Light Adaptation in glaucoma- The influence of dynamic light conditions on visual functioning.

Glaucoma is an optic neuropathy in which a degeneration of retinal ganglion
cells results in loss of the visual field and - if left untreated - blindness.
Recent studies have uncovered that significant visual complaints exist even if
the visual field is still intact or only mildly affected. These complaints are
related to light and dark adaptation.

The human retina can adjust its operating range to a wide range of illumination
levels. Adaptation refers to both the process of adjustment, that is, adapting
to a new condition, and to be adapted to a condition. Previous studies have
uncovered that adaptation to different light conditions is disturbed in
glaucoma: it is delayed and incomplete.

We aim to extend this research and to determine how patients with glaucoma
perform under rapidly varying light conditions. For this purpose we will
perform psychophysical experiments with a stimuli presented on a computer
screen where either the background luminance or the stimulus itself changes
rapidly with time. The former paradigm refers to contrast gain control (the
retina*s ability to keep its sensitivity in the presence of changing
contrasts); the latter is known as flicker sensitivity.

The measurements will be performed by glaucoma patients (n = 30) and healthy
subjects (n = 30) (see 4.4 Sample Size Calculation). By comparing the results
for each patient with data from normal observers, we will determine the extent
of the visual losses associated with glaucoma, thus yielding new insights of
light adaptation dynamics in glaucoma. Subjects with glaucoma will be recruited
from a population of glaucoma patients who visit the ophthalmology clinic at
the University Medical Center Groningen. For the recruitment of healthy
subjects, poster adverts (see Appendix E3) will be placed in and around the
UMCG

To determine the influence of dynamic light conditions on visual functioning in
glaucoma. For this purpose we measure (1) the contrast sensitivity to a small
stimuli at a time-varying background luminance and (2) the critical fusion
frequency (CFF), which is the highest frequency of flicker that can be
distinguished from steady state (temporal sensitivity).

Case-control study

Patients and healthy subjects will have one visit to the Laboratory of
Experimental Ophthalmology to perform psychophysical experiments . Healthy
subjects will undergo screening to assess their eye health, which will comprise
a questionnaire (see Appendix F1), letter chart, visual field test, optical
coherence tomography (OCT) test of retina and optic nerve head, and intraocular
pressure (IOP) measurement. Screening will take around 20 minutes. The eye will
not be touched during screening, nor are mydriatic drugs required for pupil
dilation. If abnormal screening results are obtained for healthy subjects, they
will be referred to their GP. Dtection of an eye condition may cause
psychological stress, however, an early diagnosis will allow treatments to be
initiated and therefore more preservation of visual functioning. Glaucoma
patients will not perform any screening tests, therefore there is no risk of
ientifying any other eye conditions. Subjects with glaucoma will be recruited
froam a population of glaucoma patients who visit the ophthalmology clinic at
the UMCG. For the recruitment of healthy subjects, poster adverts (see Appendix
E3) will be placed in and around the UMCG. Patients and healthy subjects will
spend 1.5 and 2 hours in our lab, respectively, to complete the required tasks.