Subjective fixation disparity affected by dynamic asymmetry, resting vergence, and nonius bias.

PURPOSE This study was undertaken to investigate how subjectively measured fixation disparity can be explained by (1) the convergent-divergent asymmetry of vergence dynamics (called dynamic asymmetry) for a disparity vergence step stimulus of 1° (60 arc min), (2) the dark vergence, and (3) the nonius bias. METHODS Fixation disparity, dark vergence, and nonius bias were measured subjectively using nonius lines. Dynamic vergence step responses (both convergent and divergent) were measured objectively. RESULTS In 20 subjects (mean age, 24.5 ± 4.3 years, visual acuity, ≥1.0; all emmetropic except for one with myopia, wearing contact lenses), multiple regression analyses showed that 39% of the variance in subjective fixation disparity was due to the characteristic factors of physiological vergence: dynamic asymmetry (calculated from convergent and divergent velocities), and dark vergence. An additional 23% of variance was due to the subjective nonius bias (i.e., the physical nonius offset required for perceived alignment of binocularly [nondichoptically] presented nonius lines). Together, these factors explained 62% of the interindividual differences in subjectively measured fixation disparity, demonstrating the influence of oculomotor and perceptual factors. CONCLUSIONS Clinically relevant subjective fixation disparity originates from distinct physiological sources. Dynamic asymmetry in vergence dynamics, resting vergence, and nonius bias were found to affect fixation disparity directly, not only via changes in vergence dynamics.

[1]  R. Jones,et al.  Anomalies of disparity detection in the human visual system. , 1977, The Journal of physiology.

[2]  Kenneth N. Ogle,et al.  Oculomotor imbalance in binocular vision and fixation disparity , 1968 .

[3]  Clifton M. Schor,et al.  The relationship between fusional vergence eye movements and fixation disparity , 1979, Vision Research.

[4]  D. A. Owens,et al.  The accuracy of binocular vergence for peripheral stimuli , 1983, Vision Research.

[5]  H. Ogmen,et al.  Neural network model of short-term horizontal disparity vergence dynamics. , 1997, Vision research.

[6]  Stephanie Jainta,et al.  Objective vs subjective measures of fixation disparity for short and long fixation periods , 2010, Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians.

[7]  R. Harwerth,et al.  The relative sensitivities of sensory and motor fusion to small binocular disparities , 2001, Vision Research.

[8]  Wolfgang Jaschinski-Kruza,et al.  Dark vergence in relation to fixation disparity at different luminance and blur levels , 1994, Vision Research.

[9]  J. E. Lieberman,et al.  Frequency limitations of the two-point central difference differentiation algorithm , 1982, Biological Cybernetics.

[10]  Stephanie Jainta,et al.  Relation between fixation disparity and the asymmetry between convergent and divergent disparity step responses , 2008, Vision Research.

[11]  W Jaschinski,et al.  Fixation disparity and accommodation for stimuli closer and more distant than oculomotor tonic positions , 2001, Vision Research.

[12]  K. N. Ogle.  Researches in binocular vision. , 1950 .

[13]  George K. Hung,et al.  Static Behavior of Accommodation and Vergence: Computer Simulation of an Interactive Dual-Feedback System , 1980, IEEE Transactions on Biomedical Engineering.

[14]  A JAMPOLSKY,et al.  Fixation disparity in relation to heterophoria. , 1957, American journal of ophthalmology.

[15]  E A Palmer,et al.  The relationship between fixation disparity and heterophoria. , 1978, American journal of ophthalmology.

[16]  Alex Pentland,et al.  Microcomputer-based estimation of psychophysical thresholds: The Best PEST , 1982 .

[17]  Barbara Griefahn,et al.  Fixation disparity and nonius bias , 1999, Vision Research.

[18]  Tara L Alvarez,et al.  The relationship between phoria and the ratio of convergence peak velocity to divergence peak velocity. , 2010, Investigative ophthalmology & visual science.

[19]  C. Schor,et al.  Fixation of disparity: a steady state error of disparity-induced vergence. , 1980, American journal of optometry and physiological optics.

[20]  G.K. Hung.  Quantitative analysis of associated and disassociated phorias: linear and nonlinear static models , 1992, IEEE Transactions on Biomedical Engineering.

[21]  Clifton M. Schor,et al.  The influence of rapid prism adaptation upon fixation disparity , 1979, Vision Research.

[22]  J. Sheedy.  Actual measurement of fixation disparity and its use in diagnosis and treatment. , 1980, Journal of the American Optometric Association.

[23]  S. Jainta,et al.  Objective and subjective measures of vergence step responses , 2007, Vision Research.

[24]  Kenneth J. Ciuffreda,et al.  Vergence eye movements : basic and clinical aspects , 1983 .

[25]  Haluk Ögmen,et al.  Vergence Dynamics Predict Fixation Disparity , 2001, Neural Computation.