The Investigation Of The AC/A Ratio With Gradient Method In Subject With Normal Binocular Vision

ObjectiveTo evaluate the AC/A ratio measured by Gradient method in subjects with normal binocular vision, why there was a difference in AC/A ratio when measured by Gradient method and distance/near disparity were studied, and why there was a difference when measured AC/A ratio by Gradient method at different visual distance was discussed.Methods65students(25males,40females) aged from23to25studying in Tianjin Medical University from January2012to December2012were recruited for this study. All students had normal binocular vision,no surgical history,no strabismus, no amblyopia, normal eye movement. Visual acuity was correctable to at least20/20in each eye. The refractive difference between the two eye was found to be less than1.00D,while myopia, less than-6.50D and astigmatism less than-2.00D.All of the students had normal near and far stereacuity, normal binocular and monocular accommodative amplitude,normal NRA (+2.25D～+2.5D) when viewed near target.The amplitude of accommodation, PRA and NRA were measured under full refractive correction. Accommodative responses were measured when subjects were viewing distant target(5m) with minus lenses (-1.50D,-2.00D,-2.50D) and viewing near (33cm)target with plus lenses(+1.50D,+2.00D,+2.50D) under binocular and monocular conditions. The accommodative responses were measured when subjects viewed the target at40cm and50cm. Response AC/A ratio and stimulus AC/A ratio were measured by Far-Gradient method with minus lenses (-1.50D,-2.00D,-2.50D) and Near-Gradient method with plus lenses (+1.50D,+2.00D,+2.50D). AC/A ratio was also measured by distance/near disparity. The AC/A ratio measured by different methods and also by the same method but under different visual distance was compared, and a statistical difference was found. ResultsThe binocular amplitude of accommodation was found to be (8.8±2.3)D, while NRA was (2.25±0.23)D and PRA was(6.13±1.78)D. The lag of accommodation were(0.80±0.30)D,(0.87±0.35)D,(0.92±0.44)D when viewed the distant target(5m) under binocular condition with minus lenses-1.50D、-2.00D、-2.50D and no statistical differences were found among the three groups (P=0.09). In the case of near target with plus lenses+1.50D,+2.00D,+2.50D,the lag of accommodation were(0.81±0.23)D,(0.60±0.22)D,(0.37±0.19)D and a statistical difference among the three groups(p=0.00) were found. A statistical difference (P=0.04) was found between the responses of accommodations measured with-2D lens and distant target(1.14±0.36)D and without lens and the target at50cm (1.58±0.26)D under binocular condition. The mean and deviation of the response accommodation was found to be (1.79±0.31) with the target at40cm and was (1.57±0.45) D when using the distance target with-2.5D lens. Thus, a statistical difference (P=0.02) was found. No statistical differences(P>0.05) were found between the responses of accommodations measured with different lenses under binocular and monocular conditions with the distance target(5m).On the country,obvious statistical differences(P<0.05) were found between them when viewed the near target(33cm).The mean±SD of AC/A ratio measured by Gradient method with the distant target(5m) with-2.5D was found to be (1.94±1.09)△/D and the AC/A ratio measured by distance/near disparity was found to be (4.95±1.22) A/D.A statistical differences between them (t=13.54,P=0.00) was found. A statistically difference was observed between the distant stimulus AC/A ratio and the near stimulus AC/A (33cm)(P<0.05)measured by Gradient method, but no difference between the distance response AC/A ratio and the near response AC/A ratio(P>0.05) were found. And no differences among the far stimulus AC/A ratio (P=0.73) and far response AC/A ratio(P=0.35)measured by three different additions were observed, also no differences among the three groups of the near stimulus AC/A ratios(P=0,49) were found, but a statistical difference was showed among the near response AC/A ratio measured with three additions (P=0.04).A positive relationship was found between the response AC/A ratios and the standard deviations of the response AC/A ratios with the distant target (5m) and the near target (33cm).Conclusions1. The AC/A ratio measured by distance/near disparity was found to be larger than which measured by Gradient method, as the proximal accommodation and vergence might have more influence on the AC/A ratio when measured by this method.2. Lag of accommodation may lead to higher response AC/A ratio compared with the stimulus AC/A ratio.3. Lag of accommodation was found to be the main reason for the difference of stimulus AC/A ratio measured by Gradient method when viewed different distance.4. Higher response AC/A ratio might increase the rate of change in response AC/A ratio when measured by Gradient method with different stimulus, which also could be investigated on later.