| Abstract |
Purpose: The purpose of the study is the evaluation of light scatter from
hydrogel and silicone-hydrogel contact lenses after pre-determined use, the
comparison between the two different lens materials and the correlation of predetermined
contact lenses’ use with subjective measurements of vision. For this
purpose, measurements of lenses’ scattering as well as measurements of visual
acuity and contrast sensitivity have been conducted to the participants in
determined time intervals.
Method: 15 adults (11 in the second part), of age between 22 and 33 years old
(age average 26,5 years), participated in the study, the total duration of which
was decided on ten weeks. The study was divided in two parts each of which
lasted 5 weeks. Each examinant wore the hydrogel lenses (AQUALENS, Ciba
Vision) on the left eye and silicone-hydrogel lenses (AIR OPTIX, Ciba Vision) on
the right eye, both types were of monthly replacement. The two types of contact
lenses were selected with the criterion of their comfort fitting and the optimum
optical correction they gave. Μeasurements of contact lenses’ scattering were
being conducted every week, while measurements of contrast sensitivity and
visual acuity were being conducted every first and fifth week of each part of the
study. In parallel, scattering measurements were conducted in non- used contact
lenses so that these would be used as measure of comparison (control).Ten
pairs of lenses (one AIR OPTIX and one AQUALENS in each pair), were
measured every week. The lens to be measured was placed on a lenses’ device.
The lens-lenses’ device system was then transferred on a metal mount in front of
which 14 sequential rings were projected on a computer screen. The scattering
was quantified as the average resulting from of the 3 rings of maximum diameter,
which corresponds to the scattering concentration of 0 to 4 angles.
Simultaneously, there was a camera behind the metal mount, which was plugged
in another computer were luminance and projected ring position adjustments
ΜΕΤΡΗΣΗ ΤΗΣ ΔΙΑΦΑΝΕΙΑΣ ΦΑΚΩΝ ΕΠΑΦΗΣ ΜΕΤΑ ΤΗΝ ΧΡΗΣΗ ΤΟΥΣ
ΣΑΧΑΝΙΔΗΣ ΑΛΕΞΑΝΔΡΟΣ,ΙΝΣΤΙΤΟΥΤΟ ΟΠΤΙΚΗΣ ΚΑΙ ΟΡΑΣΗΣ 7
were performed. The contrast sensitivity was evaluated using Gabor gratings and
seven spatial frequencies were examined: 1,2,4,8,12,16 and 24 c/deg. The
examination of visual acuity was conducted with modified EDTRS visual acuity
charts. Questionnaires were distributed to the participants for the subjective
evaluation of the contact lenses, which were filled in every week.
Results: Τhe average scattering of the participants’ contact lenses doesn’t
increase with the passage of 5 weeks, neither with the hour use per week.
Increase in contact lenses’ scatterring is not observed in the control group, as
well. Nevertheless, a stabilisation trend of the average scattering is observed in
the control group of AIR OPTIX lenses in comparison to the AQUALENS. It
doesn’t seem to arise any strong correlation between scattering and
questionnaire data, regarding the AIR OPTIX and AQUALENS. The examinants’
average contrast sensitivity remains stable for each eye, while the difference
between right and left eye, for the first part of the study, does not show almost
any difference, in opposition to the second part, where there is observed a
decrease referring to the AQUALENS. The difference between the
measurements of the examinants’ average contrast sensitivity shows a stable
decrease of the average at 16 c/deg (except the difference between the third and
second measurement at 12c/deg).The visual acuity increases in all
measurements of the study regarding AQUALENS, while relative to AIR OPTIX
lenses, a decreased trend is observed in the last measurement.
Conclusions: Τhe contact lenses’ scattering does not seem to relate to the
weeks of application or the hours of use. Factors, such as the impact of the
lenses’ position during the placement on the optical device and the interval
examinant’s rousement-measurement, may affect the final results. The decrease
in contrast sensitivity regarding the AQUALENS in the second part of the study,
confirms older studies which observe a decrease in contrast sensitivity using soft
contact lenses, including those made of hydrogel.Τhe interaction between lens
and cornea appears to play an important role in contact lenses’ scatterring.
Under this condition, potential increase in the eye’s scattering during the usage
of contact lenses would be due to epithelial and lacrimal changes, rather than
lens alterations. The extended use of contact lenses affects the corneal
metabolism, while the mechanical factors, such as the persistent rubbing of
eyelids, could affect the corneal surface. Moreover, the corneal, epithelial surface
metabolism undergoes a sort of compromise which renders it more sensitive to
inflammation. The biochemical alterations that take place in the cornea could
affect the scattering in a way similar to that where the alterations in the crystalloid
lens’ histochemistry relate to increased scattering.
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