Fusional Amplitudes: Developing Testing Standards

ABSTRACT

Purpose: The stability of binocular vision depends upon good fusional amplitudes, but the clinical assessment of fusional amplitudes varies around the world. The purpose of this study was to determine whether or not there is variation in the assessment of fusional amplitudes in normal subjects. The author looked at the testing distance, the order of testing, the role of examiner encouragement, and the subject’s level of alertness.

Methods: In a prospective study using a modified crossover design, the author assessed fusional amplitudes in 99 subjects with normal eye exams. The measurements were done in two separate sessions on different days with each subject being randomized as to the order of fusional vergence testing. All subjects were assessed without and with encouragement in the first session. In the second session, all were assessed at different testing distances.

Results: The author previously presented data on 50 subjects. In this expanded cohort, statistical significance was reached confirming the previous findings that convergence is significantly affected by encouragement, divergence is significantly reduced if assessed after convergence, and near amplitudes are significantly higher than distance amplitudes. Finally, there is a negative correlation between age and convergence break point.

Conclusions: The results of this study demonstrate that divergence is significantly reduced if assessed after convergence in the subject with normal binocular function. Next, convergence is significantly affected by the use of encouragement. Measurements at near produced significantly higher results for all of the convergence and divergence tests. Finally, there is a significant negative correlation between age and convergence break point. We need to develop a standard of testing fusional amplitudes so there is consistency in the clinical assessment.     

Variability of Fusion Vergence Measurements in Heterophoria

Purpose: The aims of this study were to compare fusional vergence measurements between orthophoria, esophoria, and exophoria, and to determine the strength of correlations between fusional convergence and divergence and angle of deviation.

Methods and materials: A cross-sectional study was performed in children with best-corrected visual acuity of 0.0 LogMAR in either eye, compensated heterophoria within 10 prism diopters (PD), full ocular rotations, presence of fusional vergence, and stereopsis (60 seconds of arc or better). Fusional amplitudes were compared between orthophoric and heterophoric children. The fusion reserve ratio was determined as compensating vergence divided by alternating cover test.

Results: Five hundred and thirty children (7.66±1.20 years) were recruited to this study. The most common heterophoria was exophoria (n=181, 34.2% for near; n=20, 3.8% for distance). Exophoric children had significant lower mean positive fusional vergences (exophoria-orthophoria: P=0.003; exophoria-esophoria: P=0.035) for near (19.54±5.23 base-out) compared with children with orthophoria (20.48±4.83 base-out) and esophoria (22.27±5.60 base-out). Smaller convergence fusion amplitudes were associated with larger angles of deviation at near (r_s=-0.115; P=0.008) and lower fusion reserve ratios were associated with larger angles of deviation at distance (r_s=-0.848; P<0.001) and at near (r_s=-0.770; P<0.001).

Conclusions: Exophoric children have reduced convergence break points when compared with orthophoric and esophoric children. Vergence measurements, taking into consideration the baseline heterophoria, give important information about the ability of the patient to increase their vergence demand and maintain ocular alignment.     

Fusional Vergence Measures and Their Significance in Clinical Assessment

Purpose: The aims of this study have been to evaluate differences between ranges in eso or exo deviances and with varying target size.

Methods: Evaluation of sensory status in compensated deviations included measures of fusional vergence (blur, break and recovery values) with randomization of target size and order of prism base. Angle of deviation measures were assessed for each case.

Results: Twenty-two subjects, 7 esophoric and 15 exophoric, were recruited. Median prism fusional vergence range at near fixation was 25BO to 10BI (central target); 35BO to 12BI (peripheral target). At distance fixation median range was 16BO to 6BI (central); 25BO to 6BI (peripheral). Esophorics had a range shift towards the base out range. Exophorics had a shift towards the base in range.

Conclusions: Smaller positive fusional vergence values were obtained with small compared with large target sizes. Additionally, esophoric subjects had a trend towards larger base out ranges while exophoric subjects had a trend towards larger base in ranges.     

The Convergence Insufficiency Treatment Trial: Design,Methods, and Baseline Data

Objective: This report describes the design and methodology of the Convergence Insufficiency Treatment Trial (CITT), the first large-scale, placebo-controlled, randomized clinical trial evaluating treatments for convergence insufficiency (CI) in children. We also report the clinical and demographic characteristics of patients. Methods: We prospectively randomized children 9 to 17 years of age to one of four treatment groups: 1) home-based pencil push-ups, 2) home-based computer vergence/accommodative therapy and pencil push-ups, 3) office-based vergence/accommodative therapy with home reinforcement, 4) office-based placebo therapy. Outcome data on the Convergence Insufficiency Symptom Survey (CISS) score (primary outcome), near point of convergence (NPC), and positive fusional vergence were collected after 12 weeks of active treatment and again at 6 and 12 months posttreatment. Results: The CITT enrolled 221 children with symptomatic CI with a mean age of 12.0 years (SD = +2.3). The clinical profile of the cohort at baseline was 9Δ exophoria at near (+/? 4.4) and 2Δ exophoria (+/?2.8) at distance, CISS score = 30 (+/?9.0), NPC = 14 cm (+/? 7.5), and near positive fusional vergence break = 13 Δ (+/? 4.6). There were no statistically significant nor clinically relevant differences between treatment groups with respect to baseline characteristics (p > 0.05).Conclusion: Hallmark features of the study design include formal definitions of conditions and outcomes, standardized diagnostic and treatment protocols, a placebo treatment arm, masked outcome examinations, and the CISS score outcome measure. The baseline data reported herein define the clinical profile of those enrolled into the CITT.     

Vergence Exercises for Six Weeks Induce Faster Recovery of Convergence Insufficiency Than Accommodation Exercises in School Children

PurposeConvergence insufficiency (CI) is characterized by abnormal vergence eye movement frequently accompanied by abnormal accommodation and subjective symptoms, such as headache, blurred vision, and diplopia. CI is treated with vergence and accommodation exercises that are integrated so that the relative contributions of vergence and accommodation exercises to the outcome are concealed. The purpose of the present study was to determine the individual contributions of vergence and accommodation exercises for the treatment of CI in school children.MethodsIn a prospective crossover study 44 children aged 9 to 13 years with CI were randomized to perform either vergence exercises followed by accommodation exercises each for 6 weeks or the 2 treatment regimes in the reverse order. The outcome measures were recovery from CI and the parameters vergence facility, positive fusional vergence, near point of convergence, monocular amplitude, and facility of accommodation.ResultsAfter the first 6-week period, full recovery from CI was significantly more frequent in the group commencing vergence exercises than in the group commencing monocular accommodation exercises (p = 0.01), whereas there was no significant difference between these proportions after the second 6-week period (p = 0.45). Vergence facility and positive fusional vergence improved significantly more after the period with vergence exercises than after the accommodation exercises, whereas there was no significant difference between the effects of the two types of exercises on the other studied parameters.ConclusionsVergence treatment induces a faster recovery of CI than accommodation treatment in school children. This may be used to improve compliance and success rate of the treatment.     

Changes in vergence and accommodation parameters after smartphone use in healthy adults

Purpose:To assess pre and post vergence and accommodation parameters after monitored reading on a smartphone device.Methods:This prospective comparative study was performed in a tertiary eye care center for a duration of 6 months (December 2017 – May 2018). A total of 47 healthy emmetropic subjects of age group ranging from 18-30 years were recruited for the study. Participants underwent an initial visual screening protocol, followed by accommodation and vergence parameters assessment. The subjects were given reading text of optotype N6 at 40cm working distance for 30 minutes in a smart phone device. Pre and post measurements were documented.Results:Among 47 subjects there were 17 male and 30 females with mean age group of 21.2+2.06 years. There was a statistically significant worsening of accommodative components (negative & positive relative accommodation, lag of accommodation). In vergence parameters, a statistically significant deterioration of negative (12.8 + 1.65 to 12.38 + 1.93 PD) and positive fusional vergence (15.48 + 1.53 to 16.08 +1.61 PD) was observed. The mean vergence facility also showed a statistically significant change in pre and post task measurements (13.51 + 1.64 to 10.71 + 1.91 cpm (cycles per minute)).Conclusion:The current study investigated that perusing text with a smart phone for 30 minutes shows significant effect on accommodative and vergence components for near task, with greater impact on vergence parameters. Drawn out exposure to digital screens at near, may bring about visual quality dysfunction.     

Vergence and accommodation responses in the control of intermittent exotropia

Purpose

Individuals with different types of intermittent exotropia (IXT) may use neurally coupled accommodation and vergence responses differently from those without exotropia to achieve eye alignment. This study examined the relationship between simultaneously recorded accommodation and vergence responses in children and young adults with a range of types of IXT while aligned and deviated.

Methods

Responses of 29 participants with IXT (4–31 years) and 24 age-matched controls were recorded using simultaneous eye-tracking and eccentric photorefraction while they watched a movie in binocular or monocular viewing at varying viewing distances. Gradient response AC/A ratios and fusional vergence ranges were also assessed. Eight participants had divergence or pseudo-divergence excess type IXT, 5 had convergence insufficiency and 16 had basic IXT.

Results

Control and IXT participants accommodated similarly both in monocular and binocular-aligned conditions to visual targets at 80 and 33 cm. When deviated in binocular viewing, most participants with IXT exhibited changes in accommodation <0.5D relative to alignment. Gradient response AC/A ratios were similar for control [0.56 MA/D (IQR: 0.51 MA/D)] and IXT participants [0.42 MA/D (0.54 MA/D); p  = 0.60]. IXT participants showed larger vergence to accommodation ratios with changes from distance to near fixation [1.19 MA/D (1.45 MA/D)] than control participants [0.78 MA/D (0.60 MA/D); p = 0.02], especially among IXT participants with divergence or pseudo-divergence excess. Participants with IXT exhibited typical fusional divergence ranges beyond their dissociated position [8.86 Δ (7.10 Δ)] and typical fusional convergence ranges from alignment [18 Δ (15.75 Δ)].

Conclusions

This study suggests that control of IXT is typically neither driven by accommodative convergence alone nor associated with over-accommodation secondary to fusional convergence efforts. These simultaneous measurements confirmed that proximal vergence contributed significantly to IXT control, particularly for divergence or pseudo-divergence excess type IXT. For IXT participants in this study, achieving eye alignment did not conflict with having clear vision.     

Evaluation of distance and near stereoacuity and fusional vergence in intermittent exotropia

Aim: To evaluate the role of distance and near stereoacuity and fusional vergence in patients with intermittent exotropia [X(T)] and their change after surgery. Materials and Methods: This prospective interventional institution-based clinical study included 31 cases of X(T) requiring surgery and 33 age, sex-matched controls. All subjects underwent complete orthoptic assessment including near stereopsis (Randot stereogram) and distance stereopsis by polaroid stereo-projector apparatus using special paired slides and fusional vergence assessment at distance and near prism bar at baseline and one week, one month, three months and six months after surgery in X(T). Results: The successful surgical alignment rate was 74.2%. Preoperatively, cases demonstrated significantly poor distance and near stereoacuity, compared to controls ( P P Conclusion: Early detection of abnormal stereoacuity (near and if possible distance) and near fusional vergence amplitudes may help to decide proper timing of surgery in X(T).     

Effect of Induced Vertical Disparity on Horizontal Fusional Reserves

Purpose: The aim of this study was to investigate the effects of induced vertical disparity on horizontal fusional reserves at near. Materials and Methods: In 170 healthy subjects wearing best corrective refraction, the negative and positive horizontal fusional reserves were measured with base-in (BI) and base-out (BO) prisms, respectively, in the presence of 0.5 prism diopters (^?) and 1^? vertical prisms placed in trial frames in front of the right eye. The prism power was slowly increased step by step until the subject reported sustained blur, break, and recovery. These were compared to horizontal fusional reserves in the same subjects without a vertical prism. Data were analyzed in SPSS.17 software using a repeated measures ANOVA. Results: Induced vertical disparity decreased negative fusional reserves (NFR) horizontally and was more significant with 1^? vertical disparity (P<0.001). There were significant differences between the blur (P<0.001), break (P<0.001), and recovery (P<0.001) for NFR before and after induced vertical disparity and no significant difference between blur (P=0.173) and recovery points (P=0.261) with a marginal difference for break points (P=0.045) for the positive fusional reserves (PFR). Conclusion: Inducing vertical disparity even with small magnitudes affects all 3 aspects (blur, break, and recovery) of horizontal negative fusional reserves while only break is affected in positive fusional reserves. These changes are statistically significant but do not seem to be clinically significant except for cases accompanied by symptoms.     

Vertical vergence in nonhuman primates depends on horizontal gaze position

ABSTRACT

The goal of this study was to compare vertical fusion capability at different orbital eye positions in normal nonhuman primates and attempt to use this information to isolate the extraocular muscles (EOMs) that mediate vertical vergence. Scleral search coils were used to record movements of both eyes as two normal nonhuman primates (M1, M2) performed a vertical vergence task at different horizontal eye positions. In a control experiment, M1 was also tested at different angles of horizontal vergence. To elicit vertical vergence, a 50° x 50° stimulus comprising a central fixation cross and random dots elsewhere was presented separately to each eye under dichoptic viewing conditions. Vertical disparity was introduced by slowly displacing the stimulus for one eye vertically. Vertical fusion amplitude (maximum disparity that the monkey was able to fuse) and vertical vergence (maximum difference in vertical position of the two eyes) were measured. Vertical fusion capability differed at different orbital eye positions. Monkey M1 had significantly smaller vertical fusion capabilities when the right eye (RE) was abducted than left eye (LE) while M2 had significantly smaller vertical fusion capabilities when the RE was adducted and LE abducted. M1 also showed greater vertical fusion capability for near gaze. M1 data suggested that the vertical recti mediated vertical vergence in the RE and the oblique muscles in the LE while M2 data suggested that the oblique muscles mediated vertical vergence in the RE and the vertical recti in the LE. The variable results within the same animal and across animals suggest that EOM involvement during vertical fusional vergence is idiosyncratic and likely a weighted combination of multiple cyclovertical muscles.     

Normal values of distance heterophoria and fusional vergence ranges and effects of age

Background Although it is well known that age affects visual function, we still have much to learn about the impact of aging on binocular vision. Our aim was to establish distance heterophoria and distance fusional vergence ranges in a large non-clinical population of wide age range, to provide normal values for comparisons.Methods A cross-sectional study was performed on 271 non-clinical subjects stratified into six age groups. Distance heterophoria measurements were obtained using the von Graefe technique and distance horizontal fusional vergence ranges using Risley rotary prisms in each subject, with best spectacle correction.Results The mean heterophoria value for distance fixation was exophoric except for the 71–80 year age group, which was esophoric. No effects of age were observed on distance heterophoria and distance base-in and base-out break means. However, a significant effect of age was noted on base-in recovery and base-out recovery. Between the youngest and oldest age groups, mean base-in recovery decreased by 2.5 Δ and mean base-out recovery by 3.3 Δ.Conclusions Distance base-in and base-out recovery means diminished significantly with age such that recovery values fell outside the norm in subjects in the 61–70 year age group and older. This study establishes statistical normal values for distance heterophoria and fusional vergence in a non-clinical population. Mean values such as these are valuable tools for identifying subjects with far binocular anomalies.     

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.     

Visual efficiency among teenaged athletes and non-athletes

AIM: To compare visual efficiency, specifically accom-modation, vergence, and oculomotor functions among athletes and non-athletes. METHODS: A cross-sectional study on sports vision screening was used to evaluate the visual skills of 214 elementary students (107 athletes, 107 non-athletes), aged between 13 and 16y. The visual screening assessed visual parameters such as ocular motor alignment, accommodation, and vergence functions. RESULTS: Mean visual parameters were compared between age-group matched athletes (mean age 14.82±0.98y) and non-athletes (mean age 15.00±1.04y). The refractive errors of all participants were corrected to maximal attainable best corrected visual acuity of logMAR 0.0. Accommodation function assessment evaluated amplitude of accommodation and accommodation facility. Vergence functions measured the near point of convergence, vergence facility, and distance fusional vergence at break and recovery point. Ocular motor alignment was not statistically significant between both groups. Athletes had a statistically significant amplitude of accommodation for both the right eye (t=2.30, P=0.02) and the left eye (t=1.99, P=0.05). Conversely, non-athletes had better accommodation facility (t=-2.54, P=0.01) and near point of convergence (t=4.39, P<0.001) when compared to athletes. Vergence facility was found to be better among athletes (t=2.47, P=0.01). Nevertheless, non-athletes were significantly better for both distance negative and positive fusional vergence. CONCLUSION: Although the findings are still inconclusive as to whether athletes had superior visual skills as compared to non-athletes, it remains important to identify and elucidate the key visual skills needed by athletes in order for them to achieve higher performance in their sports.     

[In Press] Visual efficiency among teenaged athletes and non-athletes

AIM: To compare visual efficiency, specifically accommodation, vergence, and oculomotor functions among athletes and non-athletes. METHODS: A cross-sectional study on sports vision screening was used to evaluate the visual skills of 214 elementary students (107 athletes, 107 non-athletes), aged between 13 and 16 years. The visual screening assessed visual parameters such as ocular motor alignment, accommodation, and vergence functions. RESULTS: Mean visual parameters were compared between age-group matched athletes (mean age 14.82±0.98y) and non-athletes (mean age 15.00±1.04y). The refractive errors of all participants were corrected to maximal attainable best corrected visual acuity of logMAR 0.0. Accommodation function assessment evaluated amplitude of accommodation and accommodation facility. Vergence functions measured the near point of convergence, vergence facility, and distance fusional vergence at break and recovery point. Ocular motor alignment was not statistically significant between both groups. Athletes had a statistically significant amplitude of accommodation for both the right eye (t=2.30, P=0.02) and the left eye (t=1.99, P=0.05). Conversely, non-athletes had better accommodation facility (t=-2.54, P=0.01) and near point of convergence (t=4.39, P<0.001) when compared to athletes. Vergence facility was found to be better among athletes (t=2.47, P=0.01). Nevertheless, non-athletes were significantly better for both distance negative and positive fusional vergence. CONCLUSION: Although the findings are still inconclusive as to whether athletes had superior visual skills as compared to non-athletes; it remains important to identify and elucidate the key visual skills needed by athletes in order for them to achieve higher performance in their sports.     

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.     

Vergence Profile and Prevalance of Non-Strabismic Vergence Anomalies Among School Children in Abia State,Nigeria

Purpose: To determine the prevalence of non-strabismic vergence anomalies and their relationship with age, gender, and school level in children aged 10–16 years

Method: A cross-sectional study was conducted among 537 children (255 male, 282 females; mean age 13.0 ± 2.0, years) selected from nine schools using stratified, cluster, and random sampling. The participants completed a Convergence Insufficiency Symptom Survey (CISS) and eye examinations, including the measurement of visual acuity, non-cycloplegic refraction, cover test, near point of convergence, fusional vergences, accommodative functions, and ocular health evaluation. All binocular tests were performed following the subjective refraction with the corrective lenses in place, if prescribed.

Results: The prevalence of low suspect, high suspect, and definite convergence insufficiency was 9.6%, 5.8%, and 4.1%, respectively. Other prevalence estimates included convergence excess (2.9%), fusional vergence dysfunction (2.6%), basic exophoria (1.7%), basic esophoria (2.8%), divergence insufficiency (0.8%), and divergence excess (0.6%). The prevalence of high suspect (p < 0.01) and definite (p < 0.01) convergence insufficiency was significantly higher in older than younger children, and as expected, in secondary more so than primary school children (p = 0.01). There was no statically significant association between gender and various vergence anomalies.

Conclusion: The study showed that vergence anomalies are common vision conditions among Abia State school children. Given the importance of visual skills in learning and academic achievements, there is a need to develop screening and management strategies that will target those visual conditions to prevent educational and social progress being affected.     

Repeatability and agreement in the measurement of horizontal fusional vergences

PURPOSE: This study was designed to determine the repeatability of fusional vergence ranges measured using the rotary prisms in the phoropter and in free space using the prism bar. The level of agreement between the two methods was also investigated. METHODS: In two separate sessions, negative and positive fusional vergence ranges (NFV and PFV, respectively) were measured at distance and near in 61 young adults (mean age 19.74, S.D. 2.5 years) who were unfamiliar with the methods used. Base-in and base-out blur, break and recovery points were sequentially determined. Both sets of measurements were obtained by the same examiner. At each distance, NFV was determined first and then PFV. The repeatability of the tests and agreement between measurements made with the phoropter rotary prisms and the prism bar were estimated by the Bland and Altman method. RESULTS: For both the phoropter rotary prisms and prism bar, NFV measurements showed better repeatability than PFV at both near and distance. Mean differences recorded for the NFV break and recovery points were non-significant (under 0.5Delta), while those observed for PFV were generally greater than 2Delta. When agreement between the two tests was assessed, it was found that break points were higher when determined using the phoropter rotary prisms, while recovery points were generally higher for the prism bar method. In clinical terms, according to the expected values of the NFV and PFV, agreement between the two techniques can be described as fair, because although mean differences were never greater than 5.5Delta, 95% agreement intervals were as wide as +/-8.00Delta for NFV and +/-13.19Delta for PFV. CONCLUSIONS: The two methods used to measure fusional vergences showed fairly good inter-session repeatability for measuring NFV but repeatability was reduced for PFV measurements. The level of agreement observed between the two methods was such that their interchangeable use in clinical practice is not recommended.     

Objective vs subjective measurements of dark vergence

Dark vergence is a resting position of vergence (tonic vergence), measured in a dark visual field to eliminate fusional, accommodative, and proximal stimuli. The vergence resting position is relevant for measures of phoria and fixation disparity. Dark vergence differs reliably among subjects: the average subject converges at a viewing distance of about 1 m, while the inter-individual range is from infinity to about 40 cm. In previous research, dark vergence was measured subjectively, i.e. observers adjusted the horizontal offset of dichoptically presented nonius targets to perceived alignment. Results of such subjective vergence tests do not necessarily agree with those of the objective measurements of eye position with eye trackers. Therefore, we made simultaneous subjective and objective measurements of dark vergence and found similar results with both methods in repeated tests in two sessions. Thus, the nonius test is sufficient for a subjective estimation of dark vergence.     

Vergence amplitudes with random-dot stereograms.

Random-dot stereograms were found to be capable of producing fusional vergence amplitudes in the absence of monocular contours. These vergence amplitudes are not an artefact of monocular contours provided by the target borders or test instrument and are comparable in range to vergence amplitudes measured clinically with second degree fusion targets in an amblyoscope. We conclude that diplopia of monocularly recognisable contours is not necessary for producing fusional vergence amplitudes.     

Can vergence training improve reading in dyslexics?

Background: Dyslexia affects 5%–8% of the population of the Western world. While reading, different eye movements are required. Compared to other persons, dyslexics have more and longer fixations, shorter saccade amplitude, a higher percentage of regression, and more fixation disparity when reading. In non-reading situations, dyslexics do not have more binocular problems than others. The aim of the present study was to investigate whether computerized orthoptic vergence training could improve reading ability for dyslexic children.

Methods: The study was conducted at Ängkärrskolan, Solna, an elementary school exclusively for dyslexic children. Twelve subjects, aged 13–14 years, were trained with RetCorr, a computerized vergence training program. Reading speed was assessed before and after treatment. The results were compared with an age-matched control group.

Results: The dyslexic subjects conducted on average 11.75 sessions (±2.53 SD) of orthoptic training over a 5-week period. On average, the number of words read per minute before training were 87.83 (±16.80 SD) and after training 95.58 words (±18.08 SD). The difference was statistically significant (p?=?0.0066). In the control group, the change was from 85.00 (±19.68 SD) words to 89.37 words (±19.71 SD) over the same time period. This difference was not significant (p?=?0.1235).

Discussion: Most scientists agree that dyslexia is mainly a phonological impairment. Nevertheless, the results show that vergence treatment might help dyslexics. Larger studies are required to provide guidance in this area.