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J. K. Kim, A. M. Hayden, E. A. Sadun, J. Sebag, A. A. Sadun; Vertical Vergence Amplitudes in a Normal Adult Population. Invest. Ophthalmol. Vis. Sci. 2007;48(13):884.
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To measure vertical vergence amplitudes (VVA) in normal adults using a computer-based non-invasive device and determine if there are sex or age-related differences. Alternating testing paradigms were used to determine whether there are differences depending upon which eye tracks in upgaze.
VVA was measured in 101 normal adult subjects (53 women and 48 men) using a computer based device that incrementally moves two horizontal bars away from midline in opposite directions. The point at which fusion broke (onset of diplopia) was defined as the VVA. Every subject was measured 5 times in each direction (testing paradigms = left eye up/right eye down; right eye up/left eye down) alternating between each testing paradigm. The results were averaged into two separate indices (one for each testing paradigm) in each subject.
Intrasubject reproducibility was high with individual average standard deviations of 0.17 ± 0.084 (left eye up/right down) and 0.15 ± 0.088 diopters (right eye up/ left down), while intersubject variability was considerable with VVA ranging from 0.46 to 3.13 diopters. There was no apparent relationship of VVA to age (p =0.687 left up, p = 0.885 right up) and sex (p = 0.911 left up, p =0.684 right up). Almost all (96%) subjects showed laterality, with greater VVA when one eye tracked in upgaze as compared to the fellow eye. There were significantly more subjects with a greater VVA when the left eye tracked up (65.4%) than when the right eye tracked in upgaze (32.7%), with p<0.05 (chi-square test for equal proportions). The mean VVA was 1.49 ± 0.447 diopters when the left eye tracked in upgaze (right eye down) and 1.29 ± 0.345 when the right eye tracked in upgaze (left eye down). These means were significantly different with p<.001 by paired t-test.
VVA can be quantitated with a simple laptop computer in a highly-reproducible manner. There is a wide range of VVA, but no sex or age-related tendencies were detected. Almost all subjects display VVA laterality with a two-fold preponderance demonstrating higher VVA when the left eye tracks in upgaze. Future studies will explore the possible underlying causes and determine whether quantitative VVA measurements can reflect CNS dysfunction, changes in mental status, and/or fatigue.
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