Investigating the mechanisms that may underlie the reduction in contrast sensitivity during dynamic accommodation

Abstract

Head and eye movements, together with ocular accommodation enable us to explore our visual environment. The stability of this environment is maintained during saccadic and vergence eye movements due to reduced contrast sensitivity to low spatial frequency information. Our recent work has revealed a new type of selective reduction of contrast sensitivity to high spatial frequency patterns during the fast phase of dynamic accommodation responses compared with steady-state accommodation. Here were report data which show a strong correlation between the effects of reduced contrast sensitivity during dynamic accommodation and velocity of accommodation responses, elicited by ramp changes in accommodative demand. The results were accounted for by a contrast gain control model of a cortical mechanism for contrast detection during dynamic ocular accommodation. Sensitivity, however, was not altered during attempted accommodation responses in the absence of crystalline-lens changes due to cycloplegia. These findings suggest that contrast sensitivity reduction during dynamic accommodation may be a consequence of cortical inhibition driven by proprioceptive-like signals originating within the ciliary muscle, rather than by corollary discharge signals elicited simultaneously with the motor command to the ciliary muscle.

Accommodation steps, target spatial frequency and refractive error

“…When the target is blurred substantially (≥1.5D), only low SF information will be available to the accommodation control system, as these SFs are less affected by blur 44 . More recent work has suggested that the role of high SF information is limited to final response refinement as high SF information is unlikely to be perceived during the step response 31,45 …”

“…44 More recent work has suggested that the role of high SF information is limited to final response refinement as high SF information is unlikely to be perceived during the step response. 31,45 The use of continuous negative feedback control to maintain an accurate accommodation response level is well established. Our results show that for small changes in accommodation stimulus level, target SF has considerably less effect upon the magnitude of the response, as the system can obtain accurate focusing information from all targets, irrespective of SF.…”

Investigation of the Relationship Between Subjective Symptoms of Visual Fatigue and Visual Functions

“…Our results are consistent with those from previous studies. To illustrate, Muck (Mucke et al, 2010) reported that dynamic accommodation is related with contrast sensitivity at high spatial frequency. The faster the dynamic response, the more reduced the contrast sensitivity for high but not low spatial frequency (Mucke et al, 2010).…”

“…To illustrate, Muck (Mucke et al, 2010) reported that dynamic accommodation is related with contrast sensitivity at high spatial frequency. The faster the dynamic response, the more reduced the contrast sensitivity for high but not low spatial frequency (Mucke et al, 2010). To perform well in an accommodative facility test, individuals should have a good contrast sensitivity for high spatial frequency.…”

The effect of multifocal contact lenses on the dynamic accommodation step response

“…This is expected since it is understood that the accommodation controller initially uses low spatial frequency information within a target to initiate a step response, which is then further refined using high spatial frequency information, which becomes increasingly available as the target becomes less blurred. [76][77][78][79] The vast majority of slow drift was in the correct direction, as shown by the example trace in Figure 8. This was not influenced by CL type, again suggesting that this is a normal AR as opposed to a feature of MFCL viewing.…”