Accuracy Of Various Barrett Formulae In Keratoconus Patients

To compare accuracy of various Barrett formulae in keratoconus patients

Private Eye Hospital, India

A retrospective study where keratoconus subjects diagnosed with keratoconus (Central and Grade 1 <48.00D), age ranged between 45-75 years were enrolled. Subjects with any systemic illness, previous corneal surgery, Intraoperative complications were excluded. Post operative 1 month refraction was noted. IOL power calculations were done using Barret (Barrett Univarsal 2 (Bar U2), Barrett total K (BarTK), Barrett True K (Bar TRK) and measured Barrett True K (Mea Bar TRK) formulae. Median Absolute error (MedAE) was calculated median of absolute difference between post operative and target refraction spherical equivalent. Also percentage of eyes with absolute error spherical equivalent within 0.5D, >0.51 D were noted. 

23 eyes with mean±SD age 62.21±7.0 years were included. All the Barrett variants resulted in similar refractive outcomes. Median Absolute error with Bar 2, BarTK, Pred Bar TRK, and Mea Bar TRK was 0.33, 0.22, 0.19, and 0.26D respectively.  With all four variant of Barrett, 78.26% and 21.74% eyes had spherical equivalent within 0.50D and >0.51D respectively.

Barrett true K resulted in minimal post operative refractive error and Barrett Total K had an advantage over Universal 2.