Positive Vergence Research Articles

Optical Performance of a Segmented Extended-Depth-of-Focus Intraocular Lens under the Influence of Different Values of Spherical Aberration Generated by Refractive Surgery.

Corneal refractive surgery induces high-order aberrations, specifically spherical aberration (SA). These aberrations can have implications when patients later develop cataracts and require the implantation of multifocal intraocular lenses (MIOLs). MIOLs with asymmetric designs pose challenges in predicting outcomes, particularly in these cases. The aim of this study was to evaluate how different values of SA, resulting from various types of refractive surgeries, affect the optical performance of the FEMTIS Comfort intraocular lens. The through-focus modulation transfer function (TF-MTF) curve and high-contrast images of tumbling E were used as parameters to assess the optical performance of the MIOL. These parameters were measured using an adaptive optics visual simulator. Increasingly negative values of SA make the MIOL more bifocal, moderating its extended-depth-of-focus characteristic. Conversely, higher positive SA values cause the TF-MTF curve to shift towards positive vergences, leading to worsened distance vision in the +1.00 to +2.00 D range, but improved vision in the +0.50 D to +1.00 D range. Assessing SA in patients prior to implanting MIOLs with asymmetric designs is necessary for predicting outcomes and making informed decisions based on the visual requirements of patients.

Efficacy of Smartphone-based Exercises in Conjunction with Modified Glasses Prescription in the Treatment of Convergence Insufficiency and Fusion Weakness

ABSTRACTPurpose: To determine the efficacy of Smartphone-based exercises in conjunction with modified glasses prescription in the treatment of convergence insufficiency and fusion weakness.Methods: A total of 150 patients using glasses and having asthenopia between 15 and 30 years of age were subjected to thorough eye examination including binocular vision testing and refraction. Of them 26 individuals were found to have convergence insufficiency with fusion weakness and exophoria >6 pd. Subjects with amblyopia, manifest strabismus and other ocular diseases were excluded from the study. Modified glasses (overcorrection of myopia by −0.5 D Sph & under correction of hypermetropia by +0.5 D Sph) were given along with newly designed Smartphone-based fusion exercises.Results: Near point of convergence improved by 2.89 ± 1.08 cm, positive fusion vergence by −10.2 ± 3.25 pd and near phoria by 3.13 ± 0.32 pd (p < 0.001).Conclusion: The current study demonstrates the efficacy of Smartphone-based fusion exercises, in conjunction with modified glasses prescriptions, in the management of symptomatic convergence and fusion insufficiency. Indeed, this novel, newly designed approach for convergence insufficiency improves symptoms by reducing near point of convergence and degree of exophoria and increasing fusional vergence.

A Study on the Change of Positive Vergence and Accommodative power according to Illumination

Purpose: The purpose of this study is to investigate changes of positive vergence and accommodative power with illumination. Methods: 49 subjects(mean age:24.51±2.82) having no systemic and ocular disease were recruited. Illuminance environment is going to use the light meter ((LX-101, Lutron, USA) and dimmers to change the light intensity from 10 lux to 1000 lux measured the amplitude of accommodation and far/near positive vergence. Results: Amplitude of accommodation was lowest to 8.51 D with 10 lux and the highest to 9.12 D with 800 lux. As the illuminance increases, the exponential decay fit(y=9.09-0.62e-) was maintained while also increasing amplitude of accommodation. Break point of distance positive vergence was higher by 20.81 △ at low illuminance of 10 lux, near positive vergence was higher by 21.42 △ at low illuminance of 10 lux. The exponential decay fit of Distance/near positive vergence were y=17.08+4.66e- and y=20.93+0.63e- , respectively. Conclusions: As the illuminance increases while amplitude of accommodation is increasing, Distance/near positive vergence was increase in low light, while temporarily reduced while increasing illuminance showed a pattern that changes less.

The distribution of near point of convergence, near horizontal heterophoria, and near vergence among myopic children in South Korea

Background/PurposeTo assess the distribution of near point of convergence (NPC), near heterophoria, and near vergence among myopic school children in South Korea. MethodsOne hundred and thirty-six elementary school children, aged 8–13 years, were each given a thorough eye examination including binocular vision testing, NPC using standard push-up technique, horizontal heterophoria measurement by Von Graefe, distance, and near negative and positive vergence with a phoropter and phoropter replacement card. ResultsNPC break and recovery points were highest in the age 9 years group, but the mean values of NPC were within the normal range. Of 136 individuals, 52 presented with esophoria, 53 presented with 0–6-Δ exophoria, and 31 presented with ≥7-Δ exophoria. In the younger age groups (8 years and 10 years) 0–6-Δ exophoria was prevalent, whereas in the older age groups (11 years, 12 years, and 13 years) esophoria was prevalent. Near positive fusional vergence (break and recovery point) presented with statistically significant correlations with the participants' ages. Esophoria showed higher correlations with high myopia (8.00 ± 0.000) rather than with low myopia (3.36 ± 2.499) or medium myopia (3.42 ± 2.149). The mean value of 0–6▵ exophoria was highest in medium myopia (4.04 ± 1.517), and of ≥7-▵ exophoria was the highest in high myopia (12.66 ± 1.154). ConclusionThere were no statistically significant correlations between the school childrens' ages and NPC, near horizontal heterophoria, and near fusional vergence, except near positive fusional vergence. Also, unlike many studies, myopic magnitude did not present a significant correlation with near phoria and fusional vergence.

Prevalence of general binocular dysfunctions among rural schoolchildren in South Korea

Background/PurposeTo assess the prevalence of nonstrabismic accommodative and vergence dysfunctions among primary schoolchildren in Hampyeong, a rural area of South Korea. MethodsFive hundred and eighty-nine primary schoolchildren, 8–13 years old, were each given a thorough eye examination, including binocular-vision testing, near point of convergence, horizontal phoria measurement by von Graefe, and negative and positive vergence amplitudes with prism bar, to determine any form of accommodative or vergence dysfunctions. ResultsOf the 589 participants examined, 168 (28.5%) primary schoolchildren presented some form of nonstrabismic accommodative or vergence dysfunctions. The prevalence of accommodative dysfunctions and vergence dysfunctions was 13.2% and 9%, respectively. Convergence insufficiency (10.3%) was more prevalent than convergence excess (1.9%), and accommodative insufficiency (5.3%) was more prevalent than accommodative excess (1.2%). ConclusionThis study suggests that nonstrabismic accommodative and vergence dysfunctions are prevalent in the rural area of South Korean primary schoolchildren, and convergence insufficiency was the most prevalent.

Refractive Errors and Binocular Dysfunctions in a Population of University Students

This clinical study was performed to determine the presence of refractive errors and binocular dysfunctions in a population of university students. Refraction and binocular function were evaluated in a young patient population (230 students and 234 nonstudent subjects, aged 18-27 years). Distance visual acuity (DVA) and near visual acuity (NVA), refraction, cover test (CT), ocular motility, near-point of convergence, horizontal phoria measurement by Maddox wing, negative and positive vergence amplitude in prism diopters, fusion amplitude in synoptophore, as well as stereoacuity (Titmus test) were tested. Emmetropia was the most frequent refractive status in our student and nonstudent groups (78.7%). Myopia was the most frequent refractive disorder in the whole population (13.1%). Myopia and hypermetropia were significantly more frequent in the students than in nonstudents (chi-square emp 47.55). Exophoria is significantly more frequent in myopic subjects. Vergence amplitude (t test 0.000) and fusion amplitude (t test 0.005) show significantly lower values in student population. Results of Titmus test in the student group is significantly worse than in the nonstudent group (t test 0.000). Maddox wing resulted in significantly higher degree of heterophoria in the student population (t test 0.000). Myopic subjects, in the student group (t test 0.002) as well as in the nonstudent group (t test 0.001), show significantly better results in Titmus test. High near visual demand could be the most important factor for higher incidence of myopia, worse convergence and fusion amplitude, higher degree of exophoria, and worse results in Titmus test in the student population.

Statistical normal values of visual parameters that characterize binocular function in children

A wide range of visual parameters used to evaluate binocular function were evaluated in a paediatric population (1056 subjects aged 6-12 years). Mean values are provided for these ages in optometric tests that directly assess the vergence system, horizontal phorias for near and far vision (measured by a modified version of the Thorington method), negative and positive vergence amplitude for near and far vision (step vergence testing), vergence facility (flippers 8 Delta BI/8 Delta BO), and near-point of convergence (penlight push-up technique and red-lens push-up technique), as well as stimulus accommodative convergence/accommodation ratio and stereoacuity (Randot test) which provide an overall evaluation of the vergence, accommodative and oculomotor systems. A statistical comparison (anova and Bonferroni post hoc test) of these values between ages was performed. The differences, although statistically significant, were not clinically meaningful, and therefore we identified two trends in the behaviour of these parameters. For all parameters, except for vergence facility, we established a single mean reference value for the age range studied. The difference between the means for vergence facility indicated the need to divide the population into two age ranges (6-8 and 8-12 years). This study establishes statistical normal values for these parameters in a paediatric population and their means are a valuable instrument for separating children with binocular anomalies from those with normal binocular vision.

Characteristics of near response cells projecting to the oculomotor nucleus.

1. Previous work has shown neurons just dorsal and lateral to the oculomotor nucleus that increase their firing rate with increases in the angle of ocular convergence. It has been suggested that the output of these midbrain near response cells might provide the vergence command needed by the medial rectus motoneurons. However, lens accommodation ordinarily accompanies convergence, and a subsequent study showed that only about one-half of these midbrain near response cells carried a signal related exclusively to vergence. One hypothesis suggested by this finding is that this subgroup of neurons might have a unique role in providing a "pure" vergence signal to the medial rectus motoneurons. 2. In the present study extracellular recordings were made from midbrain near response cells in monkeys while eye position and lens accommodation were measured. The monkeys viewed targets through an optical system that allowed the accommodative and ocular vergence demands to be manipulated independently. This approach was used to produce a partial dissociation of accommodative and vergence responses, so that an accommodative and vergence coefficient could be determined for each cell, by the use of the following equation FR = R0 + kda x AR + kdv x CR where FR is the firing rate of the near response cell, R0 is the predicted firing rate for a distant target, kda is the (dissociated) accommodation coefficient, AR is the accommodative response, kdv is the (dissociated) vergence coefficient, and CR is the convergence response. 3. The vergence and accommodation coefficients were determined for a large number of midbrain near response cells, including a subset that could be antidromically activated from the medial rectus subdivisions of the oculomotor nucleus. Some near response neurons were found with signals related exclusively to convergence (i.e., kdv greater than 0 and kda = 0), whereas several others had signals related exclusively to lens accommodation (i.e., kda greater than 0 and kdv = 0). The majority of the near response cells had signals related to both responses (i.e., kda not equal to 0 and kdv not equal to 0). Furthermore, the vergence and accommodation coefficients of near response cells appeared to be continuously distributed. Some cells had negative accommodation or vergence coefficients. 4. The 17 near response cells that could be antidromically activated from the oculomotor nucleus presumably provide vergence signals to the medial rectus motoneurons. Although all had positive vergence coefficients, only four of these cells carried signals that were related exclusively to vergence.(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics of convergence insufficiency.

Convergence insufficiency (CI) is a well-known syndrome of binocular visual dysfunction. In a review of 58 papers, considerable variation was noted in the criteria used to define the condition. Symptoms and decreased positive fusional vergences (both at the nearpoint) were the only criteria named in more than one-half of the studies. An extended nearpoint of convergence (NPC) and increased exophoria at near were criteria in about one-third of the papers. Examination of data in the reviewed papers shows that although considerable variability was noted, the distance exodeviation, distance negative vergences, visual acuity, refraction, and stereopsis were about the same as population norms. Positive vergences, negative vergence at near, and NPC were somewhat less than population norms. Vergences relative to Sheard's criterion, the near exophoria, accommodative amplitude, and the AC/A ratio were consistently below those derived from population norms. This considerable variation may largely be a result of different criteria used for diagnosis, subpopulations within the data, and other confounding factors.

Horizontal and vertical vergence training and its effect on vergences and fixation disparity curves: I. Horizontal data.

The purpose of this study was to assess the effects of horizontal and vertical vergence training on fusional vergences and the fixation disparity (FD) curve. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. Before and after the 4 week training period, vergences and FD curves were measured by a single individual who was intentionally uninformed of each subject's group. We hypothesized that the subjects in the horizontal training group would have increased vergence amplitudes and flatter FD slopes. Our analysis revealed that the positive vergences increased significantly for those in the horizontal group. No evidence was found to suggest changes in any variables related to the FD curve. Because type II errors were likely to be unacceptably large, further work is necessary to determine the relation between fusional vergence training and variables derived from the FD curve.

Efficacy of Computerized Vergence Therapy

The purpose of this study was to determine the efficacy of computerized fusional vergence therapy and the effect of two different vergence training velocities. Six subjects received positive vergence training using a slow vergence training rate (0.75 delta/s) and six subjects received positive vergence training using a fast vergence training rate (5.00 delta/s). Six subjects served as controls and did not receive therapy. The duration of therapy was 80 min over a period of 4 weeks. All training activities were monitored. All vergence evaluations were double masked. Subjects using a slow training rate showed significant increases in positive vergence ranges as measured with the major amblyoscope, whereas subjects training with fast rates did not. We conclude that vergence therapy using a computerized video display is an effective technique for increasing the amplitudes of positive fusional vergence and that slower rates are more productive than faster rates.

Impulse responses for reentrant discontinuities in bores

We establish an optical analogy for the processing of spherical wavefronts in conical bore segments. A reentrant discontinuity acts like a converging lens or mirror to give outgoing waves a more positive vergence than incoming waves [M.P. Keating, Am. J. Phys. 43, 766–769 (1975)]. Impulse responses for single interactions with such a discontinuity include exponentially growing wakes, which become unmanageable very quickly in digital convolutions. Geometrical considerations rule out a reentrant discontinuity existing in isolation, and its troublesome behavior is kept under control by multiple reflections involving another discontinuity of stronger, negative power. In closed systems this process shows a “sorcerer's apprentice” type of behavior, in which a temporary solution to the problem turns into the problem for the next cycle. Fortunately that problem becomes more deltalike as time progresses, and there is a tendency for it to be cancelled by a neighboring delta. In open systems the behavior is much tam...

Negative vergence training in humans.

Two healthy subjects (male and female, ages 22 and 25 years) spent 50 h over a period of 7 consecutive weeks training the negative vergence system. The training was performed in two 45-min daily sessions, usually immediately before and after the workday. The training was exclusively negative vergence training using devices such as variable vectograms, the aperture rule, the synoptophore, and loose or bar prisms. An extensive examination of the visual systems before, after, and periodically during the training demonstrated that the negative vergences increased at distance by 5.0 delta and at near by 9.1 delta (using hand-held prisms, bar prisms, and the synoptophore). The phorias of both subjects became more exophoric or less esophoric at both distance and near by 3.6 delta (using average of changes on the cover test, von Graefe subjective phoria technique, and the synoptophore). A haploscope equipped with a coincidence optometer showed only small increases in vergence amplitude but confirmed that the lag of accommodation became more stable after the training than it was before. Other testing suggested that the negative relative accommodation, the angle of deviation at both distance and near, positive vergences, the associated phoria, and the slope of the fixation disparity curve changed significantly over the period of training. I conclude that negative vergence training can increase the negative vergence capabilities and also affect the phoria position of the eyes via feed-back into the slow vergence system.

Characteristics of Exodeviations

A retrospective study of 179 patients (69 males and 110 females) with binocular visual dysfunction and an exodeviation at distance or near or at both distances has been completed. The mean age of 19.7 years was significantly younger than the population from which they were referred. The patients were classed as convergence insufficiency, equal exodeviation, or divergence excess, based on the relation of the distance and near angles of deviation. Based on these criteria, interaction was found to be present between the diagnostic class and the frequency of the deviation, the symptoms reported, and a variety of clinical parameters such as the angles of deviation at distance and near, the AC/A ratio, positive and negative vergence values, the amplitude of accommodation, and the threshold of stereopsis. A number of statistical relations were noted between the frequency of the deviation vs. the symptoms reported and a variety of the clinical parameters. The implications of these results are discussed.

A Model for Predicting the Results of Orthoptics in Patients with Equal Exodeviations

Stepwise discriminant and discriminant analysis of the data of a retrospective study of patients with equal (or basic) exodeviation has been completed. Based upon this calibration data, these analyses have allowed the formulation of a classification criterion for the success of orthoptic treatment. Included in the model were the following factors: the frequency of the deviation, the AC/A ratio, the angle of deviation at the nearpoint and the recovery value of the distance positive vergences. Patients with latent deviations, higher AC/A ratios, smaller near angles of deviation and smaller recovery values were more likely to be successful. The model in the form of a pair of linearised discriminant functions is presented. The possible relationship of the model to real-world processes, utility and limits are briefly discussed.

Predicting results in the orthoptic treatment of accommodative dysfunction.

A retrospective analysis of the records of 114 orthoptic patients diagnosed as having accommodative dysfunction (accommodative insufficiency, fatigue of accommodation, infacility of accommodation, or spasm of accommodation) has allowed the construction of models of the results of orthoptic treatment. Discriminant analysis completed on various samples of the group provides linearized discriminant functions for the success of the treatment (either total or partial/none) and for the change in accommodative amplitude. These data indicate that linearized discriminant functions using the age and AC/A ratio of the patient are effective in postpredicting the success category of 60% of a calibration sample of 99 patients. Similar functions using the patient's age, initial accommodative amplitude, and blur value of the near positive vergences allow the postprediction of the category of change in accommodative amplitude with treatment (3 D or more vs. 2 D or less). Seventy-eight percent of a sample of 68 patients were correctly classified. The application of these models in predicting the results of treatment of similarly afflicted subjects is discussed.