Some observers do not fixate accurately at the point of regard: Their vergence angle (between the visual axes of the two eyes) may correspond to points slightly nearer or farther away. This vergence error, or fixation disparity, was measured with nonius (vernier) lines at six positions of a visual display relative to the eyes. At viewing distances of 40, 60, and 100 cm, the display was located either at eye level or at a downward inclination of gaze direction of -25dG relative to horizontal. Viewing conditions resembled typical office work. Lowering the screen induced a near shift in mean vergence response of 0.6 min arc, irrespective of viewing distance; the closer the screen, the more distant was the vergence response relative to the target (by 2.5 min arc on average). The slope of this proximity-fixationdisparity curve is an individual parameter of the vergence system. Actual or potential applications of this research include recommendations for the comfortable viewing distance of visual displays.
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References
1.
Abe, S., Sotoyama, M., Taptagaporn, S., Saito, S., Villanueva, M. B. G., & Saito, S. (1995). Relationship between vertical gaze direction and tear volume. In A. Grieco, G. Molteni, B. Piccoli, & E. Occipinti (Eds.), Work with display units 94 (pp. 95-99). Amsterdam: Elsevier.
2.
Burgess-Limerick, R., Mon-Williams, M., & Coppard, V. L. (2000). Visual display height. Human Factors, 42, 140-150.
3.
Dixon, W. J. (1992). BMDP statistical software manual.Berkeley: University of California Press.
4.
Evans, B. J. W. (1997). Pickwell's binocular vision anomalies: Investigation and treatment.London: Butterworths.
5.
Heuer, H., & Owens, D. A. (1989). Vertical gaze direction and the resting posture of the eyes. Perception, 18, 363-377.
6.
Howard, I. P., & Rogers, B. J. (1995). Binocular vision and stereopsis.New York: Oxford University Press.
7.
Hung, G. K. (1992). Quantitative analysis of associated and disassociated phorias: Linear and nonlinear static models. IEEE Transactions on Biomedical Engineering, 39, 135-145.
8.
Jaschinski, W. (1997). Fixation disparity and accommodation as a function of viewing distance and prism load. Ophthalmic and Physiological Optics, 17, 324-339.
9.
Jaschinski, W. (1998). Fixation disparity at different viewing distances and the preferred viewing distance in a laboratory nearvision task. Ophthalmic and Physiological Optics, 18, 30-39.
10.
Jaschinski, W. (2001a). Fixation disparity and accommodation for stimuli closer and more distant than oculomotor tonic positions. Vision Research, 41, 923-933.
11.
Jaschinski, W. (2001b). Methods for measuring the proximity-fixation-disparity curve. Ophthalmic and Physiological Optics, 21, 368-375.
12.
Jaschinski, W., Bröde, P., & Griefahn, B. (1999). Fixation disparity and nonius bias. Vision Research, 39, 669-677.
13.
Jaschinski, W., Heuer, H., & Kylian, H. (1998). The preferred position of visual displays relative to the eyes: A field study of visual strain and individual differences. Ergonomics, 41, 1034-1049.
14.
Jaschinski, W., Heuer, H., & Kylian, H. (1999). A procedure to determine the individually comfortable position of visual displays relative to the eyes. Ergonomics, 42, 535-549.
15.
Jaschinski, W., Koitcheva, V., & Heuer, H. (1998). Fixation disparity, accommodation, dark vergence, and dark focus during inclined gaze. Ophthalmic and Physiological Optics, 18, 351-359.
16.
Jaschinski-Kruza, W. (1991). Eyestrain in VDU users: Viewing distance and the resting position of ocular muscles. Human Factors, 33, 69-83.
17.
Jaschinski-Kruza, W. (1994). Dark vergence in relation to fixation disparity at different luminance and blur levels. Vision Research, 34, 1197-1204.
18.
Lie, I., & Opheim, A. (1990). Long-term stability of prism correction of heterophorics and heterotropics: A 5 year follow-up. Journal of the American Optometric Association, 61, 491-498.
19.
Menozzi, M., von Buol, A., Krueger, H., & Miège, C. (1994). Direction of gaze and comfort: Discovering the relation for the ergonomic optimization of visual tasks. Ophthalmic and Physiological Optics, 14, 393-399.
20.
Mon-Williams, M., Burgess-Limerick, R., Plooy, A., & Wann, J. (1999). Vertical gaze direction and postural adjustment: An extension of the Heuer model. Journal of Experimental Psychology: Applied, 5, 35-53.
21.
Mon-Williams, M., Plooy, A., Burgess-Limerick, R., & Wann, J. (1998). Gaze angle: A possible mechanism of visual stress in virtual reality headsets. Ergonomics, 41, 280-285.
22.
Owens, D. A., & Tyrrell, R. A. (1992). Lateral phoria at distance: Contributions of accommodation. Investigative Ophthalmology and Vision Science, 33, 2733-2743.
23.
Pickwell, L. D., Kaye, N. A., & Jenkins, T. C. A. (1991). Distance and near readings of associated heterophoria taken on 500 patients. Ophthalmic and Physiological Optics, 11, 291-296.
24.
Rosenfield, M. (1997). Tonic vergence and vergence adaptation. Optometry and Vision Science, 74, 303-308.
25.
Scheiman, M., & Wick, B. (1994). Clinical management of binocular vision.Philadelphia: Lippincott.
26.
Schor, C. M. (1983). Fixation disparity and vergence adaptation. In C. M. Schor, & K. J. Ciuffreda (Eds.), Vergence eye movements: Basic clinical aspects (pp. 465-516). Boston: Butterworths.
27.
Sheedy, J. E., & Saladin, J. J. (1983). Validity of diagnostic criteria and case analysis in binocular vision disorders. In C. M. Schor, & K. J. Ciuffreda (Eds.), Vergence eye movements: Basic and clinical aspects (pp. 517-540). Boston: Butterworths.
28.
Sommerich, C. M., Joines, S. M. B., & Psihogios, J. P. (2001). Effects of computer monitor viewing angle and related factors on strain, performance, and preference outcomes. Human Factors, 43, 39-55.
29.
Tyrrell, R. A., & Leibowitz, H. W. (1990). The relation of vergence effort to reports of visual fatigue following prolonged near work. Human Factors, 32, 341-357.
