A model for emmetropization: predicting the progression of ametropia.

The response of a second-order feedback system is used to describe the controlling process that regulates the refraction of the human eye to achieve optimal visual acuity over the years (emmetropization). From data collected in past refractions, the equation of the feedback system has been derived for individual eyes and used to predict changes in their refraction with age with an accuracy of 0.50 diopters for 89.1% of the eyes tested. If the model is applied to other populations, the root mean square error of prediction will be between 0.20 and 0.36 diopters with a 95% degree of confidence. The model indicates that corrective lenses applied to the eyes, especially in the early years of life, will cheat the servo system and defeat the emmetropization process.