Influences of prisms on accommodative response and microfluctuation in emmetropias

How to control progression of myopia is a central issue in clinical optometry.Some clinical trials showed that wearing base-in (BI) prism can slow down progression of myopia to certain degree.However, whether BI prism or base-out (BO) prism should be used is worth discussing.

This study was to investigate the influences of different prisms on accommodative response and microfluctuation in emmetropias.

This clinical trail was approved by Ethic Committee of Peking University People’s Hospital.During July in 2014, twenty-two emmetropias of 22 normal volunteers aged 21-27 years were recruited from Peking University People’s Hospital under the written informed consent.An open-field infrared refractometer was used to monitor and record pupil diameter and accommodative response under three conditions including non-prism, 3^ΔBI prism, and 3^ΔBO prism.The accommodative response value was calculated as the difference between reading value and -3.0 D, and root mean square (RMS) of accommodative response value served as amplitude of accommodative microfluctuation.Spectrum of accommodative response was analyzed by one dimension discrete Fourier transformation.The differences of accommodative response value, amplitude of accommodative microfluctuation and pupil diameter among three conditions were compared using repeated one-way ANOVA.

The accommodative response values were (+ 0.31±0.78), (+ 0.51±0.75) and (+ 0.18±0.72) D under the non-prism, 3^ΔBI prism and 3^ΔBO prism conditions, respectively, with a significant difference among them (F=28.078, P=0.000), and compared with the non-prism condition, the accommodative lag of 3^ΔBI prism condition was increased and that of 3^ΔBO prism condition was reduced (P=0.000, 0.012). No significant difference was found in the amplitude of accommodative microfluctuation among the three conditions (F=0.062, P=0.879）. The percentages of low frequency signal power (0-0.5 Hz）/total power (0-2.5 Hz) was 97.5%, 98.3% and 91.4% under the non-prism, 3^ΔBI prism and 3^ΔBO prism condition, respectively.The pupil diameter was (5.37±0.69) mm under the 3^ΔBI prism condition, which was larger than (5.07±0.66) mm under the non-prism condition and (5.01±0.69) mm under the 3^ΔBO prism condition (both at P=0.000）.

Compared with wearing 3^ΔBI prism, wearing 3^ΔBO prism lessens the accommodative lag, decreases the pupil diameter and reduces the power of low frequency component in accommodative response.