To compare stereoacuity thresholds before and after visual acuity testing in patients with intermittent strabismus and in controls.
Prospective cohort study.
Participants and controls
We prospectively enrolled 88 patients (41 with intermittent strabismus and 47 controls) with measurable stereoacuity on their initial stereoacuity test.
Stereoacuity was measured prior to and immediately following visual acuity testing using the near Preschool Randot and Distance Randot stereotests. Stereoacuity was transformed to log units for analysis.
Main Outcome Measures
Change in stereoacuity thresholds (log arcsec).
There was no overall deterioration in distance stereoacuity or near stereoacuity thresholds in either the intermittent strabismus or control groups. The mean change for patients with intermittent strabismus was 0.02 log arcsec (95% confidence interval (CI): -0.02 to 0.06) for near stereoacuity and 0.04 log arcsec (95% CI: -0.01 to 0.09) for distance stereoacuity. Control patients demonstrated a mean change of 0.03 log arcsec (95% CI: -0.01 to 0.06) for near stereoacuity and 0.01 log arcsec (95% CI: -0.06 to 0.08) for distance stereoacuity. These mean changes correspond to less than approximately one eighth of an octave. For individual patients, deterioration in stereoacuity beyond previously reported test-retest variability (0.6 log arcsec or greater) was not observed in patients with intermittent strabismus or controls using either test.
Stereoacuity thresholds do not deteriorate following visual acuity testing and therefore measurements of stereoacuity do not need to precede visual acuity measurement or other tests that involve short periods of dissociation.
Studies of distance stereoacuity in intermittent exotropia suggest that normal stereoacuity corresponds to good control of the deviation and that reduced or negative stereoacuity signifies poorer control.
To evaluate distance stereoacuity in intermittent exotropia using the Frisby Davis Distance stereo test (FD2).
Children with intermittent exotropia where the near angle was less than or equal to distance were eligible for recruitment. Standardised prospective data collection included FD2 distance stereoacuity. This was a longitudinal study in which outcomes are reported for baseline, last follow‐up (⩾6 months before any surgery) or preoperative and last postoperative visits for those undergoing surgery.
110 children with intermittent exotropia had FD2 stereoacuity tested at baseline: 70 comprehended the test. Mean (standard deviation (SD)) age was 4.6 (1.7) years (range 2–10 years). 41/70 (59%) showed positive responses: mean (SD) stereoacuity 30 (12) s of arc. The mean follow‐up period before any surgery was 13 months (range 6–27 months). At follow‐up, mean (SD) stereoacuity was 24 (11) s of arc. Preoperative and postoperative stereoacuity were not significantly different from those not undergoing surgery.
This study was the first to report distance stereoacuity in intermittent exotropia using the FD2 stereo test: patients with intermittent exotropia can achieve normal levels of distance stereoacuity, but a considerable proportion, despite comprehending, showed a negative response. This suggests that using the FD2, distance stereoacuity in intermittent exotropia is either absent or normal rather than reduced. Possible reasons for this and its implications are discussed.
To evaluate the use of the Newcastle Control Score (NCS) in the management of intermittent exotropia (X(T)).
Participants and methods
Children aged <11 years with X(T) had an assessment of NCS as part of routine management. Other data collected included visual acuity, near and distance alignment with alternating prism cover test and near (Frisby test) and distance stereoacuity (Frisby Davis Distance Stereotest (FD2TM)). Analysis involved correlation between baseline NCS, angle and stereoacuity, examination of change over time and logistic regression to determine predictors of surgery.
Baseline data were obtained on 272 children and follow‐up data on 157. Mean (SD) age was 4 (1.9) years. Complete NCSs were obtained for all except one child at baseline, and all children at follow‐up. At baseline, total NCS and the home control component were correlated with near stereo (r = –0.22, p<0.01 and r = –0.19, p<0.02, respectively), near alignment (r = 0.34, p<0.001 and r = 0.19, p<0.02) and distance alignment (r = 0.30, p<0.001 and r = 0.26, p<0.001). The clinic near control component was correlated with near alignment (r = 0.39, p<0.001), but not near stereoacuity, and the clinic distance control with near alignment (r = 0.16, p<0.02), distance alignment (r = 0.27, p<0.001) and distance stereoacuity (r = –0.25, p<0.03). A high (poor) NCS (⩾4) at the latest follow‐up predicted surgery (p<0.001, OR 29.3, 95% CI 6.2 to 138.7).
The NCS is a useful measure of the clinical severity of X(T), can be used to serially assess improvement or deterioration and is a useful tool for the management of these patients.
Distance stereoacuity is used to monitor deterioration of intermittent exotropia (intermittent XT), but variability of stereoacuity has not been rigorously studied. The purpose of this study was to assess the variability of stereoacuity over one day, in children with intermittent XT.
Prospective cohort study.
Setting: Clinical practice.
Patient population: Twelve children with intermittent XT.
Observation procedures: Stereoacuity was assessed using the Frisby Davis Distance and Distance Randot at distance and the Frisby and Preschool Randot at near. Tests were repeated 3 or 4 times over the day, with at least 2 hours between assessments.
Main outcome measure: ‘Variable’ stereoacuity defined as a change by 2 or more log levels between any 2 time points over the day.
Variable stereoacuity at distance was found in 5 (42%) of 12 patients. Four (33%) of 12 patients were variable using Distance Randot test, 3 of whom also varied using Frisby Davis Distance. One patient was variable using Frisby Davis Distance only. Nine (75%) of 12 patients completed near stereoacuity testing; 2 (22%) of 9 showed variable near stereoacuity. Two (22%) of 9 were variable using Preschool Randot, 1 (11%) of whom also varied using Frisby. In some cases stereoacuity changed from measurable stereoacuity on one assessment to nil on another.
Nearly half of children with intermittent XT show marked changes in stereoacuity over the course of a single day. When based on isolated measures, an apparent change in distance stereoacuity between visits should be interpreted with caution.
To investigate the course of near stereoacuity in a cohort of children with untreated intermittent exotropia.
A total of 95 children aged 2 to 16 years with untreated intermittent exotropia were identified who had measurements of near stereoacuity, using the Preschool Randot (PSR) test on at least two successive examinations, with no intervening treatment. Deterioration was defined as a drop of at least 3 octaves, based on test–retest data. Alternative secondary analyses were performed defining deterioration as a drop of at least 2 octaves or as a transition from normal to subnormal. The main outcome measure was the deterioration rate calculated at 1 and 2 years using a Kaplan-Meier survival analysis.
For near stereoacuity, the rate of decreasing 3 or more octaves was 2% (95% CI, 0%-6%) at 1 year and 7% (95% CI, 0%-16%) at 2 years. The alternative secondary analyses revealed similar low deterioration rates. In most cases of apparent deterioration, near stereoacuity returned to baseline levels without treatment.
For children with untreated intermittent exotropia, deterioration in near stereoacuity at 1 and 2 years is infrequent. Therefore, performing surgery for intermittent exotropia to proactively prevent deterioration of near stereoacuity cannot be justified. Retesting stereoacuity is critical to determine whether any measured decrease in stereoacuity is real.
To evaluate whether distance stereoacuity improves following surgery for intermittent exotropia using the Frisby Davis Distance (FD2) and Distance Randot stereotests.
Eighteen patients (median age 24 years, range 5 to 68 years) with intermittent exotropia were prospectively enrolled. Stereoacuity was measured pre- and 6 weeks post-operatively using the FD2 and Frisby near tests (real depth tests) and Preschool Randot and Distance Randot tests (polaroid vectographs).
Distance stereoacuity measured with the FD2 improved from a median pre-operative value of 80 arc seconds (arcsec) to 40 arcsec post-operatively (P= 0.04) and stereoacuity measured with the Distance Randot improved from a median of nil to 200 arcsec (P= 0.06). In those that had subnormal stereoacuity pre-operatively, there was even more marked improvement in distance stereoacuity (FD2 median nil vs. 40 arcsec, P=0.002; Distance Randot median nil vs. 200 arcsec, P=0.004). Near stereoacuity measured with Frisby and Preschool Randot remained unchanged pre- and post- operatively (median 60 arcsec and 80 arcsec respectively).
There was improvement in distance stereoacuity measured with both the FD2 and Distance Randot stereotests in patients who underwent surgery for intermittent exotropia. The FD2 and Distance Randot may be useful outcomes measures in future clinical trials of interventions for intermittent exotropia.
Intermittent exotropia may be controlled by accommodative or motor convergence. Previous studies have reported that reduced binocular visual acuity in intermittent exotropia is due to the accommodation required to control the deviation. In order to test this hypothesis, we simulated convergence stress by inducing exodeviations in normal volunteers to investigate whether the transition from non-fused to fused is associated with a gradual or immediate transition in stereoacuity and binocular visual acuity.
Convergence stress was induced in 25 visually normal adults with 40pd base out prism and reduced stepwise in increments of 5pd until 20pd, and 2pd thereafter. Stereoacuity (Frisby Davis Distance (FD2) and the Distance Randot (DR)) and binocular visual acuity were measured at each step. For each subject, the recovery of fine stereoacuity (less than or equal to 60 seconds of arc) was categorized as immediate (nil to fine) or gradual (nil to moderate to fine).
24 of 25 (96%) showed gradual recovery of fine stereoacuity on either FD2 or DR. Median binocular visual acuity at baseline, first level of fusion, and subsequent levels was 20/15.
Under convergence stress, the transition from non-fused to fused is accompanied by a gradual recovery of fine stereoacuity in most individuals, consistent with some studies of patients with intermittent exotropia. Nevertheless, this degradation of stereoacuity was not associated with decreased binocular visual acuity, suggesting that accommodative convergence may not be recruited to restore and maintain binocularity under conditions of convergence stress.
To determine factors associated with pretreatment and posttreatment stereoacuity in subjects with moderate anisometropic amblyopia.
Data for subjects enrolled in seven studies conducted by the Pediatric Eye Disease Investigator Group were pooled. The sample included 633 subjects aged 3 to <18 years with anisometropic amblyopia, no heterotropia observed by cover test, and baseline amblyopic eye acuity of 20/100 or better. A subset included 248 subjects who were treated with patching or Bangerter filters and had baseline stereoacuity testing and outcome examinations. Multivariate regression models identified factors associated with baseline stereoacuity and with outcome stereoacuity as measured by the Randot Preschool Stereoacuity test.
Better baseline stereoacuity was associated with better baseline amblyopic eye acuity (P < 0.001), less anisometropia (P = 0.03), and anisometropia due to astigmatism alone (P < 0.001). Better outcome stereoacuity was associated with better baseline stereoacuity (P < 0.001) and better amblyopic eye acuity at outcome (P < 0.001). Among 48 subjects whose amblyopic eye visual acuity at outcome was 20/25 or better and within one line of the fellow eye, stereoacuity was worse than that of children with normal vision of the same age.
In children with anisometropic amblyopia of 20/40 to 20/100 inclusive, better posttreatment stereoacuity is associated with better baseline stereoacuity and better posttreatment amblyopic eye acuity. Even if their visual acuity deficit resolves, many children with anisometropic amblyopia have stereoacuity worse than that of nonamblyopic children of the same age.
To describe the clinical characteristics, treatment, and subsequent clinical course of children with exotropia and high hyperopia.
The medical records of 26 patients seen between 1990 and 2009 who had an exotropia and ≥4.00 D of hyperopia were retrospectively reviewed. We analyzed the clinical characteristics, treatments and subsequent alignment outcomes.
A total of 26 patients between the ages of 2.5 months and 9 years were included. Of these, 15 had associated medical conditions or developmental delay. Of 22 patients with measured visual acuities, 19 had amblyopia (10 unilateral, 9 bilateral). None of the patients demonstrated fine stereoacuity. Twenty-three exotropic children were treated with spectacles; 15 were fully corrected, 10 of whose exotropia improved; 8 received partial correction of their hyperopia, 3 of whose exotropia improved. Six patients who presented with large, poorly controlled exotropia and did not improve with spectacle correction required strabismus surgery.
Children with high hyperopia and exotropia are likely to have developmental delay or other systemic diseases, amblyopia, and poor stereopsis. Treatment of high hyperopia in exotropic children with their full cycloplegic refraction can result in excellent alignment.
To evaluate the effect of acrylic refractive prism and Fresnel membrane prism on stereoacuity in intermittent exotropia.
Materials and Methods
Stereoacuities of fifty-two patients (mean age, 12.4 years; range 6 to 45 years) with intermittent exotropia were measured using the Titmus and TNO stereotests, while they wore prisms of varying power on nonfixating eye or evenly on each eye.
Stereoacuities were significantly reduced with increasing prism power for both prisms, ranging from 8 to 25 prism dipotres. The effects on stereoacuity in single acrylic prism and single Fresnel prism were similar, whereas spilt Fresnel prisms reduced stereoacuity more than spilt acrylic prisms. Spilt prisms were found to have much less effect on stereoacuity than single prisms for both acrylic and Fresnel prisms.
The use of acrylic refractive prism shared evenly on each eye would be optimal method to minimize the reduction of stereoacuity during the prismatic therapy for intermittent exotropia.
Strabismus; stereoacuity; Fresnel prism; acrylic prism
To describe the long-term surgical outcomes in a population-based cohort of children with intermittent exotropia.
The medical records of all children (<19 years) who were diagnosed with intermittent exotropia as residents of Olmsted County Minnesota, from January 1, 1975, through December 31, 1994, and managed with surgery were retrospectively reviewed.
Of 184 patients with intermittent exotropia, 61 (33%) underwent surgery at a mean age of 7.6 years (range, 3.2 to 23 years). Twelve of the 61 children (19.7%) underwent a second surgery (10 for recurrent exotropia and 2 for consecutive esotropia), and no patient received 3 or more surgeries during a mean follow-up of 10 years from the first surgery. The final postoperative measurements were recorded in 56 of 61 patients (92%) at a mean of 7.4 years (range, 0 to 18 years) after the first surgery: 31 of the 56 (55%) were within 9Δ of orthotropia at distance and 25 of 55 (45%) had better than 60 seconds of stereopsis. The Kaplan-Meier rate of developing ≥10Δ of misalignment after the first surgery was 54% by 5 years, 76% by 10 years, and 86% by 15 years.
In this population-based study of surgery in children with intermittent exotropia, although only 1 in 5 received a second surgery, after a mean follow-up of 8 years, approximately half were successfully aligned and 45% had high-grade stereopsis.
To evaluate factors influencing stereoacuity after surgery to correct unilateral developmental pediatric cataracts.
We retrospectively surveyed 110 patients who had undergone removal of unilateral acquired developmental cataracts and primary posterior chamber intraocular lens implantation between February 1992 and December 2009. In all patients, stereoacuity was assessed using the Titmus test at the last follow-up period of minimum 2 years after surgery. Patients were divided into two groups according to the extent of stereoacuity: group 1 (n=42) had stereoacuity values≤100sec/arc and group 2 (n=68) values >100sec/arc. The values of ten parameters associated with stereoacuity were measured in each group: Cataract types, preoperative best corrected visual acuity (BCVA) of the affected eyes, preoperative inter-ocular difference of BCVA, age at cataract surgery, operative method, secondary cataract, postoperative strabismus, postoperative BCVA of the affected eyes, postoperative inter-ocular difference of BCVA, and anisometropia.
The extent of stereoacuity was significantly associated with both operative method and secondary cataract (P=0.000 and P=0.016, respectively). All patients in whom the posterior capsule was preserved, had poor stereoacuity >100sec/arc. Significant correlations with the extent of stereoacuity were found with postoperative strabismus (P=0.048), postoperative BCVA of the affected eyes (P=0.002), anisometropia (P=0.034).
: Postoperative stereoacuity was better in patients who underwent either optic capture or anterior vitrectomy after posterior continuous curvilinear capsulorhexis, and who didn't develop secondary cataracts or strabismus postoperatively. Furthermore, postoperative BCVA of the affected eyes, and anisometropia influenced the stereoacuity of the patients surgically treated for unilateral developmental pediatric cataracts.
anisometropia; developmental cataract; secondary cataract; stereoacuity; stereopsis; strabismus; unilateral pediatric cataract; visual acuity
Objective: To investigate the time and postoperative binocular vision of strabismus surgery for children with intermittent exotropia (X(T)). Methods: A retrospective investigation was conducted in 80 child patients with intermittent exotropia. Pre- and postoperative angles of deviation fixating at near (33 cm) and distant targets (6 m) were measured with the prolonged alternate cover testing. The binocular function was assessed with synoptophore. Twenty-one patients took the postoperative synoptophore exercise. Results: (1) A week after surgery, 96.2% of the 80 patients had binocular normotopia, while a year after surgery, 91.3% of the 80 patients had binocular normotopia; (2) Preoperatively, 58 patients had near stereoacuity, while postoperatively, 72 patients achieved near stereoacuity (P<0.05); (3) Preoperatively, 64 patients had Grade I for the synoptophore evaluation and postoperatively, 76 patients achieved Grade I. Meanwhile, 55 patients had Grade II preoperatively and 72 achieved Grade II postoperatively. For Grade III, there were 49 patients preoperatively and 64 patients postoperatively (P<0.05); (4) Patients of 5~8 years old had a significantly better recovery rate of binocular vision than those of 9~18 years old (P<0.05); (5) Patients taking postoperative synoptophore exercise had a better binocular vision than those taking no exercise (P<0.05). Conclusions: (1) Strabismus surgery can help to preserve or restore the binocular vision for intermittent exotropia; (2) Receiving the surgery at young ages may develop better postoperative binocular vision; (3) The postoperative synoptophore exercise can help to restore the binocular vision.
Intermittent exotropia (X(T)); Surgery; Binocular vision
To evaluate the role of distance and near stereoacuity and fusional vergence in patients with intermittent
exotropia [X(T)] and their change after surgery.
Materials and Methods:
This prospective interventional institution-based clinical study included 31 cases
of X(T) requiring surgery and 33 age, sex-matched controls. All subjects underwent complete orthoptic
assessment including near stereopsis (Randot stereogram) and distance stereopsis by polaroid stereo-
projector apparatus using special paired slides and fusional vergence assessment at distance and near prism
bar at baseline and one week, one month, three months and six months after surgery in X(T).
The successful surgical alignment rate was 74.2%. Preoperatively, cases demonstrated significantly
poor distance and near stereoacuity, compared to controls (P < 0.001). Mean distance stereoacuity (sec of arc)
in normals, (X)T preoperatively and postoperatively was 344.8 ± 139.5, 1149.2 ± 789.4 and 450.1 ± 259 while
mean near stereoacuity was 34.7 ± 9.5, 68.7 ± 31.1 and 47.4 ± 22.6 respectively. Postoperatively at six months,
significant improvement in stereoacuity was observed both at near and distance (P < 0.05). Mean distance
fusional convergence (in prism diopter) in normals, X(T) preoperatively and postoperatively was 20.7 ± 4.7,
18.0 ± 3.3 and 21.4 ± 3.6 respectively, mean near fusional convergence was 27.8 ± 6.3, 24.1 ± 5.5 and 29.1
± 5.5 respectively. There was good correlation between fusional vergence amplitudes for distance and near indicating
any one would suffice.
Early detection of abnormal stereoacuity (near and if possible distance) and near fusional
vergence amplitudes may help to decide proper timing of surgery in X(T).
Fusional vergence; intermittent exotropias; polaroid stereo-projector for distance stereopsis; stereoacuity
Poor control of intermittent exotropia (IXT) has been considered an indication for surgical intervention, and poor distance stereoacuity may be an indicator of poor control. We evaluated two new measures of distance stereoacuity, the Frisby Davis Distance (FD2) test and Distance Randot® (DR) test, both of which have been previously validated in normal and strabismic subjects, and we compared stereoacuity to scores on a recently described control scale.
Prospective case series.
25 consecutive patients with IXT.
Office-based control was graded at distance and near on a 0 to 5 scale and distance control ranged from 1 (recovery in 1–5 seconds after monocular occlusion) to 4 (>50% spontaneously tropic). Stereoacuity was measured using the FD2 and DR tests at distance and the Preschool Randot® and Frisby tests at near.
Main outcome measures
Distance stereoacuity measured using the FD2 and DR tests.
Measurable distance stereoacuity thresholds in IXT were poor with the DR test and excellent with the FD2 test (medians: nil and 40”, p<0.0001). Near stereoacuity was excellent with both the Preschool Randot® and Frisby (medians: 60” and 60”, p=0.99). There was poor correlation between distance control score and either FD2 (rs=0.1, p=0.6) or DR (rs=0.3 p=0.2). Control scores correlated with magnitude of deviation at distance (rs=0.5, p=0.02) and near (rs=0.5, p=0.01).
The real world contour-based targets of the new distance FD2 test appear to stimulate fusion in IXT, even when distance control is poor. In contrast, the new Polaroid vectograph-based Distance Randot® test is very sensitive to disturbances of binocularity. Two new distance stereoacuity tests appear sensitive to opposite ends of the IXT spectrum; FD2 performance deteriorates when the patient is constantly tropic whereas DR performance deteriorates at the earliest stages of intermittency.
Measurement of distance stereoacuity may be useful in assessing strabismic patients, especially those with intermittent exotropia. We developed the Distance Randot Stereotest as an easily administered quantitative test for distance stereoacuity in children. Using a prototype,1 we reported testability, validity, and normative data. Here we report normative and validity data for the final, commercially available version of the test.
We administered both the Prototype and the Final Version Distance Randot Stereotest to 156 normal volunteers (2–40 years of age) and 77 strabismic patients (4–62 years of age). Test–retest data were collected for the Final Version.
Normative Final Version scores were similar to those obtained with the Prototype; 96% were ≤100 arcsec. Test–retests were identical in 82% and within one disparity level in 100%. Final Version scores were correlated with Prototype scores (rs = 0.64, p < 0.05). Among strabismic patients, 62.3% had abnormal stereoacuity; those with normal scores had incomitant or intermittent deviations. Nil stereoacuity was found in 27 patients, confirmed in 90.9%of retests; 17 had measurable stereoacuity, confirmed in 96.3%of retests. Patients with constant strabismus were more likely to have nil stereoacuity than patients who had intermittent strabismus (95% vs 12.2%).
Distance Randotscores from normal subjects have low variability within each age group and high test–retest reliability. There is little overlap between Distance Randot® scores from normal controls and strabismic patients. The Distance Randot Stereotest is a sensitive measurement of binocular sensory status that may be useful in monitoring progression of strabismus and/or recovery following strabismus surgery.
To examine how stereoacuity changes with age as measured by a variety of stereotests.
Stereoacuity has been measured in 60 normal subjects aged 17–83 years by a single observer using TNO, Titmus, Frisby near, and Frisby‐Davis distance stereotests. Motor fusion was measured at ⅓ metre and 6 metres.
Overall stereoacuity measured by all tests showed a mild decline with age (p<0.001 for all tests; Spearman rank correlation). A marked reduction to screening or absent levels of stereoacuity was seen in five subjects aged over 55, but only with the TNO stereotest. All these subjects were able to achieve a stereoacuity of 200 seconds of arc or better with the Titmus test and 340 seconds of arc or better using the Frisby near stereotest. There was a small decline with age in the base out motor fusion range measured at 6 metres (p<0.05; Spearman rank correlation). No subject described difficulty in judging distances for everyday tasks.
Although subjects showed some decline in stereoacuity with age by all tests, the large drop in stereoacuity seen in some older subjects using the TNO test was probably due to difficulty overcoming the dissociative effect of the test rather than a true reduction in cortical disparity detection. Results of random dot stereotests should be interpreted with caution in older patients, particularly with respect to their ability to perform everyday visual tasks.
ageing; binocularity; stereoacuity; stereotests; motor fusion
In an initial study of prism-induced exodeviation, degraded stereoacuity was not associated with decreased binocular visual acuity, suggesting that accommodative convergence was not recruited. Distance stereoacuity degraded earlier when measured with the Frisby Davis Distance (FD2), than when measured with the Distance Randot (DR). We now describe a follow-up study in which we reversed the prism order and also addressed potential biases of testing order and different measurable levels of stereoacuity to clarify the relationship between exodeviation, distance stereoacuity, and binocular visual acuity.
Convergence stress was induced with base-out prism in 20 adults and increased stepwise. Stereoacuity and binocular visual acuity were measured at each step. Disparities tested were 200, 100, and 60 seconds of arc, and testing was repeated at each prism step.
Most subjects showed degraded stereoacuity with the FD2 in contrast to the DR (80% vs 45%, P = 0.02). Reduction of stereoacuity occurred earlier on the FD2 than on the DR (median 18Δ vs. 40Δ, P = 0.001). Degradation of stereoacuity was associated with minimal change in binocular visual acuity from baseline to maximal convergence stress (median 20/15 to 20/20).
Convergence stress is associated with decreased distance stereoacuity that does not appear to be due to accommodative convergence. Performance on real world stereotests (FD2) is affected more than random dot tests (DR), in contrast to previous findings in intermittent exotropia. There appear to be different mechanisms for decreased stereoacuity in intermittent exotropia and under conditions of convergence stress in nonstrabismic subjects.
To review what is known about the normal maturation of stereoacuity, the stereoacuity deficits associated with infantile and accommodative esotropia, the rationale for making improved stereoacuity a goal of treatment, and strategies for improving stereoacuity outcomes.
Studies of stereoacuity maturation during normal development, studies of stereoacuity outcomes following treatment for infantile and accommodative esotropia, and studies of primate models of esotropia are reviewed.
Stereoacuity maturation normally proceeds rapidly during the first year of life. Infantile and accommodative esotropia are associated with profound and permanent disruption of stereopsis. While rehabilitation of stereoacuity following treatment of esotropia remains a challenge, even the achievement of subnormal stereoacuity may have real benefits to the child.
Some abnormalities in stereoacuity may exist before the onset of esotropia, but others may result directly from abnormal binocular experience. Several strategies for improving stereoacuity outcomes in esotropia are currently under active investigation. Improved stereoacuity outcomes are associated with better long term stability of alignment, reduced risk for and/or severity of amblyopia, improved achievement of sensorimotor developmental milestones, better reading ability, and improved long-term quality of life.
stereoacuity; infantile esotropia; accommodative esotropia
AIMS/BACKGROUND—The basis of binocular single vision in microtropia remains a matter of contention. This paper discusses the implications of recovery, in a group of primary microtropes following treatment, in relation to current concepts on the aetiology of the condition and proposed retinocortical correspondence.
METHODS—Nine previously untreated primary microtropes whose condition resolved, were reviewed in detail to assess the patterns of change in retinal correspondence, uniocular fixation, stereoacuity, and visual acuity in response to treatment.
RESULTS—Anomalous retinal correspondence (ARC), a central scotoma, reduced or absent stereoacuity, amblyopia, and uniocular eccentric fixation were present in all patients before treatment. Following treatment, all cases attained normal retinal correspondence (NRC), elimination of the central scotoma, stereo acuity levels of between 20 and 40 seconds of arc, 6/5 Snellen visual acuity in both eyes, and foveal fixation in both eyes.
CONCLUSION—A hypothesis is put forward that for the patients described, a period of normal development is likely to have preceded the onset of microtropia, during which the retinocortical "foundations" for NRC were established. Precise pairing of foveo-foveal receptive fields was not abolished by the presence of amblyopia and a central scotoma, but this relation was temporarily suspended and binocular single vision was sustained via the neural substrate of paired receptive fields over a wide retinocortical area.
Keywords: anomalous retinal correspondence; stereoacuity; retinocortical connections
To evaluate change from baseline to 12 months follow-up in study and nonstudy (fellow) eye visual fields from the Ischemic Optic Neuropathy Decompression Trial (IONDT).
Randomized controlled trial and observational study.
The IONDT enrolled patients ≥50 years with acute nonarteritic ischemic optic neuropathy (NAION). Randomized patients (n = 258) had visual acuity ≤20/64; nonrandomized patients (n = 160) had visual acuity >20/64 or refused randomization.
Optic nerve decompression surgery (n = 127) or careful follow-up (n = 131).
Main Outcome Measures
We measured visual fields at baseline and at 6 and 12 months follow-up. Using a computerized system, we classified visual field defects by pattern, location, and severity. We examined changes over time by treatment group, age, baseline comorbidities, and change in visual acuity. In fellow (nonstudy) eyes, we assessed change by whether NAION was present at baseline and also incidence of NAION by whether a visual field defect was present at baseline.
We analyzed 245 study eye visual field pairs (179 and 66, randomized and nonrandomized, respectively) for change from baseline to 12 months. We observed significant changes in defect distribution within the central field (P = 0.02) for randomized eyes. Superior and inferior altitudinal defects were less severe at follow-up in both randomized and nonrandomized eyes. We observed an association between change in central field severity and change in visual acuity from baseline (P<0.001 at 6 months; P = 0.01 at 12 months; Kendall’s tau-b), but no association between visual field change and treatment group, age, or baseline comorbidities. Superior and inferior visual field defects present at baseline in nonstudy eyes improved at follow-up. Fellow (nonstudy) eyes with normal fields did not have an increased risk of developing NAION compared with eyes with ≥1 defects.
Visual fields of NAION patients enrolled in the IONDT were relatively stable from baseline to follow-up. A visual field defect in the nonstudy eye at baseline was not associated with development of NAION during follow-up compared with eyes with normal fields.
To compare the outcomes of unilateral lateral rectus recession between the first operation and second operation for exotropia.
Thirty-two patients who underwent unilateral lateral rectus recession for exotropia of 15 to 20 prism diopters (PD) were investigated. The follow-up period was at least 6 months. We classified 17 patients without a surgical history for exotropia (first operation group) and 15 patients with a previous procedure (second operation group). Surgical success was defined as an exodeviation or esodeviation of less than 10 PD at the primary position. Postoperative deviation angles and success rates were compared between the two groups.
There were no significant differences in the age, gender, visual acuity (logarithm of the minimal angle of resolution), preoperative deviation, and amount of recession between the two groups. Postoperative deviations were -1.7 ± 5.5:1.3 ± 5.1 PD at one day, 4.3 ± 3.8:5.6 ± 5.1 PD at 1 month, 4.3 ± 4.3:3.0 ± 8.1 PD at 3 months, and 5.0 ± 4.3:4.5 ± 7.2 PD at 6 months post-operation, and there was no statistically significant difference between the two study groups. Surgical success rate were 95.2:100% at one day, 95.2:92.9% at 1 month, 90.5:85.7% at 3 months, and 90.0:92.9% a 6 months post-operation.
In patients with exotropia of 15 to 20 PD, no significant difference was found in terms of the postoperative deviation angle and the surgical success rate between the first operation and the second operation groups. Unilateral lateral rectus recession can lead to similar results in 15 to 20 PD exotropia for the first operation or recurrent exotropia.
Exotropia; Recurrence; Surgery
Although intermittent exotropia may deteriorate with time, there are no widely accepted criteria for measuring progression in this disorder. The purpose of this study was to prospectively evaluate a new scale for assessing the level of control in children with intermittent exotropia.
Thirty consecutive pediatric patients (< 14 years) with intermittent exotropia were prospectively evaluated from July 1, 2004, through June 30, 2005, using a new scale to assess the level of control for both distance and near fixation. The distance score (0 to 5) was combined with the near score (0 to 5) to yield an overall control score from 0 to 10.
The 30 patients were examined at a median age of 72 months (range, 15 months to 13 years). The level of control at distance was worse than or equal to the near level of control in all 30 patients. The control scores ranged from 0 to 5 for distance and 0 to 4 for near, with an overall control score range from 0 to 8 (median of 3).
This new scale for assessing control in children with intermittent exotropia can be easily applied in the office setting and characterizes the wide range of control in this disorder.
Assessing control is thought to be important in the management of intermittent exotropia (IXT), including the decision to perform surgery. The purpose of this study was to assess the presence and degree of any change in control occurring over the course of 1 day using a previously described 6-point clinic control scale, and to evaluate inter-observer and minute-to-minute variability.
Prospective case series.
25 patients with intermittent exotropia.
Inter-observer agreement was determined in 17 patients by comparing control scores assessed simultaneously by 2 observers (kappa test). Minute-to-minute variability was observed in the same 17 patients by assessing control twice within 5 minutes. Variability over one day was assessed in 5 of these patients plus 8 additional patients (n=13) by comparing 3 or 4 assessments at least 2 hours apart.
Main outcome measure
Control of IXT measured using a 6-point clinic control scale.
Inter-observer agreement was high (k=0.94 for distance and k=0.95 for near fixation). Disagreements were no more than one level on the control scale; therefore, for further analysis, change in control was defined as 2 or more levels. For minute-to-minute variability, 4 (24%) of the 17 patients tested twice within 5 minutes showed a change in control: 1 (6%) changed from tropia to phoria at distance, 3 (18%) from phoria to tropia at near. Of the 13 patients assessed over 1 day, 6 (46%) showed change in control, 2 at distance fixation only, 3 at near only and 1 at near and distance.
Control of IXT can vary throughout the day, even within minutes, including from phoric to spontaneously tropic, and vice versa. The worst level of control was not always later in the day. This suggests that an isolated assessment of control may not categorize severity of IXT in an individual patient.
We measured stereoacuity using TNO test on 25 patients without fixation disparity (FD) and compared the result with other 25 patients exhibited FD related to visual stress. All patients were presbyopes of ages ranging from 40 to 80 years, with visual acuity 6/6 or better in each eye, free from ocular diseases and generally healthy. The results showed statistically significant difference in the stereoacuities measured between the groups (Mann-Whitney U = 181.0, p < 0.01), suggesting that FD significantly reduced stereoacuity. Although the correlation between the magnitudes of FD and stereothreshold is statistically not significant (Spearman’s rs = 0.33, p>0.01), elimination of FD using prisms correction statistically improved stereoacuity (Wilcoxon’s Z = 2.43, p<0.01). The findings conclude that visual stress manifested as FD causes deficit in stereoperformance measurable with the TNO test and can be improved by prism correction.
Visual stress; fixation disparity; stereopsis; stereoacuity; prism correction