| Abstract |
Introduction The vision is the most fundamental and the most complex sense in the
evolution progress. Although, the complete process of the visual function has not been fully
understood, there are several essential factors take part in the vision. The optics of the eye,
the retina, and the visual cortex should be considered as a complete structure while
evaluating the visual performance. The interaction between the light and the structures of the
eye determine the quality of the retinal image which is the key factor for the visual
performance.
Two different interaction mechanisms of the light and the eye exists. The first mechanism is
the optical interactions, which is detailed as optical properties of the eye and the second
mechanism is detailed as the material properties of the eye. It is very important to understand
and distinguish the difference between these two mechanisms. In order to have the good
vision or in other words good retinal image quality, having the best refraction is as important
as having transparent optics and clear optical way.
Amount of the irregularities or defects induce straylight in the eye. Although, effects of
intraocular scattering exist for ages and observed in the clinical practice, the knowledge and
understanding of the intraocular scattering is not as good as the understanding of the
refraction or aberrations. We believe that a complete analysis of visual performance will
only be completed with analyzing the intraocular straylight.
In this thesis, a novel optical device for measuring forward intraocular scattering with double
pass method is developed and results are shown. The relevant chapters focus on several
studies which worked on measuring, quantifying and understanding of the straylight
phenomenon.
Methods The proof of concept, repeatability, functionality of the device was tested
with either in test or clinical conditions. The first study on the proof and concept and constancy evaluations were performed on an artificial eye and previously documented
lenses. The straylight difference were evaluated of the artificial eye between different hard
contact lenses which induce different amount of straylight.
The second study was performed with an artificial eye for determining the effect of defocus
on the measurements. The measurements were collected by changing the position of the
retina which was corresponding inducing myopia or hyperopia. Additionally, the
repeatability and the effect of axial alignment of the pupil camera was tested by taking
consecutive measurements from the different axial positions from a healthy eye of a subject.
In the third study, the scattering difference between healthy subjects and the effect of
different diffusing filters which induce straylight were measured. Measurements with and
without lenses and were evaluated.
The final studies were performed under clinical conditions with healthy subjects and cataract
patients. Optical and psychophysical measurements were performed as well as the LOCS III
grading in these studies. Correlation between two methods of measuring intraocular
scattering and LOCS III grading system were evaluated.
Results Outcomes of these study showed the system is capable of detecting the
amount straylight between different scatterers. The results also showed that the system is
capable of detecting different amounts of straylight on human eyes and the system is
immune for measuring patients with refractive error which is smaller than the 5D. The
measurements of the optical and psychophysical measurements showed %80,3 and %84,4
(p<0,01) correlation. Furthermore, the psychophysical measurement and optical
measurement showed 0,17 and 0,16 statistical significant difference (P<0,001). In addition,
Bland-Altman analysis also confirmed that the bias was significant. The analysis of optical
measurements between different groups of cataract gradings revealed significant differences
between all groups (P<0,004). Conclusion Development of this novel device, which is described in this thesis, gives
advancement for the clinical routine beyond the aberrations and reflections. Besides the
subjective methods of grading cataract, this method gives fast, relevant, sensitive and
significant information for the effects of the forward scattering. This device could be a step
forward in the clinical routine and helps clinicians for the objective evolution of the material
properties of the eye.
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