Sensorial anomalies in strabismus. (suppression, anomalous correspondence, amblyopia)

Efficacy of anti-suppression therapy in improving binocular vision in children with small-angle Esotropia

PURPOSE

To evaluate the efficacy of anti-suppression exercises in children with small-angle esotropia in achieving binocular vision.

METHODS

A retrospective review of patients aged 3-8 years who underwent anti-suppression exercises for either monocular or alternate suppression between January 2016 and December 2021 was conducted. Patients with esotropia less than 15 prism diopters (PD) and visual acuity ≥ 6/12 were included. Patients with previous intra-ocular surgery or less than three-month follow-up were excluded. Success was defined as the development of binocular single vision (BSV) for distance, near, or both (measured clinically with either the 4 prism base out test or Worth four dot test) and maintained at two consecutive visits. Qualified success was defined as the presence of diplopia response for both distance and near. Additionally, improvement in near stereo acuity was measured using the Stereo Fly test.

RESULTS

Eighteen patients with a mean age of 5.4 ± 1.38 years (range 3-8 years) at the time of initiation of exercises were included in the study. The male female ratio was 10:8. The mean best corrected visual acuity was 0.18 LogMAR unit(s) and the mean spherical equivalent was +3.8 ± 0.14 diopters (D). The etiology of the esotropia was fully accommodative refractive esotropia (8), microtropia (1), post-operative infantile esotropia (4), partially accommodative esotropia (1), and post-operative partially accommodative esotropia (4). Patients received either office-based, home-based, or both modes of treatment for an average duration of 4.8 months (range 3-8). After therapy, BSV was achieved for either distance or near in 66.6 % of patients (95 % CI = 40.03-93.31 %). Binocular single vision for both distance and near was seen in 50 % of children. Qualified success was observed in 38.46% of patients. Persistence of suppression was observed in one patient (5.5 %). Near stereopsis improved to 200 s of arc or more in 60% of the patients. The mean esotropia reduced from 5.7 ± 4.0 PD for distance and 6.2 ± 4.66 PD for near to 2.7 ± 2.4 PD and 3.38 ± 4.7 PD respectively, at the last follow-up (p-value 0.004 and 0.006). Failure of therapy was noticed after six months of follow-up in the child with infantile esotropia.

CONCLUSION

Anti-suppression exercises may be beneficial to improve binocular vision functions in children with small-angle esotropias of variable etiologies. Recurrence of suppression after cessation of therapy is possible, warranting regular follow up.

Acquired comitant esotropias - comparison of surgical outcomes of accommodative vs non-accommodative types

Purpose: To compare the motor and sensory outcomes of strabismus surgery and the factors affecting surgical success in acquired acute non-accomodative esotropia (ANAET) and partially accommodative refractive esotropia (pARET). Methods: A retrospective chart review of patients with ANAET and pARET who underwent unilateral or bilateral horizontal rectus muscle surgery between January 2020 and December 2021 was conducted. Patients with postoperative follow-up of at least six weeks were included. Patients with pattern deviation, lateral incomitance, and near-distance disparity were excluded. Motor success was defined as a postoperative deviation within eight prism diopters of orthophoria. Sensory success was defined as presence of binocular single vision (BSV) for both distance and near (Worth four dot test). The effect of factors like age at onset, age at surgery, amblyopia before surgery, duration of squint before treatment, presence or absence and magnitude of vertical deviation, preoperative angle of deviation, and spherical equivalent on the motor and sensory success in each group were analyzed and compared. Results: 38 patients with ANAET and 33 patients with pARET were included. The mean age of onset of esotropia was 8.55 ± 4.65 years and 4.39 ± 2.27 years (p < .001) and the mean age at surgery was 10.62 ± 4.99 years and 7.89 ± 2.84 years (p = .006) in the ANAET and the pARET group respectively. The mean duration of the final follow-up was 38.51 weeks in the ANAET and 48.68 weeks in the pARET group (p = .089). Patients were successfully aligned for both distance and near in 81.5% of patients in the ANAET and 78.9% of patients in the pARET group at the final follow-up (p. 0.775). A BSV for both distance and near at the final follow-up was seen in 81.2% vs 66.6% of patients in the ANAET and the pARET group respectively (p = .25). A good near stereoacuity (<120 arcsecs) was seen in 60.6% and 41.9% of the ANAET and the pARET groups respectively (p = .175). The percentage of patients in the ANAET group who had orthophoria, any esodeviation, and any exodeviation for distance at the final follow-up was 63.1%, 34.2% and, 2.6%. The percentage of patients in the pARET group in similar categories was 36.3%, 42.4% and, 21.2%. None of the demographic and preoperative factors were found to affect the surgical outcomes in the two groups. Conclusions: The motor and sensory outcomes were similar in the two groups. A higher proportion of ANAET patients remained orthophoric during the follow-up. The patients in the pARET group showed a tendency toward exodrift.

Recent understanding of binocular vision in the natural environment with clinical implications

Technological advances in recent decades have allowed us to measure both the information available to the visual system in the natural environment and the rich array of behaviors that the visual system supports. This review highlights the tasks undertaken by the binocular visual system in particular and how, for much of human activity, these tasks differ from those considered when an observer fixates a static target on the midline. The everyday motor and perceptual challenges involved in generating a stable, useful binocular percept of the environment are discussed, together with how these challenges are but minimally addressed by much of current clinical interpretation of binocular function. The implications for new technology, such as virtual reality, are also highlighted in terms of clinical and basic research application.

Reduced evoked activity and cortical oscillations are correlated with anisometric amblyopia and impairment of visual acuity

Amblyopia is a developmental disorder associated with abnormal visual experience during early childhood commonly arising from strabismus and/or anisometropia and leading to dysfunctions in visual cortex and to various visual deficits. The different forms of neuronal activity that are attenuated in amblyopia have been only partially characterized. In electrophysiological recordings of healthy human brain, the presentation of visual stimuli is associated with event-related activity and oscillatory responses. It has remained poorly understood whether these forms of activity are reduced in amblyopia and whether possible dysfunctions would arise from lower- or higher-order visual areas. We recorded neuronal activity with magnetoencephalography (MEG) from anisometropic amblyopic patients and control participants during two visual tasks presented separately for each eye and estimated neuronal activity from source-reconstructed MEG data. We investigated whether event-related and oscillatory responses would be reduced for amblyopia and localized their cortical sources. Oscillation amplitudes and evoked responses were reduced for stimuli presented to the amblyopic eye in higher-order visual areas and in parietal and prefrontal cortices. Importantly, the reduction of oscillation amplitudes but not that of evoked responses was correlated with decreased visual acuity in amblyopia. These results show that attenuated oscillatory responses are correlated with visual deficits in anisometric amblyopia.

Late Surgical Correction of Longstanding Constant Strabismus in Adults: Is Fusion Possible in All Successfully Aligned Patients?

PURPOSE

To determine whether late surgical correction provides fusion in adults who have constant strabismus beginning in early childhood.

MATERIALS AND METHODS

This was a prospective study that included 34 consecutive adults with a history of early onset strabismus who had not previously undergone surgery. They were tested with the Bagolini striated glasses (BSG), Worth four-dot (W4D) test, cover test, and four-prism diopter (4-PD) test, preoperatively, and 6 weeks after surgery.

RESULTS

The mean age was 23.8 years, 17 patients had esotropia and 17 patients had exotropia. Preoperatively, all patients demonstrated a manifest horizontal deviation ranging from 30^∆ to 60^∆ and had suppression. At 6 weeks postoperatively, 33 patients had a horizontal manifest deviation of <15^∆ (range, 2^∆-14^∆; median, 6^∆), and none were orthotropic as determined by the cover test together with the 4-PD test. All of these 33 patients achieved anomalous retinal correspondence (ARC) with the BSG at near, and 25 (75%) had ARC with the W4D test at near.

CONCLUSIONS

Although our study has limited number of patients its findings suggest it is possible to develop ARC after surgery in almost all adult patients with childhood-onset strabismus associated with suppression, and who have not previously been operated upon, if satisfactory alignment is achieved in adulthood.

Could Modifying the Bagolini Glasses Improve the Reliability of Responses?

Aims:

Bagolini striated lenses are a useful test of binocular vision, but the variations in the striations (frequency and thickness) can impact on the perceived image. Also, responses can be difficult to interpret in young children. Therefore, the aims of this project were to evaluate the impact of striation frequency and the addition of coloured filters on subjective responses.

Methods:

Three sets of striated lenses were made (small, medium and large striations), each produced in two forms (both lenses clear, or with a red and blue lens). Also, Bagolini glasses (Optiker Ryser) were used, with and without the addition of red and blue filters. Subjects were asked to report what they perceived, with subsequent questions regarding the number and length of lines.

Results:

Forty-two adult subjects were tested, with uniocular VA ranging from –0.18 to 1.10 logMAR (mean 0.08 ± 0.25). The number of lines seen when varying the line thickness did not vary between coloured and clear lenses (post-hoc analysis following ANOVA, p > 0.1 in all comparisons). Adding red/blue filters to the original Bagolini glasses did not alter the rates of subjects perceiving a cross (Chi-square, p = 0.8). However, the laser-cut lenses produced a significantly shorter light streak than the original lenses (One-way ANOVA, p < 0.001), but the colour of the filters made no difference to the length of streak perceived (Tukey’s Test, p = 0.20).

Conclusions:

The addition of coloured filters did not impact on the responses given to the original or laser-cut lenses, suggesting this modification may aid responses in children. However, further evaluation is required with finer striations and thinner lenses to improve the visibility of the lines.

The Importance of the Interaction Between Ocular Motor Function and Vision During Human Infancy

Numerous studies have demonstrated the impact of imposed abnormal visual experience on the postnatal development of the visual system. These studies have provided fundamental insights into the mechanisms underlying neuroplasticity and its role in clinical care. However, the ocular motor responses of postnatal human infants largely define their visual experience in dynamic three-dimensional environments. Thus, the immature visual system needs to control its own visual experience. This review explores the interaction between the developing motor and sensory/perceptual visual systems, together with its importance in both typical development and the development of forms of strabismus and amblyopia.

Fluoxetine does not enhance the effect of perceptual learning on visual function in adults with amblyopia

Amblyopia is a common visual disorder that is treatable in childhood. However, therapies have limited efficacy in adult patients with amblyopia. Fluoxetine can reinstate early-life critical period-like neuronal plasticity and has been used to recover functional vision in adult rats with amblyopia. We conducted a Phase 2, randomized (fluoxetine vs. placebo), double-blind, multicenter clinical trial examined whether or not fluoxetine can improve visual acuity in amblyopic adults. This interventional trial included 42 participants diagnosed with moderate to severe amblyopia. Subjects were randomized to receive either 20 mg fluoxetine (n = 22) or placebo (n = 20). During the 10-week treatment period, all subjects performed daily computerized perceptual training and eye patching. At the primary endpoint, the mean treatment group difference in visual acuity improvement was only 0.027 logMAR units (95% CI: −0.057 to 0.110; p = 0.524). However, visual acuity had significantly improved from baseline to 10 weeks in both fluoxetine (−0.167 logMAR; 95% CI: −0.226 to −0.108; p < 0.001) and placebo (−0.194 logMAR; 95% CI: −0.254 to −0.133; p < 0.001) groups. While this study failed to provide evidence that fluoxetine enhances neuroplasticity, our data support other recent clinical studies suggesting that improvement of vision can be accomplished in adults with amblyopia.

Visual Recognition Time in Strabismus: Small-Angle versus Large-Angle Deviation

Purpose

To measure the possible differences in monocular detection time of a threshold visual acuity stimulus (recognition time [RT]) between patients with small-angle and large-angle strabismus.

METHODS

Ten patients with free alternating esotropia were tested (10 to 18 years old): five with small-angle esotropia (≤7°), five with large-angle esotropia (15° to 20°). Six age-matched normal subjects served as controls. The RT of the threshold stimulus was measured in both eyes sequentially for stimuli presented in the center of a computer monitor (RT 1). Moreover, we measured the time necessary for identifying the same threshold visual acuity stimulus generated on the computer screen in the moment in which fixation is taken up by one eye after occlusion of the second eye (RT 2). Using the same setting, RT was also measured monocularly in all strabismic and normal subjects who were originally looking at a luminous fixation point positioned horizontally at 6.5 and 15 degrees from the center of the monitor (RT 3).

Results

The multivariate analysis of variance for repeated measures indicated that there was no statistical difference in RT 1 between groups. The mean RT2 was significantly longer (p<0.001) in large-angle strabismic eyes when compared with that of normal control eyes. The mean RT 2 in small-angle strabismic eyes did not differ significantly from that of normal eyes. Finally, RT 3 (both at 6.5° and 15° of eccentricity) did not show any significant difference in the three different study groups.

CONCLUSIONS

The authors hypothesized that alternating strabismus patients may have a significant advantage in maintaining a small-angle deviation, as a large-angle deviation would require longer RT in the moment the deviated eye takes up fixation. It can be speculated that the extension of re-fixation movement, obviously shorter in small-angle strabismus patients, is the main factor responsible for longer RT occurring in large-angle strabismus patients.

Assessment of the Density of Suppression to Identify Risk of Intractable Diplopia in the United Kingdom

BACKGROUND/AIMS

Occlusion used to treat amblyopia towards the end of the developmental component of the critical period gives a risk of inducing intractable diplopia. In the United Kingdom, the density of suppression is assessed via the Sbisa/Bagolini filter bar, but there is very little research evidence to guide clinical practice or interpretation of the tests used. The aims of this study were to determine current practice and estimate the incidence of intractable diplopia following amblyopia treatment.

METHODS

Current practice and incidence of intractable diplopia following amblyopia were determined via a questionnaire distributed to head orthoptists in every eye department in the United Kingdom. The questionnaire explored testing and test conditions, interpretation of the test results, and cases of intractable diplopia over the last 5 years.

RESULTS

There was considerable variation in clinical practice of the measurement of the density of suppression and interpretation of the results to guide the treatment of amblyopia. The minimum age of patients taking the test ranged from 2 to 8 years and the minimum filter considered still safe to continue treatment ranged from 4 to 17. It is estimated there were 24 cases of intractable diplopia over the last 5 years.

CONCLUSION

The issue of intractable diplopia and amblyopia treatment is likely to become increasingly important as there appears to be greater plasticity and scope to treat amblyopia in teenagers and adults than was previously thought. Lack of knowledge of how to evaluate the risk may lead to more cases of intractable diplopia or alternatively treatment being withheld unnecessarily.

Microstrabismus: Fixation point scotoma, a perimetric artefact

The contribution of the strabismic eye to binocular vision has frequently been studied with stimuli presented solely to the strabismic eye, on a binocular background. These studies revealed a central suppression scotoma in the strabismic eye, the so-called fixation point scotoma. Considering that this scotoma might be an artefact due to the unnatural viewing condition, we employed stereoperimetry that allowed examining the contribution of the strabismic eye under natural viewing, and compared the stereoresolution with the Vernier resolution of the strabismic eye. On the retina of the strabismic eye, the stereotarget was imaged at one of seven locations, between 2 degrees nasally and 2 degrees temporally, whereas on the retina of the non-strabismic eye, the stereotarget was imaged always in the centre. The mean stereoresolution of three micro-esotropic observers was 96'', averaged over all seven locations. A reduction of the stereoresolution in relation to the monocular Vernier resolution and to the performance of three non-strabismic observers indicated a slight diffuse suppression, rather than a circumscribed scotoma. We conclude that the strabismic eye contributes more to binocular vision than has been assumed on the basis of tests with targets presented solely to the strabismic eye (on a binocular background).

Why do the eyes cross? A review and discussion of the nature and origin of essential infantile esotropia, microstrabismus, accommodative esotropia, and acute comitant esotropia

PURPOSE

To try to explain the long-term stability of bilateral medial rectus botulinum toxin (botox) chemo-denervation in essential infantile esotropia; to evaluate divergent fusion amplitude in accommodative esotropia and acute comitant esotropia of emmetropes; to look for accommodation anomalies in high AC/A ratio accommodative esotropia and acute comitant esotropia of myopes; and to discuss characteristics of microstrabismus.

METHODS

Retrospective analysis of 61 essential infantile esotropia patients with early treatment with one botox injection in both medial rectus; measurement of divergent fusion amplitude in accommodative esotropia and acute comitant esotropia; measurement of Near point of accommodation in high AC/A ratio accommodative esotropia and acute comitant esotropia of myopes.

RESULTS

Stable results were found in 85.24% of essential infantile esotropia treated patients; reduced divergent fusion amplitude was detected in accommodative esotropia and acute comitant esotropia; hypo-accommodation was found in some patients with high AC/A ratio accommodative esotropia and a convergence spasm in acute comitant esotropia of myopes.

CONCLUSIONS

Very early botox treatment probably eradicates the effect of an excessive convergence tonus in essential infantile esotropia. A prevention of accommodative esotropia with full retinoscopic correction is only mandatory with a significantly reduced amplitude of fusional divergence. A deficit in accommodation should be looked for in high AC/A ratio accommodative esotropia, before bifocal lenses prescription. Early diagnosed acute comitant esotropia of myopic patients can be treated as a convergence spasm. Only surgery treats acute comitant esotropia, in patients with emmetropia or moderate hypermetropia.

The irvine prism test: does the positive response indicate suppression scotoma?

PURPOSE

To investigate whether the positive prism test response is due to the presence of a suppression scotoma or the absence of bifoveolar fixation.

METHODS

Fifty-one subjects with esotropia (microtropia, small-, moderate- or large-angle esotropia), and 22 subjects with nonstrabismic anisometropic amblyopia were examined. The prism test was performed by using base-out prisms of two different powers (4-PD and 30-PD), and base-in prism of 20-PD, as well as base-down prism of 10-PD for each subject.

RESULTS

All the subjects with esotropia showed a positive prism test response, whereas all the subjects with nonstrabismic anisometropic amblyopia had a negative prism test response. All the esotropic subjects showed positive response to all magnitudes and positions of the prisms tested.

CONCLUSIONS

The positive response to the prism test does not indicate suppression scotoma in subjects with microtropia and small-angle esotropia because all the esotropic subjects showed the positive response regardless of the amount of deviation or the sensorial adaptation mechanisms. Also, the positive response, seen in the esotropic subjects, did not alter to negative by using the prisms of different powers and directions.

Acute onset concomitant esotropia: sensorial evaluation, prism adaptation test, and surgery planning

BACKGROUND AND OBJECTIVE

Acute acquired concomitant esotropia is a rare form of strabismus that usually presents during infancy or early childhood with diplopia and minimal refractive error. The aim of this study was to evaluate the response to the prism adaptation test in a group of normosensorial patients with acute acquired concomitant esotropia and to determine its predictive value for surgical outcome.

PATIENTS AND METHODS

Six patients (median age, 11 .5 years) with acute acquired concomitant esotropia underwent the prism adaptation test by applications of Fresnel press-on and prismatic lenses. The sensorial condition of each patient had been evaluated with theTNO stereopsis test, the Irvine test, Bagolini striated glasses, and the Worth four-dot test during the prism adaptation test, when maximum compensation angle was achieved, and after surgery. In all patients, surgery was performed based on the angle of the squint after the prism adaptation test. Patients were observed 1 day, 3 months, 6 months, and 1 year after surgery.

RESULTS

An increase in the angle of the squint occurred in all patients during prism adaptation. The maximum value was obtained in the same amount of time whether with prisms of increasing power or by direct application of the final value of the prisms. The final prismatic value (target angle) was always the same.

CONCLUSIONS

The accuracy of the patients' selection confirmed the existence of highly reproducible compensational movements to the prismatic correction in not only patients with anomalous retinal correspondence but also normosensorial patients. Prism adaptation test results were useful in these patients because of their high predictive value for the surgical treatment.

Visual evoked potentials during suppression in exotropic and esotropic strabismics: strabismic suppression objectified

BACKGROUND

We performed an electrophysiological study in order to objectify suppression in strabismus. The extent of cortical involvement in the process of interocular suppression was also explored. Possible differences in the suppressive process of esotropic and exotropic strabismics were also studied.

METHODS

An electroencephalographic recorder with eight leads was applied to the posterior one-third of the skull; three occipital, three parietal, and two temporal leads. We measured the activity of these visual cortical areas during stimulation of each eye under monocular as well as binocular viewing conditions with hemisinusoidal light pulses in a nature-like complex visual background. Recordings were made from six primary esotropic strabismic subjects and four primary exotropic and one consecutive exotropic strabismic subject. Also, five normal controls were studied.

RESULTS

A characteristic, triphasic response complex was found at approximately 80 ms following the start of each light pulse under monocular viewing conditions in the dominant and the nondominant eye. However, under dichoptic viewing conditions in the nondominant eye of all esotropic cases as well as in the nondominant eye of three of five exotropic cases, this response complex was completely absent. They showed approximately 100% reduction of their cortical response activity.

CONCLUSIONS

These results show the vast extent of the cortex that is involved in the suppressive process, giving a good insight in the power of suppression.

Strabismic suppression depends on the amount of dissimilarity between left- and right-eye images

Suppression in strabismus is more likely to occur when the images for the left- and right-eye are similar. In this study the relationship between the depth of strabismic suppression and the amount of dissimilarity between the images was quantified. Six subjects with microstrabismus looked at two identical colorful, cartoon images via mirrors. In the middle of each screen was a circular aperture with an opal glass, which was illuminated from the back by a halogen lamp during 300 ms with a gradual on- and offset in intensity. In the circular aperture images that slightly differed in shape were presented to both eyes. The dominant eye was presented a circle, the squinting eye a circle that, in four steps, changed its shape into a square. Under each of these four conditions, the image for the dominant eye was attenuated progressively by neutral density filters. When the image for the squinting eye was perceived, the depth of the suppression was thereby measured. It was found that suppression decreased with dissimilarity of the images.

Binocularity in refractive accommodative esotropia

PURPOSE

To investigate whether restoration of normal stereo acuity is possible in refractive accommodative esotropia.

METHODS

Twenty patients with refractive accommodative esotropia were included in the study. The cycloplegic refraction and the best corrected visual acuity of each patient were recorded. The patients were evaluated by the 4-prism-diopter test, Bagolini striated glasses, the Worth 4-dot test, the TNO stereo test, and the stereo fly plate of the Titmus test.

RESULTS

Eight patients had orthotropia with normal retinal correspondence and 12 patients had a small deviation with abnormal retinal correspondence. Nine patients (8 patients with orthotropia and 1 patient with microtropia) demonstrated a gross level of stereo acuity, whereas the others demonstrated no stereopsis.

CONCLUSION

In patients with refractive accommodative esotropia, the prognosis is not favorable for restoration of normal stereopsis, even if orthotropia is achieved.

Effects of anisometropia on binocularity

PURPOSE

To investigate the effects of anisometropia on binocular function and the relationship between stereopsis and fusion in anisometropia.

METHODS

Twenty-five patients with anisometropia were studied. The manifest refraction and best-corrected Snellen visual acuity of each patient was recorded. Patients, corrected with spectacles, were evaluated using Bagolini glasses, the 4-diopter (D) prism test, Worth four-dot test, and TNO stereotest.

RESULTS

All patients indicated fusion by the Bagolini glasses. Although the 4-D prism test was positive in the anisometropic eye of all 25 patients, it was slower than the response of the other eye in 19 patients with reduced stereoacuity. On the distant Worth four-dot test, fusion response was positive in 15 patients. On theTNO test, stereoacuity levels were reduced or absent in 19 patients.

CONCLUSION

The depth of amblyopia is more effective than the amount of anisometropia in causing a deterioration in binocularity. Even if fusion is weak, almost all patients with anisometropia have bifoveal fusion. Fusion becomes weak and stereoacuity decreases in proportion to the anisometropic amblyopia. Stereoacuity is related to the strength of fusion, and the TNO stereotest effectively detects those patients with significant anisometropic amblyopia.

Quantitative perimetry under binocular viewing conditions in microstrabismus

In order to elucidate the type, size and depth of suppression scotomata in microstrabismus and small angle convergent strabismus, we performed binocular static perimetry in 14 subjects with strabismus and four normal observers. The strabismic cases had an objective angle of convergent squint between 1 and 8 deg, visual acuity between 0.1 and 1.25, and limited stereopsis. During testing the subjects fused pictures on two Friedmann visual field analyzers. Right and left eyes were studied separately under both monocular and binocular viewing conditions. In five strabismics a suppression scotoma was found in the squinting eye, with a diameter of 5-30 deg and a depth ranging from 4 to 14 dB. No suppression scotomata could be detected in the nine other subjects nor in the four normal observers. In conclusion, only 36% of subjects with strabismus were found to have a suppression scotoma. These scotomata were centered around the fixation point of the squinting eye, in some cases also encompassing the foveal area, and varying in depth and size.

Biases of motion perception revealed by reversing gratings in humans who had infantile-onset strabismus

Motion perception was tested by requiring adult subjects to view gratings that remained stationary but reversed in contrast several times per second. Subjects viewed monocularly and judged whether the gratings were stationary, or moving in one direction, in successive 3s trials. Subjects who had early-onset strabismus most frequently perceived vertically oriented gratings to be moving nasalward, and horizontally oriented gratings to be moving up or down. Normal subjects and subjects who had late-onset strabismus most frequently perceived the gratings to be stationary. The asymmetries of motion perception in early-onset strabismus imply that the visual motion neurons of cerebral cortex develop properly only if they receive normal binocular input during infancy.

Bagolini lenses vs the Polarized Four-Dot test

The applicability and accuracy of two minimally dissociative sensory tests were compared in a pediatric ophthalmology clinic. The Polarized Four-Dot (P4D) test and Bagolini striated lenses (BAG) were used to evaluate 133 patients who were at least 3 years old. The outcomes measured were test failure rate and mean age at the test failures. Test sensitivity and specificity were determined using the distance vectograph as a reference. The failure rate for the BAG test, 14%, was significantly higher than that for the P4D test, 5% (P = .0005). The mean age of the test failures also was higher for the BAG test (4.7 vs 3.8 years). Both sensitivity and specificity for the detection of central suppression were greater using the P4D test. The P4D test is simple to use, widely applicable, and accurate in the detection of peripheral fusion, central fusion, or suppression, without the confounding colors of the Worth Four-Dot test. We recommended the P4D test as the test of choice for routine evaluation of binocular fusion status.

Binocular interactions and steady-state VEPs. A study in normal and defective binocular vision (Part II)

BACKGROUND

Recent evidence indicates that an index of binocular activity may be found in some properties of steady-state visual evoked potentials (VEPs), such as amplitude facilitation and phase shortening. We evaluated binocular interactions with steady-state VEPs in normal subjects as well as in patients with concomitant strabismus and defective binocular vision.

METHODS

Steady-state (8-Hz) VEPs to counterphased sinusoidal gratings (1.2 c/deg spatial frequency) of low contrast (3.2%) were recorded in 19 esotropic patients and in 18 age-matched controls. Patients had either anomalous retinal correspondence (ARC, n = 10) or suppression (n = 9) in casual seeing conditions (striated glasses). In all subjects, both binocular and monocular VEPs displayed a major component at twice the stimulation frequency (second harmonic), whose amplitude and phase were measured. A binocular interaction index was obtained by comparing binocular VEPs (BVEPs) with the sum (vectorial) of the two monocular VEPs (SMVEPs).

RESULTS

In normal subjects, BVEPs were larger in amplitude than SMVEPs (facilitation), and shortened in latency (phase). On average, both ARC and suppression patients displayed loss in amplitude facilitation and absence of phase shortening. However, 50% of ARC patients showed clear VEP facilitation. In both ARC and suppression patients, the amplitude ratio BVEP/SMVEP was negatively correlated with the amount of the angle of deviation.

CONCLUSION

These results suggest that losses in amplitude facilitation and phase shortening of binocular steady-state VEPs reflect abnormal binocular interactions associated with different forms of sensorial adaptation in concomitant strabismus.

Influence of existing retinal correspondence on the results of squint operations in alternating convergent strabism

In our study we examined the influence of existing retinal correspondence on the result of squint operations for alternating convergent strabism. 157 patients under 10 years of age at the time of their first or only operation were included. They were divided into groups, depending on their age at the onset of squint and subgroups according to their type of retinal correspondence. The development of distance and near deviation was investigated separately. Covariance analysis demonstrated that the preoperative sensorial state is a predictor for the motor outcome of surgery with regard to postoperative distance deviation. Statistically we found at least noticeable results (p < 0.15) in all groups of patients--for acquired esotropia a significant result (p < 0.01). With regard to the postoperative near deviation we found a significant influence of the preoperative sensorial state only in the group of patients with a late onset of squint (p = 0.05). For patients with an earlier onset (before the 30th month) of strabismus, the preoperative angle of near deviation proved to have a significant impact on the postoperative development of near deviation (p < 0.05). Sensorio-motorial adaptational phenomena in esotropia are presumed to be the major cause for this difference.

Stereoscopic cooperation between the fovea of one eye and the periphery of the other eye at large disparities. Implications for anomalous retinal correspondence in strabismus

In normal human observers we searched for the largest amount of visual disparity that can still provide depth information; we compared (1) crossed and uncrossed disparities and (2) symmetrical and asymmetrical locations of disparate stimuli. A pair of 3 degrees discs projected for 100 ms served as targets. Symmetrical stimuli were projected on temporal or nasal retinal loci in both eyes; asymmetrical stimuli were projected on the fovea of one eye and on the nasal or temporal periphery of the other eye. Thresholds were determined using a two-alternative forced choice procedure. Subjects had to distinguish binocular disparate images from monocular double images of identical angular separation. Among six subjects, crossed disparities were recognized by one up to 6 degrees, by three up to 9 degrees, by one up to 18 degrees, and by one up to 21 degrees. Uncrossed disparities were recognized by two at 3 degrees, by two up to 6 degrees and by two up to 9 degrees. Hence, crossed disparities could be recognized up to higher angles than uncrossed. No consistent difference was found between symmetrical and asymmetrical stimuli. Stimuli with crossed disparity appeared smaller and with uncrossed disparity larger than monocular stimuli of the same objective size, suggesting that the size-constancy mechanism operates when disparity stimuli are presented as briefly as 100 ms, i.e., without simultaneous vergence eye movements. We speculate that the far-reaching interocular connections demonstrated in normal subjects might also be utilized in the case of strabismus: these interocular connections could form the basis for anomalous retinal correspondence.

Worth vs Polarized four-dot test

A direct comparison between the Worth four-dot (W4D) and Polarized four-dot (P4D) flashlights is reported in a randomized trial on 107 unselected patients greater than 2.5 years old. The primary outcome variable was the interpretable response rate. Secondary outcomes were response time and age of test failure. There were 29 patients who failed to complete the W4D test, but only 10 patients who could not complete the P4D test, giving interpretable response rates of 73% and 91%, respectively (p < .001). The P4D test was found to be less dissociative and easier to administer. It also had a higher detection rate for fusion. We recommend its use as a tool in the clinical evaluation of binocular sensorial states.

Suppression scotomas in primary microstrabismus--a perimetric artefact

Static perimetry with stereoscopic targets, "stereo-perimetry", was performed on eight patients with primary microstrabismus to find out how strabismic subjects see under natural conditions, i.e. how they ordinarily make use of their squinting eye. In all cases, suppression scotomas were detectable using dissociating perimetric techniques. By means of stereoperimetry, however, the scotomas were not detectable. On the contrary, stereo-acuity was always best in the center of the suppression scotomas. This result indicates that suppression scotomas of the microstrabismic subjects examined here represented perimetric artefacts. In microstrabismic patients, the cooperation of the deviated eye in the central visual field is probably much better than has previously been thought.

Role of the central field in disparity-induced vergence movements in strabismus

Disparity-induced vergence movements (fusional movements) were analyzed in esotropic patients by calculating the time required for compensation of a prismatic correction of their angle of deviation. The effect of central and peripheral field stimulation on these movements was studied by masking the central or the peripheral field. Both the center and the periphery were effective in triggering disparity-induced vergence movements. The center even seemed to prevail over the periphery. It is concluded that in comitant esotropia motor fusion is present not only in the periphery but also in the center, if appropriately tested.

Distance judgement in comitant strabismus with anomalous retinal correspondence

Judgement of distances was evaluated in 19 patients with comitant esotropia and without appreciable stereopsis. In nine patients anomalous retinal correspondence (ARC) was present at Bagolini's striated glasses. In the remaining patients there was suppression with the same test. Distance judgement of strabismics with ARC does not differ statistically from that one of normals. Significantly different results were found in strabismics with suppression. It is concluded that ARC is not only an anti-diplopic mechanism, but provides the patients with useful clues in their daily life.

Incremental binocular amplitude of the pattern visual evoked potential during the first five months of life: electrophysiological evidence of the development of binocularity

The amplitude of the pattern visual evoked potential (VEP) of a binocular stimulus has been shown to be generally larger than the VEP obtained monocularly. There is evidence that this effect can be considered an electrophysiological index of fusion. To study how binocular vision develops in infancy we evaluated the incremental binocular amplitude (IBA) in three infants in a longitudinal investigation during the first five months of life. The stimuli were phase-alternating square-wave gratings with spatial and temporal parameters chosen to be appropriate for neonates. IBA was defined as the percentage increment of the largest binocular response compared with the monocular response. In the first two months of life IBA values were near zero, that is, no summation occurred. Between the second and third month IBA values rose markedly and after the third month its value was greater than 100%, demonstrating binocular facilitation. Thus in the first two months of life the eyes do not seem to cooperate as in adults. By the second and third month the binocular pattern VEP reflects an increasing binocular interaction. Other studies of the development of stereopsis have also found evidence of binocularity at similar ages.

Surgical correction of convergent strabismus: its relationship to prism compensation

Esotropic patients whose angle of strabismus has been corrected by prisms frequently increase their angle deviation to compensate for the prismatic correction. This sensorio-motorial reaction to prism correction has been given the name of anomalous movements (a.m.). Quantification of a.m. has been made according to the amount of prisms that an esotropic patient is capable of compensating for (progressive prism compensation test--p.p. test). Some esodeviation does not compensate for any prisms at all since a.m. have not yet developed. Other cases compensate for as much as 40 or 60 prism diopters and more of over-correction of the angle deviation and they therefore have powerful a.m. The interference of these innervational forces acting on the medial recti to corrective surgery has been studied in 126 operated esotropic patients. A significant decrease from the expected surgical result (p less than 0.001) has been found in patients having powerful a.m., as can be judged by the p.p. test. It is believed that a.m. are an important drawback contributing to vitiate any formula on the amount of muscle surgery to be performed in patients having no possibilities of restoring normal binocular vision. Practical advice on how to eliminate this drawback and theoretical reasoning on the significance of a.m. are offered.

Objective evaluation of sensorial and sensorimotorial status in esotropia: their importance in surgical prognosis

Appropriate use of base-out prisms may be useful objective test for detecting persistence of normal binocular vision (4-dioptre prism test). By prolonged observation of prismatic correction of an esotropic patient one may infer the presence of an anomalous sensorial status. This can be done when the prismatic correction is compensated for by an increase of the angle of esotropia (prism adaptation test). The increase in the angle of esotropia induced by base-out prisms, here called anomalous movements, is probably related to a type of anomalous movement fusional in nature. When anomalous movements are present, it is important to realise how powerfully they have developed. This may be inferred by determining what amount of prism overcorrection of the esotropic angle the patient is capable of compensating for (progressive prism compensation test). This has important implications for surgery. It has been statistically demonstrated that esotropia with strong anomalous movements tends to respond less effectively to surgery than esotropia without or with weak anomalous movements.

Critical analysis of visual function evaluating techniques in newborn babies

The most widely-used techniques for testing visual function in babies are reviewed. Advantages and limitations of optokinetic nystagmus testing, visual evoked responses and preferential looking techniques are considered. The theoretical basis and the clinical applicability of those techniques are outlined. Other simple methods are considered as well, which allow practicing ophthalmologists to assess the presence or absence of vision in babies. The importance of early diagnosis for prevention and treatment of visual deficits in babies is stressed.

Binocular visual perception in strabismics studied by means of visual evoked responses

Ten normal subjects and 14 patients with comitant esotropia were examined by means of pattern visual evoked responses (VER) under monocular and binocular viewing conditions. When both eyes were stimulated together a VER summation was noted both in normals and in strabismics with small-angle deviation and anomalous retinal correspondence (ARC). This is considered as an objective proof of binocularity. Patients with large-angle strabismus and/or suppression of the image of the deviated eye did not show summation. The significance of summation and its relationship with binocular vision was analyzed by recording binocular VER in normals in which diplopia was artificially induced and in strabismics who spontaneously exhibited double vision. A simple way for differentiating normals from strabismics by means of VERs is presented, considering that the presence or absence of summation per se does not achieve this result. This method is based on the anteposition in front of the fixing eye of neutral filters of increasing density. Summation disappears in strabismics with much weaker filters than in normals (0.5 versus 1.6 log. unit).

Long-term changes of orienting behavior in cats with artificial divergent strabismus

Orienting behavior was measured in two monocular spatial localization tasks in normal cats and in cats with artificially induced monocular divergent strabismus. Immediately, and for several weeks after the operation, cats made large "past-pointing errors" with the deviated eye in a direction opposite to the misalignment. These errors were replaced later by "over compensation errors" in the same direction as the strabismus deviation, which persisted for many months after the operation. Over-compensation did not occur when the non-deviated eye was sutured in early life. Electrophysiological measures like grating VEP and A17 single unit responses demonstrated the dominance of the non-deviated eye in the strabismic cats. It is suggested that long-term binocular exposure may lead to a reorganization of visual direction for the deviated eye in divergent strabismus.

Binocularity in comitant strabismus: II. Objective evaluation with visual evoked responses

Campos (1982a) reported on his psychophysical studies on the binocularity of patients with comitant strabismus. With binocular visual field techniques, it was possible to show that patients with small-angle eso- and exotropia exhibit a binocular vision, without suppression of the deviated eye. In the present paper visual electrophysiology is used objectively these findings and to provide more insight in the problem. First, the studies on binocularity in normals and strabismics, done by using visual evoked responses (VER) are reviewed. This type of investigation is relatively new and the results of the literature are still conflicting. Then personal results of the authors are reported. It is shown that with VER it is possible to objectively assess the presence of anomalous binocular vision (ABV) sustained by anomalous retinal correspondence (ARC) in small-angle strabismus. In patients with large angle deviations this type of binocularity is absent. A correlation between psychophysical and electrophysiological data is provided. Lastly a simple method is described for differentiating the binocularity of normals from that of Strabismics with ARC. This method is based on the recording of binocular VER with the anteposition in front of the fixing eye of neutral filters of increasing density.

Adaptation to tilting of the visual environment in cyclotropia

We evaluated adaptations to tilting of the visual environment in 18 patients with cyclotropia by comparison of subjective tests for torsion with the actual rotation of the globes determined by fundus photography. Patients with congenital cyclotropia had a sensory reorientation of the spatial values of retinal meridians in the cyclotropic eye that prevented awareness of tilting of the environment under uniocular and binocular conditions. Patients with cyclotropia acquired as adults in many instances also had retinal sensory reorientations of the cyclotropic eye or eyes. Additionally, they used spatial clues from the visual environment to correct for image tilting under uniocular conditions. Under dissociated binocular conditions, however, these patients became aware of tilting of the visual environment, and therefore these adaptations were less deeply rooted than those in patients with congenital cyclotropia. Because certain patients with acquired cyclotropia showed evidence of using these adaptations under uniocular conditions but had constant or intermittent torsional diplopia under casual binocular viewing conditions, binocular mechanisms such as cyclofusion, suppression, and anomalous retinal correspondence may also be necessary to eliminate subjective tilting of the visual environment.

Binocularity in comitant strabismus: binocular visual fields studies

A critical review is made of the literature on binocular perimetry in strabismus. A broad range of results was obtained by various authors, because different testing techniques were used. The concept of sensory testing of strabismic patients in casual seeing condition should be introduced also into binocular perimetry. Therefore a series of experiments is presented in which patients with small-angle comitant strabismus were tested. It was shown that: a) in small-angle esotropia the areas of single vision previously thought to be due to suppression are, instead, areas of binocular vision sustained by anomalous retinal correspondence (ARC); b) this can be seen only when using fusable stimuli as test targets; c) no suppression scotomas were found in patients with small-angle strabismus in the whole visual field; d) appropriate control-marks for binocularity are necessary, i.e. monocularly presented items. They influence the results, as well e) the area of binocular single vision in strabismus (called pseudo-Panum's area) is wider than the Panum's area of normals. Moreover it is easier to disrupt binocular cooperation sustained by ARC causing diplopia than binocular cooperation in normals; f) ARC seems to be more deeply rooted in the center than in the periphery of the visual field; g) superimposable findings were obtained in small-angle constant exotropia; h) in large-angle exotropia wide suppression scotomas were found, which often override the midline. Hemianopic suppression scotomas in exotropia can be found only when 'dissociating' testing techniques are used; i) the same group of patients with small-angle esotropia was examined with the author's technique and with the classical method proposed by Harms. The results were strongly dependent on the method used and the same patient responded differently to the two tests. It is concluded that in small-angle strabismus there is an anomalous type of binocular single vision, which can be tested with binocular visual field techniques. This binocularity can only be found when non-artificial testing conditions are used. The usefulness of this anomalous binocular vision in the every day seeing condition of the patient is discussed.

Suppression scotomata in concomitant strabismus with harmonious anomalous correspondence

With binocular scotometry it was shown how the peripheral suppression scotoma of the squinting eye in cases of concomitant strabismus with harmonious anomalous correspondence can be split into 2 parts by a vertical prism. The parts are called the rivalry scotoma and the residual scotoma. This observation has not been described earlier.