Abstract
Purpose: :
To investigate the influence of microfluctuations of accommodation upon the characteristics of the dynamic accommodation step response.
Methods: :
20 subjects (10 emmetropes and 10 myopes) participated with informed consent in the experiment. The mean age of the subjects was 23.2±2.6 years and the mean spherical refractive error ranged from -4.00DS to +0.50DS. Cylindrical correction was ≤0.75DC and VA was ≤0.0 logMAR or better in all subjects. Subjects viewed sinusoidal gratings (0.5, 4 and 16 c/deg) in a Badal optical system at vergence levels of 1D and 4D achieved using a beamsplitter. Dynamic accommodation recordings were made with a modified Shin-Nippon SRW-5000 infrared autorefractor. Subjects made 10 accommodation step responses in each direction and mean step response characteristics were calculated. Accommodation microfluctuations were obtained from 2 minute recordings of the static accommodation response to the 1D target and an average rms calculated.
Results: :
In all subjects, the rms of the accommodation microfluctuations was smallest for the 4 c/deg grating and was significantly larger for both the 0.5 c/deg (p<0.01) and the 16 c/deg (p<0.01) gratings. The rms was significantly greater (p<0.01) in the myopic group at all spatial frequencies. The rms was significantly positively correlated with the accommodation step response latency (r=0.38, p<0.01). The rms was significantly negatively correlated with accommodation step response amplitude (r=-0.43, p<0.01) and also significantly negatively correlated with accommodation step response duration (r=-0.40. p<0.01).
Conclusions: :
Increases in the magnitude of the accommodation microfluctuations are correlated with reductions in the quality of accommodation step responses. The relationship between microfluctuations and step response dynamics is consistent with the negative feedback model of accommodation response control. These findings suggest that the accommodation microfluctuations are intrinsically related to the dead space component in accommodation response control.
Keywords: accomodation • ocular motor control • myopia