In normal people, the length of the eye axis is around 16mm at birth, and from birth to about 2 years of age, the eye axis grows at about 0.6mm per year. Between the ages of 2 and 3 years, the growth rate is around 0.5mm. Between the ages of 3 and 12, the growth rate is around 0.3mm; between the ages of 12 and 15, the growth rate is around 0.2mm. Between the ages of 15 and 18, the growth rate is around 0.1 to 0.2. It is normal for a normal person to have an eye axis length of about 24mm by about 18 years of age. The eye axis length is also combined with the curvature of the cornea to determine if it is orthokeratology. If the eye axis increases by 300 degrees for every 1mm, myopia will increase.