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P-14 Factors associated with the disparity between manifest refractive cylinder and keratometric astigmatism in keratoconic eyes
  1. Jesse Panhtagani1,
  2. Elizabeth Law1,
  3. Max Davidson1,2,
  4. Mohamed Elkadim3,
  5. Harry Roberts4,
  6. Philip Buckhurst5,
  7. James Myerscough1,6
  1. 1Southend University Hospital, Mid and South Essex NHS Trust, Southend, UK
  2. 2Sheffield Teaching Hospitals NHS Trust, Sheffield, UK
  3. 3Tanta University Hospital, Tanta, Egypt
  4. 4West of England Eye Unit, Royal Devon University Healthcare NHS Trust, Exeter, UK
  5. 5School of Health Professions, University of Plymouth, Plymouth, UK
  6. 6University of Plymouth Faculty of Medicine and Dentistry, Plymouth, UK


*Correspondence, Jesse Panhtagani:

Objective To investigate the factors associated with the disparity between manifest refractive cylinder (MRC) and keratometric astigmatism (KA) in keratoconic eyes to refine the refractive outcomes of toric intraocular lenses in keratoconic cataract surgery.

Methods A retrospective study at Southend University Hospital assessing 145 keratoconic eyes from 75 patients (57 male, 18 female, mean age 27±8.6 years), and comatic aberration of >0.3 µm (defined with Pentacam HR (Oculus, Germany) at a diameter of 6 mm). MRC power was correlated to corneal tomographic variables including higher order aberrations measured using univariate and multivariate regression analysis. Vector difference between KA and MRC was also explored, to detect tomographic variables associated with this disparity. Axis of MRC was compared and correlated to the axis of corneal coma.

Results Both KA and coma showed a significant correlation with the MRC power. The vector difference between KA and MRC is correlated to the KA, posterior keratometric astigmatism and comatic aberration. MRC axis had significant correlation to the axis of coma, with an inverse relationship between MRC axis and coma axis.

Conclusion Corneal comatic aberration is a significant determinant factor of manifest refractive cylinder power and axis and is correlated with the disparity between manifest and keratometric astigmatism found in keratoconic eyes. The effect of higher order aberrations, particularly vertical coma should be considered when planning intraocular procedures for visual rehabilitation.

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