Horizontal and vertical prism adaptation are different mechanisms

As part of a study on subjects with convergence insufficiency (CI), their vertical and horizontal vergence adaptation was assessed and compared with age matched controls in order to investigate whether the horizontal adaptation system can be regarded as being independent of the vertical adaptation system. Using a flashed Maddox rod technique horizontal vergence adaptation was found to be reduced in CI subjects whereas no difference could be found in vertical adaptation. These results confirm that the vertical and horizontal adaptation systems can be treated as independent mechanisms.     

Reliability of rotary prism fusional vergence ranges.

BACKGROUND: The measurement of fusional vergence ranges is an important clinical test in the assessment of binocular vision status. Fusional vergence ranges are typically measured by recording a patient's reports of blur, break, and recovery to base-in (BI) and base-out (BO) prism. Published reliability data on fusional vergence ranges are very limited. METHODS: Eight subjects underwent four testing sessions, at which repeated measurements of fusional vergence ranges were taken. Near ranges were tested at the first session only Distance ranges were tested at all four sessions. Intra-examiner standard deviations were calculated for each fusional vergence test result (BI and BO; blur, break, and recovery) for each session. Intra-examiner standard deviations were averaged. These values were used to determine 95% limits of agreement. RESULTS: The 95% limits of agreement were between 2 delta and 2.5 delta for the distance BI break and recovery and for the near BI recovery; between 3 and 4 delta for near BI break and near BO break; between 4 and 5 delta for distance BO blur and recovery and for near BI blur; and between 5 and 5.5 delta for distance BO break and near BO blur and recovery.     

Horizontal fusional responses to stimuli containing artificial scotomas

Horizontal fusional responses were studied with stimuli containing binocular or monocular, artificial, stabilized, scotomas. Binocular scotomas of 5-deg, 10-deg, and 15-deg diameters were utilized. The fusional responses to scotomatic stimuli were compared with full-field stimulus responses. All responses contained significant motor and nonmotor (sensory) components. Overall motor compensation to stimuli with 10-deg and 15-deg scotomas was reduced, while the overall motor compensation to stimuli with 5-deg scotomas was not. With full-field stimuli and with stimuli containing binocular scotomas, the changes in the two eyes' lines of sight were often asymmetric in response to symmetric disparity changes. This response asymmetry was exacerbated by the presence of monocular scotomas. Fixation was less steady with stimuli containing 10-deg or 15-deg binocular scotomas than it was in response to full-field stimulation. The fusional responses to annular stimuli were similar to those elicited by scotomatic stimuli.     

矫正眼镜的垂直屈光参差对患者垂直融像度影响分析

目的 分析矫正眼镜的垂直屈光参差对患者垂直融像度的影响.方法 样本来自我院验光配镜中心的105名患者,按双眼矫正眼镜的垂直屈光参差将研究对象分为两组:无垂直屈光参差组(双眼的垂直屈光参差差别＜1.0D)和垂直屈光参差组.在征得其本人同意的情况下,对其进行屈光检查并用综合验光仪进行平滑的垂直融像度的测定.收集的数据用相关分析探讨双眼的垂直屈光参差度与垂直融像度的关系;结果 对照组的垂直融像度(3.61±1.01)D;垂直屈光参差组的垂直融像度为(4.45±1.50)D(t=3.432,P=0.001);结论 当暴露于垂直屈光参差的刺激时,垂直融像度会相应增加,因此在屈光参差验配中要尽量避免干扰患者的双眼视功能,以保证舒适的视觉.     

Vertical fusional amplitudes in patients wearing vertical anisometropic correction.

OBJECTIVE: To examine the relationship between vertical anisometropic spectacle correction and vertical fusional amplitudes in patients. DESIGN: Comparative observational case series. PARTICIPANTS: Twenty-one patients exposed to greater than 0.5 diopters of vertical anisometropic spectacle correction were compared with 46 patients not exposed to anisometropic correction. METHODS: Vertical fusional amplitudes were recorded in all patients using a prism bar. MAIN OUTCOME MEASURES: Vertical fusional amplitudes and vertical anisometropia. RESULTS: In patients exposed to greater than 0.5 diopters of vertical anisometropic spectacle correction, vertical fusional amplitudes measured 5.2+/-1.4 prism diopters. Patients not exposed to anisometropic correction had vertical fusional amplitudes of 2.7+/-1.2 prism diopters (P < 0.0001). CONCLUSION: Patients with vertical anisometropic correction have increased vertical fusional amplitudes. This finding is relevant when evaluating patients with ocular motility disorders, especially with regard to distinguishing acquired versus longstanding deviations.     

Vergence adaptive changes with varying magnitudes of prism-induced disparities and fusional amplitudes

Vergence adaptation response monitored with various prism disparities demonstrated that the rates of adaptation decreased as the prismatic effect was increased. However, the amount adapted increased with the increase in the value of the prism until this value fell outside the fusional amplitude; the amount adapted then decreased. However, a large disparity can be adapted to with ease if the prismatic effect is increased gradually in small steps. The clinical implications of these results are discussed.     

有晶状体眼后房型人工晶状体植入术后水平隐斜及融合功能的变化

目的评价有晶状体眼后房型人工晶状体（PPC-ICL）植入治疗高度近视术后患者水平隐斜及融合功能的变化。方法自身对照研究。被检者为行PPC-ICL植入术治疗高度近视的患者42例（84眼）,分别于术前、术后1个月和术后6个月行远、近水平隐斜及远、近内外融合的测定。采用重复测量的方差分析对术前、术后1个月及6个月以上各参数进行统计分析。结果术后1个月时看远、看近水平隐斜分别为（-2.24±3.33）△和（-4.95±5.45）△,术后6个月时分别为（-2.02±2.93）△和（-3.55±5.10）△,均低于术前[（-4.33±4.62）△和（-8.88±6.74）△],差异有统计学意义（F=5.00、9.53,P＜0.01）。术后1个月时看远、看近内融合分别为（12.74±3.52）△和（14.36±3.96）△,术后6个月时分别为（13.95±4.01）△和（16.79±3.90）△,均高于术前[（9.83±2.68）△和（10.95±3.28）△],差异有统计学意义（F=15.83、25.96,P＜0.01）。术后1个月时看远、看近外融合分别为（8.05±2.15）△和（15.29±3.52）△,术后6个月时分别为（7.74±1.86）△和（14.64±3.11）△,均高于术前[（7.36±2.66）△和（13.43±3.11）△]。术后看近外融合较术前差异有统计学意义（F=3.53,P＜0.05）,看远外融合差异无统计学意义（F=0.99,P＞0.05）。结论PPC-ICL植入术后患者水平隐斜和融合范围较术前改善,视觉舒适度提高。     

Surgical outcome after prism adaptation for esotropia with a distance-near disparity.

INTRODUCTION: Prism adaptation for patients with esotropia and a distance-near disparity is controversial. The purpose of this study was to evaluate the surgical outcome for patients who underwent prism adaptation for esotropia with a distance-near disparity and determine whether both preoperative sensory and motor fusion are necessary to determine surgical success. METHODS: The medical records of 65 prism-adapted patients with a distance-near disparity of 9 PD or more were reviewed. Prism responders had a fusion response to near Worth 4-dot test and a deviation with prisms of 8 PD or less of esotropia at near, and 5 PD or less of exotropia at distance, or both. The same criteria were used postoperatively to assess a successful surgical outcome. Patients were operated for the near angle or greater than the near angle. RESULTS: Fifty-eight of 65 patients (89%) demonstrated fusion with prisms. Twenty of 65 patients (31%) had increased deviations that were greater than their original near angle (prism builders). Eleven percent (7 of 65) had no fusion. Postoperatively, 88% (51 of 58) of all fusers, 95% (18 of 19) of prism builders, and 71% (5 of 7) of nonfusers had a good surgical outcome of 8 PD or less of esotropia at near, 5 PD or less of exotropia at distance, or both. CONCLUSIONS: Prism response for distance-near disparity esotropia is a good indicator of postoperative outcome. Responders to prism adaptation had a better surgical outcome compared with nonresponders. In particular, prism adaptation aids in detecting those patients who will benefit from larger amounts of surgical correction.     

Horizontal and vertical deviations after prism neutralization and diagnostic occlusion in intermittent exotropia

The long-term result of surgery in intermittent exotropia is often an undercorrection and relapse into tropia. This may be due to an underestimation of the horizontal angle and/or an undetected vertical component. The aim of the present study was to test which method, prism neutralization or diagnostic occlusion was best suited to attain the maximal angle of horizontal and vertical deviation. Twenty-two patients with intermittent exotropia but without initial vertical or incomitant components participated in the study. The horizontal deviation was neutralized with prisms for periods of 14 days on four different occasions with diagnostic occlusion three times for periods of one, three or ten days in between. Measurements of sensory functions and the amount of deviations were performed before and after the procedures. It was shown that the largest horizontal deviation was elicited by prism neutralization without previous occlusion and the largest vertical deviation by diagnostic occlusion for ten days. Conditions of initial divergence excess and lateral incomitances usually were restored by both procedures.     

Preoperative prism adaptation test in normosensoric strabismus

In 19 patients with normosensoric esotropia, the squint angles measured with the alternate cover test were compared with those after prolonged prismatic correction of the squint angle and with those after prolonged occlusion of one eye. All patients showed an increase of the squint angle after prism adaptation. The angle was generally smaller after diagnostic occlusion of one eye than after prism adaptation. We assume that the increase in the squint angle after prism adaptation is caused by an anomalous sensorial relationship between the two eyes that was not detected with the usual psychophysical tests. Surgery tailored to the squint angle after prism adaptation seems advisable in patients with normosensoric esotropia.     

The effect of saccades and brief fusional stimuli on phoria adaptation.

PURPOSE: The purpose of this experiment was to determine whether brief fusional stimuli and saccades similar to those seen in the alternate cover test affect phoria disadaptation. METHODS: Three cover test conditions were performed randomly. Before each test condition, subjects fused for 2 min at an angle convergent to the subjective phoria. In one test condition, subjects viewed monocularly. In another condition, subjects alternately fixated with each eye (no binocular time). In a third condition, subjects alternately fixated with each eye, and there was a 100-ms period of binocular viewing between alternations. The ocular vergence angle was monitored using scleral search coils. RESULTS: Vergence angle was plotted against time for each condition. The area under this plot was determined using a computer program. The area reflected the rate at which ocular vergence returned to the original phoria position. The mean area for the monocular condition was 300.9, the mean area for alternate fixation with no binocular time was 300.3, and the mean area for alternate fixation with binocular time was 205.2. CONCLUSIONS: Saccadic alternations do not affect phoria adaptation. However, short periods in which binocular disparate images are viewed significantly increase the rate at which phoria adaptation declines for some subjects.     

The source of disparity vergence innervation determines prism adaptation

A physiological model of prism adaptation argues that adaptation magnitude and rate are functions of the magnitude of reflex vergence innervation. It has also been shown that there is reduced prism adaptation magnitude for a given disparity stimulus where only peripheral sensory fusion is present (the 'eccentricity effect'). This study attempted to determine whether the eccentricity effect is attributable to reduced reflex vergence innervation in peripheral fusion. Experiments were run in a Maxwellian view haploscope. Convergence and divergence adaptation to 6 Δ disparity stimuli were quantified for seven binocularly normal subjects using subjective heterophoria measurements. Vergence response during central or peripheral fusion was quantified objectively by infrared oculography. Six of seven subjects revealed an eccentricity effect. However, in three of seven subjects the eccentricity effect was not predictable from the manifest vergence response. The results suggest that the source of reflex vergence innervation affects prism adaptation. A model is proposed whereby different sources of reflex disparity vergence innervation stimulate prism adaptation by way of separate neurological pathways of differing responsiveness.     

Mirror symmetrical transfer of perceptual learning by prism adaptation

Recent study of [Sugita, Y. (1996) Global plasticity in adult visual cortex following reversal of visual input. Nature, 380, 523-526.] demonstrated that prism adaptation to reversed retinal input generates the transfer of neuronal activities in monkey V1 to the opposite visual cortex. This raises the question if perceptual learning on one side of the visual field can transfer to the other side. We tested this in using the Gabor lateral masking paradigm. Before adaptation, long-range interaction was induced vertically on one side (i.e., the right) of the visual field with training (perceptual learning). Prism adaptation was achieved by wearing right-left reversing goggles. During adaptation period, perceptual learning transferred to a mirror symmetrical region across the vertical meridian. Results in the post adaptation period revealed that both learning and transfer persisted for over three months. These results provide direct evidence of transferred perceptual plasticity across the visual field, the underlying mechanism of which is supported by the mirror symmetrical connection between the right and left cortices.     

Preoperative prism adaptation in acquired esotropia with convergence excess.

PURPOSE: The prism adaptation test (PAT) is used preoperatively to determine the surgical target angle for acquired esotropia. We assessed the surgical outcomes for children with convergence-excess esotropia (near esotropia greater than distance esotropia by 10 prism diopters [PD] or more) whose target angle was based on the results of the PAT geared to the near deviation. METHODS: We reviewed the charts for all of one surgeon's patients who underwent the PAT for near convergence-excess esotropia and who were followed-up for at least 6 months after surgery. Patients who wore prisms were classified as PAT responders (esotropia <= 8 PD at distance and near with four-dot fusion at near) or nonresponders (exotropia at distance or lack of four 4-dot fusion at near). Responders underwent surgery for the adapted angle at near. The nonresponders who had exotropia at distance had surgery for an angle between the near and distance angles. Nonresponders with esotropia angles <= 8 PD at distance and near underwent surgery for the total near deviation. RESULTS: Fifty-four (83%) of the 65 children were PAT responders. Thirty-nine (72%) of the 54 responders and 6 (55%) of 11 nonresponders had excellent results (heterotropia <= 8 PD at distance and near with four-dot fusion at near). All 13 responders whose angles built with prism had excellent results. Among 61 patients who had an esotropia <= 8 PD at near with prisms preoperatively, only 4 (6.6%) developed overcorrections at distance by the latest follow-up examination; 3 were responders and 1 a nonresponder. CONCLUSIONS: PAT for the near deviation in children who have convergence-excess esotropia is a useful test in estimating the target angle for surgery. Responders whose angles built with prism had a particularly high success rate. Surgery geared to the near-adapted angle has a low risk of creating an overcorrection in the distance regardless of the response to PAT.     

The influence of rapid prism adaptation upon fixation disparity.

Small errors of fusional vergence (fixation disparity) were examined as a function of the magnitude of horizontal prism stimulating convergence or divergence for a short (30sec) duration. Marked differences were observed between the amplitude of fixation disparity resulting from convergent and divergent stimulus disparities. In another experiment, subjects wore a horizontal prism for 30 sec after which time one eye was occluded for 40 sec. Measurements of vergence eye movements revealed an incomplete relaxation of fusional vergence (prism adaptation) after 40 sec of occlusion. Marked differences were observed between the amplitude of prism adaptation resulting from convergent and divergent stimuli. Maximum prism adaptationand minimum fixation disparity occurred with the same direction of prism, suggesting that a slow fusional vergence mechanism minimizes errors of binocular vergence.     

Preoperative prism adaptation for acquired esotropia: long-term results.

PURPOSE: The efficacy of preoperative prism adaptation in subjects with acquired esotropia has been established at 6 and 12 months postoperatively. We evaluated the outcomes of subjects with acquired esotropia who had preoperative prism adaptation and were followed longer than 12 months. METHODS: A retrospective analysis was undertaken of 2 groups of subjects with acquired esotropia who underwent bilateral medial rectus recessions based on the distance angle of deviation and were followed more than 12 months postoperatively. Group A subjects had preoperative prism adaptation to determine the target angle for corrective surgery. In Group B subjects, surgery was based on the maximum angle of strabismus at distance, determined by alternate prism cover test without preoperative prism adaptation. RESULTS: We compared 17 subjects in Group A and 19 subjects in Group B. The postoperative follow-up period was 3 +/- 1.7 years in Group A and 4.8 +/- 1.8 years in Group B. The age at the last visit was 9.1 +/- 2 years in Group A and 10 +/- 2 years in Group B. Postoperative residual esotropia was 2.6 +/- 2.5 PD at distance in Group A patients and 6.6 +/- 5.9 PD in group B patients (P =.002). Residual esotropia at near was 3 +/- 3.8 PD in Group A and 11.5 +/- 8.12 PD in Group B (P <.01). More Group B subjects required bifocal spectacles to achieve optimal alignment at near (P =.001). CONCLUSION: Acquired esotropia subjects operated on for their distance prism-adapted angle maintained better motor alignment over a long-term follow-up period when compared with nonprism-adapted subjects operated on for their distance angle.