The Study Of Astigmatism With Accommodation

ObjectiveTo analyze the existence of astigmatism with accommodation and its change tendency by comparing the astigmatism among different level of accommodation. To analyze the different effect on different kinds and different degree of astigmatism, to find out the possible mechanism of accommodative astigmatism. To study the possible effect of astigmatism with accommodation on near vision work by comparing the distance corrected vision acuity and accommodative astigmatism corrected near vision acuity. To find out a proper and easy handing way to measure the near astigmatism.Methods166university volunteer students,166astigmatic right eyes, aged18to21years old, were recruited in this study. They were divided in two different ways (1) according to the kinds of astigmatism, into with-the-rule, against-the-rule and oblique astigmatism, and (2) according to the degree of astigmatism, into less than0.50D, between0.50D and1.00D, and more than1.00D.43university volunteer students, with a difference of spherical refractive error less1.00D and astigmatism less than0.50D between two eyes, were recruited to analyze the difference of accommodation and accommodative astigmatism between two eyes.1.The corneal curvature radius and corneal diopter were measured by kerotometer.2.The refraction of166astigmatic eyes were measured at distance (at5m).3.The amplitude of accommodation and accommodative facility wear measured by push-up technique and±2.00D flipper respectively. The lag of accommodation was measured by FCC, with cross pattern chart.4.The distance corrected near vision acuity in40cm(DCNVA1)was measured with distance-corrected glasses.5.The astigmatism at near (at40cm) was measured under monocular condition with cross-cylinder lenses, with the tested eye looking straight ahead at the line of its best corrected vision acuity in near vision chart.6.The accommodative astigmatism corrected near vision acuity in40cm(ACNVA1) was measured with near-corrected glasses in40cm,using near vision chart. 7.The distance corrected near vision acuity in20cm(DCNVA2), the astigmatism at40cm and the accommodative astigmatism corrected near vision acuity in20cm (ACNVA2)were measured the same way as step4to6.8.The degree of astigmatism between each two of the three different distances, the axis of astigmatism between each two of the three different distances, DCNVA vs ACNVA at40cm and20cm, the accommodative astigmatism and the change of near vision acuity between two eyes of43subjects were compared by paired t-test respectively if the data is normal distribution, if not, compared by Wilcoxon matched-pairs signed-ranks test. Analyze the association between the accommodative astigmatism and corneal astigmatism, residual astigmatism, lag of accommodation, amplitude of accommodation and accommodative facility.Results1.The degree of astigmatism with accommodation was increased significantly as follow order:fixating at20cm,40cm and distance.(Z=-5.316, P<0.0167; Z=-5.672, P<0.0167; Z=-2.463;P<0.0167respectively);2.The axis of astigmatism showed no statistical significance among different level of accommodation(t=0.905;P=0.367(5m-40cm);r=0.403, P=0.688(5m-20cm);t=0.485, P=0.629(20cm-40cm));3.The near vision acuity when fixing at40cm and20cm were both increased significantly when accommodative astigmatism corrected(Z=-5.741,P<0.01; Z=-6.848,P<0.01,respectively);4.The with-the-rule and oblique astigmatism group have the same tendency as the all subjects. The degree of astigmatism with accommodation was significantly increased (Z=-4.252, P<0.0167; Z=-3.983, P<0.0167; Z=-2.586, P<0.0167respectively for with-the-rule astigmatism group; and Z=-2.685,P<0.0167;Z=-2.869,P<0.0167; Z=-2.568,P<0.0167respectively for oblique astigmatism group).The near vision acuity when fixing at40cm and20cm were both increased significantly when accommodative astigmatism corrected (Z=-3.575, P<0.01; Z=-5.432, P<0.01respectively with-the-rule astigmatism group;and Z=-3.571,P<0.01;Z=-2.954,P<0.01respectively for oblique astigmatism group).However, there is no significant difference in against-the-rule astigmatism group(t=-0.224,P>0.05; t=2.016,P>0.05; t=-2.37,P>0.05);5.Groups that the astigmatism less than1.00DC had the same tendency as the all subjects. The degree of astigmatism with accommodation was significantly increased (Z=-3.437,P<0.0167; Z=-5.416,P<0.0167; Z=-2.553,P<0.0167respectively for group with astigmatism less than0.50DC;and Z=-2.690,P<0.0167; Z=-2.737,P<0.0167; Z=-2.450,P<0.0167respectively for group with astigmatism between0.50DC and1.00DC). The near vision acuity when fixing at40cm and20cm were both increased significantly when accommodative astigmatism corrected (Z=-3.198, P<0.01; Z=-5.150,P<0.01respectively for group with astigmatism less than0.50DC;and Z=-3.510,P<0.01; Z=-4.656,P<0.01group with astigmatism between0.50DC and1.00DC).However, there is no significant difference in group with more than1.00DC astigmatism(Z=-1.848,P>0.05;t=-1.406,P>0.05;Z=-1.717,P>0.05);6.Astigmatism changes showed no significant difference between two eyes(Z=-1.024,P>0.05(40cm-5m);Z=-0.198,i>>0.05(20cm-5m);Z=-0.728,P>0.05(20c m-40cm)).Conclusion1.The power of accommodation are not the same in all meridians of the eyes;2.A change in astigmatism with accommodation does indeed exist, the degree of astigmatism has a tendency of increasing with accommodation., especially for those who had with-the-rule and oblique astigmatism and astigmatism less than1.00DC. But it may be various among individual;3.The changes of astigmatism with accommodation sometimes affects near vision work;4.The astigmatism with accommodation may be the same between two eyes in the same person;5.Using cross-cylinder lenses may be a good method to measure near astigmatism.