High Accommodative Convergence Research Articles

Efficacy of vision therapy in impaired stereoscopic depth with intermittent exotropia (true divergence excess) with unilateral amblyopia: a case report

Divergence excess (DE) can be described clinically as exotropia at far greater than the near deviation by at least 10 prism dioptres (PD). We are reporting a rare case of 25-year-old female visited in the eye department for a routine eye check-up with a history of decreased vision in one eye. On examination, it was detected as a case of unilateral amblyopia with intermittent exotropia of true divergence excess with high accommodative-convergence over accommodation (AC/A) ratio. The patient was asymptomatic from exo-deviation due to the presence of binocular vision and good fusional reserve. The patient was started on active conventional vision therapy along with occlusion therapy. Post 16 weeks of constant therapy, a vision assessment with complete squint assessment along with binocular vision tests were performed. The result interprets to support the use of active conventional vision therapy as an integral part of the clinical treatment of amblyopia and intermittent exotropia. The rate of recovery of several monocular functions monitored during the vision therapy period provides the evidence of neural plasticity at multiple sites in the visual pathway in this adult amblyope. Therefore, if an ordered plan is being followed for the management of the patient of unilateral amblyopia and divergence excess, it can yield long-lasting improvement in visual acuity and binocular functions of any age.

Modified Faden operation -A new surgical technique.

Faden operation was first described in 1912. It weakens the muscle in its field of action without much slackening and alteration in the primary position. When combined with recession the weakening effect is more. It is a useful surgery in esotropia with high accommodative convergence, nystagmus blockage syndrome, dissociated vertical deviation, Duane's retraction syndrome with up or downshoots, and in sixth nerve paresis, where it is performed on the contralateral normal yoke muscle to increase the field of binocular vision. The conventional procedure is cumbersome due to small working space, entanglement of sutures, and posterior location of Faden site which is not easily accessible. We have modified the Faden operation by using a single 5-0 double-armed polyester suture, which is much easier and simpler to perform, and have done it in a series of small angle esotropias combined with recession. This paper demonstrates the surgical technique so that this surgery can be performed with ease by more surgeons.

Esotropia and Exotropia Preferred Practice Pattern®

Esotropia and Exotropia Preferred Practice Pattern®

Are high lags of accommodation in myopic children due to motor deficits?

Children with a progressing myopia exhibit an abnormal pattern of high accommodative lags coupled with high accommodative convergence (AC/A) and high accommodative adaptation. This is not predicted by the current models of accommodation and vergence. Reduced accommodative plant gain and reduced sensitivity to blur have been suggested as potential causes for this abnormal behavior. These etiologies were tested by altering parameters (sensory, controller and plant gains) in the Simulink model of accommodation. Predictions were then compared to the static and dynamic blur accommodation (BA) measures taken using a Badal optical system on 12 children (6 emmetropes and 6 myopes, 8–13years) and 6 adults (20–35years). Other critical parameters such as CA/C, AC/A, and accommodative adaptation were also measured. Usable BA responses were classified as either typical or atypical. Typical accommodation data confirmed the abnormal pattern of myopia along with an unchanged CA/C. Main sequence relationship remained invariant between myopic and nonmyopic children. An overall reduction was noted in the response dynamics such as peak velocity and acceleration with age. Neither a reduced plant gain nor reduced blur sensitivity could predict the abnormal accommodative behavior. A model adjustment reflecting a reduced accommodative sensory gain (ASG) coupled with an increased AC cross-link gain and reduced vergence adaptive gain does predict the empirical findings. Empirical measures also showed a greater frequency of errors in accommodative response generation (atypical responses) in both myopic and control children compared to adults.

New strabismus surgical techniques

Five new strabismus surgical procedures were developed by the authors and were presented as a workshop at the AAPOS annual meeting of the American Association for Pediatric Ophthalmology and Strabismus. They are summarized here to introduce these methods to the reader and provide surgeons with more options in approaching difficult strabismus problems. Diagnosis and correction of consecutive strabismus attributable to stretched scar is discussed. The pulley posterior fixation procedure is a unique approach to correct high accommodative convergence or to augment a maximal medial rectus recession. Diagnosis and repair of the partial avulsion (flap tear) of a rectus muscle allows correction of some restrictive strabismus following blunt trauma. The nasal myectomy of the inferior oblique muscle corrects persistent inferior oblique overaction without sacrificing the tether effect gained by a previous anterior transposition of the inferior oblique. The full advancement of the superior oblique tendon offers another option to strengthen a weak superior oblique muscle.

Medial rectus Faden operations with or without recession for partially accommodative esotropia associated with a high accommodative convergence to accommodation ratio

AimsTo evaluate the results of Faden operations on the medial rectus (MR) muscles with or without recession for the treatment of partially accommodative esotropia associated with a high accommodative convergence...

Long-Term Outcome of Medial Rectus Recession and Pulley Posterior Fixation in Esotropia With High AC/A Ratio

Purpose: Medial rectus (MR) recession with pulley posterior fixation (PF) can be used to treatesotropia (ET) with a high accommodative convergence to accommodation (AC/A) ratio as effectively in the short term as MR recession with scleral PF. This study provides a novel examination of the long-term results of MR recession with pulley PF (PPF).Methods: In 21 children we performed bilateral MR recession and pulley PF for ET greater at near than distance (high AC/A). Mean follow-up was 3.5 ± 2.5 (standard deviation [SD]) years.Results: Mean age at presentation was 2.7 ± 1.8 and at surgery 4.3 ± 1.6 years. Fourteen (67%) children had amblyopia. Distance and near pre-operative ET averaged 19.6Δ ± 10.5Δ and 36.9Δ ±18.9Δ, respectively. Mean near-distance (N-D) disparity was 16.4Δ ± 12.3Δ. The MR recession averaged 4.4 ± 0.9 mm. Early mean postoperative ET was 1.3 ± 3.3Δ at distance and 2.8Δ ± 5.2Δ at near. Mean late postoperative ET was 0.1Δ ± 5.8Δ and 1.0Δ ± 6.2Δ at distance and near, respectively. At the final postoperative examination, mean N-D disparity was reduced to 0.9Δ ± 3.6Δ.Discussion: MR recession with PPF has a high long-term effectiveness, even in patients with amblyopia and autism. Since no posterior scleral suturing is required, it minimizes the perforation risk associated with scleral PF.Conclusion: MR recession with PPF is a safe and highly effective long-term treatment for ET with high AC/A ratio. Long-term results may surpass those of alternate procedures.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

Long-term follow-up of high accommodative convergence to accommodation (AC/A) ratio

Purpose: Although there are a number of reports on patients with accommodative esotropia and a high accommodative convergence to accommodation (AC/A) ratio, all are from referral-based or tertiary care centers. The purpose of this study was to describe the long term outcomes of high AC/A ratio from a population-based cohort.

Convergence Excess Esotropia: A Proposed New Classification and the Effect of Monocular Occlusion on the Ac/A Ratio

Convergence excess esotropia defines an esotropia on accommodation at near fixation with binocular single vision and motor fusion at distance fixation associated with a high accommodative convergence: accommodation (Ac/A) ratio. The effect of occlusion on exotropia has been well described and is known to alter the Ac/A ratio. This study examines the effect of monocular occlusion on convergence excess esotropia. The Ac/A ratio was measured using the gradient method at 1/3 and 6 m in 10 patients with convergence excess esotropia immediately prior to and following a 30-minute period of monocular occlusion. Clinically and statistically significant differences to the angle of deviation and the Ac/A ratio were found in some patients following occlusion. Ac/A ratio measurement in convergence excess esotropia is influenced by fusional tenacity. Disrupting this fusion with a period of monocular occlusion results in changes to the angle of deviation in some patients, suggesting subcategorization of this condition into true and simulated convergence excess esotropia. Measurements of the Ac/A ratio are influenced by fixation distance.

Strabismus Surgery for Elimination of Bifocals in Accommodative Esotropia

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. Retrospective interventional case series. 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. 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. 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.

Strabismus Surgery for Elimination of Bifocals in Accommodative Esotropia

Introduction: 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. 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.

Diagnosis of Pseudo-Divergence Excess Exotropia Secondary to High Accommodative Convergence to Accommodation Ratio

IntroductionCalculation of the AC/A ratio in divergence excess exotropia is accomplished by measurement at near through convex lenses following a period of monocular occlusion to eliminate tenacious proximal fusion (TPF). The purpose of this study was to determine if the AC/A ratio could be accurately calculated using minus lenses at distance fixation, thereby eliminating the need for occlusion.MethodsThis was a prospective study of 33 consecutive patients with exotropia who had been judged to be surgical candidates. All had a sensorimotor exam in addition to measurement at distance through −2.00 lenses, a 60-minute Patch Test, and remeasurement through +3.00 lenses at near. Measurement of the AC/A using plus lenses at near following occlusion was accepted as the standard to which the results of the minus lens AC/A measurement were compared.ResultsNineteen patients (58%) had an increase in the near exotropia by more than 5Δ with occlusion (mean = 8.6 ± 1.4Δ). There was no statistical difference between the AC/A calculated with the plus lens method and that calculated using the minus lens method (P > 0.7). Seven patients (21%) had a high AC/A ratio using the plus lens method. There were two false negatives with the minus lens method.ConclusionTesting with minus lenses at distance is effective in identifying a high AC/A, and may be used to determine the risk of surgical over-correction at near, or identify patients who may benefit from optical rather than surgical management.

Medial rectus pulley posterior fixation is as effective as scleral posterior fixation for acquired esotropia with a high AC/A ratio

PurposeTo compare traditional medial rectus (MR) scleral posterior fixation versus MR pulley posterior fixation without scleral sutures for the treatment of acquired esotropia (ET) with a high accommodative convergence over accommodation (AC/A) ratio. DesignNonrandomized interventional case series. MethodsMedical records were retrospectively reviewed for twenty–two patients who underwent bilateral MR posterior fixation for acquired ET with a high AC/A ratio, with or without associated MR recessions. The main outcome measure was the reduction in distance-near disparity created by MR scleral posterior fixation compared with MR pulley posterior fixation. ResultsNine patients underwent MR scleral posterior fixation surgery, seven in combination with MR recessions for distance ET. Postoperatively, the distance-near disparity decreased an average of 11.8 prism diopters, stereoacuity improved in six patients, and eight patients no longer needed bifocals. Thirteen patients underwent MR pulley posterior fixation surgery, 10 in combination with MR recessions for distance ET. Postoperatively the distance-near disparity decreased an average of 14.4 prism diopters, stereoacuity improved in eight patients, and 12 patients no longer required bifocals. Statistically, the two procedures were equivalent. One patient in each group was undercorrected at near only, with the residual near ET controlled with bifocals. One patient who underwent MR pulley posterior fixation combined with large MR recessions was overcorrected at distance only. ConclusionTraditional MR scleral posterior fixation and MR pulley posterior fixation are equally effective in treating acquired ET with a high AC/A ratio.

Risk factors for abnormal binocular vision after successful alignment of accommodative esotropia

Purpose The purpose of this study was to identify clinical factors associated with abnormal binocular vision outcomes among children with accommodative esotropia (ET) whose eyes were successfully realigned with spectacles only or with spectacles and surgery. Methods The participants were 69 children with accommodative ET who were followed up prospectively from the time of diagnosis. Clinical factors examined in this study included high accommodative convergence–to–accommodation (AC/A) relationship, high hyperopia, anisometropia, age of onset, and duration of eye misalignment. Binocular vision was assessed using measures of stereopsis, fusional vergence, sensory foveal fusion, and motion visual-evoked potential (mVEP). Results Children with a high AC/A relationship are 2.2 times more likely to have an absence of fusional vergence than are children with a normal AC/A relationship. Children having a duration of constant eye misalignment ≥ 4 months before being successfully treated are 4.6 times more likely to have abnormal stereopsis, 33 times more likely to have no stereopsis, 37 times more likely to have an absence of fusional vergence, 31 times more likely to have an absence of sensory foveal fusion, and 17 times more likely to have an asymmetric mVEP response than children with a duration of constant ET diagnosed at 0 to 3 months. Conclusions Following successful eye alignment, as many as 75% of patients with accommodative ET had anomalous binocular vision. A high AC/A relationship poses a significant risk for abnormal fusional vergence only. A constant eye misalignment lasting ≥ 4 months poses a significant risk for anomalous binocular vision on all measures studied.

Fifteen-year outcome of surgery for the near angle in patients with accommodative esotropia and a high accommodative convergence to accommodation ratio.

To determine the 15-year outcome of patients with partly accommodative esotropia with a high accommodative convergence to accommodation (AC/A) ratio who underwent surgery based on the angle of esotropia at one-third meter while wearing full hyperopic correction. A retrospective chart review to determine the 15-year outcome of 25 patients whose 6-month outcome had been previously reported as part of a prospective, randomized, masked clinical trial. All patients had partly accommodative esotropia with a high AC/A ratio and underwent surgery based on their esotropia at one-third meter while wearing full-distance optical correction. Fifteen years after surgery, 19 of the 22 patients for whom follow-up data are available had between 0 and less than 10 prism diopters of esotropia. Only 6 of the 19 needed to continue to wear optical correction to maintain satisfactory alignment; however, 8 more needed spectacles for visual purposes. Only 1 patient needed to use a bifocal add to have satisfactory alignment at one-third meter. All patients showed some degree of sensory fusion, with 4 obtaining 40 seconds of stereopsis and another 8 obtaining between 60 and 200 seconds of stereopsis. Surgery for the near angle obtained with patients wearing their full hyperopic distance correction provides excellent motor and sensory results in patients with partly accommodative esotropia with a high AC/A ratio.

Bimedial Rectus Recession for Alternating Esotropia

Summary The results of 179 consecutive Bimedial Rectus Recession operations performed for alternating esotropia are reported. Successful outcome was achieved in 54% of cases, but a higher success rate of 64% was obtained where there was an associated accommodative element or a high accommodative convergence: accommodation ratio, and 70% success was obtained when the angle of deviation was 20° or less. The results justify Bimedial Rectus Recession for selected cases of alternating convergent strabismus.

Management of intermittent esotropia.

Management of patients with intermittent esotropia having either normal or high accommodative convergence to accomodation (AC:A) ratios is discussed. Treatment should be based on liberal use of miotics to build up fusional reserves and use of hyperopic corrections or bifocals or both whenever specifically indicated. Divergent fusional reserve training is time-consuming and the cost/benefit ratio so low that most patients and doctors prefer the former treatment.