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M.V. Cigada, W. Albisetti, F. Caronni, S. Simonetta, R. Ratiglia; Looking for the Influences of Posture and Dental Occlusions on Eye Movements . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2763.
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Purpose: To analyze whether artificially induced postural positions, modifications in dental occlusions and deglutition, can influence phoria values in healthy subjects. Methods: Far and near, vertical and horizonatal phorias were examinated in 20 healthy subjects (10 males and 10 females) in 6 different conditions: 1. sitting up tilted backwards 2. sitting up straight 3. with tongue between teeth 4. with an asymmetrical thickness (1 cm) clenched between the teeth 5. standing up 6. standing up, body tilted forwards The number of measurements that differed between the following conditions were registered: 1 vs. 2 2 vs. 3 2 vs. 4 2 vs. 5 5 vs. 6 In 5 random subjects all 24 measurements were replicated under the same conditions. The number of variations between the two replications were used as a control. All the data were analyzed with a chi-square test. Phoria was measured by a test frame with a maddox rod glass and a 10 pd prism on the same eye. The prism was rotated while the maddox rod was kept still until the subject saw the correct alignment between the light source and the maddox line. At this point the phoria pd value corresponded to the value of the prism used (10) by the sinus of the angle between the prism axis and the maddox rod. Results: In passing from the seated to the standing position (2 vs.5) and introducing an occlusal imbalance (2 vs. 4), a statistically significant increase in the differences in phoria measurements was noted, compared to the control: (2 vs. 4) 37 diff. meas. on 80 (46 %) control 25 on 120 (20 %) chi-square = 13,33 P<0.01 (2 vs. 5) 35 diff. meas. on 80 (44 %) control 25 on 120 (20 %) chi-square = 10, 94 P<0.01 With tongue protrusion we had a small increase in differences (24 on 80 = 30%), which was not statistically significant. All other comparisons were not statistically significant. We found similar results when analyzing only vertical or only horizontal phorias. All modifications are aspecific: an exophoria can become an esophoria and viceversa, or it can simply increase or decrease in value. Conclusions: Phoria measurement is not indipendent from posture and/or dental occlusions in normal subjects; our data does not give a clear response to deglutition.
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