Introduction: Diagnostic monocular occlusion may be used to minimize the effect of fusion on the strabismus angle. The optimal duration of occlusion has not been established.
Methods: In this monocenter, prospective, non-randomized, masked trial, adult patients with intermittent or decompensated strabismus and intact binocularity were enrolled. Exclusion criteria were previous eye muscle surgery, ocular or orbital trauma, craniofacial malformations, nystagmus, neurological or myopathic disorders and paretic strabismus. The strabismus anlge in prism diopters (PD) was measured before (baseline) and after 1 hour, 4-6 hours and 48 hours of diagnostic occlusion. We present the results of an interim analysis.
Results: Of 15 patients, 5 had an exo- and 10 an esodeviation. Average baseline strabismus angle with distance fixation was 23.5 +/- 7.9 PD (standard deviation), and with near fixation 24.4 +/- 13.3 PD. After 48 hours of occlusion, It increased to 27.1 +/-7.9 PD (distance) and 27.4 +/- 16.1 PD (near), the difference was not statistically significant. In 4/5 patients with exodeviation and a mean baseline distance / near difference of 18.5 +/- 5.1 PD, this difference decreased to 11.7 +/- 2.9 PD (p = .0.15). In the remaining patients with a baseline distance / near difference up to 10 PD, it increased from 2.4 +/- 2.8 PD to 6 +/- 4.6 PD (p = .24).
Conclusion: The effect of duration on diagnostic occlusion to evaluate strabismus is variable. On average, the angle increased, which was more pronounced in patients with exodeviation. In patients with baseline distance / near difference up to 10 PD, it increased, whereas it decreased in patients with baseline distance / near difference greater 10 PD.