Alternate Prism Cover Test Research Articles

Diurnal variation of control in intermittent exotropia

Purpose: Measuring control may be important in assessing progression in intermittent exotropia (IXT). We used a previously described scale to assess variability in control during the course of a single day in children with intermittent exotropia. Methods: Thirteen patients (age, 3 to 13 years) with IXT were prospectively enrolled. The angle of deviation and level of control at both distance and near were assessed by a single examiner at three or four times (minimum 2 hours apart) throughout the day. Change was defined as >1 level on the 0 to 5 control scale, and >10Δ on alternate prism cover test. Results: Seven (54%) patients showed no change in distance or near control throughout the day, while the remaining six (46%) demonstrated a change at distance for all six and at near in four. Those demonstrating no change had a median distance score of 1 compared with 2.75 for those whose control was variable (p = 0.04). Variable patients changed by as much as three levels, including phoric to spontaneously tropic, and vice versa. The distance angle did not change during the day in any patient. Conclusions: Control varied throughout the day in half of the study patients despite no change in angle. Patients with poorer levels of control tended to have more variability, and the worst level of control could occur at any time of the day. These findings suggest that an isolated measure of control may be insufficient to categorize the severity of control in an individual patient.

Reexploration and inferior oblique myectomy temporal to the inferior rectus to treat persistent inferior oblique overaction

Persistent symptomatic inferior oblique (IO) muscle overaction (IOOA) after IO muscle weakening surgery is a common problem. We describe the results of reexploration and myectomy of the IO muscle using a standard inferotemporal approach to treat this clinical entity. A retrospective noncomparative consecutive series of patients referred for treatment of persistent IOOA. The following preoperative and postoperative measurements were recorded in each case: (1) the ductions and versions of the overacting IO muscle and its antagonist superior oblique (SO) muscle; and (2) alternate prism cover test, using loose prisms at 6 m, in primary position and right- and leftgaze. The preoperative and longer term postoperative findings were compared. Eight patients were identified. Three had previously undergone a standard IO myectomy, and five had undergone a standard IO muscle recession. The median period of postoperative follow-up was 12 months (range, 7 months to 2 years). The IOOA was eliminated in three patients and a reduction of IOOA of at least 1 unit was achieved in all patients. Seven patients showed improvement of their SO muscle underaction on versions, postoperatively. All patients achieved a marked improvement in their alignment across the three standard horizontal positions of gaze. The mean vertical deviations pre- and postoperatively was 23(Delta) versus 7(Delta) in contralateral gaze, 17(Delta) versus 4(Delta) in primary gaze, and 7(Delta) versus 1(Delta) in ipsilateral gaze. Reexploration and myectomy of the IO muscle near to the temporal border of the inferior rectus muscle is a reliable and effective way of treating persistent IOOA.

Preoperative prism adaptation for acquired esotropia: Long-term results

Purpose: The efficacy of preoperative prism adaptation in subjects with acquired esotropia has been established at 6 and 12 months postoperatively. We evaluated the outcomes of subjects with acquired esotropia who had preoperative prism adaptation and were followed longer than 12 months. Methods: A retrospective analysis was undertaken of 2 groups of subjects with acquired esotropia who underwent bilateral medial rectus recessions based on the distance angle of deviation and were followed more than 12 months postoperatively. Group A subjects had preoperative prism adaptation to determine the target angle for corrective surgery. In Group B subjects, surgery was based on the maximum angle of strabismus at distance, determined by alternate prism cover test without preoperative prism adaptation. Results: We compared 17 subjects in Group A and 19 subjects in Group B. The postoperative follow-up period was 3 ± 1.7 years in Group A and 4.8 ± 1.8 years in Group B. The age at the last visit was 9.1 ± 2 years in Group A and 10 ± 2 years in Group B. Postoperative residual esotropia was 2.6 ± 2.5 PD at distance in Group A patients and 6.6 ± 5.9 PD in group B patients (P =.002). Residual esotropia at near was 3 ± 3.8 PD in Group A and 11.5 ± 8.12 PD in Group B (P <.01). More Group B subjects required bifocal spectacles to achieve optimal alignment at near (P =.001). Conclusion: Acquired esotropia subjects operated on for their distance prism-adapted angle maintained better motor alignment over a long-term follow-up period when compared with nonprism-adapted subjects operated on for their distance angle. (J AAPOS 2002;6:168-73)

Importance of unilateral occlusion in examination of the pupillary light reflex in an aged patient with large-angle exophoria-tropia

We report on a 60-year-old man, who was referred with a suspected absence of light reflex in his left eye. Exophoria-tropia with a large angle of deviation was found during the alternating prism cover test. The range of eye movement was normal. On macroscopic examination, both pupils appeared to be miotic and the light reflex was prompt, but incomplete. When one eye was occluded, the patient's miosis disappeared and the light reflex became prompt and complete, i.e., normal. Since he subconsciously performed convergence to achieve a phoric position and gradually noted asthenopia, he underwent strabismus surgery for his exophoria-tropia. After surgery, his pupils were normal even in the binocular state. Therefore, doctors should pay attention to the pupillary findings in elderly patients with comparatively large-angle exophoria-tropia, because their pupils falsely appear to be miotic (phoria-miosis) with a reduced or absent light reflex in the orthophoric position.

Bilateral posterior fixation sutures on the medial rectus muscles for correction of nonaccommodative esotropia with infantile onset criteria.

Bilateral posterior fixation sutures on the medial rectus muscles can be used in the management of nonaccommodative esotropia with criteria indicative of infantile onset. The postoperative results of posterior scleral fixation of bilateral medial rectus muscles on ocular motility and the angle of esotropia in different directions of gaze, as well as on the near point of convergence, have been studied. Twenty-six patients suffering nonaccommodative esotropia of the infantile onset type, showing variable angles, adduction overshooting, and esodeviation, which had started within the first year of life, were examined. The angle of esotropia was measured at near, distance, and in the different directions of gaze. All patients underwent post-equatorial scleral fixation of both medial rectus muscles at 12 mm to 14 mm from the insertion, depending on the preoperative angle of esotropia. With the alternate prism cover test, 20 patients (76.9%) showed an angle <10 prism diopters (delta) in the primary position, as well as in the different directions of gaze. Fifteen of the 20 patients (57.7%) even showed simultaneous perception at near and at distance with Bagolini's striated glasses. Six patients were under-corrected. Bilateral posterior fixation of the medial rectus muscles is a good procedure to correct the angle of esotropia in patients who meet the following criteria: essential infantile esotropia, showing overacting medial rectus muscles, variable angles, and nonaccommodative convergence excess.

The Effect of Edrophonium Chloride on Muscle Balance in Normal Subjects and Those with Nonmyasthenic Strabismus

Because the Lancaster red-green test and the Hess screen are not widely used by most ophthalmologists, we used the alternate prism-cover test to study the effect of intravenous edrophonium chloride (Tensilon) on the ocular alignment of 30 normal subjects and 14 individuals with nonmyasthenic strabismus. After measurement of their baseline phorias and tropias, patients received an intravenous injection of Tensilon via the incremental dose technique until autonomic effects of the drug were noted or until 10 mg was administered. Another set of measurements of muscle balance was taken immediately postinjection and 2 and 5 min later. Apart from a small increase (mean, 2 prism dipoters; p = 0.004) in their exophoria at near, normal subjects exhibited no significant change in their phorias after Tensilon injection. One third to one half of the nonmyasthenic strabismics, however, showed a change in their vertical deviation after Tensilon (46% at distance and 38% at near), with the majority of them increasing their angle of squint. These changes were small (mean, 1.7 prism diopters; maximum, 5 prism diopters). In only one case did reversal of the direction of deviation occur. Tensilon produces a statistically significant increase in near exophorias of normal subjects and in vertical distance deviations of nonmyasthenic strabismics. These changes, however, are clinically insignificant and should not be considered to constitute a positive Tensilon test.

A clinical evaluation of stereopsis required to see 3-D images.

Some children with esotropia who have been diagnosed as 'stereoblind' on the basis of conventional stereotests (which principally use static images with small disparity) may nevertheless enjoy stereopsis for three-dimensional (3-D) animations that use dynamic images with large disparity. The purpose of this study was to develop a new stereotest equipped with dynamic random-dot stereogram (DRDS) which has larger disparity with movement and use it with esotropic children to see if they can attain stereopsis for such images. Subjects were 17 esotropic children between 5 and 10 years old (mean age 6.8 years) who had failed to demonstrate stereopsis with the Titmus fly test. Seven children had infantile esotropia and 10 had partially accommodative esotropia. The test images were DRDS that were presented on a fluorescent screen (12 x 9 cm) viewed through a lenticular lens. The dots were displayed in circle and triangle patterns that have counterphase front-rear movement with maximum disparity of 800 s. Patients were placed with eyes at a distance of 60 cm from the screen and were instructed to point out the pattern (circle or triangle) that was produced. The average angle of strabismus was 7.7 delta by alternating prism cover test (5 m). Seven patients passed and 10 failed the DRDS test. There was no significant difference in the mean angle of strabismus or the age of examination between the two groups; however, the age at onset of strabismus was significantly higher in those who passed the DRDS test. These results suggest that the DRDS test is useful in evaluating the potential stereopsis in children with esotropia who do not pass conventional stereotests.