Anterior and total corneal astigmatism measured using CorT compared to refractive astigmatism in the absence of lenticular astigmatism

Session Details

Session Title: Pseudophakic IOLs: Toric I

Session Date/Time: Saturday 10/09/2016 | 16:00-18:00

Paper Time: 16:48

Venue: Hall C2

First Author: : M.Goggin AUSTRALIA

Co Author(s): :    J. Slattery                    

Abstract Details

Purpose:

For toric IOl calculation, the principal that post-operative refractive astigmatism is wholly derived from the cornea is applied. If this is true, refractive astigmatism should equal corneal astigmatism in eyes with spherical IOLs. CorT, a measure of anterior or total corneal astigmatism may provide optimal corneal astigmatism values for toric IOL calculation given its more extensive corneal sampling. This study examines the difference between refractive and corneal astigmatism using this measure and comparing it to more conventional measures. The method that produces the lowest difference is likely to be the best corneal astigmatism measure for toric IOL cylinder calculation..

Setting:

Publicly funded tertiary referral hospital The Queen Elizabeth Hospital, Adelaide, Australia

Methods:

31 consecutive eyes were examined. All had been previously implanted with spherical IOLs and had 6/7.5 or greater corrected visual acuity. Eyes with corneal, capsular bag or macular pathology were excluded. Manifest refraction was carried out by one observer with refinement of the cylinder power to 0.12D. Corneal power was measured with the Pentacam and CorT values derived using iASSORT software. Automated keratometry values using a Nidek ARK-510 were also obtained. The vector difference between the corneal plane refractive astigmatism and the various keratometric measures was derived, the lowest power value indicating the best match of corneal and refractive values.

Results:

The summated vector mean (or centroid) difference between the refractive and corneal stigmatism values were as follows. Refraction v. Nidek ARK, 0.54 at 3 degrees. Refraction v Pentacam anterior sagittal 3 mm zone 0.52D @ 6 degrees. Refraction v CorT anterior surface 0.51D @ 1 degree. Refraction v CorT total (anterior and posterior surfaces combined) 0.45D @ 180 degrees

Conclusions:

While CorT total (anterior and posterior combined) yielded the lowest power value, a value approaching 0.5D is clinically significantly larger than the ideal value of zero. However, it still represents the best of the assessed values. If used for toric IOL calculation it may assist in producing better refractive astigmatic outcome from toric IOLs.

Financial Disclosure:

NONE