Motion perception in glaucoma: detecting oscillatory motion with foveal vision

Glaucoma is an eye disease in which a degeneration of retinal ganglion
cells results in loss of the visual field and - if left untreated - blindness.
Early stages are usually unnoticed and for that reason, screening is advisable.
Current methods for screening glaucoma often do not detect glaucomatous defects
until a large amount of irreversible damage has occurred. Moreover, recent
studies have uncovered that significant visual complaints exist even if the
visual field is still intact or only mildly affected. For example, many
glaucoma patients give-up driving after sunset in an unexpectedly early disease
stage. One possible explanation for this is impaired visual function
specifically at low luminances. We recently studied and confirmed this
possibility. Alongside progressive visual field loss, individuals with
glaucoma are also found to have deficits in seeing moving objects (Shabana et
al., 2003), not unimportantly for driving. Furthermore, a decline in motion
perception may precede loss of other visual functions. A screening test based
around motion perception may, therefore, enable glaucoma diagnoses and
treatment decisions to be made sooner, thereby preserving more of the visual
system. In general, we aim to better understand why glaucoma patients express
visual complaints in disease stages that are considered early based on
conventional visual field testing. The fact that motion detection is performed
by a subclass of retinal ganglion cells, the primary site of glaucomatous
damage, makes a detailed study of motion perception in glaucoma long overdue.

One commonly used task for assessing motion perception in glaucoma is a
motion displacement test, where the subject must indicate if they perceive a
simple line stimulus to be moving. Using this task, previous studies have
found impaired motion perception in peripheral regions of the visual field that
were apparently healthy, according to standard perimetry tests (Westcott et
al., 1998). However, there has been a lack of research which focuses on the
integrity of the motion perception pathway in foveal vision, the most important
part of the visual field from the point of view of the patient. Our study will
investigate motion perception thresholds of an oscillating line stimulus seen
with foveal vision, over a range of oscillation frequencies, in glaucoma and
healthy subjects. Comparisons of the oscillation amplitudes required to
perceive motion can then be made between glaucoma and control groups to assess
determine if motion perception deficits are present in foveal fixation in
glaucoma. Given our recent studies that showed the importance of luminance, we
will perform the measurements over a range of luminance values.

The main objective is to compare motion perception thresholds in glaucoma
patients with healthy subjects as a function of oscillation frequency and
luminance.

Case-control study

Patients and healthy subjects will have one visit to the Laboratory of
Experimental Ophthalmology to perform a motion perception experiment. 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. Detection of signs 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
identifying any other eye conditions. Subjects with glaucoma will be recruited
from 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 hours and 2 hours in our lab, respectively, to complete the required
tasks.