101
|
Abstract
Phoria adaptation (PA) provides innervation to help maintain the correct vergence posture for binocularly viewing objects. Once fusion is disrupted, such as is required for measuring a (dissociated) phoria, this innervation is slowly depleted. Thus, extended periods of monocular occlusion can be required to dissipate PA and reveal the full extent of the phoria. Two versions of a forced vergence modification of the alternating cover test (CT) have been proposed to rapidly show the full phoria. We evaluated the ability of these forced vergence CTs (FVCT-1 and FVCT-2) to deplete the PA induced by a 15 min adaptation period to base out prism. In both experiments, the CT followed by the FVCT was performed before and after the adaptation period. In Experiment 1 (n = 13), the FVCT-1 was evaluated at 40 cm. Experiment 2 (n = 32) evaluated the FVCT-2 at 4 m. In Experiments 1 and 2, the difference between pre- and post-adaptation CTs showed significant PA occurred during the adaptation period (7.8(Delta), p < 0.0005, and 5.4(Delta), p < 0.0005 respectively). In Experiment 1, the FVCT-1 did not reveal a larger phoria than the CT before (mean difference: 0.4(Delta), p = 0.34) or after (no difference for all subjects) the adaptation period. Thus, the FVCT-1 did not alter PA. In Experiment 2, the FVCT-2 did show a shift in the phoria compared to the CT. However, this shift was found to be equivalent before and after the adaptation period (mean difference in shift: 0.22(Delta), 95% CI: -0.52 to 0.96(Delta)). Thus, the FVCT-2 shifts the phoria a constant amount independent of the amount of PA present. We conclude that neither FVCT's behaviour is dependent on the PA present. Thus, these procedures are unlikely to be effective clinical procedures for revealing the full magnitude of the phoria.
Collapse
|
102
|
Nguyen D, Vedamurthy I, Schor C. Cross-coupling between accommodation and convergence is optimized for a broad range of directions and distances of gaze. Vision Res 2008; 48:893-903. [PMID: 18281073 PMCID: PMC2323401 DOI: 10.1016/j.visres.2008.01.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Revised: 01/04/2008] [Accepted: 01/08/2008] [Indexed: 11/19/2022]
Abstract
Accommodation and convergence systems are cross-coupled so that stimulation of one system produces responses by both systems. Ideally, the cross-coupled responses of accommodation and convergence match their respective stimuli. When expressed in diopters and meter angles, respectively, stimuli for accommodation and convergence are equal in the mid-sagittal plane when viewed with symmetrical convergence, where historically, the gains of the cross coupling (AC/A and CA/C ratios) have been quantified. However, targets at non-zero azimuth angles, when viewed with asymmetric convergence, present unequal stimuli for accommodation and convergence. Are the cross-links between the two systems calibrated to compensate for stimulus mismatches that increase with gaze-azimuth? We measured the response AC/A and stimulus CA/C ratios at zero azimuth, 17.5 and 30 deg of rightward gaze eccentricities with a Badal Optometer and Wheatstone-mirror haploscope. AC/A ratios were measured under open-loop convergence conditions along the iso-accommodation circle (locus of points that stimulate approximately equal amounts of accommodation to the two eyes at all azimuth angles). CA/C ratios were measured under open-loop accommodation conditions along the iso-vergence circle (locus of points that stimulate constant convergence at all azimuth angles). Our results show that the gain of accommodative-convergence (AC/A ratio) decreased and the bias of convergence-accommodation increased at the 30 deg gaze eccentricity. These changes are in directions that compensate for stimulus mismatches caused by spatial-viewing geometry during asymmetric convergence.
Collapse
|
103
|
Kim JK, Hayden AM, Sadun EA, Sebag J, Sadun AA. Response pattern asymmetry of binocular vision vertical fusion amplitudes in a normal population. BINOCULAR VISION & STRABISMUS QUARTERLY 2008; 23:23-30. [PMID: 18393936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
PURPOSE To compare the maximum vertical fusion amplitudes in vertical directions (response pattern by respective higher eye), to investigate for possible asymmetry. METHODS Vertical fusion amplitude (VFA) was measured in one hundred normal adults with normal single binocular vision using a computer based device that produced a gradually increasing, but optically distant test distance, Vertical fusion amplitudes in the vertical left- over-right (L/R, elevation of the left eye above the right eye) pattern direction were compared to the vertical fusion amplitudes in the vertical right-over-left direction pattern(R/L). RESULTS The mean VFA was 4.08 +/-1.01 prism diopters, with vertical fusion amplitudes of 4.40 +/-1.44 prism diopters in the L/R direction and 3.75 +/-1.19 prism diopters in the R/L direction. There was no association between ocular dominance and the direction of greater VFA. Asymmetry in the vertical fusion response was found, with 77/100 subjects showing greater than a 10% difference between the means of the L/R and R/L measurements. The group with asymmetry had 17% greater mean VFA than the symmetric group. CONCLUSION Normal adults frequently have asymmetric directional vertical fusion amplitudes. The asymmetry appears to be due to the contribution of the direction with the greater VFA, rather than the result of both alternatives. These results are intriguing and bear further investigation. Possible explanations my be asymmetry of orbital anatomy or functional asymmetry of either muscular or neuronal origin. They do not appear to be due to the relative ocular dominance. Inherent VFA asymmetry should therefore be considered in all forms of vergence testing in the vertical direction.
Collapse
|
104
|
Nitta T, Akao T, Kurkin S, Fukushima K. Involvement of the cerebellar dorsal vermis in vergence eye movements in monkeys. Cereb Cortex 2007; 18:1042-57. [PMID: 17716988 DOI: 10.1093/cercor/bhm143] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Frontal-eyed primates use both smooth pursuit in frontoparallel planes (frontal pursuit) and pursuit-in-depth (vergence pursuit) to track objects moving slowly in 3-dimensional (3D) space. To understand how 3D-pursuit signals represented in frontal eye fields are processed further by downstream pathways, monkeys were trained to pursue a spot moving in 3D virtual space. We characterized pursuit signals in Purkinje (P) cells in the cerebellar dorsal vermis and their discharge during vergence pursuit. In 41% of pursuit P-cells, 3D-pursuit signals were observed. However, the majority of vermal-pursuit P-cells (59%) discharged either for vergence pursuit (43%) or for frontal pursuit (16%). Moreover, the majority (74%) of vergence-related P-cells carried convergence signals, displaying both vergence eye position and velocity sensitivity during sinusoidal and step vergence eye movements. Preferred frontal-pursuit directions of vergence + frontal-pursuit P-cells were distributed in all directions. Most pursuit P-cells (73%) discharged before the onset of vergence eye movements; the median lead time was 16 ms. Muscimol infusion into the sites where convergence P-cells were recorded resulted in a reduction of peak convergence eye velocity, of initial convergence eye acceleration, and of frontal-pursuit eye velocity. These results suggest involvement of the dorsal vermis in conversion of 3D-pursuit signals and in convergence eye movements.
Collapse
|
105
|
Kodaka Y, Sheliga BM, FitzGibbon EJ, Miles FA. The vergence eye movements induced by radial optic flow: some fundamental properties of the underlying local-motion detectors. Vision Res 2007; 47:2637-60. [PMID: 17706738 PMCID: PMC2082139 DOI: 10.1016/j.visres.2007.06.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Revised: 06/04/2007] [Indexed: 11/20/2022]
Abstract
Radial optic flow applied to large random dot patterns is known to elicit horizontal vergence eye movements at short latency, expansion causing convergence and contraction causing divergence: the Radial Flow Vergence Response (RFVR). We elicited RFVRs in human subjects by applying radial motion to concentric circular patterns whose radial luminance modulation was that of a square wave lacking the fundamental: the missing fundamental (mf) stimulus. The radial motion consisted of successive 1/4-wavelength steps, so that the overall pattern and the 4n+1 harmonics (where n=integer) underwent radial expansion (or contraction), whereas the 4n-1 harmonics--including the strongest Fourier component (the 3rd harmonic)--underwent the opposite radial motion. Radial motion commenced only after the subject had fixated the center of the pattern. The initial RFVRs were always in the direction of the 3rd harmonic, e.g., expansion of the mf pattern causing divergence. Thus, the earliest RFVRs were strongly dependent on the motion of the major Fourier component, consistent with early spatio-temporal filtering prior to motion detection, as in the well-known energy model of motion analysis. If the radial mf stimulus was reduced to just two competing harmonics--the 3rd and 5th--the initial RFVRs showed a nonlinear dependence on their relative contrasts: when the two harmonics differed in contrast by more than about an octave then the one with the higher contrast completely dominated the RFVRs and the one with lower contrast lost its influence: winner-take-all. We suggest that these nonlinear interactions result from mutual inhibition between the mechanisms sensing the motion of the different competing harmonics. If single radial-flow steps were used, a brief inter-stimulus interval resulted in reversed RFVRs, consistent with the idea that the motion detectors mediating these responses receive a visual input whose temporal impulse response function is strongly biphasic. Lastly, all of these characteristics of the RFVR, which we attribute to the early cortical processing of visual motion, are known to be shared by the Ocular Following Response (OFR)--a conjugate tracking (version) response elicited at short-latency by linear motion-and even the quantitative details are generally very similar. Thus, although the RFVR and OFR respond to very different patterns of global motion-radial vs. linear-they have very similar local spatiotemporal properties as though mediated by the same low-level, local-motion detectors, which we suggest are in the striate cortex.
Collapse
|
106
|
Kapoula Z, Bucci MP. Postural control in dyslexic and non-dyslexic children. J Neurol 2007; 254:1174-83. [PMID: 17676356 DOI: 10.1007/s00415-006-0460-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2006] [Revised: 10/09/2006] [Accepted: 10/24/2006] [Indexed: 10/23/2022]
Abstract
Postural control relies to visual-motion processing (afferent or efferent) and this is thought to be deficient in dyslexics. There is a controversy between clinic and fundamental studies as to the presence of posture abnormalities in dyslexics. To explore further this issue, this study examines posture stability in quite stance in 13 dyslexics (mean age: 13.5 years) and in 13 non-dyslexics (mean age: 13 years). Experiment 1 shows that, similarly to adults and elderly, all children (dyslexics and non-dyslexics), present better stability at near distance (i.e. smaller surface area of the COP, smaller lateral and antero-posterior oscillations). This could be due to reduced angular size of retinal motion signals at far, but also to convergence relaxation. Importantly, the surface area of the COP, lateral and antero-posterior oscillations are significantly higher in dyslexics. Experiment 2 examines posture stability while subjects make active vergence movements between a far and a near target. For many dyslexics, moving the eyes back and forth in depth rather improved postural stability. The only significant difference was that the lateral oscillations were still higher in dyslexics. Experiment 3 uses eye movement recordings (video-oculography) and demonstrates that dyslexics have problems with maintaining stable the angle of vergence for a prolonged period. We conclude that mild postural instability may exist in dyslexics but it could be improved by oculomotor and attention processes.
Collapse
|
107
|
Laird PW, Hatt SR, Leske DA, Holmes JM. Stereoacuity and binocular visual acuity in prism-induced exodeviation. J AAPOS 2007; 11:362-6. [PMID: 17419082 PMCID: PMC2042509 DOI: 10.1016/j.jaapos.2007.01.116] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2006] [Revised: 01/08/2007] [Accepted: 01/10/2007] [Indexed: 11/20/2022]
Abstract
BACKGROUND Intermittent exotropia may be controlled by accommodative or motor convergence. Previous studies have reported that reduced binocular visual acuity in intermittent exotropia is due to the accommodation required to control the deviation. To test this hypothesis, we simulated convergence stress by inducing exodeviations in normal volunteers to investigate whether the transition from nonfused to fused is associated with a gradual or immediate transition in stereoacuity and binocular visual acuity. METHODS Convergence stress was induced in 25 visually normal adults with 40(Delta) base-out prism and reduced stepwise in increments of 5(Delta) until 20(Delta), and 2(Delta) thereafter. Stereoacuity (Frisby Davis Distance [FD2] and the Distance Randot [DR]) and binocular visual acuity were measured at each step. For each subject, the recovery of fine stereoacuity (< or =60 arcsec) was categorized as immediate (nil to fine) or gradual (nil to moderate to fine). RESULTS Twenty-four of 25 (96%) showed gradual recovery of fine stereoacuity on either FD2 or DR. Median binocular visual acuity at baseline, first level of fusion, and subsequent levels was 20/15. CONCLUSIONS Under convergence stress, the transition from nonfused to fused is accompanied by a gradual recovery of fine stereoacuity in most individuals, consistent with some studies of patients with intermittent exotropia. Nevertheless, this degradation of stereoacuity was not associated with decreased binocular visual acuity, suggesting that accommodative convergence may not be recruited to restore and maintain binocularity under conditions of convergence stress.
Collapse
|
108
|
Semmlow JL, Alvarez TL, Pedrono C. Dry dissection of disparity divergence eye movements using independent component analysis. Comput Biol Med 2007; 37:910-8. [PMID: 16867300 DOI: 10.1016/j.compbiomed.2006.03.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Revised: 03/27/2006] [Accepted: 03/30/2006] [Indexed: 10/24/2022]
Abstract
Dry dissection, a concept developed by Lawrence Stark, includes a variety of techniques designed to isolate internal neural control components by using cleverly designed stimulus or measurement protocols. As envisioned by Stark, the concept applies only to motor systems that have multiple stimulus inputs and/or response behaviors. A new application of independent component analysis (ICA) can be used to extend the dry dissection concept to identify motor components from a single, isolated response. It is only necessary that multiple responses can be obtained to the same stimulus. This "ensemble ICA" technique is well suited to analyze various eye movement behaviors as even isolated motor systems often include multiple control processes. Here we apply ensemble ICA to vergence eye movements: the inward (convergence) or outward (divergence) turning of the eyes that allows us to view images at various distances. Previous studies concerning the dynamics of convergence and divergence eye movements have produced varied, sometimes contradictory, results: most studies report that convergence is considerably faster than divergence, but opposite results have also been reported. Experimental results have shown that the dynamics of divergence movements depend on the initial vergence position while those of convergence do not: divergence eye movements in response to targets initially near to the subject can attain peak velocities twice that of those driven by more distant targets. To determine the underlying cause of this behavior, ensemble ICA was applied to divergence responses. Results show that both convergence and divergence contain a sustained (step-like) and a transient (pulse-like) control component, but the amplitude of the transient component in divergence is dependent on initial stimulus position.
Collapse
|
109
|
Merriam SW, Kushner BJ. An investigation into the mechanisms causing antipodean strabismus. J AAPOS 2007; 11:249-53. [PMID: 17360204 DOI: 10.1016/j.jaapos.2006.10.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2006] [Revised: 10/24/2006] [Accepted: 10/25/2006] [Indexed: 11/30/2022]
Abstract
BACKGROUND Antipodean strabismus is a rare clinical entity in which a patient manifests an esotropia when fixating with one eye and an exotropia when fixating with the other eye. It has been described in the settings of marked uncorrected anisometropia, dissociated strabismus or combinations of paresis, and mechanical restriction of eye movement. METHODS A retrospective review of four patients with antipodean strabismus. RESULTS All patients demonstrated a unique and uncommon pattern in which there was esotropia with one eye fixating and exotropia with the other eye fixating. None of the patients demonstrated anisometropia or signs of dissociated horizontal deviation. One patient developed antipodean strabismus after prior surgery to correct a traumatic sixth nerve palsy. Another patient had an associated pseudotumor cerebri. The other two patients had no pertinent medical history and, on clinical examination, demonstrated markedly asymmetric accommodative convergence/accommodation (AC/A) ratios. CONCLUSIONS Antipodean strabismus is an atypical heterotropia, which can be associated with a variety of clinical findings. This article demonstrates the uniqueness of this clinical entity and illustrates the first association of this pattern with a markedly asymmetric AC/A ratio.
Collapse
|
110
|
Bharadwaj SR, Hoenig MP, Sivaramakrishnan VC, Karthikeyan B, Simonian D, Mau K, Rastani S, Schor CM. Variation of binocular-vertical fusion amplitude with convergence. Invest Ophthalmol Vis Sci 2007; 48:1592-600. [PMID: 17389488 PMCID: PMC2198903 DOI: 10.1167/iovs.06-1018] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE The maximum binocular vertical disparity that can be fused with disparity vergence (vertical-fusion amplitude or VFA), varies with convergence angle. VFA is larger for convergence responses to near than to far viewing distances; however, the clinical norms for changes in VFA with convergence have not been established. VFA at several convergence angles was measured to obtain a quantitative description of the changes in VFA with convergence. METHODS Fifty-six adults took part in the study. Horizontal and vertical disparity stimuli were presented on a computer monitor by using the red-green anaglyphic technique. Stimulus to convergence was altered either by changing horizontal disparity on the computer monitor (experiment I: nine horizontal disparities: 1.2-22.5 PD [Delta]) or by changing the binocular viewing distance (experiment II: five viewing distances: 25-300 cm). Convergence was held constant during an experimental session, while vertical disparity was incremented in steps of 0.05 Delta after a subjective report of fusion, until the subject reported diplopia. The maximum vertical disparity that could be fused was defined as the VFA. RESULTS VFA increased linearly over the range of convergence stimuli (y = 0.10x + 1.62) and intersubject variability of VFA increased marginally with the amount of convergence. Linear regression equations with similar slopes and y-intercepts were observed in experiments I and II. CONCLUSIONS The results of the experiments provide a quantitative description of a linear relationship between VFA and convergence. The linear regression equation could be used in a clinical setting to establish norms and to screen for vertical vergence abnormalities.
Collapse
|
111
|
Abstract
AIM Recent studies suggest that Asian strabismus patterns are different from those in the West. This study aims to determine the profile of children with comitant horizontal strabismus in Singapore. METHOD 682 children aged <or=16 years presenting with strabismus for the first time between 2000 and 2002 were included in this study. The type and size of the squint, visual acuity, refractive error and stereopsis were noted. RESULTS 493 children (72%) were exotropic, the majority (92%) of whom had intermittent exotropia, X(T). The divergence excess type X(T) was most common (59.5%), followed by basic (29.0%) and convergence-weakness (11.5%). Children with X(T) demonstrated stereopsis for near in 92% and distance in 50%. Esotropia was present in 191 (28%) children (23% infantile and 53% accommodative). Children with infantile esotropia presented significantly younger (2.8 years vs 4.5 years), had larger squint size (35D vs 26D) and were less hyperopic (+0.78D vs +2.79D). Amblyopia or ocular preference was noted in 50% of children with infantile esotropia, and 43% with accommodative esotropia. CONCLUSION Twice as many Singaporean children presented with exotropia than esotropia. However, within the exotropia and esotropia groups, the distribution and characteristics of various strabismus subtypes bore similar characteristics to those described in the West.
Collapse
|
112
|
Caines E, Dahl M, Holmström G. Longterm oculomotor and visual function in spina bifida cystica: a population-based study. ACTA ACUST UNITED AC 2007; 85:662-6. [PMID: 17403023 DOI: 10.1111/j.1600-0420.2007.00905.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE To document and describe the development from birth of visual and oculomotor functions in a group of children with spina bifida cystica (myelomeningocele and myeloschisis [MMC]). The emphasis in this study is on findings at 12-14 year follow-up. METHODS Twenty children aged 12-14 years with myelomeningocele and Chiari-related malformations were examined by an orthoptist and a paediatric ophthalmologist. A further child who did not wish to participate actively in the study is also reported. Visual acuity for near and distance, refractometer readings in cycloplegia, the presence of ocular motility disorders and nystagmus were recorded. Accommodation, convergence, colour vision and stereo acuity were assessed and the fundus and media were examined. RESULTS Six children (29%) in the study group had subnormal vision, although no child was visually impaired. Eleven (52%) showed manifest strabismus and 17 (81%) had a significant refractive error. Near visual acuity was normal in nearly all the children, but accommodation was defective in 10. Nine children had nystagmus and two had optic atrophy. No visual field defects were found. CONCLUSIONS The high incidence of ocular disturbances in children with spina bifida highlights the importance of regular ophthalmological investigation and follow-up.
Collapse
|
113
|
Wang ZI, Dell'Osso LF, Tomsak RL, Jacobs JB. Combining recessions (nystagmus and strabismus) with tenotomy improved visual function and decreased oscillopsia and diplopia in acquired downbeat nystagmus and in horizontal infantile nystagmus syndrome. J AAPOS 2007; 11:135-41. [PMID: 17280849 DOI: 10.1016/j.jaapos.2006.10.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Revised: 10/23/2006] [Accepted: 10/23/2006] [Indexed: 11/20/2022]
Abstract
PURPOSE To investigate the effects of combined tenotomy and recession procedures on both acquired downbeat nystagmus and horizontal infantile nystagmus. METHODS Patient 1 had downbeat nystagmus with a chin-down (upgaze) position, oscillopsia, strabismus, and diplopia. Asymmetric superior rectus recessions and inferior rectus tenotomies reduced right hypertropia and rotated both eyes downward. Patient 2 had horizontal infantile nystagmus, a 20 degrees left-eye exotropia, and alternating (abducting-eye) fixation. Lateral rectus recessions and medial rectus tenotomies were performed. Horizontal and vertical eye movements were recorded pre- and postsurgically using high-speed digital video. The eXpanded Nystagmus Acuity Function (NAFX) and nystagmus amplitudes and frequencies were measured. RESULTS Patient 1: The NAFX peak moved from 10 degrees up to primary position where NAFX values improved 17% and visual acuity increased 25%. Vertical NAFX increased across the -10 degrees to +5 degrees vertical range. Primary-position right hypertropia decreased approximately 50%; foveation time per cycle increased 102%; vertical amplitude, oscillopsia, and diplopia were reduced, and frequency was unchanged. Patient 2: Two lateral, narrow high-NAFX regions (due to alternating fixation) became one broad region with a 43% increase in primary position (acuity increased approximately 92.3%). Diplopia amplitude decreased; convergence and gaze holding were improved. Primary-position right exotropia was reduced; foveation time per cycle increased 257%; horizontal-component amplitude decreased 45.7%, and frequency remained unchanged. CONCLUSIONS Combining tenotomy with nystagmus or strabismus recession procedures increased NAFX and visual acuities and reduced diplopia and oscillopsia in downbeat nystagmus and infantile nystagmus.
Collapse
|
114
|
Abstract
PURPOSE Convergence insufficiency (CI) is the most prevalent of binocular dysfunctions. A prime finding in the diagnosis of CI is the near point of convergence (NPC). METHODS The NPC was measured six different times on the same 539 children, once in the fall and once in the spring, over the course of 3 years. At each evaluation, the NPC was performed three consecutive times. An accommodative target was used in the testing and the breaks and recoveries were carefully measured and recorded to the nearest centimeter. Normative data for the break and recovery finding were calculated. RESULTS We found that the NPC measures receded significantly over three consecutive tests. The recession was not considered clinically significant for either the break or recovery measures. When various break and recovery findings were compared with reported symptoms, it was discovered that one of the break findings statistically predicted the symptomatic group from the asymptomatic group. CONCLUSIONS The NPC break and recovery does not change appreciably with multiple administrations of the test in the same test period. The criteria for a NPC break score to differentiate the more symptomatic and less symptomatic, elementary school children on the average should be 5 cm, or less. The NPC break and recovery criteria described here should be tentatively used as one of the benchmarks in the diagnosis of convergence insufficiency.
Collapse
|
115
|
Quinlan DJ, Culham JC. fMRI reveals a preference for near viewing in the human parieto-occipital cortex. Neuroimage 2007; 36:167-87. [PMID: 17398117 DOI: 10.1016/j.neuroimage.2007.02.029] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2006] [Revised: 02/12/2007] [Accepted: 02/13/2007] [Indexed: 10/23/2022] Open
Abstract
Posterior parietal cortex in primates contains several functional areas associated with visual control of body effectors (e.g., arm, hand and head) which contain neurons tuned to specific depth ranges appropriate for the effector. For example, the macaque ventral intraparietal area (VIP) is involved in head movements and is selective for motion in near-space around the head. We used functional magnetic resonance imaging to examine activation in the putative human VIP homologue (pVIP), as well as parietal and occipital cortex, as a function of viewing distance when multiple cues to target depth were available (Expt 1) and when only oculomotor cues were available (Expt 2). In Experiment 1, subjects viewed stationary or moving disks presented at three distances (with equal retinal sizes). Although activation in pVIP showed no preference for any particular spatial range, the dorsal parieto-occipital sulcus (dPOS) demonstrated a near-space preference, with activation highest for near viewing, moderate for arm's length viewing, and lowest for far viewing. In Experiment 2, we investigated whether the near response alone (convergence of the eyes, accommodation of the lens and pupillary constriction) was sufficient to elicit this same activation pattern. Subjects fixated lights presented at three distances which were illuminated singly (with luminance and visual angle equated across distances). dPOS displayed the same gradient of activation (Near>Medium>Far) as that seen in Experiment 1, even with reduced cues to depth. dPOS seems to reflect the status of the near response (perhaps driven largely by vergence angle) and may provide areas in the dorsal visual stream with spatial information useful for guiding actions toward targets in depth.
Collapse
|
116
|
Suryakumar R, Meyers JP, Irving EL, Bobier WR. Vergence accommodation and monocular closed loop blur accommodation have similar dynamic characteristics. Vision Res 2006; 47:327-37. [PMID: 17187839 DOI: 10.1016/j.visres.2006.10.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 09/27/2006] [Accepted: 10/23/2006] [Indexed: 10/23/2022]
Abstract
Retinal blur and disparity are two different sensory signals known to cause a change in accommodative response. These inputs have differing neurological correlates that feed into a final common pathway. The purpose of this study was to investigate the dynamic properties of monocular blur driven accommodation and binocular disparity driven vergence-accommodation (VA) in human subjects. The results show that when response amplitudes are matched, blur accommodation and VA share similar dynamic properties.
Collapse
|
117
|
Kapoula Z, Bucci MP, Jurion F, Ayoun J, Afkhami F, Brémond-Gignac D. Evidence for frequent divergence impairment in French dyslexic children: deficit of convergence relaxation or of divergence per se? Graefes Arch Clin Exp Ophthalmol 2006; 245:931-6. [PMID: 17186259 DOI: 10.1007/s00417-006-0490-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2006] [Revised: 09/07/2006] [Accepted: 10/21/2006] [Indexed: 10/23/2022] Open
Abstract
AIM There is a controversy as to whether dyslexic children present visuo-motor disabilities such as vergence and accommodative problems assessed with orthoptic tests. The purpose of this study is to re-examine this issue in a large population of children. METHODS Extensive orthoptic evaluation was made in 57 dyslexic and 46 non-dyslexic ("normal") age-matched children. Convergence and divergence capacities were evaluated at two distances (30 cm and 400 cm). RESULTS Binocular vision measured with stereo-acuity tests was normal in dyslexics. In contrast, the near point of convergence was significantly more remote in dyslexics; most importantly, divergence at both far and near distance was significantly more reduced in dyslexics (median value 4 pD and 10 pD, respectively, at far and near) than in "normals" (median value 6 pD and 12 pD, at far and near). CONCLUSION The existence of the divergence deficit at far distance indicates the presence of deficit of divergence per se, independently from convergence and accommodation relaxation. This result is novel and corroborated by physiological studies indicating distinct control of convergence and divergence, both at the cortical and subcortical premotor level. We conclude that vergence deficits are frequently present in dyslexics, and that dyslexics should be re-educated; training should address distinctively convergence and divergence subsystems.
Collapse
|
118
|
Sheliga BM, FitzGibbon EJ, Miles FA. Human vergence eye movements initiated by competing disparities: evidence for a winner-take-all mechanism. Vision Res 2006; 47:479-500. [PMID: 17118422 PMCID: PMC2170857 DOI: 10.1016/j.visres.2006.09.027] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 09/28/2006] [Accepted: 09/29/2006] [Indexed: 11/25/2022]
Abstract
Vergence eye movements were elicited in human subjects at short latencies (approximately 70 ms) by applying binocular disparities briefly (200 ms) to large grating patterns (46 degrees wide, 35 degrees high). The positions of both eyes were recorded with the electromagnetic search coil technique. Using a dichoptic viewing arrangement (Wheatstone stereoscope), each eye viewed two overlapping 1-D sine waves that had the same orientation but different spatial frequencies. These two sine waves each had a binocular disparity that was 1/4 of its wavelength and the effect of varying their relative contrasts was examined (15 contrast ratios ranging from 0.125 to 8). The first experiment used horizontal gratings and recorded the vertical vergence responses when the two sine waves had spatial frequencies in the ratio 3:5 and vertical disparities of opposite sign. Initial vergence responses showed a highly nonlinear dependence on the contrast ratio. On average, when the contrast of one sine wave exceeded that of the other by a factor of >2.2, the sine wave with the higher contrast dominated responses and the sine wave with the lower contrast had almost no influence: winner-take-all. A second experiment, which used vertical gratings and recorded the horizontal vergence responses when the two sine waves had spatial frequencies in the ratio 3:5 and horizontal disparities of opposite sign, also uncovered nonlinear interactions but these were much more variable from one subject to another and, on average, one sine wave did not achieve complete dominance until its contrast exceeded that of the other by a factor of >4.5. When these two experiments were repeated with grating patterns in which the two sine waves had spatial frequencies in the ratio 3:7 and disparities of the same sign, similar nonlinear interactions were apparent. We attribute the nonlinear dependence on relative contrast to mutual inhibition between the neural elements processing the disparities of the two sine waves. We further suggest that this interaction will help to maintain binocular alignment on the objects in the plane of regard because the retinal images of those objects will tend to be better focused-and hence tend to have higher contrasts-than the images of objects in other depth planes.
Collapse
|
119
|
Read JCA, Cumming BG. Does depth perception require vertical-disparity detectors? J Vis 2006; 6:1323-55. [PMID: 17209738 DOI: 10.1167/6.12.1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2006] [Accepted: 08/23/2006] [Indexed: 11/24/2022] Open
Abstract
Stereo depth perception depends on the fact that objects project to different positions in the two eyes. Because our eyes are offset horizontally, these retinal disparities are mainly horizontal, and horizontal disparity suffices to give an impression of depth. However, depending on eye position, there may also be small vertical disparities. These are significant because, given both vertical and horizontal disparities, the brain can deduce eye position from purely retinal information and, hence, derive the position of objects in space. However, we show here that, to achieve this, the brain need measure only the magnitude of vertical disparity; for physically possible stimuli, the sign then follows from the stereo geometry. The magnitude of vertical disparity--and hence eye position--can be deduced from the response of purely horizontal-disparity sensors because vertical disparity moves corresponding features off the receptive fields, reducing the effective binocular correlation. As proof, we demonstrate an algorithm that can accurately reconstruct gaze and vergence angles from the population activity of pure horizontal-disparity sensors and show that it is subject to the induced effect. Given that disparities experienced during natural viewing are overwhelmingly horizontal and that eye position measures require only horizontal-disparity sensors, this work raises two questions: Does the brain in fact contain sensors tuned to nonzero vertical disparities, and if so, why?
Collapse
|
120
|
Miyata M, Hasebe S, Ohtsuki H. Influence of accommodative lag upon the far-gradient measurement of accommodative convergence to accommodation ratio in strabismic patients. Jpn J Ophthalmol 2006; 50:438-442. [PMID: 17013696 DOI: 10.1007/s10384-006-0353-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Accepted: 02/09/2006] [Indexed: 11/26/2022]
Abstract
PURPOSE To determine the influence of the lag of accommodation (LOA) on the accommodative convergence to accommodation (AC/A) ratio measured by the far-gradient method in strabismic patients. METHODS The AC/A ratio was measured with a distance target viewed with and without -3.00 diopter (D) addition lenses in 63 patients with different types of strabismus (age range, 7-34 years; range of strabismic angle, -60 to +40 prism diopters; refractive error range, -7.33 to +6.63 D). The LOA for the same lens was measured with an open-view-type autorefractometer. The stimulus AC/A ratio and the AC/A ratio adjusted by the individually measured LOA (adjusted AC/A ratio) were compared. RESULTS The mean +/- SD of the LOA to the -3.00 D lenses was 1.06 +/- 0.43 D. The mean adjusted AC/A ratio was 41% greater than the stimulus AC/A ratio. The LOA differed widely among patients (0.13 to 2.14 D), and a large LOA tended to appear in myopic or young patients. CONCLUSIONS The AC/A ratio obtained using the conventional far-gradient method is significantly biased by the LOA, and thus does not always represent the actual relationship between accommodation and vergence control systems.
Collapse
|
121
|
Coubard OA, Kapoula Z. Neural correlates of the visual vertical meridian asymmetry. J Vis 2006; 5:1-19. [PMID: 15831062 DOI: 10.1167/5.1.1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Indexed: 11/24/2022] Open
Abstract
Human visual performance is better below than above fixation along the vertical meridian-a phenomenon we refer to as vertical meridian asymmetry (VMA). Here, we used fMRI to investigate the neural correlates of the VMA. We presented stimuli of two possible sizes and spatial frequencies on the horizontal and vertical meridians and analyzed the fMRI data in subregions of early visual cortex (V1/V2) that corresponded retinotopically to the stimulus locations. Asymmetries in both the spatial extent and amplitude of the fMRI measurements correlated with the behavioral VMA. These results demonstrate that the VMA has a neural basis at the earliest stages of cortical visual processing and imply that visual performance is limited by the pooled sensory responses of large populations of neurons in the visual cortex.
Collapse
|
122
|
Lueder GT, Norman AA. Strabismus surgery for elimination of bifocals in accommodative esotropia. Am J Ophthalmol 2006; 142:632-5. [PMID: 17011856 DOI: 10.1016/j.ajo.2006.05.046] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Revised: 05/23/2006] [Accepted: 05/25/2006] [Indexed: 11/19/2022]
Abstract
PURPOSE This study reports the outcomes of strabismus surgery to eliminate bifocals in patients with accommodative esotropia with a high accommodative convergence to accommodation (AC:A) ratio. DESIGN Retrospective interventional case series. METHODS Sixteen patients who wore bifocals for treatment of accommodative esotropia with a high AC:A ratio underwent strabismus surgery following prism adaptation testing (PAT) for the near angle of esotropia without bifocals. Outcomes were considered successful if patients had microtropias and maintained fusion without bifocals. RESULTS All patients had successful outcomes after one or two surgeries. Three of 13 (23%) patients with positive PATs required two surgeries. Two of three (67%) patients with negative PATs required two surgeries. Binocularity remained the same in 13 patients and improved in three patients. Glasses were eliminated entirely in eight of 16 (50%) patients. CONCLUSIONS Strabismus surgery may eliminate the need for bifocal glasses in patients with accommodative esotropia with a high AC:A ratio, with many patients able to discontinue glasses entirely. Preoperative PAT may help predict the risk of requiring more than one surgery.
Collapse
|
123
|
Blythe HI, Liversedge SP, Joseph HSSL, White SJ, Findlay JM, Rayner K. The binocular coordination of eye movements during reading in children and adults. Vision Res 2006; 46:3898-908. [PMID: 16879851 DOI: 10.1016/j.visres.2006.06.006] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Revised: 06/08/2006] [Accepted: 06/10/2006] [Indexed: 11/29/2022]
Abstract
Recent evidence indicates that each eye does not always fixate the same letter during reading and there has been some suggestion that processing difficulty may influence binocular coordination. We recorded binocular eye movements from children and adults reading sentences containing a word frequency manipulation. We found disparities of significant magnitude between the two eyes for all participants, with greater disparity magnitudes in children than adults. All participants made fewer crossed than uncrossed fixations. However, children made a higher proportion of crossed fixations than adults. We found no influence of word frequency on children's fixations and on binocular coordination in adults.
Collapse
|
124
|
Lê TT, Kapoula Z. Distance impairs postural stability only under binocular viewing. Vision Res 2006; 46:3586-93. [PMID: 16899270 DOI: 10.1016/j.visres.2006.06.018] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2005] [Revised: 06/23/2006] [Accepted: 06/27/2006] [Indexed: 11/20/2022]
Abstract
Prior studies indicate that postural stability under binocular viewing is not better than under monocular viewing. This was tested at the distances of 145 cm [Fox, C.R. (1990). Some visual influences on human postural equilibrium: binocular versus monocular fixation. Perception and Psychophysics, 47 (5), 409-422] and 90 cm [Isotalo, E., Kapoula, Z., Feret, P.H., Gauchon, K., Zamfirescu, F., & Gagey, P.M. (2004). Monocular versus binocular vision in postural control. Auris Nasus Larynx, 31 (1), 11-17]. On the other hand, postural stability is known to decrease with distance increase. We re-examined the effect of binocular versus monocular viewing on postural stability at near and far distances (40 and 200 cm), and for both young (25.7+/-2.7 years), and old subjects (61.2+/-4.6 years). For both groups of subjects, proximity decreased the area of CoP, the standard deviation of antero-posterior sway (SDy) and the variance of speed. The group of elderly presented increased variance of speed at far distance in comparison with young subjects. The novel finding is the interaction between distance and viewing condition. Under binocular viewing, the area of CoP was significantly higher at far distance than at near; in contrast, monocular viewing produced similar CoP values at both distances. Increased instability at far distance when both eyes are viewing is attributed to decreased sensitivity to binocular disparity cues and to visual motion in depth resulting from body sway. Monocular viewing would provide similar stability at far and at near distance, because sensitivity to lateral visual motion, detected monocularly, decreases less with distance than sensitivity to binocularly detected motion in depth. Alternatively, such monocular viewing could increase subject's attention and lead to tighter postural control regardless of the distance.
Collapse
|
125
|
Kumar AN, Han YH, Liao K, Leigh RJ. Tests of Hering- and Helmholtz-type models for saccade-vergence interactions by comparing visually guided and memory-guided movements. Ann N Y Acad Sci 2006; 1039:466-9. [PMID: 15827001 DOI: 10.1196/annals.1325.046] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We compared the dynamic properties of memory-guided and visually-guided saccade-vergence movements. For memory-guided responses, convergence components were slowed proportionally more than corresponding saccadic components, compared with visually-guided responses. This result is consistent with independent saccadic and vergence systems, and supports a Hering-type model for saccade-vergence interactions.
Collapse
|