Highlights
- •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.
Abstract
Purpose
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.
Methods
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.
Results
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%).
Conclusions
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.
Keywords
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Article info
Publication history
Published online: February 22, 2020
Accepted:
February 12,
2020
Received in revised form:
December 4,
2019
Received:
May 22,
2019
Identification
Copyright
© 2020 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
