The accommodation microfluctuations are thought to be used by the accommodation controller to obtain information about the direction and magnitude of the required response by monitoring changes in the contrast gradient of this image. The contrast gradient can be altered by presenting different spatial frequency (SF) targets to the eye. Twelve myopes (MYOs) and 12 emmetropes (EMMs) viewed sine and square wave targets of SF 0.5, 1, 2, 4, 8, 16 cpd in a Badal optical system. Accommodation responses were recorded continuously using the Shin-Nippon SRW-5000 autorefractor. There is no change in magnitude of the accommodation microfluctuations as the SF of square waves is altered. While viewing sine wave targets, the microfluctuations are smallest for mid (2, 4 cpd) SFs and increase for low (0.5 cpd) and high (16 cpd) SFs. MYOs show a significantly larger increase in the microfluctuations for the 16 cpd target compared to the EMMs. MYOs have significantly larger microfluctuations than the EMMs throughout. The microfluctuations seem to be monitoring the contrast gradient of the cortical image, which is likely to be used by the accommodation control system during error detection. The results indicate that MYO subjects may have a shallower contrast gradient and the potential reasons and implications of this are discussed.

^{2}, whereupon it becomes progressively shallower (Day et al., 2009a). The shallower contrast gradient available at luminances ≤0.002 cd/m

^{2}is caused by a reduction in the SF content available to the accommodation error detector (Day et al., 2009a). Accommodation microfluctuations are found to increase in magnitude at these lower luminance levels, and it is thought that the microfluctuations increase because larger changes in focus are required to produce alterations in the contrast gradient detectable by the accommodation controller (Day et al., 2009a; Gray et al., 1993b).

^{2}, can be ignored (Day et al., 2009a).

*SD*age: 21 ± 2.12 years) adult volunteers participated in the study. All subjects had ≤0.50 D of astigmatism, no ocular or systemic disease and 0.0 logMAR visual acuity or better. All subjects gave informed consent and the study was approved by the Glasgow Caledonian University, School of Life Sciences ethics committee and was conducted in accordance with the Declaration of Helsinki.

*t*

_{22}= −1.693,

*p*= 0.120) and there was a significant difference in MSE between the two groups (t-test

*t*

_{22}= 5.812,

*p*< 0.001).

Refractive Group | EMMs | MYOs |
---|---|---|

Number of subjects | 12 | 12 |

Age (years) | 20.6 ± 1.9 | 21.4 ± 2.4 |

Age of myopia onset (years) | N/A | 11.6 ± 3.7 |

MSE (D) | −0.08 ± 0.59 | −3.27 ± 1.72 |

^{2}) with SFs of 0.5, 1, 2, 4, 8 and 16 cpd ( Figure 1). Targets were presented to the subjects in a random order with a break of at least 3 minutes between conditions so that retinal adaptation effects were minimized. Ten static measurements were taken for each condition and an average of these was used to plot the accommodation response function.

*F*

_{5, 66}= 0.421,

*p*= 0.832; Sin, MYOs: ANOVA,

*F*

_{5, 66}= 0.300,

*p*= 0.911; Square, EMMs: ANOVA,

*F*

_{5, 66}= 0.278,

*p*= 0.923; Square, MYOs: ANOVA,

*F*

_{5, 66}= 0.293,

*p*= 0.915). Additionally there was no significant difference in static accommodation response between sine and square wave targets of the same SF (ANOVA,

*F*

_{1, 264}= 0.170,

*p*= 0.681), nor between refractive groups (ANOVA,

*F*

_{1, 264}= 1.102,

*p*= 0.295).

*F*

_{5, 72}= 1.301,

*p*= 0.277; MYOs: ANOVA,

*F*

_{5, 72}= 0.413,

*p*= 0.838). The rms values are significantly larger in the MYOs than the EMMs (ANOVA,

*F*

_{51 144}= 42.160,

*p*< 0.001).

*F*

_{5, 144}= 7.528,

*p*< 0.001). The microfluctuations are significantly larger while viewing both the 0.5 and 16 cpd targets than when viewing the 2 and 4 cpd targets (Scheffe post hoc,

*p*< 0.015 for all comparisons).

*F*

_{1, 144}= 99.683,

*p*< 0.001). Both refractive groups have a significant variation in the size of the microfluctuations as SF changes (EMMs: ANOVA,

*F*

_{5, 72}= 5.919,

*p*< 0.001; MYOs: ANOVA,

*F*

_{5, 72}= 5.663,

*p*< 0.001). EMMs have significantly larger microfluctuations when the target SF is 0.5 cpd compared to the 2, 4 and 8 cpd targets (Scheffe post hoc,

*p*< 0.02 for all three comparisons). MYOs have significantly larger microfluctuations when viewing the 0.5 cpd target than viewing the 4 cpd target, while the 16 cpd target results in significantly larger microfluctuations than the 2 and 4 cpd targets (Scheffe post hoc,

*p*< 0.04 for all 3 comparisons). For each target SF, the increase in the microfluctuations compared to that while viewing the 4 cpd target was calculated, since this SF produced the smallest microfluctuations. MYOs have a significantly larger increase in the magnitude of the microfluctuations than the EMMs when viewing the 16 cpd target (t-test,

*t*

_{22}= −2.259,

*p*< 0.05), while there is no significant difference between the refractive groups for the other SFs.

*F*

_{5, 72}= 0.730,

*p*= 0.604; LFC, MYOs: ANOVA,

*F*

_{5, 72}= 0.601,

*p*= 0.699; MFC, EMMs: ANOVA,

*F*

_{5, 72}= 0.500,

*p*= 0.775; MFC, MYOs: ANOVA,

*F*

_{5, 72}= 0.824,

*p*= 0.538; HFC, EMMs: ANOVA,

*F*

_{5, 72}= 0.331,

*p*= 0.892; HFC, MYOs: ANOVA,

*F*

_{5, 72}= 1.050,

*p*= 0.398). There was a significant difference in power between the frequency components (ANOVA,

*F*

_{2, 432}= 102.539,

*p*< 0.001), with the LFC having significantly greater power than the MFC and HFC (Scheffe post hoc,

*p*< 0.001 for both comparisons). There was no significant difference in power between the MFC and HFC (Scheffe post hoc,

*p*= 0.327).

*F*

_{5, 72}= 3.595,

*p*< 0.01) and the MYOs (ANOVA,

*F*

_{5, 72}= 3.478,

*p*< 0.01) with varying SF, but no significant change in the MFC (EMMs: ANOVA,

*F*

_{5, 72}= 2.055,

*p*= 0.085; MYOs: ANOVA,

*F*

_{5, 72}= 0.616,

*p*= 0.688) or HFC (EMMs: ANOVA,

*F*

_{5, 72}= 1.447,

*p*= 0.222; MYOs: ANOVA,

*F*

_{5, 72}= 1.027,

*p*= 0.411). There was a significant difference in power between the frequency components (ANOVA,

*F*

_{2, 432}= 102.141,

*p*< 0.001), with the LFC having significantly greater power than the MFC and HFC (Scheffe post hoc,

*p*< 0.001 for both comparisons). There was no significant difference in power between the MFC and HFC (Scheffe post hoc,

*p*= 0.134).