Research Article| Volume 43, ISSUE 4, P333-337, August 2020

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Characterisation of internal, refractive, and corneal astigmatism in a UK university student population

Published:February 22, 2020DOI:


      • This study presents new data on refractive error components: corneal, refractive and internal astigmatism, in a group of young UK based adults.
      • A weak, but significant correlation is noted for both axial length and MSE, with both internal and refractive (total) astigmatic components of J45, i.e. oblique astigmatism.



      There is a clear benefit in defining internal (IA) and corneal astigmatic error (CA) prior to surgical and other refractive interventions, such as orthokeratology, to minimise risk of unsatisfactory refractive outcomes. Such data would also be of relevance to broader areas of ophthalmic care such as spectacle dispensing and other types of rigid lens fitting. This study offers a detailed characterisation of astigmatic error in a group of university students and specifically investigates compensation of corneal astigmatism by the eye’s internal optics.


      For 176 young-adult participants, objective measurements of refractive error were obtained using the open-view Grand Seiko WAM-5500 autorefractor; corneal curvature and axial length were measured using the Aladdin biometer. Clinical measurements of corneal and refractive astigmatism were converted into vector components J0 and J45; followed by an assessment of corneal astigmatism compensation.


      Mean total refractive astigmatism (RA), CA, and IA were 0.24 ± 0.32D, 0.46 ± 0.27D and -0.21 ± 0.25D respectively for J0 and -0.05 ± 0.20D, 0.01 ± 0.16D, and -0.06 ± 0.18D for J45. Significant linear correlations were noted between RA, CA, and IA for both J0 and J45 (P < 0.01). A significant linear regression was also noted between axial length and J45 RA and IA, but not CA. Levels of full compensation were low, 7% and 9% for J0 and J45 respectively, however, a complete absence of compensation was also uncommon particularly for J45 (2%).


      In general, partial compensation for corneal astigmatism by the eye’s internal optics is noted, but it is unclear whether this is an active compensatory mechanism. Further, larger scale, studies would be required to characterise differences in corneal astigmatic compensation with respect to ethnicity.


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