Time-averaged accommodation response to flickering stimuli

The effects of colour and temporal frequency of flickering light on variability of the accommodation response in emmetropes and myopes

Background

Myopia is hypothesized to be influenced by environmental light conditions. For example, it has been shown that colour and temporal frequency of flickering light affect emmetropisation in animals. Considering the omnipresence of flickering light in our daily life, we decided to analyze the effect of colour flickers on variability of the accommodation response (VAR) in emmetropes and myopes.

Methods

We measured the dynamic accommodative responses of 19 emmetropic and 22 myopic adults using a Grand Seiko WAM-5500 open-field autorefractor. The subjects focused for more than 20 s on a black Snellen E target against three different backgrounds made up of three colour flicker combinations (red/green, red/blue and blue/green) and under five frequency conditions (0.20 Hz, 0.50 Hz, 1.00 Hz, 1.67 Hz, and 5.00 Hz).

Results

Flicker frequency and colour both had a significant effect on VAR. Lower frequencies were associated with larger variability. Colour had an effect only at low frequencies, and red/blue colour flicker resulted in the largest variability. The variability in myopes were larger than those in emmetropes.

Conclusions

These findings support the hypothesis that further studies on the colour and temporal frequency of flickering light can lead to a better understanding of the development and progression of myopia.

No evidence for prolonged latency of saccadic eye movements due to intermittent light of a CRT computer screen

Despite previous studies it remains unclear, whether saccadic eye movements across computer screens may be adversely affected by the intermittency of light of cathode ray tubes (CRT). We measured the latency of simple saccades to peripheral targets presented on a CRT-screen, operated at refresh rates of 50, 100 and 150 Hz, compared with a special fluorescent lamp display (FLD). Our results suggest that the intermittent light of CRT screens does not prolong the latency of saccades not even relative to a control condition of unmodulated steady light at the FLD. Further, there was no evidence for any individual effect in possibly susceptible subjects, e.g. at high critical flicker frequencies (CFF).

Accommodation, convergence, pupil diameter and eye blinks at a CRT display flickering near fusion limit

This study investigates possible effects of temporally modulated light stimulation near critical fusion frequency (CFF) when subjects observe a cathode ray tube (CRT) operated at different refresh rates. Various visual functions were measured in a series of tests of 2.5 min duration. In experiment 1, at a repetition rate of 50 Hz mean pupil size was 0.055 mm smaller than at 300 Hz. The precision of convergence and accommodation in binocular vision was not affected. In experiment 2, 300 Hz was compared with the lowest frequency that did not produce visible flicker for each subject. At the lower rate (55 to 90 Hz), mean accommodation in monocular vision was 0.06 D weaker, median eye blink duration was 6% shorter, and mean eye blink interval was 15% longer. Individual differences and possible fatigue effects of intermittent light at visual display units are discussed.