Monofixation with eso-, exo-, or hypertropia: is there a difference?

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

Does "Touching Four" on the Worth 4-dot test indicate fusion in young children? A computer simulation.

PURPOSE: "Touching four" dots on the Worth 4-dot test is used sometimes as an indication of fusion in young children. The authors examined the reliability of this test. METHODS: A computer simulation of the Worth 4-dot test generated images representing fusion, suppression, and alternate fixation. Sixteen children, ranging in age from 32 to 48 months, were examined using this test. RESULTS: None of the children could accurately describe the images verbally. Alternate fixation could not be distinguished from fusion by asking the subjects to touch the dots. Monocular suppression was identified accurately in all subjects. CONCLUSION: Touching four dots on the Worth 4-dot test does not distinguish fusion from alternate fixation in children with normal ocular alignment. This has important implications regarding the diagnosis of monofixation syndrome and assessment of the response to a prism adaptation trial in young children.

Surgery for esotropia with a high accommodative convergence/accommodation ratio: effects on accommodative vergence and binocularity.

BACKGROUND AND OBJECTIVE: To determine the effectiveness of strabismus surgery as an alternative treatment for high accommodative convergence/accommodation (AC/A) ratio (nonrefractive accommodative) esotropia. PATIENTS AND METHODS: Twenty-three consecutive children with an AC/A ratio of 5:1 or greater and a distance-near disparity of 10 prism diopters (PD) or more were studied in a prospective design. Each patient was treated by recession of both medial rectus muscles for the full amount of esotropia measured at near fixation through the full distance hyperopic correction. The magnitude of eso deviation, the AC/A ratio, and the grade of binocularity were measured before and a minimum of 4 months after strabismus surgery. RESULTS: Surgery reduced the mean preoperative eso deviation at near fixation by a factor of 4 (from a mean of 37 PD to a mean of 9 PD). Surgery eliminated the need for bifocals in 96 percent of the patients. The grade of binocular fusion or stereopsis improved in 70 percent of the patients, remained unchanged in 26 percent, and was degraded in 4 percent. Three (13 percent) of the children became exophoric; none of the children were exotropic. CONCLUSION: These results demonstrate that strabismus surgery is an effective alternative to the long-term use of bifocals in the treatment of high AC/A ratio esotropia. Surgery may be more effective than bifocals in restoring normal stereopsis and binocular fusion.

Prevalence of intracranial lesions in children initially diagnosed with disconjugate nystagmus (spasmus nutans)

A small number of children who develop disconjugate nystagmus, torticollis, and head titubation (spasmus nutans) have been found to have optic chiasm or third ventricle gliomas. However, the prevalence of glioma or other developmental abnormalities in this disorder is unknown because no large series of spasmus nutans cases has previously been reported. A reviewer of the records of 67 consecutive children initially diagnosed with spasmus nutans and followed for an average of 3.3 years at the St Louis Children's Hospital revealed the following: 61% had a history of prematurity, developmental delay, or other systemic abnormality; strabismus, most commonly infantile esotropia, developed in 55%; 43% had neuroimaging studies; and 0% had evidence of a glioma or showed signs of tumor on follow-up examinations. From this consecutive patient series, we estimate the prevalence of tumor in spasmus nutans to be less than 1.4%. Without other evidence of an intracranial mass lesion, neuroimaging of infants initially diagnosed with spasmus nutans may not be immediately warranted.

Color dissociation artifacts in double Maddox rod cyclodeviation testing.

BACKGROUND: The double Maddox rod test, based on a red Maddox rod in front of one eye and a clear Maddox rod in front of the other, is used to measure cyclodeviation, typically in patients with superior oblique muscle pareses. Discrepant results between the double Maddox rod test and other torsion measures, and reports of "paradoxic" cyclodeviation in the normal eye of some patients with superior oblique paresis, suggest the two-color format of the double Maddox rod test may produce artifactual torsion measures. METHODS: Forty patients with superior oblique paresis were tested twice using the double Maddox rod test, reversing the red and white Maddox rods between eyes for the second test, and 18 were tested further with same-color red or clear Maddox rods in front of both eyes. RESULTS: With the standard double Maddox rod test, 33 (83%) of 40 patients localized their cyclodeviation to the eye viewing through the red Maddox rod, irrespective of laterality of the paresis or fixation preference. In all 33 patients, laterality of the perceived torsion changed between eyes when testing was repeated with red and white Maddox rods interchanged between eyes. With same-color Maddox rods before both eyes, 17 (94%) of 18 patients localized extorsion to the paretic eye. There was 7.6:1 ratio of luminance transmission and a 1.6:1 ratio of grating spatial frequency bandpass in the plano meridian between the clear and red Maddox rods, which appear to be responsible for the double Maddox rod test artifact. CONCLUSION: The traditional double Maddox rod test may produce artifactual cyclodeviation measurements. An alternative version of the test, based on same-color Maddox rods in front of both eyes, is proposed. The relatively high spatial frequency bandpass characteristics of the plano meridian of the Maddox rod (as high as 20/25 Snellen equivalent resolution through the clear Maddox rod) also suggests double Maddox rod testing should be conducted in a dark room to avoid biases from visual environment cues.

Lateral incomitance in exotropia: fact or artifact?

The prevalence of significant lateral incomitance in patients with nonparetic exotropia is reported to be 22%. We speculated that measurement artifact may be the cause for some cases of apparent lateral incomitance. We measured the effective power of plastic ophthalmic prisms using a helium-neon laser in the frontal plane position and at 10 degrees, 20 degrees, and 30 degrees of rotation from the frontal plane. The rotated prisms represented the situation in which a neutralizing prism rotates with the head during measurement of lateral gaze positions. For prisms of 35 prism diopters or more, even 10 degrees of rotation produced significant artifactual incomitance. For smaller prisms, 20 degrees or more of rotation was necessary to induce significant lateral incomitance. We prospectively measured 40 consecutive patients with exotropia. Only three patients (9%) had true incomitance greater than 5 delta, and only one had incomitance in both directions of gaze. Significant lateral incomitance could be induced in every patient examined by improperly positioning the neutralizing prism. Because the detection of lateral incomitance causes most strabismus surgeons to reduce the amount of surgery they perform, special care is necessary when measuring deviations in lateral gazes.