Intraocular pressure of patients with normal tension glaucoma in sitting and side-lying positions using the Goldmann applanation tonometer

Primary open angle glaucoma (POAG) is a gradually progressive optic neuropathy,
resulting in irreversible visual field loss. Elevated intraocular pressure
(IOP) remains the most important known risk factor for progression of glaucoma.
The IOP level and fluctuation seems to play a role in the disease development
and progression, even in cases with statistically normal pressures. The average
diurnal IOP, the peak diurnal IOP and the daily fluctuation of IOP were each
shown to be an independent risk factor for glaucoma progression [1]. Diurnal
IOP fluctuation is greater in glaucomatous patients than in normal patients
[2]. In most individuals, including glaucoma suspects and glaucoma patients,
lying down causes a substantial increase in the IOP [1,2]. This is highly
relevant because people spend about one third of their lives lying down [1].
Therefore, it seems very important that besides office measurement of IOP in
the sitting position, measurements of IOP when lying down are done as well.

Numerous studies evaluated the difference in IOP between sitting and lying down
[2]. However, most of these studies used pneumatic tonometry. Quaranta et al.
[3] showed that the untreated mean supine IOP with Perkins applanation
tonometry is not higher at night when compared to daytime sitting Goldmann
applanation tonometry. However, Perkins applanation tonometry in this study is
compared to Goldmann applanation tonometry. Glovinsky et al. [1] showed that
the IOP (measured by Goldmann applanation tonometry) when lying down was
significantly higher than the mean maximal diurnal sitting IOP among untreated
subjects with ocular hypertension or patients with optic discs suspicious for
glaucoma. Over 20% had an IOP increase of 6 mmHg or more when lying down.
Tuskahara et al. [4] found a 32% greater mean IOP rise (from sitting to supine
position) in patients with normal tension glaucoma (NTG) when compared to those
with primary open-angle glaucoma.

A new system for IOP measurement by slit lamp mounted Goldmann applanation
tonometer in the side lying position was developed by Dr Y. Glovinsky in the
Sheba Medical Centre in Israel. The purpose of this study is to measure the IOP
in sitting and side lying position in patients with NTG, using the device
developed by Dr Y. Glovinsky.

Also the blood pressure will be measured digitally in the sitting and side
lying position. Ocular perfusion pressure (OPP) is defined as the mean arterial
pressure (MAP) minus the IOP. Low OPP is a risk factor for the development and
progression of glaucoma. Low OPP is related to decreased MAP, increased IOP or
both [5]. In this study we want to measure the IOP in patients with NTG in the
sitting and side lying position and measure the blood pressure to calculate
ocular perfusion pressure. These measurements are of clinical relevance because
a higher IOP at night together with a low diastolic blood pressure will alter
perfusion of the optic nerves.

The primary objective is to assess the IOP and MAP in sitting and side lying
position in healthy subjects and in patients with NTG.

A prospective, single center, diagnostic pilot study.

The examination will take 10-15 minutes. First, the participant will be asked
to sit down in a chair. One drop of oxybuprocaine (4 mg/ml) combined with
fluorescine will be instilled in both eyes and the IOP will be measured using a
Goldman applanation tonometer. Then, the blood pressure will be measured
digitally. Secondly, the participant will be asked to lie down on a bed in side
lying position. After 5 minutes, the IOP and blood pressure will be measured
again while the participant is still in side lying position. Both IOP
measurements will be performed with the same tonometer. Finally, the CCT will
be measured, using a pachymeter. All measurements will be performed by an
ophthalmologist or ophthalmologist resident.