneal aberrations.

PURPOSE: We compared the ability of four discriminant models to detect keratoconus (KC) using Zernike coefficients of corneal aberrations. METHODS: We studied 51 eyes with KC, 46 with KC suspect, 50 after laser in situ keratomileusis, and 65 normal eyes. Four statistical discriminant analyses-linear discriminant analysis, k-nearest neighbor algorithm, Mahalanobis distance method, and neural network method-were performed using Zernike coefficients of corneal aberrations obtained by a Placido-based topographer. The detection scheme was constructed using a training set of data from one half of the randomly selected study participants, and performance was evaluated by a validation set in the other half. RESULTS: Performance of the four models was different when <12 explanatory variables were included. Performance using the 2nd- to 4th-order Zernike terms did not differ significantly among models; average accuracy was 79 %. CONCLUSIONS: Determining explanatory variables of Zernike expansion coefficients of the corneal topography in discriminant models may contribute to improving accuracy of KC detection over the discriminant model, as appropriate selection of explanatory variables gave similar results despite different discriminant models.

Comparing retinal reflectance changes elicited by transcorneal electrical retinal stimulation with those of optic chiasma stimulation in cats.

PURPOSE: To compare retinal reflectance changes (RCs) elicited by transcorneal electrical stimulation (TES) to those elicited by electrical stimulation of the optic chiasma (OX). METHODS: Two eyes of two cats were studied under general anesthesia. Biphasic electrical pulses at 20 Hz were applied for 5 ms in TES, and monophasic pulses were applied for 50 µs at 100 Hz in OX stimulation. Fundus images observed with near-infrared light (800-880 nm) were recorded every 25 ms for 26 s, beginning 2 s before and ending 20 s after the electrical stimulation. To improve the signal-to-noise ratio, the images of ten consecutive recordings were averaged. Two-dimensional topographic maps of the RCs were constructed by subtracting images before the stimulation from those after the stimulation. The electrically evoked potentials (EEPs) were recorded at the OX. The effect of an intravitreal injection of tetrodotoxin (TTX) on the RCs elicited by electrical stimulation was also determined. RESULTS: After electrical stimulation, RCs were observed at the optic disc, retinal arteries, and retinal veins. The two-dimensional maps of the RCs elicited by both TES and OX stimulation were similar. The latency of the RCs ranged from 2.0 to 4.0 s, and the peak occurred 6 to 9 s after the onset of the ES. The intensity of the RCs was correlated with the amplitude of EEP elicited by TES stimulation. The RCs disappeared after the TTX injection in both TES and OX stimulation. CONCLUSIONS: TES activates principally the retinal ganglion cells, and a change in the blood flow is initiated thereafter.

Time course of changes in ocular wavefront aberration after instillation of 0.5% timolol gel-forming solution.

AIMS: To investigate the influence of 0.5% timolol gel-forming solution on ocular wavefront aberrations. METHODS: In 17 normal volunteers, ocular aberration was assessed before and 5 min, 30 min, 1 h, 2 h, 3 h, 6 h and 12 h after instillation of timolol gel-forming solution. Ocular aberration was sequentially measured over a period of 10 s, and the root-mean-square (RMS) of the second-, third-, fourth- and total higher-order aberrations (HOAs) were determined. From the time course of changes in total HOAs in 10 s, the stability index (SI) and fluctuation index (FI) were calculated. The authors also investigated sequential changes in specific Zernike components such as vertical coma, horizontal coma and spherical aberration. RESULTS: No significant changes in second-order RMS were observed (p=0.452, repeated-measures ANOVA). Topical instillation significantly increased HOAs such as third-, fourth- and total higher-order RMS (p=0.023, p=0.007 and p=0.003, respectively). Multiple comparison analysis revealed significant increases in HOAs 5 min after instillation (p=0.005 for third-, p=0.001 for fourth- and p<0.001 for total higher-order RMS, Dunnett post hoc test). FI increased significantly 5 min after instillation (p=0.013), but SI did not change significantly. With respect to sequential changes in specific components, significant changes were observed in vertical coma (p=0.004, repeated-measures ANOVA) and horizontal coma (p=0.005), but not in spherical aberration. CONCLUSION: Instillation of timolol gel-forming solution significantly degrades optical quality of the eye for approximately 5 min by increasing HOAs, which may cause blurred vision.

Influence of induced decentered orthokeratology lens on ocular higher-order wavefront aberrations and contrast sensitivity function.

PURPOSE: To quantitatively evaluate the effect of overnight orthokeratology lenses intentionally left decentered after 3 months of wear and assess the influence on clinical outcomes such as ocular higher-order wavefront aberrations and contrast sensitivity function. SETTING: Department of Ophthalmology, Tsukuba University Hospital, Ibaraki, Japan. METHODS: This prospective study assessed refraction, visual acuity, corneal topography, wavefront aberration, and contrast sensitivity function before and 3 months after overnight orthokeratology treatment. Decentration of the treatment zone from the center of the entrance pupil was determined using computerized videokeratography (TMS-4) and data-analysis software (MatLab). The relationship between decentration and the clinical parameters was analyzed. RESULTS: The mean age of the 23 patients (46 eyes) was 24.2 years+/-3.3 (SD) and the mean spherical equivalent refraction before treatment, -2.38+/-0.98 diopters. The mean magnitude of decentration (0.85+/-0.51 mm) was statistically significantly correlated with the amount of myopic correction (P<.05), increases in coma-like aberration (P<.01), increases in spherical-like aberration (P<.01), and reductions in contrast sensitivity function (P<.0001). Changes in contrast sensitivity function were also statistically significantly correlated with the amount of myopic correction (P<.05), changes in coma-like aberration (P<.01), and changes in spherical-like aberration (P<.01). Stepwise multiple regression analysis showed that the magnitude of decentration was the only explanatory variable related to contrast sensitivity function (P<.0001). CONCLUSION: Decentered treatment of orthokeratology resulted in decreased contrast sensitivity after treatment, showing that centration of the procedure is crucial to good outcomes.

Characteristics of ocular higher-order aberrations in patients with pellucid marginal corneal degeneration.

PURPOSE: To evaluate the characteristics of higher-order aberrations (HOAs) in eyes with pellucid marginal corneal degeneration (PMCD). SETTING: Department of Ophthalmology, Osaka University Medical School, Osaka, Japan. METHODS: Ocular HOAs were measured by aberrometry in 20 eyes with PMCD (PMCD group), 76 eyes with keratoconus (KC group), and 105 normal eyes (control group) with a 4.0 mm pupil. The magnitudes and axes of trefoil, coma, tetrafoil, and secondary astigmatism and the magnitude of spherical aberration were compared between the 3 groups using vector analysis of Zernike terms. RESULTS: The mean axes of coma in the PMCD group (85.5 degrees) and KC group (82.5 degrees) were opposite the axis in the control group (253.7 degrees). The magnitude of coma was significantly lower in the PMCD group (0.27 microm +/- 0.19 [SD]) than in the KC group (0.70 +/- 0.37 microm) (P < .05). The mean axes of trefoil in the PMCD group (27.1 degrees) and control group (35.4 degrees) were opposite the axis in the KC group (93.8 degrees). The magnitude of spherical aberration was significantly higher in the PMCD group (0.086 +/- 0.10 microm) than in the KC group (-0.030 +/- 0.13 microm) (P < .05); the spherical aberration signs were opposite in the groups. CONCLUSIONS: Although PMCD and KC are categorized as noninflammatory corneal thinning disorders, the HOA patterns in the 2 groups differed, possibly due to differences in the positions of the corneal apex. PMCD and KC may cause distinctively different deterioration in the quality of vision.

Binocular open-view Shack-Hartmann wavefront sensor with consecutive measurements of near triad and spherical aberration.

We have developed a binocular open-view Shack-Hartmann wavefront sensor for measuring time variation of binocular accommodation, vergence, pupil sizes (i.e., the binocular near triad), and monochromatic aberrations. The device measures these values16 times per second for up to 1 min. Our purpose is to introduce the new instrument. We have confirmed the accuracy of the device. Refractions for a 4 mm pupil were accurate across the range of measurements of model eyes and normal human eyes. We measured binocular dynamics of accommodation, vergence, and spherical aberrations.

Effects of suppression of blinking on quality of vision in borderline cases of evaporative dry eye.

PURPOSE: To study the effects of suppression of blinking on quality of vision in borderline cases of evaporative dry eye. METHODS: Ocular higher-order aberrations (HOAs) were measured sequentially for 30 seconds in 10 eyes with a short tear film breakup time (TBUT; 3.0 +/- 0.6 seconds) without ocular surface staining or tear deficiency. During measurements, the subjects suppressed blinking to every 10 seconds, which is more than double the TBUT. The aberration data were analyzed for comalike and spherical-like aberrations and total HOAs to the sixth-order Zernike polynomials. RESULTS: Sequential changes in total HOAs in subjects with a short TBUT showed a sawtooth pattern with a marked upward curve that increased after blinking. From 5 to 9 seconds after blinking, the total HOAs were significantly higher than immediately after blinking (P < 0.001). CONCLUSIONS: Serial HOA measurements showed that optical quality might deteriorate in subjects with a short TBUT by suppressed blinking, such as when gazing at a video display terminal, even with sufficient tear volume.

Effect of internal lubricating agents of disposable soft contact lenses on higher-order aberrations after blinking.

PURPOSE: To investigate whether the polymer composition of disposable soft contact lenses affects sequential changes in higher-order aberrations (HOAs). METHODS: Fifteen subjects who wore disposable soft contact lenses with dryness-related symptoms and 15 non-contact lens wearers were enrolled in this study. Ocular HOAs were measured for 60 seconds in each subject wearing a disposable etafilcon A lens (conventional lens) or a disposable etafilcon A lens with polyvinyl pyrrolidone (PVP) (lens with PVP) after 1 hour of contact lens wear. During the measurement, subjects were forced to blink every 10 seconds. The aberration data were analyzed in the central 4-mm diameter up to the sixth-order Zernike polynomials. Total HOAs, the fluctuation index (FI), and the stability index (SI) of the total HOAs over time were compared between the two groups. The subjective ocular dryness also was scored. RESULTS: In symptomatic wearers of disposable soft contact lenses, the total HOAs, the FI, and the SI with the lens with PVP were significantly (P=0.013, P=0.014, P=0.019, respectively) lower than with the conventional lens, whereas a significant (P=0.018) difference between the two lenses was observed only in the FI in non-contact lens wearers. Subjective ocular dryness with the lens with PVP significantly decreased compared with the conventional lens in both groups. CONCLUSIONS: Sequential measurement of HOAs may be a useful objective method to evaluate the effect of internal lubricating agents of disposable soft contact lenses on optical quality.

Serial measurements of higher-order aberrations after blinking in patients with dry eye.

PURPOSE: To study the sequential postblink changes in ocular higher-order aberrations (HOAs) in patients with dry eye. METHODS: A wavefront sensor was used to measure HOAs sequentially for 30 seconds in 20 eyes of 20 patients with dry eye. The 20 eyes were classified into two groups, with or without superficial punctate keratopathy (SPK) in the central cornea. During the measurement, subjects were required to blink every 10 seconds. The aberration data were analyzed in the central 4-mm diameter for coma-like, spherical-like, and total HOAs up to sixth-order Zernike polynomials. Total HOAs, as well as fluctuation index (FI) and stability index (SI) of the total HOAs over time were compared between the two groups. The sequential changes in coma-like aberration, spherical-like aberration, and total HOAs were also investigated. RESULTS: The total ocular HOAs were significantly (P = 0.001) greater in dry eyes with central SPK than in dry eyes without central SPK. The sequential pattern of the total ocular HOAs had higher initial and consistently higher values in dry eyes with central SPK, whereas that of dry eyes without central SPK showed consistently lower total HOAs that were similar to the pattern of normal eyes. CONCLUSIONS: Increased HOAs in dry eye at least partially result from SPK above the optical zone. The low tear volume in dry eye may not cause sequential increases in HOAs after blinking. Sequential measurement of HOAs may be useful for evaluating the sequential changes in optical quality in patients with dry eye.

Optical imaging to evaluate retinal activation by electrical currents using suprachoroidal-transretinal stimulation.

PURPOSE: To determine whether reflectance changes of the retina after electrical suprachoroidal-transretinal stimulation (STS) can be detected with a newly developed optical imaging fundus camera. METHODS: Ten eyes of 10 cats were studied. A small retinal area was focally stimulated with electric currents passing between an active electrode placed in the fenestrated sclera and a reference electrode in the vitreous. Biphasic pulses were applied for 4 seconds with a current up to 500 muA. Images of the fundus illuminated with near-infrared (800-880 nm) light were obtained every 20 msec for 26 seconds between 2 seconds before and 20 seconds after the STS. Twenty images of 20 consecutive experiments were averaged. A two-dimensional map of the reflectance changes was constructed by subtracting the images before the stimulation from those after the stimulation. STS-evoked potentials (EPs) were recorded from the optic chiasma. RESULTS: Approximately 0.5 second after the onset of STS, reflectance changes were observed around the retinal locus, where the stimulating electrodes were positioned. The intensity of the reflectance changes was correlated with the intensity of the stimulus current. The area of the reflectance change increased as the current intensity increased and was correlated with the amplitude of the EPs (R(2) = 0.82). CONCLUSIONS: Reflectance changes after STS were localized to the area around the electrode. The strong correlation between the area of the reflectance changes and the amplitude of the EPs suggested that the reflectance changes reflected the activity of retinal neurons elicited by electrical stimulation.

Optical quality of the eye degraded by time-varying wavefront aberrations with tear film dynamics.

PURPOSE: Wavefront aberrations (WFAs) of the eye vary with time because of the tear film dynamics. We investigated, using a simulation method, the variation of optical quality with time-varying wavefront measurements of 13 eyes with different refractions. METHODS: WFAs of 13 normal eyes of 13 subjects were measured every second for 10 s. First, we simulated WFAs with conventional corneal laser refractive surgery by subtracting the second-order aberrations of the least aberrated measurement from measured consecutive WFAs. Second, we simulated customized refractive surgery by subtracting the second- to sixth-order aberrations of the least aberrated measurement from measured consecutive WFAs. We calculated Strehl ratios and retinal images from these corrected consecutive WFAs. RESULTS: In one eye, the root mean square (RMS) values of WFAs with a second-order correction were sometimes smaller than those of WFAs with a second- to sixth-order correction, when these were compared at the same time point after a blink. However, in the other 12 eyes, the RMS values with second- to sixth-order corrections were smaller than those with only a second-order correction. In eight eyes, the Strehl ratios with second- to sixth-order corrections were larger than those with second-order corrections. In the remaining five eyes, Strehl ratios with second- to sixth-order corrections were sometimes smaller than those with second-order corrections. CONCLUSIONS: In a simulation, the correction of time-invariant higher order aberrations usually reduced RMS values, but it did not always result in higher Strehl ratios than those obtained with only second-order corrections.