Abstract |
Τhe objective was to investigate the distribution and the correlation of the
overall, the corneal and the internal higher-order aberrations between two
emmetropic groups of young and presbyopic subjects as well as to compare
their contrast sensitivity scores.
At first, we tested the visual acuity of 48 subjects aged between 18 and 31
years and 35 subjects aged between 47 and 58 years. The binocular UVA in
both groups was >10/10 and >9/10 for each eye.
The total higher-order aberrations were determined using a COAS
Hartmann-Shack analyzer and the corneal aberrations were measured by the
topographic system Topolyzer (Wavelight, Germany) for a 6mm pupil while all
eyes were cyclopleged. The relative contribution of the internal optics
(posterior surface of the cornea and lens) to overall aberrations were
measured indirectly.
We found increased values of total HO RMS in the group of presbyopes
with more prominent increase the spherical aberration and the 4th order RMS.
We did not find significant differences between the two groups in 3rd order
RMS and coma. From the analysis of corneal higer aberrations we found
significant increase of the total and 4th order RMS, but not for 3rd order RMS.
We also, did not find significant difference among the two groups in the
total internal HO RMS, as well as in the 3rd and 4th internal RMS with the
exception of spherical aberration, tetrafoil (both axes) and trefoil (x axis) which
seem to be larger in the presbyopes.
The measurement of the contrast sensitivity function οf 29 young and
presbyopic subjects, was performed using Functional Vision analyzer, under
photopic and mesopic conditions and showed that older subjects had reduced
contrast sensitivity when compared with their younger counterparts.
For all the subjects, the area under the log contrast sensitivity function
(AULCSF) was not associated significantly with the total HO RMS and the 3rd
order RMS, but there was a significant negative correlation with 4th order RMS
and spherical aberration.
The present study revealed that the optical system of the human eye
behave as an auto-compensating mechanism because there is a balance
between corneal and internal aberrations that results in smaller ocular
aberrations. Further studies on the probable paths leading to that
compensation and ontogenetic changes in aberration structure should provide
further insights.
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