S. Murakami1, N. Matsushita1, S. Hayashi2, N. Nakano2, S. Saito2, M. Ishizawa1, T. Sato1
1Dep. of Occupational Therapy, School of Health Sciences,
Sapporo Medical University, Sapporo 060-8556, Japan (e-mail:shinjim@sapmed.ac.jp);
2Dep. of Neuropsychiatry, School of Medicine,
Sapporo Medical University, Sapporo 060-8556, Japan
When human observers change fixation between targets which differ in direction and distance, they make co-ordinated binocular eye movements. The movements of both eyes can be in the same or opposite directions and have different amplitudes.
The purpose of this study is to investigate these co-ordinated binocular eye movements during binocular and monocular viewing. The subjects were ten healthy adults and were requested to change fixation between three LED's. The LED's were located at point A (60 cm away from the eye) and at two far points C and F (120 cm away, with a 5 deg difference between them) and lit alternately for 3 s, in a F-A-C-A sequence. The difference in direction between C and A was less than 5 deg and that between F and A was more than 5 deg. The experiments were performed under two conditions. The first was using the normal visual field for a visual input to both eyes, that is binocular vision. The second was creating a separate visual field by placing a black board at the centre of the face producing visual input to just one eye, that is monocular vision. The movements of both eyes were recorded by a Vision Analyzer.
The results were that eye movements of equal (F-A) and opposite (C-A) directions were observed under binocular vision, but under monocular vision the directions of the movements of both eyes were the same even in the two conditions F-A and C-A.
| F-A: | In monocular vision the movements of one eye were about 70% of the movement of the other eye. The amplitudes of the eye movements during monocular viewing were larger than the amplitudes during binocular viewing. |
| C-A: | The eyes moved in opposite directions during binocular viewing, but in the same directions during monocular viewing. In monocular vision the movements of one eye were about 65% of the movement of the other eye. |
It means that monocular vision could not control exactly the non-input eye with regard to amplitude and direction. With regard to the amplitude, it drove the non-input eye 20% larger than the same eye movements during binocular vision.