Visual conditions such as anisometropia, monovision and monocular undercorrection affect the combination of visual
input from both eyes. This study investigated the effects of monocular blur, in binocularly normal participants, on
stereoacuity and binocular contrast sensitivity. Fifteen young adults (age range between 19 and 23 years old) with normal
visual acuity and binocular vision participated in this study. Stereopsis was measured using the TNO test with a series
of positive spherical lenses placed before the dominant eye. The procedure was repeated using the Titmus Stereotest on
five participants as a control experiment. Monocular and binocular contrast sensitivities were also measured using the
Pelli-Robson Contrast Sensitivity Chart. Blur was induced monocularly with a series of positive spherical lenses placed
before the dominant eye and binocular contrast sensitivity was re-measured. Stereopsis scores decreased significantly
when monocular blur was imposed. Across blur levels, absolute stereopsis scores measured with TNO test were worse
than those measured with Titmus stereotest (all p < 0.05). However, the ratio of scores obtained without blur and under
monocular blur appeared to be similar for both tests. Stereopsis without blur was between 6.82× to 8× better than that
obtained with the highest level of imposed monocular blur. Binocular contrast sensitivity score decreased significantly
with increasing level of monocular blur (p < 0.01). Binocular contrast sensitivity score without blur was 1.62× better
than that obtained under binocular viewing with highest level of imposed blur. Stereopsis tests are more sensitive than
measurements of binocular contrast sensitivity as an indicator of interocular acuity discrepancies which could occur
in anisometropic or monovision patients. However, the choice of stereopsis test is crucial, as the TNO test appears to be
more sensitive to monocular blur than the Titmus stereostest.