Increasing forward scattering in the dominant eye leads to interocular differences and reduces overall binocular visual performance, according to a study published in Ophthalmic and Physiological Optics. Clinicians should be cautious when performing monovision corrections for presbyopia or amblyopia and emmetropization procedures that can result in marked interocular differences, according to the report.

Researchers conducted a study to assess binocular visual performance in healthy individuals by using binocular summation on visual functioning. They used 4 Bangerter foils and 5 fog filters to induce monocular forward scattering in 7 healthy individuals (mean age 27.7±6.5 years, 4 men) and calculated interocular differences using objective scatter index (OSI), Strehl ratio (SR), modulation transfer function (MTF) cut off, and straylight (log[s]). 

The team found that both Bangerton foils and fog filters prompted deterioration of visual acuity, contrast sensitivity, and stereoacuity compared with baseline (P =.01 and P =.04; P =.01 and P =.04; P =.01 and P =.03, respectively). They noted that interocular difference increased for OSI, SR, and MTF cut-off for the Bangerter foil condition, but not for fog filters (with the exception of log(s)).

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Overall, investigators noted a negative association between overall interocular difference score (OIDS) and overall binocular summation score (OBSS) (r=-0.51, P <.001) and an association between OIDS and distance stereoacuity (r= 0.65, P <.001).

“The increase in forward scattering, induced mainly by the Bangerter foils and the BPM2 fog filter before the dominant eye, produced greater interocular differences which jeopardized the overall binocular visual performance,” according to the researchers who caution that “it is important to avoid considerable interocular differences in ocular parameters such as optical quality (OSI), intraocular scattering and straylight (log(s)) to preserve adequate binocular visual performance (stereopsis and binocular summation).”

Study limitations include the reduced sensitivity of the Worth-4-dot test in assessing suppression and a small sample size.


Martino F, Castro-Torres JJ, Casares-López M, Ortiz-Peregrina S, Ortic C, Jiménez JR.  Effect of interocular differences on binocular visual performance after inducing forward scattering. Ophthalmic Physiol Opt. 2022;42(4):730-743. doi:10.1111/opo.12992