Orthokeratology Necessitates Ocular Residual Astigmatism Assessment

The prevalence and magnitude of ocular residual astigmatism (ORA) is high in children with myopia and predominantly compensates for anterior corneal astigmatism (ACA), according to a study published in BMC Ophthalmology. These findings suggest that ORA should be measured prior to initiating orthokeratology treatment in order to ensure it is corrected. 

Researchers enrolled 241 children with low or moderate myopia (42% girls, mean [SD] age, 11.8 [2.2] years) in a cross-sectional study to assess the correlation between ORA and ACA. Participants completed a subjective refraction to determine refractive astigmatism and biometry to determine ACA. ORA was calculated through Thibos vector analysis. A correlation analysis was used to assess the association between ORA and ACA.

According to the report, the median magnitude of ocular residual astigmatism was 1.02 diopters (D), with an interquartile range of 0.58 D. Against-the-rule ORA was observed in 232 eyes (96.3%) and investigators noted a significant and moderate correlation between ORA and ACA (r=0.50, P <.001). 

ORA compensated for ACA in 240 eyes (99.6%) with a mean compensation value of 1.00 D (range, 0.02 – 2.34 D). A total of 37 eyes had a different axial classification of ACA and refractive astigmatism. Only 1 eye (0.4%) exhibited oblique ORA, and the ORA superimposed with-the-rule anterior corneal astigmatism.

Researchers suggest these findings may have implications for orthokeratology lens fitting. “Residual astigmatism might be more problematic than expected if orthokeratology was used,” according to the study authors. “Measuring ORA is equivalent to evaluating residual astigmatism that is not accounted for by the treatment. Therefore, the ORA should be assessed first before the completion of a course of orthokeratology.”