Abstract
During the first years of life the eye grows tremendously, while simultaneously reducing the mean ocular refraction by carefully adjusting the growth speed of the eye globe, cornea, and crystalline lens. This process is called emmetropization and takes place during the first 2–3 years of life. Next, homeostasis occurs, during which eye growth continues while maintain the near-emmetropic refractive error through a combination of scaled growth and active feedback mechanisms. Failure of homeostasis will lead to excessive axial growth and myopia, which causes the retinal image to be out of focus. Animal experiments demonstrated that eye growth involves a delicate interaction between optical and sensory components to provide retinal image clarity throughout life. So, emmetropization is the active, visually guided mechanism whereby the axial length and the combined optical powers of the cornea and lens precisely match with each other to eliminate neonatal refractive errors. Many reports on ocular growth have been published, these are often for a limited age range. Our group recently published a complete overview of normal ocular growth before birth until 18 years of age. Similarly, there are descriptive models for eye growth in the literature, but a quantitative model for the mechanisms of eye growth is currently lacking.
This project aims to model the changes of the ocular components involved in visually guided eye growth using differential equations, consisting of two exponential terms representing the scaled growth before birth and the growth with active feedback after birth.
Besides, we work on estimating the influence of variations in optical parameters on variations in refractive error using the error propagation method. Moreover, we explore how the parameters of bi-exponential functions can be adjusted to simulate various known refractive development courses described in the literature, such as instant emmetropization, persistent hypermetropia, myopia, and so on. Additionally, it is known from the literature that myopia development is affected by both retinal defocus and the spectral composition of the ambient light. Both factors are known to affect contrast sensitivity function (CSF). It is becoming increasingly clear that CSF may play a large role in refractive development. We measure the CSF of both emmetropes and myopes to investigate the combined effect of defocus and color band on the CSF. Finally, we aim to modulate the exponential function of eye growth (ODE model) and look for the retina response function by considering some important factors such as the CSF of the human eye, the luminance, and the surrounding illumination.
Objectives: 1. Propose an active model of normal and abnormal refractive development. 2. Estimate the influence of variations in biometric parameters on variations in refractive error. 3. Propose bi-exponential description for different forms of refractive development. 4. Measure the CSF within the red, green, and blue color bands across different levels of defocus. 5. Develop a modulated ODE model by considering retina function.
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