To investigate and compare different strategies of corneal power calculations using
keratometry, paraxial thick lens calculations and raytracing.Tertiary Care Center.Retrospective
single centre consecutive case series.Using a dataset with 9,780 eyes of 9,780 patients
from a cataractous population the corneal front (Ra / Qa) and back (Rp / Qp) surface
radius / asphericity, corneal thickness (CCT), and entrance pupil size (PUP) were
recorded using the Casia 2 tomographer. Beside keratometry with the Zeiss (PKZ) and
Javal (PKJ) keratometer index, a thick lens paraxial formula (PG) and raytracing (PR)
was implemented to extract corneal power for pupil sizes from 2 mm to 5 mm in steps
of 1 mm and PUP.With PUP PKZ / PKJ overestimates the paraxial corneal power PG in
around 97% / 99% of cases and PR in around 80-85% / 99%. PR is around 1/6 or 5/6 dioptre
lower compared to PKZ or PKJ For a 2 mm pupil PR is around 0.20 / 0.91 dioptres lower
compared to PKZ / PKJ and for a 5 mm pupil PR is comparable to PKZ (around 0.03 dpt
lower) but around 0.70-0.75 dioptres lower than PKJ.'True' values of corneal power
are mostly required in lens power calculations before cataract surgery, and overestimation
of corneal power could induce trend errors in refractive outcome with axial length
and lens power if compensated with the effective lens position.
