| Abstract |
Purpose:
The research of how additional dioptric blur influences visual performance at near for healthy presbyopes, and also the assessment of the advantage of binocular over monocular viewing.
Methodology:
Participants were 16 healthy presbyopes (mean age: 59.7±7.8 years , mean add: 2.22±0.34 D ), without any ophthalmopathological disorders, or previous refractive surgery and without amblyopia or anisometropia.
Reading performance was assessed with the Colenbrander Greek reading card for 3 levels of blur (best focus, -0.50 D, -1.00 D). Dioptric blur was accomplished with concave trial lenses, in front of best corrected for near vision testing eyes (40 cm).
Reading procedure was audio recorded (Audacity 1.3 Beta), and the results were converted to (1) reading acuity (the smallest print size that can be read), (2) maximum reading speed (the participant’s reading speed when reading is not limited by print size), (3) threshold print size (the print size that corresponds to an 80% of the maximum reading speed) and (4) “newsprint” reading speed (the participant’s reading speed at 0.4 logMAR print size – average newsprint).
After the reading procedure, there was a measurement of the participants’ natural pupil size for binocular and monocular (dominant eye) viewing at 40 cm.
Results:
Average reading acuity was affected with dioptric blur (p<0,001), and also between binocular – monocular condition (p=0,008). For binocular vision: -0.05±0.07 logMAR when in-focus, 0.00±0.09 logMAR at -0.50 D and 0.05±0.11 logMAR at -1.00 D blur and for monocular vision: (-0.02±0.13 logMAR when in-focus, 0.05±0.11 logMAR at -0.50 D and 0.13±0.12 logMAR at -1.00 D blur).
As it was expected, maximum reading speed was minimally affected by blur, as was the case for the binocular – monocular condition.
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On the other hand, both blur (p<0,001) and binocular – monocular condition (p=0,03) affected average threshold print size. For binocular reading: 0.23±0.13 logMAR when in-focus to 0.30±0.12 logMAR at -0.50 D blur and 0.38±0.13 logMAR at -1.00 D blur and for monocular reading: 0.28±0.15 logMAR when in-focus to 0.36±0.13 logMAR at -0.50 D blur and 0.45±0.12 logMAR at -1.00 D blur.
Finally, for the normalized values of newsprint reading speed the differences are: for binocular reading: (1,00±0,00 logMAR when in-focus to 0,93±0,08 logMAR at -0,50 D blur and 0,84±0.13 logMAR at -1.00 D blur and for monocular vision: 0.95±0.14 logMAR when in-focus to 0.86±0.10 logMAR at -0,50 D blur and 0.77±0.10 logMAR at -1.00 D blur.
Bonferroni comparisons for reading acuity, threshold print size and normalized newsprint reading speed, showed highly significant differences between the in-focus condition and the 1.0 D blur (p< 0.001) but not between the other blur levels.
Conclusions:
The changes in reading performance parameters with blur, suggest that it is susceptible to small amounts of blur corresponding to under-correction for near vision. The effect is significant for amounts of blur higher than 0.50 D. Also, the binocularity advance is higher with the increase of blur.
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