Fourier Harmonic Analysis Of Corneal Topography Following Penetrating And Deep Anterior Lamellar Keratoplasty

The aim of this study was to examine the visual outcomes and characteristics of distorted corneas, based on corneal topography using Fourier harmonic analyses in eyes with non-ectatic corneal disorders who had penetrating keratoplasty (PK) or Deep anterior lamellar keratoplasty (DALK) and maintained clear grafts at least 2 years. We've tried to explain the low visual outcomes of patients despite a succesfull surgery and a clear graft with the fourier analysis data obtained from Pentacam.

Keratometry is accurate in regular corneal surfaces but have limited validity in in eyes that deviate from spherocylindrical optics as occurs in keratoplasty.Patients were retrospectively analyzed and divided into DALK/PK surgery groups or scar/dystrophy groups based on the primary indication to quantitatively evaluate visual acquity (Vo) and even minute changes, using  Fourier analysis to decomposed corneal power into various components which have direct clinical correlation.

Distance BSCVA, refraction, and Fourier analysis constituents were assessed for 75 eye who underwent PK and 75 eye who underwent DALK surgery (total 150) with non-ectatic corneal pathology,  who had celar grafts and sutures removed were followed up for at least 24 months between January 2019 and September 2023 at the Ankara Research and Training Hospital’s Cornea Unit. 

When patients were divided into DALK and PKP groups there was no significant difference in postop Vo(p=0,318) on the other hand,by grouping them as primary diagnosis (scar/dystrophy) the scar group exhibited lower visual acuity(p=0,000).The scar group patients couldn’t reach to better Vo, we look at the fourier parameters of this group.The result of comparsion between dystrophy and scar group’s fourier analysis showed that; astigmatism center (p=0,043), astigmatism periphery (p=0,000) and irregularity (p=0,008) showed statistically significant increase. This increase in Irr of PK group, is due to scar formation at the donor–recipient junction causing uneven tractional forces on the healthy donor cornea, resulting in increased corneal Irr.

Although no significant differences were found between DALK and PK in terms of postop visual acuity and Fourier parameters, the presence of higher-order Irr in eyes with corneal scars may limit the achievement of optimal visual acuity, even in the presence of a clear graft or optical correction