September 2016
Volume 57, Issue 12
Open Access
ARVO Annual Meeting Abstract  |   September 2016
Validity of prediction models used to determine post-operative corneal shape following cataract surgery.
Author Affiliations & Notes
  • Phillip J Buckhurst
    Plymouth University, Plymouth, United Kingdom
  • Catriona Hamer
    Plymouth University, Plymouth, United Kingdom
  • Hetal Buckhurst
    Plymouth University, Plymouth, United Kingdom
  • Christine Purslow
    Cardiff University, Cardiff, United Kingdom
  • Nabil Habib
    Derriford Hospital, Plymouth, United Kingdom
  • Footnotes
    Commercial Relationships   Phillip Buckhurst, None; Catriona Hamer, None; Hetal Buckhurst, None; Christine Purslow, None; Nabil Habib, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science September 2016, Vol.57, 930. doi:
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      Phillip J Buckhurst, Catriona Hamer, Hetal Buckhurst, Christine Purslow, Nabil Habib; Validity of prediction models used to determine post-operative corneal shape following cataract surgery.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):930.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose : Toric calculators predict the post-operative corneal shape based on the pre-operative corneal power and the surgeon specific surgically induced astigmatism (SIA). If the corneal incision is placed oblique to the steepest corneal meridian then a toric calculator will predict that the orientation of the post-operative corneal steepest meridian will move away from the incision site. We conducted a prospective clinical study to examine the actual effect of corneal incisions when placed oblique to the steepest meridian.

Methods : 145 subjects (74.8±9.6 years) underwent cataract surgery with a clear corneal incision placed oblique to the steepest corneal meridian. Scheimpflug tomography was used to determine the corneal power pre-operatively and post-operatively (3-6 months). The preoperative measurements and surgeon specific SIA were used to calculate the predicted post-operative corneal power. Two models were created to examine the correction that would have been achieved had a toric intraocular lens (IOL) been implanted. The first model used the toric calculator predicted corneal astigmatism (predicted) and the second used the pre-operative corneal data alone (actual)

Results : The predicted median shift in the steepest corneal meridian was 11.2° (IQR 6.0, 20.5°) away from the incision site. The median actual change was only 2.9° (IQR -6.5, 13.7°). Toric calculators significantly overestimate the overall change in axis for this cohort (p<0.001), and a poor correlation was found between the predicted and actual corneal axis change (r=0.086, p=0.14). The two models showed significantly different residual ocular astigmatic values (P<0.001) with the predicted (0.64D) being higher than the actual (0.40D) model

Conclusions : The oblique cross cylinder formulae used in the toric IOL calculators overestimates the shift in orientation of the steepest corneal meridian following cataract surgery. The findings would suggest that when using an corneal incision oblique to the steepest meridian that the toric IOL should be selected and placed in accordance with the pre-operative corneal power alone and not the corneal power as predicted through vector analysis

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.


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