Investigations on the prevalence of axial and refractive anisometropia

Purpose
The aim of this paper was to describe the prevalence of axial and refractive anisometropia among students 18 years old.

Material and methods
The study was carried out among high school students 18 years old in Szczecin, Poland. A total of 1040 students including 381 boys and 659 girls were examined. Every student underwent retinoscopy after cycloplegia using 1% Tropicamide. The differences in spherical equivalents in the right and left eye, were calculated. Students who had anisometropia >1.00 Dsph, were qualified to the next part of the studies, in which examinations using an autorefractometer, keratometer, biometric ultrasounds as well as the IOL Master were carried out. In the group of 70 students (which makes up 7% of the examined population), qualified to the next part of the examinations, a total of 20 participants (2%) declined. The remaining 50 students (5%) were divided into two groups. One group consisted of students with axial anisometropia, while the other consisted of students with refractive anisometropia. All of the collected data were stored in an electronic database using the Microsoft EXCEL computer program and analyzed with Statistica 6.1 software. In the analysis of nominal variables the Fisher exact test was used. P values of less than 0.05 were considered statistically significant.

Results
In the conducted studies a higher prevalence of axial anisometropia (60%) compared to refractive anisometropia (40%) was observed, but the difference did not reach statistical significance (p = 0.20). No association between the type of anisometropia and gender was found in the studies. Axial anisometropia was found in 60% of boys and girls in the study group qualified to the second part of the examinations, while refractive anisometropia was found in 40% of boys and girls qualified to the next part of the examinations.

Conclusions
Anisometropia in students 18 years old is caused more often by different axial length rather than by different refraction of the eye.