Straylight measurements in patients wearing several types of contact lenses

Glare disability can be a problem among contact lens wearers. It is caused by a
reduction in contrast of the retinal image due to a veiling luminance caused by
forward light scatter within the eye. This causes halo's around bright light
sources and difficulty with against the light face recognition. These
complaints can be very distressing and invalidating to the patient, while
standard examinations are relatively normal. Until now, loss of function was
qualified only by visual acuity measurements. However, straylight measurements
may offer a significant contribution. Patients with many subjective complaints
may still have a good visual acuity. Their complaints may be explained by an
increased straylight value.

A new version of the straylightmeter, the Oculus C-Quant, is available since
June 2005. This straylight meter is able to objectively measure the amount of
straylight and to express this as a number. In the present study we are
planning to use the Oculus C-Quant to measure the amount of straylight in
contact lens wearers without other ocular pathology who are wearing several
different kinds of contact lenses. We are planning to relate the amount of
straylight to subjective complaints, the types of contact lenses and the length
of contact lens wear.

Null Hypotheses:

1) Patients with soft contact lenses have the same straylight values as
patients with rigid gas permeable contact lenses and oxygen permeable silicone
contact lenses; there will be no difference in straylight values whether or not
the contact lenses are in situ
2) Longer duration of contact lens wear (more hours during the day) will not
lead to more hypoxic corneal stromal swelling and to higher straylight values
3) More years of contact lens wear will not lead to more hypoxic corneal
stromal swelling and to higher straylight values

To determine straylight values in patients with several types of contact lenses
and a differing lenght of wear of contact lenses. This study will lead to
objective documentation of loss of function among contact lens wearers and and
will lead to more insight in the etiology of straylight among these groups. In
this way we can contribute to the determination of the place of the several
types of contact lenses among the scale of refractive possibilities.

Comparative case series.

One eye of each of 5 volunteers will be patched for one hour, while wearing a
soft contact lens.

All study visits will take place during part of one day. Patients will pay 3
study visits. The first visit will take approximately one hour, the following
visits will take place one and 3 hours later, respectively. Both these visits
will last approximately 20 minutes.

The subjects will undergo the following measurements:
They will fill in a questionnaire. Questions will pertain to types of contact
lenses, length of wear, contact lens hygiene and any visual complaints. After
this they will undergo:
1) Visual acuity measurement wearing their contact lenses
2) Straylight measurement wearing their contact lenses
3) Slitlamp examination wearing their contact lenses
After contact lens removal:
1) Autorefractor measurement
3) Best corrected visual acuity measurement wearing spectacles
4) Best corrected straylight measurement
5) Orbscan measurement
6) Slitlamp examination

The straylight measurement will be repeated one and three hours after contact
lens removal.


These measurements will not lead to an increased risk for the subjects.