¡¡¡¡Previous studies to date have concluded that rightª²eye dominance was greater than the leftª²eye dominance [19ª²21]. In our study the ratios of right eye dominance was also found higher than the left eye dominance as without gender difference the right eye dominance were 71.5 % and 61.5% (Table 2) and among females the ratios were as 67.3%, 56.4%, and in males the ratios were 78.3% and 69.6% according to McManus and G¨¹ndoan tests respectively (Table 3, 4). So in our study we also found right eye dominance were greater than leftª²eye dominance both in male and female subjects as it was found for handedness in our previous study[22]. Interestingly, slight differences in using different brain areas for language processing were recognized between males and females [23ª²25].

¡¡¡¡Authors mentioned that males use to prefer of their left eye rather than the right eye for monocular tasks such as sighting through a tube, about one third of the population was suggested to be left eye dominant [13]. In the first part of our study we assessed dominant eye with monocular activities by McManus test [15]. The subjects were asked to look trough a tip of dark bottle and the subjects were used to hold the bottle with their hand (Figure 6). As the subjects in the pictures Aª²1 and Aª²2 the bottle were holding by right hands in the picture Aª²3 and Aª²4 the other subjects prefer to hold with their left hands. This hand preference can be affected aye dominance determination as we mention before. This could be the cause of little differences between McManus [15] and G¨¹ndoan testª²retest results.

¡¡¡¡Figure 1  Ocular dominance was determined by means of the nearª²far alignment test for right eye (RE) and for left eye (LE)  A:The distance between near point (NP) and the far point (FP) from the eyes are seen;B:The centimeter schedule was placed on the two sides of the NP on the fixed transparent glass board for measuring shifting distance£¨ÂÔ£©

¡¡¡¡Figure 2  Eye dominance was measured by G¨¹ndoan performance method in the laboratory  A:Picture shows reference FP which has mobile ability, according the direction of subject;B:Picture shows the subject¡¯s NP on the transparent glass in front of the eye level and also it can be seen hands and head fixation positions£¨ÂÔ£©

¡¡¡¡Figure 3  Without gender difference dominant eye results for two methods were compared£¨ÂÔ£©

¡¡¡¡Figure 4  Dominant eye distributions among female students£¨ÂÔ£©

¡¡¡¡Figure 5  The dominant eye distributions among male students£¨ÂÔ£©

¡¡¡¡In order to exclude hand contamination, during dominant eye assessment all through the performance tests period hand movements restricted (Figure 2B). Because of the frontal eye fields, which are important for the control of voluntary saccades, are located only about 20 mm anterior to the sensorimotor cortex for the hands [26]. So our test period this hand moving restriction, was not contaminated by handedness. We thought that hand movement restrictions should be very important point for correct assessment of eye dominance. Restricting head movements was also important for correct assessment of dominant eye which was stated to be altered according to visual field is being left or right side of the target point [27]. In our study restricting head movements we prevented shifting visual field during dominant eye assessment. Moreover when we asked form the subjects to close one of their eye the shifting distances between NP to FPs means were (2.16¡À2.44)cm for right eyes and (3.35¡À2.47)cm for left eyes. The difference between two values without gender difference were significant (P<0.01). In females the right eye mean value was (2.38¡À2.38)cm, left eye (3.05¡À2.41)cm. The difference between these two values was significant (P<0.01). In males the right eye(1.81¡À2.51)cm left eye (3.83¡À2.50)cm the difference betweenFigure 6  Monocular activities of McManus test. Looking through a bottlethese two values was not significant (ns) (Table 1). The comparisons of right and left eye shifting distance for all groups were analyzed by Wilcoxon sign test.

¡¡¡¡In all subjects minimum and maximum deviation distances values for both right and left eyes were showed constant distance as (0.00ª²6.50)cm (Table 1). This is an very important point for our study when we compared with previous study of Baykal et al[21] whose shifting distance values were much more higher than ours. Further more focusing point distances of our study were more homogenous [21]. This homogenous measurement seems to confirm the reliability of the G¨¹ndoan. During monocular activities such as McManus test researcher has not chance for objective criteria as measuring shifting distance and focusing points for a reliable diagnosis. In this point we thought G¨¹ndoan method may be found more reliable method for detecting dominant eye. On the other hand we put attention on a subject reliated with questions that which property was accepted by authors for detecting dominant eye? Sighting dominance, acuity dominance or sensory dominance? In the best review of the phenomenon on the basis of the assessment eye dominance authors mentioned that a carefully distinguish should be performed by investigators for sighting dominance from the others [28]. It was seen that a wide range of performance measures of dominance, sighting dominance has been proposed for dominant eye assessment [29, 30].

¡¡¡¡If the concept of eye dominance is to be useful for detecting cerebral functional laterality it should be reliable. It is therefore worth noting that a number of studies have found high consistency of repeated measures of sighting dominance  [19, 31, 32]. This was the reason of our testing and reª²testing research procedure of our study and we compared G¨¹ndoan method results with the other most largely used monocular selection method of McManus for the same subjects.
 
¡¡¡¡Dominant eye has sometime been assessed using questionnaires concern with monocular activities [33, 34]. During monocular activities subject is asked to look through a small object which is held in one hand, then holding of object in dominant hand may well distort measure of the association between hand preference and eye dominance. In monocular activities show two specific problems; first the items may refer to activities such as holding a rifle, a bottle, or a kaleidoscope which are contaminated by hand preference [35]; and second there may be a process of set, whereby once a subject has consistently answered "right" or "left" to many handedness items, then they will merely carry on answering in same direction to other questions concerning eye dominance [10]. Because of those specific problems in our study we applied performance test for both McManus and G¨¹ndoan tests.

¡¡¡¡CONCLUSION

¡¡¡¡G¨¹ndoan performance test depend on measurement sigfting distance between reference points which can able to give a objective criterias for dominant eye assesment. It seems one of practically applicatable and reliable method for detecting dominant eye. The eye dominance was considering to show functional laterality due to the dominance one of hemisphere. It is an important topic future research in laterality, and it may well become an important model system for future research.

¡¡¡¡ACKNOWLEDGMENTS

¡¡¡¡Authors would like to appreciate Fatih zkul for his technical support during design of the eye dominance measurement device, and we would also like to thank to our university students for their voluntary participation to our reseach programme and to our medical research group students as Alp Tuna Beksac, Mehmet Emre G naydin, Sema Kurban and Isik Ocak for their excellent assistance during data collection.

ÉÏÒ»Ò³  [1] [2] [3]