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Abstract
BACK GROUND:
Ocular aberrations have a major impact on retinal image quality. They have been, recently, thought of as modifiable sources of image degradation. Many devices, using different optical principles for measurement and evaluation of human eye monochromatic aberrations, have been constructed. However, only few studies compared the results of such machines in different states of the eye.
OBJECTIVES:
The aim of this work was to evaluate optical aberrations in eyes with normal and operated corneas using aberrometers that employ different optical principles for aberration measurement.
METHODS:
The study was conducted on 200 eyes of 111 subjects that were divided into four groups; 100 eyes with normal corneas, 50 eyes with previous excimer laser photorefractive surgeries, 20 eyes with previous incisional corneal surgeries, 30 eyes with previous penetrating keratoplasty surgery. All eyes included in the study were subjected to full ophthalmologic examination, uncorrected visual acuity measurement, manifest refraction, best spectacle-corrected visual acuity, scotopic pupil size measurement, corneal topography, and evaluation of optical aberrations by the OPD-Scan, the ALLEGRO Analyzer, and the WaveScan. Eyes with best spectacle-corrected visual acuity less than 6/18, topographic evidence of ectasia, corneal opacities dystrophies or oedema, active acute or chronic ocular inflammations, significant ocular surface disorders, high intraocular pressure, posterior segment pathologies or Lenticular opacities were excluded from this study. Calculation of the RMS values of the different aberrations and radial as well as their relative percentages was performed.
RESULTS:
All three aberrometers gave comparable values for the studied parameters with the following exceptions: In the normal corneas group and the post-incisional corneal surgery group, the OPD-Scan under-estimated values of aberrations having a meridional frequency of 4 or more and over-estimated values of aberrations with meridional frequencies less than 4. The WaveScan under-estimated higher order aberration values and over-estimated spherical aberration. The ALLEGRO Analyzer under-estimated spherical aberration values. In the post-excimer laser refractive surgery group the WaveScan over-estimated higher order aberration RMS and spherical aberration. In the post-PKP group, the OPD over-estimated higher-order aberration RMS and spherical aberration values.
CONCLUSIONS:
Monochromatic aberrations vary widely within and among populations.
Different corneal surgeries were found to significantly increase ocular higher-order aberrations magnitude in comparison to eyes with normal un-operated corneas. Coma secondary astigmatism and spherical aberration were the aberrations that significantly increased in all groups with operated corneas.
Trefoil, pentafoil, and sixth order astigmatism are the aberrations least affected by excimer laser refractive surgery.
Incisional surgeries induce large amounts of the aberrations peripherally located in the Zernike pyramid especially tetrafoil and hexafoil.