The relationship between object spatial profile and accommodation microfluctuations in emmetropes and myopes

Abstract

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.

Netra

“…According to our experiments, sinusoidal patterns are the most appropriate for inducing accommodation changes with our system, and we project a 1D sinusoid along the axis of the cylindrical power for those with astigmatism. These observations seem to be supported by findings in the opthalmology literature [Day et al 2009]. We used our system to project a sinusoidal pattern at various distances from the viewers, who were asked to focus at the pattern.…”

Optical mechanisms regulating emmetropisation and refractive errors: evidence from animal models

“…On the other hand, chicks demonstrate both corneal and lenticular accommodation . Characteristics of accommodation that have been linked to emmetropisation and myopia include accommodative microfluctuations, accommodative lag, tonic accommodation, and blur interpretation…”

Visual discomfort and blur

“…This could be tested directly by measuring accommodative responses using an autorefractor. Stimuli that are less informative for the accommodative system might lead to greater uncertainty in the accommodative response; it would be predicted that this would lead to increased microfluctuations (Day et al, 2009). If an impoverished signal for accommodation is responsible for discomfort, this could be for at least two reasons.…”

“…MacKenzie et al (2010) have argued that the global amplitude of spatial frequency information is critical for driving accommodation responses: they consider only the Fourier amplitude spectrum in their model of how stimulus spatial frequency content affects accommodation responses. By contrast, Day, Gray, Seidel, and Strang (2009) make the case that the critical information for accommodation responses is contained in the steepness of the luminance gradients. It has been suggested that coarse accommodation responses might be driven by the low spatial frequencies, which are then refined by using the higher ones (Charman, 1979).…”

“…This is important as the insufficient high spatial frequency information in some stimuli might provide inadequate information to drive accommodation. Inadequate information for the accommodative system could potentially leading to uncertainty in the response, which could manifest itself as increased microfluctuations (Day et al, 2009), for example. Increased microfluctuations could potentially cause discomfort directly from muscle fatigue.…”