Wavelength Defocus and Temporal Sensitivity Affect Refractive Development in Guinea Pigs

Abstract

PURPOSE. Environmental light plays an important role in the process of emmetropization. This study investigated how the retina integrates wavelength and temporal signals to regulate eye emmetropization. METHODS. Guinea pigs (n ¼ 220) were randomly divided into 11 groups (n ¼ 20/group) that received different environmental lighting (12:12 light cycle) for 8 weeks: white, green, or blue light at steady, 0.5 or 20 Hz. White-steady group was repeated for each wavelength. Refraction, axial length, and corneal curvature were measured using streak retinoscopy, Ascan ultrasonography, and keratometry, respectively, every 2 weeks. RESULTS. (1) In white light, the white-0.5 Hz group was more myopic than the white-steady group or the white-20 Hz group (both P < 0.0001), with a longer axial length (both P < 0.0001). White-20 Hz did not significantly differ from white-steady. (2) At low temporal frequencies (0 and 0.5 Hz), green-steady (P ¼ 0.0008) and green-0.5 Hz (P < 0.0001), were more myopic than the white-steady group, with longer axial lengths (both P < 0.0001). No significant difference was found between green-0.5 Hz and green-steady. Blue-steady and blue-0.5 Hz were more hyperopic than white-steady (both P < 0.0001), with shorter axial lengths (both P < 0.0001). Blue-0.5 Hz showed no significant difference from blue-steady. (3) At high temporal frequencies (20 Hz), green-20 Hz, was more hyperopic than green-steady or green-0.5 Hz (both P < 0.0001) and had a shorter axial length (both P < 0.0001). Green-20 Hz showed a 1.10 D hyperopic shift compared to green-steady. Blue-20 Hz was less hyperopic than blue-steady (P < 0.0001) or blue-0.5 Hz (P ¼ 0.0012), with a longer axial length (both P < 0.0001). Blue-20 Hz showed a 1.18 D myopic shift compared to blue-steady. CONCLUSIONS. Eyes use both wavelength and temporal frequency of light to regulate emmetropization. Their interactions provide different cues to control eye growth. At low temporal frequencies, the eye can use wavelength defocus to guide eye growth. This signal is weakened at high temporal frequencies.

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

“…The signal at low frequencies may reach deeper levels of the anterior chamber, increasing the secretion and slowing down the outflow of fluid in the eye [ 36 ]. Our study showed that VAR at low frequencies are larger than those at high frequencies, and the colour effect is only significant at low frequencies, which is in agreement with the results obtained in animal studies [ 9 , 10 ]. These animal studies showed that colour played a more important role at low temporal frequencies than for high ones, which is an important clue for emmetropisation [ 9 , 10 ].…”

“…Our study showed that VAR at low frequencies are larger than those at high frequencies, and the colour effect is only significant at low frequencies, which is in agreement with the results obtained in animal studies [ 9 , 10 ]. These animal studies showed that colour played a more important role at low temporal frequencies than for high ones, which is an important clue for emmetropisation [ 9 , 10 ]. For high frequencies, eyes may not be fast enough to accommodate accurately after colour flickers.…”

“…Pictures change quickly in videos on the colourful screen and colourful lights shifted quickly in some places like concerts or bars are some kinds of flickering light. Animal studies have demonstrated a significant effect of colour flickers on refractive development, indicating that the eyes sense colour and temporal frequency of flickering light and use them as developmental cues [ 8 – 10 ].…”

“…Colour flickers in our daily life may play a role in myopia development and progression, which has been implicated by animal studies [ 8 – 10 ]. However, very few studies so far focused on the effect of colour flickers on human accommodation, especially in both myopes and emmetropes.…”

The Role of Dopamine in Emmetropization Modulated by Wavelength and Temporal Frequency in Guinea Pigs

“…This flattening effect induces myopic shifts in guinea pigs exposed to blue light and hyperopic shifts in those exposed to green light, as compared with those of corresponding steady conditions. 37 In particular, we were interested in whether retinal DA plays a role in these light responses.…”