Axial length reduction and choroidal thickening with short-term exposure to cyan light in human subjects

ZEISS Young Investigator Award in myopia research and Josh Wallman Memorial Lecture. Understanding Myopia Development

In this paper, three key questions regarding our understanding of myopia are addressed: predictors of myopia onset, the mechanism underlying its development and potential treatments to slow its progression. To explore these aspects, first, a non-invasive biomarker using the chicken model of myopia was investigated. A strong correlation was found between myopia development and both increased ultraviolet (UV) fundus reflectivity and thinning of the retinal nerve fibre layer (RNFL). Through electron microscopy, it was observed that, within hours of vision deprivation, significant thinning of the myelin sheaths around large axons in the RNFL occurred, accompanied by an increase in UV fundus reflectivity-changes that took place even before eye elongation. These findings suggest that early myelin degradation contributes to myopia development and may serve as a predictive biomarker in the animal model. However, the prediction of myopia onset in humans remains challenging. To investigate the mechanism of myopia development further, visual stimuli affecting emmetropic and myopic eyes differently were examined. The results indicated that myopic eyes have weaker responses to positive defocus and short-term stimulation to simulated chromatic aberrations when compared with emmetropic eyes, suggesting a possible impairment in retinal signalling pathways responsible for detecting blur and defocus. In terms of treatment, it was found that reading large text with inverted contrast (bright letters on a dark background) induced axial length shortening and choroidal thickening in both emmetropic and myopic eyes. Furthermore, repeated exposure to digitally simulated myopic chromatic defocus was shown to reduce axial length and increase choroidal thickness effectively in myopic human subjects. These findings align with results from animal models and indicate that this approach may serve as a potential strategy for myopia control. However, more research is necessary to establish an effective myopia control intervention suitable for children and adolescents.