Distribution of axial, corneal, and combined ametropia in a refractive surgery unit.

PURPOSE: To group eyes in our refractive surgery unit on the basis of the origin of their ametropia and to assess the percentage of eyes in the different groups.
METHODS: Refractive parameters and the axial eye length (AL) of 131 eyes of 131 persons with different refraction were measured. The eyes were initially classified into five groups on the basis of the grade of their ametropia: hypermetropic (> +0.5 D, n = 35), emmetropic (between +/- 0.5 D, n = 24), low myopic (between -0.75 and -4.0 D, n = 24), medium myopic (between -4.25 and -8.0 D, n = 24), and high myopic (over -8.0 D, n = 24). Then a classification scheme was made to group the origin of the ametropia on the basis of AL and corneal refractive power.
RESULTS: In the hypermetropic group pure corneal origin was found in 8.6%, pure axial origin in 62.8%, and combined origin in 28.6% of the eyes. In the low myopic group these values were 20.9%, 29.2%, and 45.8%, respectively. In the medium and high myopic groups no pure corneal myopia was found, while axial myopia was found in 16.7% and combined myopia in 83.3% of the eyes.
CONCLUSIONS: With the help of the classification scheme, an objective decision could be made as to whether the ametropia of a particular eye had axial, corneal, or mixed origin. The most interesting result was that in 83% of medium and high myopic eyes not only AL but also corneal refractive power contributed to the refractive error instead of the eyes being purely axially myopic.