title: Improving refractive outcomes at extreme axial lengths with the IOLMaster: the optical axial length and keratometric transformation.
abstract: OBJECTIVE
  To optimise the relationship between the actual and predicted refractive outcomes following phacoemulsification and axial length of the eye. Four intraocular lens (IOL) power calculation formulae were compared: SKR-T, Holladay I, Hoffer-Q and Haigis. Optical axial length transformation based on the original calibration of the IOLMaster was tested to improve the predictability of outcomes.
  
  
  METHODS
  The refractive outcomes of 155 eyes of 120 patients using the IOLMaster were reviewed following phacoemulsification. After optimising the IOL constants, the prediction error (PE; achieved spherical equivalent - calculated spherical equivalent) of each of the formulae was calculated for each eye and then correlated to the axial length of the eye with and without the optical transformation. Keratometry measurements of the IOLMaster were tested by transforming to that of standard autokeratometry. This was validated in a second group of 90 eyes.
  
  
  RESULTS
  The PE of all but the Haigis triple optimised formula were found to be positively correlated to the axial length. The optical and keratometric transformation statistically significantly reduced this correlation, leading to fewer PE at all axial lengths. PE per millimetre axial length was 0.06 D/mm (SRK-T), 0.16 D/mm (Hoffer-Q), 0.14 D/mm (Holladay I), 0.11 D/mm (Haigis single) and -0.02 D/mm (Haigis triple). Following transformation, best case PE was reduced to -0.01 D/mm (SRK-T), 0.08 D/mm (Hoffer-Q), 0.01 D/mm (Holladay I), 0.01 D/mm (Haigis single) and -0.01 D/mm (Haigis triple).
  
  
  CONCLUSIONS
  Transforming the IOLMaster measurement into the optical axial length while compensating for its keratometry measurement was able to improve the predictability of outcomes at extreme axial lengths without further modification to the standard IOL formulae.
authors.affiliation: The Eye Institute, Tan Tock Seng Hospital, Singapore.
authors.forename: H B
authors.initials: HB
authors.lastname: Fam
authors.forename: K L
authors.initials: KL
authors.lastname: Lim
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001699:Biometry / Q000379:methods; D019781:Corneal Topography / Q000379:methods; D003941:Diagnostic Techniques, Ophthalmological; D005123:Eye / Q000473:pathology*; D006801:Humans; D007368:Interferometry / Q000379:methods; D007910:Lenses, Intraocular; D008875:Middle Aged; D018918:Phacoemulsification; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D012189:Retrospective Studies; D016896:Treatment Outcome