Bifoveal Fixation Research Articles

Comparison of bilateral medial rectus recession vs recession-resection as surgery for infantile esotropia

Background: Infantile esotropia is misalignment of eyes from bifoveal fixation where surgical correction at an early age usually presents with good outcomes.
 Aims and Objective: To compare the surgical outcome between bilateral medial rectus recession (BMR) and recession- resection (RR) surgery in infantile esotropia.
 Materials and Methods: The study was conducted in Lumbini Eye Institute, Bhairahawa, from December 2017 to December 2018. Patients with infantile esotropia who underwent surgical correction were included in the study. Patients were examined pre operatively, and post operatively at day one and third month, where the angle of deviation was measured and the level of binocular single vision (BSV) was assessed. Data was entered and analyzed using the SPSS program.
 Results: Total 79 patients were included in the study out of which 33 underwent BMR and 46 underwent RR. The mean pre-operative angle by PBCT was 52.58 PD (SD ±15.468) in the BMR group and 47.83 PD (SD ±12.140) in the RR group. Post-operative deviation in the BMR group had angle <35 PD. In the RR group the post-operative deviation observed was <35 PD, whereas 1/46 patients had angle between 35-50 PD. All patients who had residual esotropia (ET) in either the BMR or RR group had a pre-operative angle above 50 PD. Pre-operatively 43% had fusion and rest of them had suppression. Post-operatively 40.5% had fusion, 15.2% had stereopsis and rest of them had suppression or BSV could not be assessed in them. Therefore, there was increase in BSV by 2.5% from fusion to stereopsis. Those who initially showed suppression or in whom the BSV could not be assessed pre-operatively now showed to have fusion or some stereopsis. In total there was 15.2% increase in stereopsis.
 Conclusion: Though cosmesis has been improved in most patients after strabismus surgery, BSV improvement was insignificant as most surgery was performed after attainment of visual maturity. No significant difference between BMR and RR was found in terms of improvement of angle of deviation and BSV.

The agreement between the Irvine 4 diopter prism test and assessment of ocular fixation in microtropia with identity

ABSTRACT Microtropia describes a primary ocular deviation of less than 10 prism diopters associated with harmonious anomalous retinal correspondence and reduced stereopsis. It is routinely accepted that children with microtropia are less likely to achieve equal vision following occlusion therapy than those with bifoveal fixation. The most commonly used methods of diagnosing a microtropia are the 4 diopter prism test (4∆PT) and assessment of ocular fixation. This study examines the agreement between the two tests. One hundred and twelve typically developing children without a manifest strabismus who were able to undertake a linear visual acuity test and had two or more lines of anisoacuity following refractive adaption to their full cycloplegic correction underwent assessment of the 4∆PT and ocular fixation along with their routine orthoptic examination. One hundred and twelve children (46 boys and 66 girls) attending the Orthoptic department who fitted the above criteria were included in the analysis. The mean age at examination was 6 years. 80.3% had anisometropia of at least 1.25 diopters. The 4∆PT indicated a microtropia in 74 cases, whereas assessment of fixation indicated a microtropia in 68 cases. In 88 cases (78.6%), the results of the two tests agreed. Analysis found only moderate agreement between the two tests (k = 0.540 (CI 0.379–0.700)). Logistic regression analysis comparing those children where the two tests agreed with those where they disagreed found no difference in the level of anisoacuity (p = 0.7823), degree of anisometropia (p = 0.9385), the vision in the worst eye (p = 0.5260), the refractive error in the “worst” eye (p = 0.865), or the age at the time of testing (p = 0.4485) between the two groups. When assessing for a microtropia, it was found that not all children who elicit a central suppression response on the 4∆PT are found to be fixing eccentrically and vice versa. This could potentially have implications for the treatment of their amblyopia. It is important not to rely on just one test at one time to make the diagnosis of microtropia. Rather, if one or other test indicates a microtropia the first time they are attempted, this should be reassessed regularly as treatment progresses and certainly before treatment is stopped and suboptimal visual acuity is accepted.

Surgical outcomes of acute acquired comitant esotropia of adulthood

BackgroundAcute acquired comitant esotropia (AACE) is a type of strabismus characterized by a sudden onset of large angle esotropia with diplopia, which often occurs in children after infancy, teenagers, and young adolescents. However, studies on the surgical outcomes of only adults are rare. The purpose of this article is to analyze the surgical outcomes for adult patients diagnosed with AACE.MethodsMedical records of 24 patients who had undergone surgery for AACE were retrospectively analyzed. The main outcome measures were the final motor and sensory success rate after surgery and factors affecting motor and sensory outcomes. Motor success was considered alignment within 8 prism diopter (PD) at both near and distance and sensory success was stereoacuity ≥ 60 sec/arc.ResultsThe preoperative mean esodeviation angles were 33.1 ± 10.4 PD at distance and 33.3 ± 11.2 PD at near. The mean period of postoperative follow up was 7.5 ± 4.5 months (range 1–8 months). The postoperative mean esodeviation angles at final follow-up time were 3.4 ± 6.1 PD at distance and 3.8 ± 6.7 PD at near. The surgical motor success rate at final follow-up was 79.2% (19/24). The sensory success rate at final follow-up was 50.0% (12/24). The factor affecting the motor outcome was the type of surgery (p < 0.05). The factor affecting sensory outcome was postoperative follow-up time (p < 0.05).ConclusionsSurgery type appears to affect surgical motor outcomes in adults with AACE. Although the sensory outcome was favorable, it seems that regaining bifoveal fixation takes time.

Stereopsis before and after Inferior Oblique Weakening Surgery.

PurposeTo analyze stereopsis change before and after inferior oblique weakening surgery.MethodsWe retrospectively reviewed the medical records of 31 patients who had undergone inferior oblique weakening surgery. The factors analyzed included sex, age at surgery, preoperative and postoperative visual acuity (VA), time from first detection to surgery, degree of inferior oblique overaction (IOOA), primary/secondary IOOA, exotropia/hypertropia, bilaterality, and type of surgery.ResultsEighteen patients with a mean age 7.3 ± 3.1 years exhibited stereopsis of 60 arc seconds or better before surgery and 17 had stereopsis better than 60 arc seconds after surgery. Postoperatively, stereopsis improved in 13 patients and deteriorated in 9. Better preoperative VA and the absence of superior oblique underaction were associated with better preoperative stereopsis. Better preoperative VA, postoperative VA, and the presence of head tilt were associated with better postoperative stereopsis. Unilateral inferior oblique weakening surgery and accompanying hypertropia were associated with improved stereopsis, while the absence of hypertropia was associated with deteriorated stereopsis.ConclusionsIn this retrospective study, 58.1% of patients tended to have bifoveal fixation. When a vertical deviation is present in the primary position due to unilateral IOOA, IO weakening surgery can be expected to improve binocular function.

Assessment of the effect of academic examination stress on binocular vision functions among secondary school-aged children

Background: Binocular single vision involves the simultaneous use of both eyes with bifoveal fixation, and this process helps individuals to use their both eyes for reading, writing, and other near activities; the stress on this system could lead to ocular complaints and affect the near task for the school-aged children. Aim: The aim of this study was to assess the effect of academic examination stress on binocular vision functions among secondary school-aged children in Khartoum State of Sudan. Materials and Methods: This is an experimental study of 148 secondary school-aged children, selected randomly from Alfath Secondary School, and their ages ranged from 13 to 17 years with a mean age of 14.6 ± 1.13 years. Investigation was performed before and after the academic examinations in 2017. The clinical examinations include visual acuity measurements using Snellen vision testing chart, refraction using autorefractometer, dissociated near phoria by Maddox Wing, associated near phoria by Mallet Fixation Disparity Test, amplitude of accommodation and near point of convergence (NPC) measured by R.A.F rule, and near positive fusional vergence (PFV) and near negative fusional vergence by prism bar. All these investigations were done before 15 days of academic examinations and on the day after the students finished their academic examinations. Results: The findings indicated that most of the students (62.8%) before the academic examinations reported that they were free from any ocular complaints, whereas 37.2% had ocular symptoms. After stress due to examinations, the percentage of students who had ocular complaints increased to 71.6, whereas those free of ocular complaints decreased to 28.4. The mean of amplitude of accommodation before taken the examinations was 9.81 ± 2.16, and after the examination, the mean of amplitude of accommodation decreased to 8.77 ± 1.97 (P Conclusion: The academic examination stress had a major effect on binocular vision functions, result in decompensated heterophoria, as well as decline in amplitude of accommodation, and NPC. Thus, comprehensive eye examination including binocular vision function assessment should be made annual for school-aged children.

High specificity of the pediatric vision scanner in a private pediatric primary care setting

The Pediatric Vision Scanner (PVS) directly detects strabismus and amblyopia by analyzing binocular scans for birefringence that, due to the organization of the radially arranged Henle fibers, is characteristic of steady, bifoveal fixation. In a pediatric ophthalmology office setting,1 we found that the PVS had 97% sensitivity and 87% specificity for detection of strabismus and amblyopia. However, this study did not directly assess performance of the PVS in a primary care screening setting, where it is designed to be used. Here we report PVS specificity and positive likelihood ratio for a cohort of children screened in a pediatric primary care setting.

Antimetropia in a 10-year-old boy with unilateral tilted disc syndrome

Antimetropia in a 10-year-old boy with unilateral tilted disc syndrome Shinji MakinoDepartment of Ophthalmology, Jichi Medical University, Shimotsuke, Tochigi, JapanAbstract: Antimetropia is a condition in which one eye is myopic, while the fellow eye is hyperopic. This report describes a case of antimetropia associated with unilateral tilted disc syndrome. A 10-year-old boy presented with the complaint of diminished vision for distant objects in his right eye for several months. His uncorrected distance visual acuity was 0.15 in the right eye and 1.0 in the left eye. Best corrected visual acuity was 1.0, with -6.00 D/-2.00 D 170&deg; in the right eye and +1.50 D in the left eye. The cover test revealed right esotropia and hypertropia. Bifoveal fixation was achieved using a 14 prism diopter (PD) base at 220&deg; in the right eye. Fundus examination revealed a tilted disc with inferior staphyloma in the right eye, but no abnormal findings were observed in the left eye. In addition, the patient occasionally experienced diplopia under casual viewing conditions. A cycloplegic refraction revealed -6.00 D/-2.00 D 170&deg; in the right eye and +1.50 D/-2.00 D 5&deg; in the left eye. Thus, prism glasses were prescribed. While wearing the prism glasses, the patient has shown no diplopia and maintains good binocular function.Keywords: amblyopia, strabismus, anisometropia, staphyloma

Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression

To test the hypothesis that fixational stability of the amblyopic eye in strabismics will improve when viewing provides both bifoveal fixation and reduced inter-ocular suppression by reducing the contrast to the fellow eye. Seven strabismic amblyopes (Age: 29.2 ± 9 years; five esotropes and two exotropes) showing clinical characteristics of central suppression were recruited. Interocular suppression was measured by a global motion task. For each participant, a balance point was determined which defined contrast levels for each eye where binocular combination was optimal (interocular suppression minimal). When the balance point could not be determined, this participant was excluded. Bifoveal fixation was established by ocular alignment using a haploscope. Participants dichoptically viewed similar targets (a cross of 2.3° surrounded by a square of 11.3°) at 40 cm. Target contrasts presented to each eye were either high contrast (100% to both eyes) or balanced contrast (attenuated contrast in the fellow fixing eye). Fixation stability was measured over a 5 min period and quantified using bivariate contour ellipse areas in four different binocular conditions; unaligned/high contrast, unaligned/balance point, aligned/high contrast and aligned/balance point. Fixation stability was also measured in six control subjects (Age: 25.3 ± 4 years). Bifoveal fixation in the strabismics was transient (58.15 ± 15.7 s). Accordingly, fixational stability was analysed over the first 30 s using repeated measures anova. Post hoc analysis revealed that for the amblyopic subjects, the fixational stability of the amblyopic eye was significantly improved in aligned/high contrast (p = 0.01) and aligned/balance point (p < 0.01) conditions. Fixational stability of the fellow fixing eye was not different statistically across conditions. Bivariate contour ellipse areas of the amblyopic and fellow fixing eyes were therefore averaged for each amblyope in the four conditions and compared with normals. This averaged bivariate contour ellipse area was significantly greater (reduced fixational stability, p = 0.04) in amblyopes compared to controls except in the case of aligned and balanced contrast (aligned/balance point, p = 0.19). Fixation stability in the amblyopic eye appears to improve with bifoveal fixation and reduced interocular suppression. However, once initiated, bifoveal fixation is transient with the strabismic eye drifting away from foveal alignment, thereby increasing the angle of strabismus.

High sensitivity and specificity of the Pediatric Vision Scanner in detecting strabismus and amblyopia in preschool children

The Pediatric Vision Scanner (PVS) directly detects strabismus and amblyopia by analyzing binocular scans for the presence or absence of birefringence, which is characteristic of steady, bifoveal fixation. In a preliminary study (AAPOS 2012), the PVS demonstrated 98% sensitivity and 88% specificity. Here we report the sensitivity and specificity for a large cohort, confidence intervals, and analyses of screening errors. 250 children (2-6y) were enrolled; 103 controls and 147 with strabismus and/or amblyopia. In addition to the PVS, children were tested with the SureSight autorefractor and the Randot Preschool Stereoacuity test (RPST). Each test yielded a recommendation of “pass” or “refer.” A comprehensive pediatric ophthalmic examination served as the gold-standard. The PVS correctly identified 144 of 147 children with strabismus and/or amblyopia; sensitivity = 98% (95%CI: 95-100%). The PVS correctly identified 89 of 102 control children; specificity = 87% (95% CI, 79%-96%). The SureSight misclassified 81 children, failing to detect 49 children with strabismus and/or amblyopia and over-referring 18 children with astigmatism. The RPST misclassified 51 children, including similar numbers of affected and control children. Misclassifications were not consistent across tests. Using Bayesian analysis to estimate the performance of each test in a preschool screening setting (assuming a prevalence of 4%), accuracies of 88%, 69%, and 77% were predicted for the PVS, SureSight, and RPST tests, respectively. The PVS identifies children with strabismus and/or amblyopia with high sensitivity, outperforming the SureSight and the RPST. Preschool vision screening may be more efficient with a device that directly detects strabismus and/or amblyopia.

Factors affecting postoperative stereopsis in acquired nonaccommodative esotropia

To identify and examine factors that affect postoperative binocularity in children diagnosed with acquired nonaccommodative esotropia (ANAET). Retrospective chart review. Thirty-four pediatric patients who received surgery for ANAET by 1 surgeon (I.M.) at the Ivey Eye Institute, University of Western Ontario (London, Ont.). A multivariate logistic regression analysis was performed to evaluate the effect of the following factors on achieving stereopsis postoperatively: age at onset of esotropia (AO), duration of misalignment (DOM), presence of A/V pattern, recent intermittency of esotropia, and presence of dense amblyopia. Forty-one percent of all patients achieved stereoacuity of 100 seconds of arc or better. AO was found to be the only factor significantly associated with postoperative stereopsis (adjusted odds ratio = 1.063, P<0.05). None of the children with AO who were younger than 30 months regained bifoveal fixation regardless of their DOM. Age of onset appears to play a crucial role on postoperative functional outcome in children with ANAET. Delayed surgery in children with an age of onset beyond 30 months did not seem to be detrimental to regaining bifoveal fixation.

Objective detection of amblyopia and strabismus . . . not just screening for risk factors

To date, preschool vision screening for strabismus and/or amblyopia involves assessment of risk factors, including refractive error and stereoacuity. Most children who are positive for risk factors never develop strabismus or amblyopia. The Pediatric Vision Scanner (PVS) is the first objective, automated screening device that directly assesses bifoveal fixation. This study was undertaken to assess the ability of the PVS to identify patients with strabismus and/or amblyopia in a pediatric ophthalmology office setting.

Anomalous head posturing in essential infantile esotropia: a hypothesis

1This editorial presents our understanding of why a child with infantile esotropia syndrome may manifest a visually directed anomalous head posture (AHP). Many aspects of essential infantile esotropia (EIE) or infantile esotropia syn-drome remain controversial and ill-defined (1). The recent National Eye Institute, National Institutes of Health, USA–sponsored Classification of Eye Movement Abnormalities and Strabismus (CEMAS) workshop and document has at-tempted to consolidate its definition (2). Table I presents the CEMAS description of EIE.Torticollis in childhood is most commonly the result of ab-normalities of the central nervous system, the ocular motor system, or the neck musculature. Head posturing associ-ated with abnormalities of the ocular motor system is usu-ally compensatory. The visual purpose of head posturing serves to enhance bifoveal fixation, singular binocular vi-sion, or visual acuity. The ocular etiologies of anomalous head posture include strabismus, nystagmus, refractive errors, dissociated ocular deviations, and visual pathway obstruction (e.g., lid, corneal, lens, and vitreous anoma-lies). Although clinical differentiation of these disorders is accurately accomplished after a thorough history and ophthalmic examination, the etiology of anomalous head posture is often elusive in patients with a combination of strabismus and nystagmus. Children with nystagmus will have anomalous head posture due to multiple causes. A “gaze null” is a position of one or both eyes with respect to the orbit where the nystagmus intensity is the least and vision is the best and is usually associated with infantile nystagmus syndrome or more rarely, forms of acquired nystagmus with an eccentric gaze null position, e.g., gaze evoked, upbeat, and downbeat nystagmus. An “adduction null” is a position of a preferred eye in adduction charac-

Comparison of sensory outcomes in patients with monofixation versus bifoveal fusion after surgery for intermittent exotropia

The predictive value of preoperative stereopsis on the surgical outcome of patients with intermittent exotropia is unknown. We hypothesize that it may predict motor and sensory outcome. We report our experience with fusional status at near measured using Titmus circles before and after eye muscle surgery for intermittent exotropia. In this retrospective case series, 95 children underwent bilateral lateral rectus muscle recession. Visual acuity, near stereoacuity, and ocular alignment were measured before surgery and 2 months postoperatively. Testing variability by use of Titmus circles was examined. A change of greater than 3 stereo circles was found to be substantial (90% confidence interval). Of the 42 children with poor-to-nondetectable stereopsis preoperatively (400 arcsec or worse), 3 improved substantially (140, 140, 60 arcsec). The remaining 53 had moderate- (200 arcsec) to high-grade (60 arcsec or better) stereopsis preoperatively. The majority of children had no change in stereopsis after surgery. Only 4 children had improved stereopsis after surgery; 6 lost stereopsis, of whom 4 had persistent small-angle esodeviations, whereas 1 child had a large overcorrection requiring additional surgery. All children who maintained or improved their stereopsis postoperatively were orthotropic or had persistent exodeviation after surgery. No child with high-grade stereopsis at 2 consecutive preoperative visits lost stereoacuity after surgery. A persistent small-angle esotropia at the 2-month postoperative visit is associated with a loss of near stereopsis (p=0.0001) and may occur more frequently in children with subnormal stereopsis preoperatively than in patients with bifoveal fixation. Prism or reoperation may be necessary to treat this complication.

Preschool Worth 4-Shape test: Testability, reliability, and validity

Purpose: The Worth 4-Dot is used to assess binocular fusion, but it is difficult to use with young children. We modified the Worth 4-Dot by replacing the circles with shapes while maintaining the same color configuration. The purpose of this study was to determine the testability, reliability, and validity of the Worth 4-Shape test. Methods: Subjects aged 2 to 8 years and 4 patients aged over 8 years with best-corrected visual acuity of 20/40 or greater (n = 131 patients, n = 123 normals) attempted test and retest at 35 cm and 3m using the Worth 4-Shape and Worth 4-Dot. To provide a gold standard, medical history, bifoveal fixation, and stereoacuity were reviewed. Results: Testability of the Worth 4-Shape was significantly higher than the Worth 4-Dot both in children aged less than 4 years (95.9% vs 79.5% at 35 cm, P <.001; 79.5% vs 55.1% at 3 m, P <.001) and older than 4 years (98.5% vs 88.6% at 35 cm, P <.001; 90.9% vs 82.4% at 3m, P =.04). Test-retest analysis found comparable concordance for the Worth 4-Shape and Worth 4-Dot tests (P >.3). The sensitivity and specificity of the Worth 4-Shape (92%, 97%) and Worth 4-Dot (90%, 94%) were comparable. Between-test analysis found 96% agreement between both tests at 35 cm and 97% agreement at 3m. Conclusions: The success rate for the Worth 4-Shape is higher than the Worth 4-Dot, especially in children aged less than 4 years, and has equivalent accuracy. The Worth 4-Shape test-retest reliability is high supporting its validity for use with young children. (J AAPOS 2002;6:247-51)

Acquired nonaccommodative esotropia in childhood

Purpose: Acquired nonaccommodative esotropia (ANAET) in childhood is reported to occur infrequently and is often associated with an underlying neurologic or neoplastic disorder. The primary objective of this study was to ascertain the prevalence and clinical characteristics of this form of childhood esotropia. Methods: A cohort of all children younger than 11 years with esotropia from a predominantly rural Appalachian region was prospectively identified from August 1, 1995, through July 31, 1998. The age at onset, family history of strabismus, perinatal and medical history, ophthalmologic findings, and surgical results were reviewed for all patients with ANAET. Results: Twenty-three (10.4%) of 221 consecutive children with esotropia were diagnosed with ANAET compared with 12 (5.4%) diagnosed with congenital esotropia. The median age at esotropia onset for the 23 children with ANAET was 31.4 months (range, 8-63 months) with a mean initial angle of esotropia of 24 PD. Although at least 2 children presented with diplopia, none of the 23 patients were known to have harbored intracranial tumors or other lesions of the central nervous system during the follow-up period. Fourteen of the 19 patients who underwent surgery attended follow-up visits for at least 6 months after their last surgical procedure: 13 were within 8 PD or less of orthotropia, whereas the final patient had persistent esotropia. Twelve of the 13 patients within 8 PD of orthotropia demonstrated some level of stereopsis, including 2 children with bifoveal fixation. Two (10.5 %) of the 19 operated patients later required a low hyperopic spectacle correction to control their deviation. Conclusions: ANAET was more prevalent than congenital esotropia in this cohort of children with esotropia. This clinically distinct form of strabismus typically begins between 1 and 5 years of age and appears to be infrequently associated with underlying disease. The angle of deviation is relatively small and early surgical correction is more likely to achieve bifoveal fixation for these patients than for those with congenital esotropia. (J AAPOS 2001;5:85-9)

Monofixation with Eso-, Exo-, or Hypertropia: Is There a Difference?

Monofixation syndrome is considered the next best thing to bifoveal fixation because it allows excellent binocular vision and long-term stability of alignment in patients with small angle strabismus. The purpose of this study was to determine if there exists an anatomic or physiologic reason for the visual system to prefer small angle esotropia over exotropia or hypertropia.Of 259 cases of strabismus ≤10Δ, esotropia was the most common and the most stable form of microtropia. Stability was statistically associated with sensory fusion, motor fusion, and stereopsis. Micro-ET cases outperformed the exotropic and hypertropic cases in all sensory categories, but particularly in the case of motor fusion. Instability was associated with the presence of an A- or V-pattern, oblique dysfunction, a history of infantile esotropia, dense amblyopia, and a significant change in refractive error. Micro-XT and HT were more likely to display these signs.In order to ensure long-term stability through fusion and stereopsis, the visual cortex must link the fovea of the dominant eye with the nasal retina in esotropic eyes, or the temporal retina in exotropic eyes. However, temporal retinal input is at a competitive anatomic and physiologic disadvantage. Compared to the connections necessary for binocular vision in micro-ET, those required for XT or HT may be more difficult to form and easily disrupted once established.

Schizophrenic vulnerability: a deficiency of the correlation between foveal perception and oculomotor proprioception?

In a previous paper published in Medical Hypotheses, the author proved by a simple mirror test a dissociation between the goals of selective attention and bifoveal fixation in a schizophrenic patient. In the present article, she enters into the details of the patient’s results in ophthalmological tests which revealed an opposite deviation of accommodation and vergence, compensated in a way incompatible with Hering’s law. She expounds that Hering’s law is based on the correlation of retinal data with proprioceptive information of the exterior eye-muscles, and that schizophrenic vulnerability might consist of a disturbance of this correlation favouring fusion of patterns in the remote and external space over fusion in the near and central space. Some phenomena found in schizophrenic patients and their carrier parents are explained in the light of this hypothesis. Finally, the author gives detailed advice on how to overcome difficulties in the correction of the ophthalmological deviations that induce the vulnerability to take effect.

The somatic component of schizophrenia: a dissociation of the goals of visual attention and bifoveal fixation?

The presence of disorders of eye movements is today regarded as ‘the strongest candidate for a genetically transmitted biological trait marker of schizophrenic disorders’ (1). The present study is based on the experience, rather than the behaviour, of one patient in a search for a method of objectifying his visual problems. This method was found to be a simple test, which demonstrates a disturbance of fixation: while one eye accommodated on the figure without vergence, the other, vergent, eye fused with the image of the related background.The disorder had been misdiagnosed as ‘exophoria’ in conventional ophthalmological examinations, because prevailing ophthalmological theory accepts only one mode of vision; according to the most recent researches, however, it is necessary to distinguish two complementary modes of vision – one for panorama and one for detail – which differ in their coordination of vergence and accommodation.This new bimodal theory of vision – presented here for the first time – made it possible to understand the cause of the disorder as asubstitution of sighting for fixation, due either to a disinhibition of panorama vision during fixation vision, or to an interchange of ipsilateral temporal and contralateral nasal projections from the retina, both associated with a fixation disparity. After correction of the patient's fixation disparity according to an unusual method, the dissociation of the visual goals was remedied and the mental disturbances of the patient vanished.

Motor and sensory fusion in monkeys: psychophysical measurements.

Motor and sensory fusion, the basic processes of binocularity, must be present for bifoveal fixation with true fusion and stereopsis during ordinary viewing. The characteristics of motor and sensory fusion have been established for patients with normal and subnormal binocular vision; the present report describes our psychophysical studies of these processes in the macaque monkey. Three recent investigations of motor and sensory fusion in monkeys are described. The studies involved: (1) the comparability of motor and sensory fusion in monkeys and humans with normal binocular vision, (2) the effects of an early period of abnormal binocular vision on motor and sensory fusion in monkeys, and (3) the contrast sensitivity for binocular disparity in monkeys with stereo-deficiencies. The results of these studies demonstrated an excellent homology between the normal binocular vision of monkeys and humans. We also found that a period of esotropia during infancy caused deficiencies in sensory fusion, but not motor fusion. In some monkeys, the sensory deficiency persisted over the entire range of binocular disparities that were compatible with stereopsis, while other subjects demonstrated normal stereo-sensitivity for the largest fusible binocular disparities. The stereo-deficiencies of these monkeys, along with other visual attributes, suggest that their binocular vision is a viable model for the binocularity of patients with subnormal binocular vision or the monofixation syndrome.

Microtropia versus bifoveal fixation in anisometropic amblyopia

Microtropia with identity is a unique condition in which amblyopes have parafoveal eccentric fixation in the amblyopic eye in either monocular or binocular viewing, plus a macular scotoma. The condition has previously been described in anisometropic amblyopia. The records of 55 consecutively presenting anisometropic amblyopes were scrutinised and the cases divided into microtropes or non-microtropes (bifoveal fixators). The features of the two groups were then compared to identify factors associated with microtropia and to determine whether microtropes or bifoveal patients responded better to amblyopia therapy. Results show that 45% of anisometropic amblyopes have microtropia rather than bifoveal fixation. There appears to be no association between the microtropic phenomenon and age, depth of amblyopia or amount of anisometropia. Bifoveal patients may respond better to amblyopia therapy although the difference between groups was not great. The sensitive period during which amblyopia may be treated is the same for each group.