Diplopia and Visual Acuity: Magnitude, Orientation and Contrast.

Abstract

Purpose : Patients report visually disturbing diplopia as the consequence of optical and neural anomalies, even in the presence of good, apparently normal, visual acuity. We investigated the effects of different diplopia parameters on visual acuity, by simulating diplopia on computer generated acuity charts.

Methods : Participants were 10 visually normal observers (6M,4F) aged 21 to 28 years (mean 22.4+/-2.3). We used repeated measures designs, testing participants' left eyes corrected with trial lenses to give the best spectacle correction. Stimuli, generated on a HD monitor HP ZR2440W, were eight rows of 5 Sloan letters, from 0.4 to -0.3 logMAR. In experiment 1, the ghost image was as bright as the main image. The following conditions were assessed (order randomized): diplopia horizontal, vertical, and two oblique meridians (135 and 45) and with the following magnitudes, 0, 0.25, 0.5, 1, 2, 4, 8 and 16 minutes of arc. (Example Figure 1) For experiment 2, diplopia levels of 0, 0.5, 1, 2, 4, 8 and 16 minutes of arc were tested in the horizontal meridian, with the contrast of the ghost image being 10%,20%, 30%,40% and 50%. (Example Figure 2)

Results : Experiment 1. There was a significant effect of diplopia level on visual acuity. (F_7,63 =52.0, p<0.001) For no diplopia the mean acuity was -0.11logMAR+/-0.024 SEM with acuity only rising for diplopia levels greater than 1 minute of arc, being greatest at diplopia of 16 minutes at 0.12logMAR+/-0.028 SEM, an increase of 2 lines. Orientation had no significant effect on acuity thresholds (F_3,27 =0.707 p=0.556), nor was there a significant orientation/diplopia level interaction (F_21,189=0.778 p=0.745). Experiment 2. The effect of diplopia level on acuity varied with ghost image contrast levels (i.e. a contrast/diplopia level interaction F_20,180=6.12 p<0.001). For higher ghost image contrasts diplopia significantly affected acuity, i.e. for 16 min of diplopia, acuity thresholds averaged 0.10 logMAR+/-0.043SEM (50% contrast) and 0.0 logMAR+/-0.025 SEM (40% contrast), but for 30% contrast or less were less than 0.04 logMAR worse than no diplopia.

Conclusions : Diplopia levels larger than 1 minute of arc will cause acuity thresholds to slightly rise, if ghost images are of high contrast, but good acuity levels can be obtained under conditions of very obvious diplopia.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Example Expt 1. Diplopia 2 min, oblique, 50% ghost contrast

 

Example Expt 2. Diplopia 2 min, Horizontal, 30% ghost contrast