Background: No study to date has looked into the relationship between ocular biometrics with anisometropia exclusively; therefore, the purpose of this study was to determine the relationship between anisometropia and ocular biometrics.

Methods: In a cross-sectional study with multistage cluster sampling, 6311 people in the 40-64-year-old age group from the population of Shahroud, Iran, were selected. Of these, 5190 people participated in the study. For all participants, tests for visual acuity, cycloplegic and non-cycloplegic refraction, slit lamp test and fundoscopy were performed. All participants underwent biometric examinations using the Allegro Biograph (WaveLight AG, Erlangen, Germany).

Results: Asymmetry of axial length, corneal power, vitreous chamber depth, anterior chamber depth, lens thickness and lens power were significantly more among participants who were anisometropic than those who were non-anisometropic. The correlation of anisometropia with axial length asymmetry was 0.735, 0.273 with corneal power, 0.183 with anterior chamber depth and 0.311 with lens power (p<0.001). In a multiple linear regression model, anisometropia was found to have significant associations with axial length asymmetry (standard coefficient (SC)=0.905), corneal power asymmetry (SC=0.350), lens power asymmetry (SC=0.454), nuclear opacity asymmetry (SC=0.074) and age (SC=0.28) (R(2)=85.1%). According to the linear regression model, corneal power had the strongest association with anisoastigmatism.

Conclusions: Axial length asymmetry has the strongest correlation with anisometropia; nonetheless, other components of ocular biometrics such as corneal power, lens opacity, lens power and anterior chamber depth are related to anisometropia as well. More than 10% of changes in anisometropia can be explained with changes in factors other than asymmetry of ocular biometrics and lens opacity.