*Clinical significance of new OCT parameters in diagnosis and follow-up of primary open angle glaucoma*

Primary open angle glaucoma (POAG) is a gradually progressive optic neuropathy,
resulting in irreversible visual field loss. POAG is accompanied by dysfunction
and apoptosis of retinal ganglion cells, whose axons make up most of the
retinal nerve fibre layer (RNFL). The standard test for progression, on which
most treatment decisions are based, is the VF examination. A disadvantage of VF
testing is the fact that it is subjective, and is not particular sensitive for
the earliest changes in glaucoma.

Optical Coherence Tomography (OCT) is an objective imaging technique, based on
coherence interferometry. Spectral domain (SD) OCT, also known as Fourier
Domain OCT, allows fast acquisition of images with high resolution, and with
SD-OCT one can make very accurate measurements.

Studies have shown that RNFL measurements are highly correlated with visual
function. More importantly it has been demonstrated that up to 25 to 35 % of
RNFL thickness is lost before visual field (VF) defects can be detected.(1) It
is estimated that this so called pre-perimetric phase can last up to 5 years.

Recently some new measurements with SD-OCT have been investigated that show
promise in the diagnostic evaluation of glaucoma patients. These are thickness
measurements of the ganglion cell layer, the lamina cribrosa and the
peripapillary choroid.

It is relevant for clinical practice to determine how these new structural
SD-OCT measurements, either as single measurement or in combination, perform in
the diagnosis of different stages of POAG, compared to functional testing. Also
relevant is to know how these measurements differentiate between glaucoma
patients with a normal and with an elevated baseline IOP, and how sensitive
these measurements are to detect progression over time.

We want to assess the diagnostic performance of retinal nerve fiber layer
(RNFL) thickness, macular ganglion cell layer (GCL) thickness, lamina cribrosa
thickness and choroid thickness around the optic disc measured with SD-OCT in
differentiating patients from healthy controls, between stages of glaucoma,
between patients with a normal and an elevated baseline IOP, and to establish
the accuracy to detect progression of glaucoma.
The new parameters could add to an improved, earlier diagnosis of glaucoma, and
shed light on the pathophysiologic differences between patients with a normal
or higher baseline eye pressure.

This study is a multicenter cross-sectional and follow up study involving
glaucoma patients and healthy subjects.

After signing informed consent, participating patients will be included in each
of the following categories, based on the Hodapp classification: ocular
hypertension, suspect glaucoma, early glaucoma and moderate glaucoma.
Based on intra ocular pressure (IOP) day curves before any kind of treatment,
patients in each of the glaucoma category will also be divided in subgroups of
normal tension glaucoma and high pressure glaucoma. For baseline IOP the
highest documented IOP without treatment is taken.
All patients and healthy controls will undergo a complete ophthalmologic
examination, including best-corrected visual acuity, eye pressure measurement
and slit-lamp examination, including gonioscopy.
RNFL thickness, GCL thickness, lamina cribrosa, and peripapillary choroid
thickness will be measured using SD-OCT (Spectralis, Heidelberg). Visual field
testing will be performed using the Humphrey Field Analyzer (HFA), Swedish
Interactive Thresholding Algorithm (SITA) standard 24-2 perimetry. Age, gender,
family history of glaucoma, duration of ocular hypertension, suspect or other
category of glaucoma will be recorded.

Participants of this study will not be exposed to invasive methods. The study
will require more time of patients than a regular check-up. Furthermore
mydriatic drops will be instilled that can temporarily cause a slight decrease
in vision. In rare cases an allergic reaction can occur, which can temporarily
cause redness of the eye.