A comparison between transepithelial photorefractive keratectomy (T-PRK) and femtolaser in situ keratomileusis (FemtoLASIK): changes in the higher order ocular aberrations and vector analysis of astigmatic corrections at 6 months postop

Session Details

Session Title: Presented Poster Session: Keratorefractive Surgery Results I

Venue: Poster Village: Pod 2

First Author: : S.Patel UK

Co Author(s): :    A. Biščević   M. Bohač   A. Pidro   M. Ahmedbegović Pjano   A. Pašalić           

Abstract Details

Purpose:

To determine if changes in astigmatism and the magnitude of higher order ocular aberrations (HOAs) are related to pre-op values for treatment of myopia and myopic astigmatism above -5.00DS and upto -2.00DC after either T-PRK or FemtoLASIK.

Setting:

University Eye Clinic ‘Svjetlost’ Zagreb Croatia & ‘Svjetlost’ Saravejo Bosnia and Herzegovina.

Methods:

Patients (30 per group) underwent unremarkable T-PRK(group I) or FemtoLASIK(group II) using Schwind Amaris 750S laser. Higher order ocular aberrations(HOAs) were measured objectively using L80 wave+TM,(Luneau SAS, Prunay-le-Gillon, France) at pre-and 6months postoperative in each case. HOAs evaluated using this aberrometer were coma, trefoil and spherical aberration (SA) for pupil sizes of 3mm and 5mm. Difference between pre-and post-op values(y) were compared with pre-op values(x) using standard linear regression. Astigmatic data acquired by subjective refraction were subjected to vector analysis, according to Alpins’ method, to determine the association between surgically induced(SIA) and target induced(TIA) astigmatic powers and axes.

Results:

Preop, there was no significant difference between groups I&II in relation to either each of the three HOAs or required sphero-cylindrical correction. Linear regression revealed some significant findings (from right eyes only in bilateral cases) for the 5mm pupil. The significant relationships between the changes of individual HOA values (y) and pre-op HOA values (x) were as follows. Group I coma y=0.621x-0.109(r=0.409,p=0.025) and SA,y=0.689x-0.002(r=-0.498, p=0.005), Group II trefoil,y=1.045x-0.068(r=0.869,p<0.001) and SA,y=0.884x-0.013(r=0.952,p<0.001). The relationships between SIA (power=S,sine of axis=α) and TIA(power=T,sine of axis=β) were as follows. Group I,S=0.638T-0.399(r=0.655,p<0.001), α=0.853β+0.102(r=0.657,p<0.001), Group II, S=1.012T+0.034(r=0.940,p<0.001), α=0.733β+0.122(r=0.840,pp<0.001).

Conclusions:

The numerical indices of the linear expressions show that changes in magnitude of specific HOAs can be predicted on an individual case-by-case basis for both T-PRK and FemtoLASIK. The relevant expressions predict greater discrepancies between SIA and TIA axes for corrections that lean towards against-the-rule astigmatism. There is a tendency towards a larger mismatch between SIA and TIA power after correcting with T-PRK compared with FemtoLASIK. The expressions show, T-PRK tends to induce unwanted astigmatism.

Financial Disclosure:

None