Enantiomorphism and Rule Similarity in the Astigmatism Axes of Fellow Eyes: A Population-Based Study; [Enantiomorfismo Y Similitud De La Regla En Los Ejes Del Astigmatismo En Ojos Contralaterales: Estudio Poblacional] Publisher Pubmed



Hashemi H¹ ; Asharlous A² ; Yekta A³ ; Ostadimoghaddam H⁴ ; Mohebi M⁵ ; Aghamirsalim M⁶ ; Khabazkhoob M⁷
Source: Journal of Optometry Published:2019

Abstract

Purpose: To evaluate the relationship patterns between astigmatism axes of fellow eyes (rule similarity and symmetry) and to determine the prevalence of each pattern in the studied population. Methods: This population-based study was conducted in 2015 in Iran. All participants had tests for visual acuity, objective refraction, subjective refraction (if cooperative), and assessment of eye health at the slit-lamp. Axis symmetry was based on two different patterns: direct (equal axes) and mirror (mirror image symmetry) or enantiomorphism. Bilateral astigmatism was classified as isorule if fellow eyes had the same orientation (e.g. both eyes were with-the-rule) and as anisorule if otherwise. Results: Of the total cases of bilateral astigmatism, 80% were isorule, and in the studied population, the prevalence of isorule and anisorule astigmatism was 14.89% and 3.53%, respectively. The prevalence of isorule increased with age (p < 0.001). The prevalence of both isorule and anisorule increased at higher degrees of spherical ametropia (p < 0.001). Median inter-ocular axis difference was 10° in mirror symmetry and 20° in direct symmetry with no significant difference between two genders (p > 0.288). Both symmetry patterns reduced with age (p < 0.001). Among cases of bilateral astigmatism, 15.5% and 19.8% had exact direct and mirror symmetry, respectively. Conclusion: Bilateral astigmatism is mainly isorule in the population and anisorule astigmatism is rare. The enantiomorphism is the most common pattern in the population of bilateral astigmatism. © 2018 Spanish General Council of Optometry