No abstract

Neither the RKT-7700 nor the CT-80 can be used interchangeably with the Goldmann tonometer, although all three tonometers give repeatable measurements of IOP, in this sub-population. IOP differences between GAT and the NCTs significantly correlated with CCT, with the possibility of even greater differences in thicker corneas.

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.

Visual suppression of low-spatial frequency information during eye movements is believed to contribute to a stable perception of our visual environment. While visual perception has been studied extensively during saccades, vergence has been somewhat neglected. Here, we show that convergence eye movements reduce contrast sensitivity to low spatial frequency information around the onset of the eye movements, but do not affect sensitivity to higher spatial frequencies. This suggests that visual suppression elicited by convergence eye movements may have the same temporal and spatial characteristics as saccadic suppression.

Purpose:  Step changes in accommodation from distance to near take approximately 500 ms, during which time it is uncertain what visual information we perceive. A process of visual suppression seems to occur as we do not notice any blurring. In the present study we examine the visual processing capabilities by measuring contrast sensitivity during accommodation responses. Methods:  Contrast thresholds were measured for two viewing conditions (dynamic and static) using a 2‐alternative forced‐choice staircase procedure. Sinusoidal [1, 4 cycles per degree (cpd)] and square wave (9 cpd) gratings were presented on a monitor at 1 m for the duration of 26 ms. In the dynamic condition a 2 dioptre (1–3D) far to near accommodation step response (ASR) was induced while contrast threshold measurements were taken every 100 ms after onset of the ASR. Results were compared to measurements taken in the static condition, where steady state accommodation responses were induced for five stimulus distances ranging from 1 m–33 cm. Results:  We found that contrast sensitivity in the high spatial frequency condition (9 cpd) was significantly reduced in dynamic compared with static conditions. Differences found between the dynamic and static thresholds at low and mid spatial frequencies (1, 4 cpd) were inconsistent. Conclusion:  The results suggest that the visual system employs high spatial frequency suppression during ASRs in order to minimize blur. These findings support a theory of oculomotor control in which the various oculomotor subsystems have both fast and slow components. The fast component exhibits pre‐programming and suppression of fine spatial detail, while the slow component shows continuous feedback control.