Microtropia (monofixation syndrome) in flying personnel

Comparison of sensory outcomes in patients with successful motor outcome versus recurrent exotropia after surgery for intermittent exotropia

Here, we compared sensory outcomes between patients with successful motor outcomes and recurrent exotropia after intermittent exotropia surgery. We retrospectively analyzed 303 patients who underwent surgery for intermittent exotropia, divided into two groups: successful motor outcome defined as an alignment between 10 prism diopters (PD) exodeviation and 5PD esodeviation at the final follow-up (Group A, n = 177) and residual or recurrent exotropia defined as exodeviation > 10 PD (Group B, n = 126). Preoperative and postoperative (at final visit) sensory outcomes were compared using the Titmus stereotest and distance Worth 4-dot test. Stereoacuity significantly improved postoperatively in both successful motor outcome group (Group A) and residual or recurrent exotropia group (Group B). However, stereoacuity did not differ between groups preoperatively and postoperatively. On the other hand, fusion rates for the Worth 4-dot test were significantly higher in group A than in group B, preoperatively and postoperatively, and significantly increased postoperatively only in group A. Therefore, the distance Worth 4-dot test may be useful for evaluating postoperative prognosis and preoperative sensory status.

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.

Distance alternate-letter suppression test for objective assessment of sensorial status in intermittent exotropia

PURPOSE

To investigate the value of distance alternate-letter suppression testing in the objective assessment of fusional control of intermittent exotropia.

METHODS

A total of 71 consecutive patients with intermittent exotropia (study group) and 112 normal subjects (control group) underwent a series of measurements including distance alternate-letter suppression testing, Worth 4 Dot test at distance and near, and distance and near stereo acuity tests to see whether sensorial behavior differed in the study and control groups. The distance alternate-letter suppression test and distance stereo acuity tests were performed using the Mentor B-VAT II-SG Video Acuity Tester and Binocular Vision Testing System. The TNO test was used to measure near stereo acuity.

RESULTS

Seventeen patients with intermittent exotropia (24%) presented suppression with the distance alternate-letter suppression test, but none of the normal subjects (p<0.001, chi2 test). Only, three patients (4%) showed suppression on the Worth 4 Dot test at distance, and all had fusion on the Worth 4 Dot test near. Patients with intermittent exotropia had significantly diminished distance stereo acuity compared to normal subjects (p<0.001). Normal subjects and patients had good near stereo acuity (p>0.05). Patients with intermittent exotropia who had fusion with the distance alternate-letter suppression test had significantly better distance stereo acuity than patients who had suppression (p<0.001).

CONCLUSIONS

Distance alternate-letter suppression testing and distance stereo acuity tests may be useful as objective measures for assessing sensory loss in patients with intermittent exotropia.

Assessment of central and peripheral fusion and near and distance stereoacuity in intermittent exotropic patients before and after strabismus surgery

PURPOSE

To determine whether central fusion and distance stereoacuity are useful as objective measures in assessing the need for and success of surgery for intermittent exotropia (X[T]).

METHODS

A prospective, institutional, clinical trial was conducted of 26 consecutive patients with X(T) who were undergoing strabismus surgery in whom fusion (central and peripheral) and stereoacuity (at near and distance) were assessed preoperatively and postoperatively, as well as in 112 normal subjects. To obtain accurate measurements with sensory tests, the lower age was limited to 5 years for inclusion. A successful surgical alignment was defined as an exotropia of 10 prism diopters or less at 6 m. Sensory and motor outcome measures were determined 1 year after surgery.

RESULTS

The successful surgical alignment rate was 69%. All patients with X(T) demonstrated peripheral fusion, whereas 35% demonstrated central suppression preoperatively and postoperatively. Central fusion was not predictive of surgical outcome (P = .078); however, there was a trend toward less surgical success in patients with central suppression. Patients with X(T) exhibited good near stereoacuity before and after surgery. Distance stereoacuity in patients with X(T) preoperatively was significantly diminished compared with normal subjects (P < .001) and was improved in 58% postoperatively. Patients who achieved successful surgical alignment had a greater likelihood of demonstrating distance stereoacuity improvement postoperatively than patients who failed to achieve successful surgical alignment (P = .003). Patients with central suppression were unlikely to improve their distance stereoacuity postoperatively (P = .014).

CONCLUSIONS

Successful surgery may improve distance stereoacuity. Better distance stereoacuity and central fusion are frequently associated with better surgical success in X(T).

Second Generation Binocular Polaroid Test

BACKGROUND

The aim of the study was to introduce a new test to detect small areas of suppression in the binocular visual field and to lower the minimum age at which a suppression test could be identified correctly. Two tests were compared: the Binocular Polaroid Test (poltest), introduced in clinical practice a few years ago and used in screening programs for vision impairment; and the Second Generation Binocular Polaroid Test (polstar), more recently designed to have simpler answers than the poltest.

METHODS

One hundred and eighty-two children were examined consecutively. To assess the validity of the two tests, sensitivity, specificity, predictive value, and phi coefficient were calculated. The applicability of the two tests and the speed of the responses was assessed by means of the test of probability of binomial distribution.

RESULTS

The polstar has appeared to be simpler and easier in younger patients (age range 20 to 36 months, P = 0.078), and has shown 100% of specificity with a sensitivity of 84% for the polstar 1 and of 100% for the polstar 2.

CONCLUSION

The results appear to demonstrate that the poltest has been improved, and that the polstar may be considered an interesting investigation device for early detection of monocular visual impairment.

Preschool vision screening: rationale, methodology and outcome

Although population outcome studies support the utility of preschool screening for reducing the prevalence of amblyopia, fundamental questions remain about how best to do such screening. Infant photoscreening to detect refractive risk factors prior to onset of esotropia and amblyopia seems promising, but our current understanding of the natural history of these conditions is limited, thus limiting the prophylactic potential of early screening. Screening for strabismic, refractive and ocular disease conditions directly associated with amblyopia is more clearly proven, but the diversity of equipment, methods and subject populations studied make it difficult to draw precise summary conclusions at this point about the efficacy of photoscreening. Sensory-based testing of preschool-age children exhibits a similar combination of promise and limitations. The visual acuity tests most widely used for this purpose are prone to problems of testability and false negatives. Moreover, the utility of random-dot stereograms has been confused by misapplication, and new small-target binocularity tests, while attractive, are as yet inadequately field-proven. The evaluation standard for any screening modality is treatment outcome. However, variables in amblyopia classification and quantitative definition differences, timing of presentation, nonequivalent treatment comparisons, and compliance variability have been uncontrolled in virtually all extant studies of amblyopia treatment outcome, making it difficult or impossible to evaluate either the relative efficacy of different treatment regimens for amblyopia or the effects of age on treatment outcome within the preschool age range. The latter issue is a central one, since existence of such an age effect is the primary rationale for screening at younger rather than older preschool ages. The relatively low prevalence of amblyopia makes it difficult to achieve a high screening yield in terms of predictive value, but functionally increasing prevalence by selective screening of high risk populations causes further problems. Unless a "supertest" can be devised, with very high sensitivity and specificity, health policy decisions will be required to determine which of these two characteristics should be emphasized in screening programs. Performance of screening tests can be optimized, however, with adequate training, perhaps via instructional videotapes.

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.

Binocular Polaroid test

A test is presented for the detection of small suppression scotomas in strabismic and in anisometropic patients. Three small light-spots (the central is polarized) are viewed through Polaroid filters placed in front of the eyes. This arrangement produces the perception of the central spot only from one eye, but normal fusion provides the perception of three light-spots. Complete suppression of the central light indicates the presence of a scotoma in the binocular visual field. An inhibition scotoma in the non-dominant eye was found in all cases of small angle esotropia and of anisometropic amblyopia.

Depth perception in strabismus

The monocular and binocular depth thresholds of strabismic subjects have been measured with a modified Howard-Dolman apparatus. Seven out of the 14 strabismic subjects tested were found to have binocular thresholds significantly higher than their monocular ones. These strabismic subjects all had small angles of deviation less than 8 prism dioptres and high acuities in both eyes.