Effect of optical quality on retinal thresholds

Optical aberrations degrade image quality. Optical aberrations are well
understood for central (foveal) vision, but not for peripheral vision. In
glaucoma, peripheral optical aberrations affect quality of life (as they add to
the glaucoma-related loss of peripheral vision) and interfere with the most
important diagnostic test in glaucoma, perimetry (visual field testing).

Peripheral optical aberrations may differ between patients with primary open
angle glaucoma (POAG), who are most of the time myopic or emmetropic, and
patients with a narrow anterior chamber angle (primary angle closure; PAC), who
tend to be hyperopic (their lens is relatively large and located closer to the
cornea). Also, the aberrations may differ between patients who had a cataract
extraction in the past (pseudophakic patients) and those who did not (phakic
patients). Especially for peripheral vision, the optical quality of the human
lens is better than that of an artificial intraocular lens (IOL).

Therefore, we propose the current study to further understand these factors.
The main study parameter of this research is the relation between optical
quality and perimetry. We will study this in healthy subjects, POAG patients,
and PAC patients. We aim to include both phakic and pseudophakic subjects in
each group. This is to cover a wider range of peripheral optical quality
because current IOL technology increases peripheral aberrations. Healthy
subjects and POAG patients are only operated if there is a significant
cataract. For that reason, we recruit separate groups for phakic and
pseudophakic subjects. PAC patients are often operated before their lens
becomes cloudy, because the removal of their lens widens the anterior chamber
angle and thus improves their situation from the point of view of intraocular
pressure. This procedure is called a clear lens extraction (CLE) and is the
treatment of choice for narrow angle ocular hypertension or glaucoma. The CLE
offers the opportunity to do a within-subject paired comparison between a clear
human lens and an IOL.

(1) To determine the influence of optical quality on peripheral retinal
sensitivity (as measured with perimetry) for phakic and pseudophakic healthy
eyes, (2) to compare the optical quality between healthy subjects and (phakic
and pseudophakic) POAG patients to check the hypothesis that optics is similar
in these two groups, and (3) to determine the effect of a CLE on the optical
quality and retinal sensitivity in patients with PAC. For classification
purposes, we will also measure retinal sensitivity in the POAG patients.
Hence, we will (1) measure foveal and peripheral optical aberrations and (2)
perform perimetry in phakic and pseudophakic healthy subjects and POAG
patients, and PAC patients before and after a CLE.

Prospective, observational, study.

The healthy volunteers and POAG patients will have one visit to the Laboratory
of Experimental Ophthalmology to perform the experiments. Patients with PAC
scheduled for CLE will be measured before and after the surgery, following the
same protocol and measurements.

Healthy subjects will undergo screening to assess their eye health, which will
comprise a questionnaire (see Appendix F1), visual acuity test (letter chart),
screening visual field test, OCT test of retina and optic nerve head, IOP
measurement, and measurement of the anterior chamber angle. Screening will take
around 20 minutes. If abnormal results are obtained in the screening for
healthy subjects, they will be referred to their GP. Detection of signs of an
eye condition may cause some stress, however, an early diagnosis will allow
treatments to be timely initiated and therefore more preservation of visual
functioning. POAG patients and patients with PAC will not perform any screening
tests, therefore there is no risk of identifying any other eye conditions.
Patients will be recruited from a population of 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 not spend more than 2 hours in our lab to
complete the required tasks.