Potential role for microfluctuations as a temporal directional cue to accommodation.

The goal was to revisit an important, yet unproven notion that accommodative microfluctuations facilitate the determination of direction (sign) of abrupt focus changes in the stimulus to accommodation. We contaminated the potential temporal cues from natural accommodative microfluctuations by presenting uncorrelated external (screen) temporal defocus noise that combined with the retinal image effects of natural microfluctuations. A polychromatic Maltese spoke pattern thus either modulated defocus at a combination of two temporal frequencies (on-screen noise condition) or was static (control condition). The on-screen conditions were combined with step changes in optical vergence that were randomized in direction and magnitude. Five subjects monocularly viewed stimuli through a Badal optical system in a Maxwellian view. An artificial 4-mm aperture was imaged at the entrance pupil of the eye. Wavefront aberrations were measured dynamically at 50 Hz using a custom Shack-Hartmann aberrometer. Dynamic changes in the Zernike defocus term with step changes in optical vergence were analyzed. We calculated the percentage of correct directional responses for 1, 2, and 3 D accommodative and disaccommodative step stimuli using preset criteria for latency, velocity, and persistence of the response. The on-screen noise condition reduced the percent-correct responses compared to the static stimulus, suggesting that this manipulation affected the detectability of the sign of the accommodative stimulus. Several possible reasons and implications of this result are discussed.

Adaptation of visual tracking synchronization after one night of sleep deprivation.

The temporal delay between sensory input and motor execution is a fundamental constraint in interactions with the environment. Predicting the temporal course of a stimulus and dynamically synchronizing the required action with the stimulus are critical for offsetting this constraint, and this prediction-synchronization capacity can be tested using visual tracking of a target with predictable motion. Although the role of temporal prediction in visual tracking is assumed, little is known of how internal predictions interact with the behavioral outcome or how changes in the cognitive state influence such interaction. We quantified and compared the predictive visual tracking performance of military volunteers before and after one night of sleep deprivation. The moment-to-moment synchronization of visual tracking during sleep deprivation deteriorated with sensitivity changes greater than 40 %. However, increased anticipatory saccades maintained the overall temporal accuracy with near zero phase error. Results suggest that acute sleep deprivation induces instability in visuomotor prediction, but there is compensatory visuomotor adaptation. Detection of these visual tracking features may aid in the identification of insufficient sleep.

The impact of higher-order aberrations on the strength of directional signals produced by accommodative microfluctuations.

It has been proposed that the accommodation system could perform contrast discrimination between the two dioptric extremes of accommodative microfluctuations to extract directional signals for reflex accommodation. Higher-order aberrations (HOAs) may have a significant influence on the strength of these contrast signals. Our goal was to compute the effect HOAs may have on contrast signals for stimuli within the upper defocus limit by comparing computed microcontrast fluctuations with psychophysical contrast increment thresholds (Bradley & Ohzawa, 1986). Wavefront aberrations were measured while subjects viewed a Maltese spoke stimulus monocularly. Computations were performed for accommodation or disaccommodation stimuli from a 3 Diopter (D) baseline. Microfluctuations were estimated from the standard deviation of the wavefronts over time at baseline. Through-focus Modulation Transfer, optical contrast increments (ΔC), and Weber fractions (ΔC/C) were derived from point spread functions computed from the wavefronts at baseline for 2 and 4 cycles per degree (cpd) components, with and without HOAs. The ΔCs thus computed from the wavefronts were compared with psychophysical contrast increment threshold data. Microfluctuations are potentially useful for extracting directional information for defocus values within 3 D, where contrast increments for the 2 or 4 cpd components exceed psychophysical thresholds. HOAs largely reduce contrast signals produced by microfluctuations, depending on the mean focus error, and their magnitude in individual subjects, and they may shrink the effective stimulus range for reflex accommodation. The upper defocus limit could therefore be constrained by discrimination of microcontrast fluctuations.

Does ethnicity influence the short-term adaptation to first reading correction?

PURPOSE: Ethnic variations in accommodative amplitude (AA) are not uncommon. Accommodation can become reduced in response to short-term wear of first near spectacles. Whether ethnicity has an influence on the magnitude of this adaptation is not well understood. We investigated the impact of first near spectacles on changes in AA and on convergence cross-link interactions in incipient presbyopes of Chinese and Caucasian ethnicities. METHODS: Forty-one subjects (22 Caucasians and 19 Chinese) aged 36 to 44 years completed the study. Accommodative stimulus response function, AA, and AC/A and CA/C ratios were measured before and after single vision reading spectacles were used for near tasks over a 2-month period and then again 2 months after discontinuing near spectacle wear. RESULTS: After wearing reading spectacles for 2 months, the accommodative stimulus response slopes and AC/A and CA/C ratios remained invariant irrespective of ethnicity. The accommodative, but not vergence, bias decreased (p < 0.05). The nearpoint of accommodation shifted distally producing an average decrease in AA of 0.52 D from baseline (p < 0.05). Recovery to near baseline values occurred after discontinuing the reading glasses for 2 months. Differences based on ethnicity were not significant. The baseline AA vs. age plots showed steeper slopes for Chinese than the Caucasian subjects in the sample. CONCLUSIONS: The pattern of adaptation by accommodation and cross-link interactions to short-term first reading spectacles is not influenced by ethnicity.

The effect of perceptual grouping on perisaccadic spatial distortions.

Perisaccadic spatial distortion (PSD) occurs when a target is flashed immediately before the onset of a saccade and it appears displaced in the direction of the saccade. In previous studies, the magnitude of PSD of a single target was affected by multiple experimental parameters, such as the target's luminance and its position relative to the central fixation target. Here we describe a contextual effect in which the magnitude of the PSD for a target was influenced by the synchronous presentation of another target: PSD for simultaneously presented targets was more uniform than when each was presented individually. Perisaccadic compression was ruled out as a causal factor, and the results suggest that both low- and high-level perceptual grouping mechanisms may account for the change in PSD magnitude. We speculate that perceptual grouping could play a key role in preserving shape constancy during saccadic eye movements.

Time Course of Perceived Visual Distortion and Axial Length Growth in Myopic Children Undergoing Orthokeratology.

Purpose: To establish the time course of the subjective visual function changes during the first month of orthokeratology treatment in myopic children, and to investigate how the time course variations are associated with the objective optical quality changes and the axial length growth (ALG) after 1 year of treatment. Methods: A total of 58 myopic children aged from 8 to 16 years participated in this self-controlled prospective study. All subjects were fitted with designed spherical four-zone orthokeratology lenses. Subjective visual function was evaluated with orientation discrimination threshold (ODT), and objective optical quality was quantified with the high-order aberration root-mean-square (HOA-RMS) and the changing speed of HOA. The measurements were done before the lens fitting and 1 day, 1-, 2-, and 4-weeks after lens wear. Axial length was obtained at baseline and 1-year follow-up, and ALG was defined as the difference. One-way ANOVA was conducted to compare the difference for statistical analysis. Results: After lens fitting, the ODT time courses peaked on day 1 in 28 children, 1 week in 15 children, 2 weeks in 11 children, and 4 weeks in 4 children. In contrast, the HOA-RMS steadily rose during the first month, and the changing speed of HOA was only transiently elevated on day 1 after the initial lens wear. The ALG was 0.12 ± 0.20 mm in subjects whose ODT peaked at day 1, 0.08 ± 0.09 mm in subjects whose ODT peaked on 1-week, and 0.12 ± 0.15 mm in subjects whose ODT peaked on 2-week or later. There was no difference in axial growth among the subjects whose ODT peaked at different days (P = 0.734). Conclusion: While half ODT time course resembled the changing speed of HOA with a transient elevation on day 1, about a quarter of the ODT time course resemble the steadily rising of HOA-RMS, and the rest was located in the middle. The ALGs in children with different types of ODT time courses were similar.

Orientation discrimination with macular changes associated with early AMD.

PURPOSE: Age-related macular degeneration (AMD) is a condition that progressively reduces central vision in elderly individuals, resulting in a reduced capacity to perform many daily activities and a diminished quality of life. Recent studies identified clinical treatments that can slow or reverse the progression of exudative (wet) AMD and ongoing research is evaluating earlier interventions. Because early diagnosis is critical for an optimal outcome, the goal of this study is to assess psychophysical orientation discrimination for randomly positioned short line segments as a potential indicator of subtle macular changes in eyes with early AMD. METHODS: Orientation discrimination was measured in a sample of 74 eyes of patients aged 47 to 82 years old, none of which had intermediate or advanced AMD. Amsler-grid testing was performed as well. A masked examiner graded each eye as level 0, 1, 2, or 3 on a streamlined version of the Age-Related Eye Disease Study (AREDS) scale for AMD, based on the presence and extent of macular drusen or retinal pigment epithelium (RPE) changes. Visual acuity in the 74 eyes ranged from 20/15 to 20/40, with no significant differences among the grading levels. Humphrey 10-2 and Nidek MP-1 micro-perimetry were used to assess retinal sensitivity at test locations 1 degrees from the locus of fixation. RESULTS: Average orientation-discrimination thresholds increased systematically from 7.4 degrees to 11.3 degrees according to the level of macular changes. In contrast, only 3 of 74 eyes exhibited abnormalities on the Amsler grid and central-field perimetric defects occurred with approximately equal probability at all grading levels. CONCLUSIONS: In contrast to Amsler grid and central-visual-field testing, psychophysical orientation discrimination has the capability to distinguish between eyes with and without subtle age-related macular changes.

The temporal impulse response function in infantile nystagmus.

Despite rapid to-and-fro motion of the retinal image that results from their incessant involuntary eye movements, persons with infantile nystagmus (IN) rarely report the perception of motion smear. We performed two experiments to determine if the reduction of perceived motion smear in persons with IN is associated with an increase in the speed of the temporal impulse response. In Experiment 1, increment thresholds were determined for pairs of successively presented flashes of a long horizontal line, presented on a 65-cd/m2 background field. The stimulus-onset asynchrony (SOA) between the first and second flash varied from 5.9 to 234 ms. In experiment 2, temporal contrast sensitivity functions were determined for a 3-cpd horizontal square-wave grating that underwent counterphase flicker at temporal frequencies between 1 and 40 Hz. Data were obtained for 2 subjects with predominantly pendular IN and 8 normal observers in Experiment 1 and for 3 subjects with IN and 4 normal observers in Experiment 2. Temporal impulse response functions (TIRFs) were estimated as the impulse response of a linear second-order system that provided the best fit to the increment threshold data in Experiment 1 and to the temporal contrast sensitivity functions in Experiment 2. Estimated TIRFs of the subjects with pendular IN have natural temporal frequencies that are significantly faster than those of normal observers (ca. 13 vs. 9 Hz), indicating an accelerated temporal response to visual stimuli. This increase in response speed is too small to account by itself for the virtual absence of perceived motion smear in subjects with IN, and additional neural mechanisms are considered.

Motion sensitivity during fixation in straight-ahead and lateral eccentric gaze.

Despite motion of the entire retinal image that results from fixational eye-movements, the visual scene is perceived as stationary. One hypothesis to account for this observation is that normal motion sensitivity is limited by the variability of fixational eye velocity. The present experiments tested this hypothesis by comparing motion sensitivity and the variability of fixational eye velocity in corresponding meridians. Speed thresholds to detect horizontal, vertical, and rotary motion in a set of eight random-dot patches were measured, while normal observers monocularly viewed the stimulus with gaze either straight-ahead or deviated to the left by 45 degrees. Eye-movement recordings using the search-coil technique were used to estimate the variability of eye velocity in the horizontal, vertical, and torsional meridians during fixation. As reported previously by Murakami (2004), the averaged thresholds for horizontal and vertical motion correlated with the averaged variability of eye velocity in the horizontal and vertical meridians when observers looked straight-ahead. However, no relationship existed between the threshold for rotary motion and the variability of eye velocity in the torsional meridian. Furthermore, no relationship existed between the motion threshold and the variability of eye velocity in any meridian during fixation in lateral eccentric gaze. These results are only partly consistent with the hypothesis that fixation variability limits motion sensitivity.

Signals of eye-muscle proprioception modulate perceived motion smear.

Achieving clear perception during eye movements is one of the major challenges that the human visual system has to face every day. Like most light sensitive mechanisms, the human visual system has a finite integration time that may cause moving images to appear smeared. By comparing the perceived motion smear during ongoing eye movements and fixation, previous studies indicated that smear is reduced by a neural compensation mechanism that uses "extra-retinal information" about eye movements. However, it is not clear whether eye-muscle proprioception (afferent input), internal copies of efferent oculomotor commands (efference copy), or both contribute to the smear reduction. The present study found that similar reductions of perceived motion smear occur during passive eye movement (which is signaled only by eye-muscle proprioception) and during active pursuit tracking (for which efference copy signals exist as well). These results reveal a novel neural contribution for maintaining visual clarity and stand in contrast to previous reports that eye-muscle proprioception makes only a minor contribution to visual perception.

Effects of fixation instability on multifocal VEP (mfVEP) responses in amblyopes.

The cortical activity of subjects with compromised central vision (e.g., amblyopes) is thought to be much weaker for stimulation of the affected eye than in the fellow eye. Because these subjects are known to exhibit considerable difficulties in keeping steady fixation, we investigated the effects of anomalous fixation on their multifocal visual-evoked potential (mfVEP) responses using a dual Purkinje image (dPi) eye tracker. Our results show that mfVEP responses to stimulation of the central 5 degrees were depressed in the affected eye compared to those in the normal eye and the magnitude of response reductions was proportional to the degree of visual acuity loss in amblyopic subjects. Fixation was far less stable while viewing with the affected eye than with the fellow eye, some exhibiting jerk nystagmus and/or saccadic oscillations. Normal subjects with artificially imposed nystagmus showed similar reductions of VEP responses. The relative magnitudes of the deficits in mfVEP responses were tightly correlated with the degree of fixation instability. These results suggest that the interpretation of anomalous neural or perceptual processing in amblyopic subjects must take the effects of unsteady fixation during measurements into consideration in order to reveal the true nature and extent of sensory neural deficits.

The Associations among Metamorphopsia, Orientation Discrimination Threshold, and Retinal Layer Thickness in Patients with Idiopathic Epiretinal Membrane.

PURPOSE: To explore the association among the metamorphopsia identified by Amsler grid test, orientation discrimination threshold (ODT), and retinal layer thickness in patients with idiopathic epiretinal membrane (ERM). METHODS: A total of 48 ERM patients were divided into a fovea-spared (FS) group (n = 12) and a fovea-involved (FI) group (n = 36). A total of 23 visually normal people served as controls. Metamorphopsia was first assessed with an Amsler grid. The ODT was quantified with groups of briefly displayed short line segments. Inner and outer retinal layer thickness (IRLT and ORLT) was measured with spectral domain optical coherence tomography. RESULTS: A total of 12 patients with ERM (1 in FS and 11 in FI) reported abnormalities in the Amsler grid test. The ODT values were significantly elevated in patients in both FS (7.48 ± 1.94°, p < 0.001) and FI groups (10.14 ± 2.28°, p < 0.001) when compared to normal (4.22 ± 0.80). Receiver operating characteristic (ROC) analyses of ODT to distinguish Amsler positive and negative patients yielded an area under the curve (AUC) of 0.829. The IRLT was significantly thicker (386.6 ± 95.1 µm vs. 127.5 ± 17.6 in normal) and ORLT were significantly thinner (88.11 ± 8.24 vs. 94.39 ± 5.66 in normal) in the FI group. ROC analyses to distinguish Amsler positive and negative patients yield an AUC of 0.917 using IRLT and 0.719 using ORLT. ODT correlated tightly with the thicker IRLT in both the FS and FI groups, and with the thinner ORLT in the FI group. CONCLUSIONS: In patients with ERM, ODT reflects functional changes that are not detected by the Amsler grid test and correlates with changes in inner retina layer thickness well.

Direction and extent of perceived motion smear during pursuit eye movement.

Smooth pursuit eye movements superimpose additional motion on the retinal image of untracked visual targets, potentially leading to the perception of motion smear and a distortion of the perceived direction of motion. Previously, we demonstrated an attenuation of perceived motion smear when the untracked target moves in the opposite direction of an ongoing pursuit eye movement. In this study, the extent of perceived motion smear and the direction of perceived smear were compared for a single bright dot that moved in a wide range of directions with respective to horizontal pursuit at 8 deg/s. Comparable data were obtained during fixation as a control. The results indicate that a significant attenuation of perceived motion smear occurs when the dot's motion includes a horizontal component in the opposite direction of eye movement. In contrast, the direction of perceived smear approximates the trajectory of the retinal image motion, during both fixation and pursuit. These results suggest a selective application of extra-retinal signals to compensate specific aspects of visual perception that results from the retinal image motion during smooth pursuit eye movements.

Relationships of orientation discrimination threshold and visual acuity with macular lesions in age-related macular degeneration.

PURPOSE: To measure visual acuity and metamorphopsia in patients with age-related macular degeneration (AMD) and to explore their relationship with macular lesions. METHODS: In this cross-sectional study, a total of 32 normal subjects (32 eyes) and 35 AMD patients (35 eyes) were recruited. They were categorized into 4 groups: normal, dry AMD, non-active wet AMD, and active wet AMD. Best-corrected visual acuity (BCVA) was measured using the Early Treatment Diabetic Retinopathy Study protocol. Metamorphopsia was quantified with the orientation discrimination threshold (ODT). Macular lesions, including drusen, sub-retinal fluid (SRF), intra-retinal fluid (IRF), pigmented epithelium detachment (PED), and scarring, were identified with spectral-domain optical coherence tomography (SD-OCT). A linear regression model was established to identify the relationships between the functional and structural changes. RESULTS: BCVA progressively worsened across the normal, dry AMD, non-active wet AMD, and active wet AMD groups (P < 0.001), and ODT increased across the groups (P < 0.001). The correlation between BCVA and ODT varied among the groups. The partial correlation between BCVA and ODT was -0.61 (P < 0.001). Linear regression showed that ODT significantly depended on IRF (ß = 0.61, P < 0.001), SRF (ß = 0.34, P = 0.003), and scarring (ß = 0.26, P = 0.050), while BCVA significantly depended only on scarring (ß = -0.52, P < 0.001), and IRF (ß = -0.36, P = 0.016). CONCLUSIONS: From dry AMD to active wet AMD, BCVA gradually worsened while ODT increased. The correlation between BCVA and ODT varied among these groups, indicating that AMD lesions affect them differently. ODT and BCVA should be used concurrently for better monitoring of the disease.

The attenuation of perceived motion smear during combined eye and head movements.

The extent of perceived motion smear was compared for targets that underwent similar velocities of retinal image motion during the vestibulo-ocular reflex (VOR) in the dark, the visually enhanced VOR (VVOR), VOR suppression, and fixation. Compared to the extent of perceived motion smear during fixation, observers reported significantly less smear when the target moved either in the same direction or against the direction of the head movement during the VVOR and VOR. We also confirmed a previous finding that perceived smear is attenuated asymmetrically during VOR suppression, with attenuation occurring primarily for targets that move against the direction of the observer's head motion. The results support the hypothesis that the visual system employs extra-retinal signals that accompany eye and head movements to reduce the perception of motion smear for targets that move physically in the opposite direction of eye and/or head movements.

Degradation of Binocular Coordination during Sleep Deprivation.

To aid a clear and unified visual perception while tracking a moving target, both eyes must be coordinated, so the image of the target falls on approximately corresponding areas of the fovea of each eye. The movements of the two eyes are decoupled during sleep, suggesting a role of arousal in regulating binocular coordination. While the absence of visual input during sleep may also contribute to binocular decoupling, sleepiness is a state of reduced arousal that still allows for visual input, providing a context within which the role of arousal in binocular coordination can be studied. We examined the effects of sleep deprivation on binocular coordination using a test paradigm that we previously showed to be sensitive to sleep deprivation. We quantified binocular coordination with the SD of the distance between left and right gaze positions on the screen. We also quantified the stability of conjugate gaze on the target, i.e., gaze-target synchronization, with the SD of the distance between the binocular average gaze and the target. Sleep deprivation degraded the stability of both binocular coordination and gaze-target synchronization, but between these two forms of gaze control the horizontal and vertical components were affected differently, suggesting that disconjugate and conjugate eye movements are under different regulation of attentional arousal. The prominent association found between sleep deprivation and degradation of binocular coordination in the horizontal direction may be used for a fit-for-duty assessment.

Asymmetry of perceived motion smear during head and eye movements: evidence for a dichotomous neural categorization of retinal image motion.

We measured perceived motion smear when retinal image motion was created either by a physically moving object or by movement of the eyes or head. Consistent with previous reports, the extent of perceived motion smear during an eye or head movement is less than that produced by physical object motion when the eyes are stationary. Moreover, perceived smear is substantially smaller when the motion of the retinal image is in the same direction as the eye or head movement compared to when image motion is in the opposite direction. These results imply that extra-retinal signals associated with eye and head movements contribute to a reduction of perceived motion smear, thereby fostering perceptual clarity. We hypothesize that the visual system uses a simple dichotomous strategy in applying these extra-retinal signals, based only on the direction of retinal image motion with respect to the ongoing eye or head movement.

Multi-directional shifts of optokinetic responses to binocular-rivalrous motion stimuli.

Previous dichoptic experiments showed that dissimilar stationary pattern stimuli resulted in the perception of binocular rivalry, whereas oppositely-directly moving grating stimuli resulted in alternating optokinetic nystagmus (OKN) and the perception of binocular motion rivalry. The present study extended these dichoptic motion experiments by introducing obliquely-oriented targets with the aim of probing further the cortical mechanisms underlying binocular processing of motion. Two-dimensional eye movements were recorded along with their subjective perceptual responses. The stimuli consisted of two tilted gratings, one moving diagonally upwards and to the right (UR, 45 degrees ) and the other diagonally upwards and to the left (UL, 135 degrees ), which were presented dichoptically to subjects under two stimulus modes. For the non-exchange mode, the OKN slow phases exhibited three types of directional shifts. Two of these directional shifts tracked the stimuli (i.e. UR or UL), whereas the third moved purely upwards (UP). Since physically there was no upward-moving target, the OKN and perceptual responses appeared to be associated with a perceptual interocular grouping of the two dichoptic stimuli in their reassembled vector-sum direction. The OKN shifts were also found to be highly correlated with the psychophysical responses of motion perception. For the rapid-exchange mode, in which the stimuli were rapidly exchanged between the two eyes, the OKN slow phases exhibited primarily two types of directional shifts, UR and UL, but no UP responses for most subjects. It also appeared that these two coherent motion percepts, UL and UR, were interocularly regrouped from the exchanged stimuli. Moreover, the lack of perceptual grouping to create an UP response in the rapid-exchange mode indicated that temporal integration of at least 200 ms was necessary for the development of a reassembled vector-sum-direction motion percept. The findings under both stimulus modes support the stimulus-feature rivalry hypothesis, in which higher cortical centers mediate interocular perceptual grouping and the associated motor response.

Dual-directional optokinetic nystagmus elicited by the intermittent display of gratings in primary open-angle glaucoma and normal eyes.

PURPOSE: To compare optokinetic nystagmus (OKN) responses to the intermittent display of stimuli between normal subjects and patients with primary open-angle glaucoma (POAG). METHODS: Optokinetic nystagmus (OKN) was recorded in 9 glaucomatous patients and 7 normal subjects. The computer-generated stimuli displayed sinusoidal luminance gratings (16 cd/m(2) mean luminance, 0.5 cyc/deg) with a pi/2 phase shift between successive stimulus gratings. These stimulus gratings were separated by an interstimulus interval (ISI), during which a homogeneous luminance field of 16 cd/m(2) was presented. The ISI duration and the luminance contrast were set at different values. RESULTS: For normal subjects, dual-directional alternating OKN could be evoked in the ISI range from 33 to 100 ms. The dual-directional alternating OKN was defined as that OKN slow phase alternatively tracked in the direction of pi/2 shift (forward OKN) and against the pi/2 shift (reverse OKN). By contrast, for most glaucomatous eyes, nearly no reverse OKN could be evoked at any ISI value. CONCLUSIONS: The lack of reverse OKN in POAG patients in the present experiments is a meaningful finding. The occurrence of reverse OKN during a certain range of ISI duration could be related to the biphasic characteristics of the temporal impulse response in normal subjects, whereas, the lack of reverse OKN might suggest the plausible damage of magnocellular cells in POAG.

Short-term adaptation of accommodation, accommodative vergence and disparity vergence facility.

Previous studies have found that subjects can increase the velocity of accommodation using visual exercises such as pencil push ups, flippers, Brock strings and the like and myriad papers have shown improvement in accommodation facility (speed) and sufficiency (amplitude) using subjective tests following vision training but few have objectively measured accommodation before and after training in either normal subjects or in patients diagnosed with accommodative infacility (abnormally slow dynamics). Accommodation is driven either directly by blur or indirectly by way of neural crosslinks from the vergence system. Until now, no study has objectively measured both accommodation and accommodative-vergence before and after vision training and the role vergence might play in modifying the speed of accommodation. In the present study, accommodation and accommodative-vergence were measured with a Purkinje Eye Tracker/optometer before and after normal subjects trained in a flipper-like task in which the stimulus stepped between 0 and 2.5 diopters and back for over 200 cycles. Most subjects increased their speed of accommodation as well as their speed of accommodative vergence. Accommodative vergence led the accommodation response by approximately 77 ms before training and 100 ms after training and the vergence lead was most prominent in subjects with high accommodation and vergence velocities and the vergence leads tended to increase in conjunction with increases in accommodation velocity. We surmise that volitional vergence may help increase accommodation velocity by way of vergence-accommodation cross links.