Evaluation of dynamic stereopsis in intermittent exotropia patients.

AIM: To delineate the characteristics of the dynamic stereopsis test and analyze related parameters in intermittent exotropia [X(T)] patients. METHODS: Fifty-seven X(T) patients and 55 normal subjects were enrolled in this study. The normal and X(T) groups were used to test the reproducibility and reliability of the dynamic stereopsis test, and Bangerter filters with densities of 0.2 were then used to simulate suppression to test for traditional and dynamic stereopsis. In the X(T) group, the measurements included 1) dynamic stereopsis test comprising three parts: motion+disparity, motion only and disparity only; 2) ocular deviation angle; 3) Bagolini striated lens test; 4) disease course; and 5) Titmus stereopsis test. RESULTS: The test-retest reliability of the dynamic stereopsis method was 0.901 in the normal and X(T) groups, and none of the X(T) patients were able to pass the static and dynamic stereopsis tests after using the 0.2 Bangerter filter. The accuracy rate was greater than 80% in the normal group and 31.81%, 36.36%, and 45.45% for the motion+disparity, motion-only and disparity-only components of the traditional test for X(T) patients diagnosed with stereoblindness via traditional tests, respectively. Patients with a long disease course (>1y) had worse dynamic stereopsis than those with a short disease course (<1y; P<0.05, Chi-square test). The deviation angle was not correlated with the motion+disparity, disparity-only, or the motion-only test components (all P>0.05, Chi-square test). CONCLUSION: Dynamic stereopsis is preserved in certain X(T) patients diagnosed with stereoblindness via traditional tests. A long disease course was shown to be a negative factor for dynamic stereopsis in X(T) patients which might be associated with worse progression, and provide good references clinically.

Exploring the Divergence Range for Stereopsis Maintenance With a Computer-Simulated Troposcope in Patients With Intermittent Exotropia.

PURPOSE: To investigate whether sensory input or motor signal of the extraocular muscle is the main activator of suppression in human intermittent exotropia (X(T)). METHODS: A case-control study was performed. Ten subjects with X(T) and 10 control participants were enrolled. The divergence range between both eyes when binocular vision was maintained was measured by using stereotests with a self-written computer program mimicking a troposcope. The break point, defined as the deviation angle at which stereopsis broke during eye deviation, was compared between the experimental and control groups by using a t test. RESULTS: The median near deviation angle in the experimental group was 42.5 prism diopters (PD) (mean, 44.5 ± 10.82 PD). The mean break point was 40.45 ± 10.79 PD in the X(T) group and 26.86 ± 2.62 PD in the control group (P = 0.003). The mean ratio of the break point to the near deviation angle was 0.92 ± 0.23 in the X(T) group, with the ratio close to 1 in 7 of 10 subjects. CONCLUSIONS: Binocular vision can be maintained if similar images are projected onto corresponding retinas during the tropic phase of X(T). The antidiplopic mechanism in X(T) patients (i.e., suppression) is evoked by sensory input from binocular rivalry rather than by motor signal of the extraocular muscle.

Interocular Shift of Visual Attention Enhances Stereopsis and Visual Acuities of Anisometropic Amblyopes beyond the Critical Period of Visual Development: A Novel Approach.

Aims. Increasing evidence shows that imbalanced suppressive drive prior to binocular combination may be the key factor in amblyopia. We described a novel binocular approach, interocular shift of visual attention (ISVA), for treatment of amblyopia in adult patients. Methods. Visual stimuli were presented anaglyphically on a computer screen. A square target resembling Landolt C had 2 openings, one in red and one in cyan color. Through blue-red goggles, each eye could only see one of the two openings. The patient was required to report the location of the opening presented to the amblyopic eye. It started at an opening size of 800 sec of arc, went up and down in 160 sec of arc step, and stopped when reaching the 5th reversals. Ten patients with anisometropic amblyopia older than age 14 (average age: 26.7) were recruited and received ISVA treatment for 6 weeks, with 2 training sessions per day. Results. Both Titmus stereopsis (z = -2.809, P = 0.005) and Random-dot stereopsis (z = -2.317, P = 0.018) were significantly improved. Average improvement in best corrected visual acuity (BCVA) was 0.74 line (t = 5.842, P < 0.001). Conclusions. The ISVA treatment may be effective in treating amblyopia and restoring stereoscopic function.

KIF21A gene c.2860C>T mutation in congenital fibrosis of extraocular muscles type 1 and 3.

PURPOSE: To determine, in Taiwanese patients, the genetic basis of congenital fibrosis of the extraocular muscles (CFEOM) type 1 and 3, a group of diseases characterized by congenital restrictive ophthalmoplegia affecting muscles innervated by the oculomotor nerve. METHODS: Linkage analysis with microsatellite markers at chromosome 12q and direct sequence analysis of the KIF21A gene were performed on three families and one sporadic CFEOM case. RESULTS: Two of the families were classified by clinical criteria as CFEOM1 and another family as CFEOM3. All three families were shown to be linked to the 12q CFEOM1 locus. Sequence analysis disclosed a heterozygous c.2860C>T mutation in the KIF21A gene in all families and in the sporadic case. Affected family members were further confirmed by a BsrDI polymorphism. CONCLUSIONS: CFEOM is present in Chinese populations. Both CFEOM1 and CFEOM3 can be caused by the same mutation at the KIF21A gene. The occurrence of this mutation in different ethnic groups suggests a mutation hot spot.