Stability of near stereoacuity in childhood intermittent exotropia

Abstract

Purpose: To investigate the course of near stereoacuity in a cohort of children with untreated intermittent exotropia.

Methods: A total of 95 children ages 2-16 years with untreated intermittent exotropia were identified who had measurements of near stereoacuity using the Preschool Randot (PSR) test on at least 2 successive examinations, with no intervening treatment. Deterioration was defined as a drop of at least 3 octaves, as determined by 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.

Results: 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.

Conclusions: 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.

FIG 1

Distribution of baseline stereoacuity thresholds at presentation. Black shading indicates subjects with subnormal stereoacuity (sensory monofixation). Applying previously published age-specific thresholds for normal Preschool Randot stereoacuity (Table 1), 49% had bifixation (40–60 arcsec) on their first measurable assessment, 23% indeterminate (within normal range but worse than 60 arcsec) and 27% monofixation (subnormal). Note that depending on child age, a threshold of 100 to 400 arcsec could either be normal, and therefore indeterminate regarding monofixation/bifixation, or subnormal, and therefore consistent with sensory monofixation (Table 1).

FIG 2

Kaplan-Meier plot of deterioration in near Preschool Randot stereoacuity defined as a reduction in stereoacuity of 3 octaves. At initial examination, 75 of the cohort (79%) had 200 arcsec or better stereoacuity and were therefore at risk for deterioration using this definition. Dots above the line indicate when a subject was censored for no further follow-up or intervening treatment. At 1 year, 46 subjects were still at risk of deterioration; at 2 years, 18. The 1-year rate of deterioration was 2% (95% CI, 0%-6%), and the 2-year rate was 7% (95% CI, 0%-16%). Of the 2 subjects that met deterioration criteria, 1 had a subsequent measurement and passed their original stereoacuity threshold with no intervening treatment.

FIG 3

Kaplan-Meier plot of deterioration in near Preschool Randot stereoacuity defined as a reduction in stereoacuity of 2 octaves. At initial examination 85 of the cohort (89%) had stereoacuity of 400 arcsec or better and were therefore at risk for deterioration by this definition. Dots above the line indicate when a subject was censored for no further follow-up or intervening treatment. At 1 year, 50 subjects were still at risk of deterioration; at 2 years, 20. The 1-year rate of deterioration was 8% (95% CI, 1%-14%), and the 2-year rate was 12% (95% CI, 1%-21%). Of the 6 subjects that met deterioration criteria, 4 (67%) had a subsequent measurement and all 4 passed their original stereoacuity threshold with no intervening treatment.

FIG 4

Kaplan-Meier plot of deterioration in near Preschool Randot stereoacuity defined as a change from normal to subnormal stereoacuity. At initial examination, 69 of the cohort (73%) were normal and were therefore at risk for deterioration by this definition. Dots above the line indicate when a subject was censored for no further follow-up or intervening treatment. At 1 year, 43 subjects were still at risk of deterioration; at 2 years, 16. The 1-year rate of deterioration was 12% (95% CI, 3%-20%), and the 2-year rate was 25% (95% CI, 9%-39%). Seven (64%) of the 11 subjects that met deterioration criteria had a subsequent measurement and 5 (71%) of 7 returned to normal stereoacuity on a subsequent examination with no intervening treatment.