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Procedure
McManus Tests Eye dominance assessed by monocular procedure, in which sighting was primarily with a single eye chosen by participants. All subjects were tested individually in the day lightened laboratory room during 12.0013.00 with adequate instruments. Eye dominance was assessed by performance measurement according to McManus test in which there were three items for eye sighting such as: looking through a narrow opening into a dark bottle, looking through keyhole, looking down monocular microscope [1315]. This test was performed twice. The eye that was unequivocally preferred in this situation was scored on a point scale 1=always left, 2=either, 3=always right. Dominant eye was accepted to be the left eye if the average score < 2 and to be the right eye if total score was ≥2[15]. Participants who had either eye dominant and who were aware of having a difference in acuity of more than two dioptres in their eyes were excluded.
Gündoan Test’s The same subjects were retested in the same laboratory conditions by means of the nearfar alignment test. The subject has to align two reference points in the horizontal eyelevel plane. The line running through the two targets intersects the interocular axis at mid point between the eyes. The intersection can be imagined as the fictive vantage point from which the two targets appear in the same direction. Two equal size black round shape reference points were used. The first point as a near point (NP) was on the middle of the fixed transparent thin glass board 0.4m away from the eyes which had two centimeter schedule were placed on both sides. The second reference point was a mobile far point (FP) 3.0 m away from the eyes on the wall (Figure 1A and Figure 2A). The subjects were asked to place their jaws and foreheads on the jaw support and headrest, and an elastic band was gently secured in order to avoid head movements. Then the subjects were asked to focus both eyes on the FP as the examiner move the FP till it comes at the same line with the reference NP. When the two points were overlapping in the same line, the subject was then directed to close one eye without moving his or her head and eyes. The examiner questioned whether points were shifting or not. If the reference NP shifted from the FP in the horizontal plane when one eye was closed, examiner asked to read the shifting distance between two points from the transparent board where centimeter schedule was placed on the two sides of the reference NP (Figure 1B,2B). The same procedure was repeated for other eye. The eye representing minimum shifting distance between two points was accepted to be dominant. Some subjects have very slight mismatches of shifting distant for both eyes were considered as two of them were dominant and these few subjects were excluded.Dominant eye measurement illustrated by Figure 2.
Statistical Analysis Data were shown as n(%). χ2 test and Fisher exact test were used for the analysis of categorical data. The agreement between different methods was analyzed with Kappa statistics. Comparison of proportions was made by two proportions z test. P<0.05 was considered as significant. Statistical analysis was performed using the SPSS 11.5 and MINITAB 13.0 for Windows.
RESULTS
Gündoan method depends on the measurement of shifting distance between NP and FPs on the horizontal plane for each eye when one of eye was closed. Without gender difference the mean values of shifting distance for all participants were (2.16±2.44)cm for the right eye, (3.35±2.47)cm for the left eye, the difference was significant (P<0.01). Among females the mean values of shifting distance were (2.38±2.38)cm for the right eye, (3.05±2.41)cm for the left eyes, the difference was also significant (P<0.01). In males the mean values of shifting distance were (1.81±2.51)cm for right eye, (3.83±2.50)cm for left eyes, the difference was not significant. It was remarkable that minimum and maximum values were exactly similar in all groups for both of two eyes (Table 1).
Without gender difference the incidence of right eye dominance were found for 128 subjects (71.50 %) by McManus test and for the same population the right eye dominance were found for 110 (61.5 %) subjects by Gündoan test. The left eye dominance were also found for 51 (28.5%) subjects by McManus test [15] and 69 (38.5%) subjects were found by Gündoan methods (P<0.05) for the same population (Table 2). 128 subjects which were found with right eye dominant by Mc Manus test, only 89 subjects of those were assessed with right eye dominant by Gündoan method and rest of 39 were assessed as they had left eye dominant.
According to McManus method, 51 subjects were assessed as they had left eye dominant, but among those only 30 subjects assessed with left eye dominant according to Gündoan test method. The rest of 21 subjects assessed as they had right eye dominant (Table 2). These two methods for detection of dominant eye was found to be related significantly according to Kappa test (P<0.001;κ=0.256). In females 74 subjects were found with right eye dominant and 36 subjects were found with left eye dominant by McManus test. But only 48 subjects of those were assessed with right eye dominant by Gündoan method and rest of 26 were assessed with left eye dominant. According to McManus method, 36 subjects were assessed as they had left eye dominant, but among those only 22 subjects assessed with left eye dominant according to Gündoan test method. The rest of 14 subjects assessed as they had right eye dominant. According to Gündoan test 62 subject were found with right eye dominance, 48 subjects were found with left eye dominant (Table 3).
In males, 54 subjects were found with right eye dominant and 15 subjects were found with left eye dominant by McManus test. But only 41 subjects of 54 subjects were assessed with right eye dominant by Gündoan method and rest of 13 were assessed with left eye dominant. According to McManus[15] method, 15 subjects were assessed as they had left eye dominant, but among those only 8 subjects assessed with left eye dominant according to Gündoan test method. The rest of 7 subjects assessed as they had right eye dominant. According to Gündoan test, 48 subjects were found with right eye dominance, 21 subjects were found with left eye dominant ( Table 4).
DISCUSSION
Ocular dominance was determined by means of the nearfar alignment test [16]. In this test the subject is asked to hold a pencil in one hand directly in front of himor herself. Then the subject is asked to align the tip with a point on distant wall with both eyes open. The subject is then asked alternatively to close one eye. Only when dominant eye is open and the other eye closed will the tip of pencil remain in good alignment with the point on the wall. The rest is repeated with the pencil in other hand [16, 17]. When in doubt a variant of the test another test method was administered, in which the subject is asked to focus on a point on distant wall through a hole formed by the opposed thumb and index finger of one hand then the hand is moved toward the face while focusing on the same point, until one of the eyes is reached, which indicates the dominant eye [18, 19]. Holding a pencil in hand or forming a hole by two fingers eye dominance can be contaminated by handedness.
On the other hand during monocular activities for assessing dominant eye holding some objects by hands, for instance observing the eye used to sight down a rifle may produce a spurious association with handedness due to the rifle typically being held with a finger of dominant hand on the trigger. Similarly looking through a small object such as kaleidoscope or bottle which is held in one hand, then the holding of object in dominant hand may well distort measures of association between handedness and eye dominance [10,15]. These methodological insufficiencies for detecting dominant eye were caused errors by hand use contamination. For this reason these methods were modified by Gündoan with restricting hand movements all through the tests (Figure 2). More over we add centimeter schedules on the two sides of NP which were gave us opportunity to have objective and measurable results for diagnosis of dominant eye (Figure 1B, Figure 2B).
Table 1The descriptive analyses(minmax)cm for measurements of shifting distance between two reference points for both eyes（略）
Table 2 Without gender difference dominant eye results for two methods were compared（略）
Table 3 Dominant eye results of two methods were compared for female subjects（略）
Table 4 Dominant eye results of two methods were compared for male subjects（略）
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