The relationship between planned astigmatic treatment and actual astigmatic treatment in cases of unexpected refractive outcomes following LASIK for a moderate to high hyperopic (mixed) astigmatism

Session Details

Session Title: LASIK II

Session Date/Time: Tuesday 08/09/2015 | 14:00-16:00

Paper Time: 14:30

Venue: Room 10

First Author: : S.Patel UK

Co Author(s): :    M. Bohac   N. Gabric                 

Abstract Details

Purpose:

The calculation of the actual astigmatic treatment (AAT) is complicated when the axis of any residual astigmatism (RA) differs from the planned axis for example if the RA. A computational procedure (previously reported for use in myopic astigmatism) was used to calculate the AAT in more complex cases and determine if there was any association between AAT and planned astigmatic treatment (PAT) in cases where the post-op residual astigmatism ≥0.50DC following unremarkable LASIK and healing for moderate to high hyperopic astigmatism using two separate platforms.

Setting:

University Eye Hospital, Svjetlost, Zagreb, Croatia

Methods:

The planned correction along a particular axis was calculated (a1) together with the power of the residual refractive along the same axis (a2). Actual treatment(AT) =a1-a2. A graphical plot of each AT value over 180 º against meridian angle was sinusoidal and, AAT was derived from the best fit sphero-cylindrical description of the sinusoidal construct. This was applied to PAT and post-op RA values for cases treated with either Wavelight AllegrettoIQ400Hz (group I, n= 56) or Schwind Amaris750S (group II, n=81). The PAT and AAT values were suitably compared analysed.

Results:

Reporting the key findings (p less than 0.001) A) The effective astigmatic power (y) was significantly correlated with the planned astigmatic power (x) and sine of the planned axis (z). Multiple linear regression revealed, I) y = 1.088x+0.232z+ 0.535, (r=0.874, n=56, F=848.0) II) y = 1.050x-0.139z+ 0.471, (r=0.894, n=81, F=170.0) B) The sine of the effective astigmatic power axis (z1) was significantly correlated with the planned astigmatic power (x) and sine of the planned axis (z). Multiple linear regression revealed, I) z1 = 0.953z+0.013x+ 0.086, (r=0.962, n=56, F=318.4) II) z1 = 0.968z-0.005x+ 0.003, (r=0.987, n=81, F=1559)

Conclusions:

Linear regression predicts for1)Allegretto platform, the effective astigmatic power was up to 13% less than expected when the PAT axes were between 45º and 135º. The effective astigmatic axis for cylinder corrections ≥ 6.00DC were closer to 80º when the planned axis was 90º.2) Amaris platform the effective astigmatic axis for cylinder corrections ≥ 3.00DC were closer to 80º when the planned axis was 90º and for cylinder corrections of -6.00DCx180, the effective astigmatic axis was closer to 2º. This procedure assists in better understanding the mechanism that can lead to unwanted surprise astigmatic corrections after LASIK.

Financial Interest:

NONE