Optic Nerve Compliance Study
Information source: Capital Vision Research Trust
ClinicalTrials.gov processed this data on August 20, 2015 Link to the current ClinicalTrials.gov record.
Condition(s) targeted: Glaucoma
Intervention: Brief Elevation of IOP (Procedure)
Phase: N/A
Status: Completed
Sponsored by: Capital Vision Research Trust Official(s) and/or principal investigator(s): Anthony P Wells, FRANZCO, Principal Investigator, Affiliation: CVRT, Wellington School Of Medicine - University of Otago
Summary
Chronic glaucoma is one of the leading causes of blindness and visual loss in the developed
world. It is a condition where long term exposure to high eye pressures (intra-ocular
pressure) damages the nerve fibres in the eye. This damage can be seen by examiners as
changes in the optic nerve. The exact mechanism of how the high intra-ocular pressure causes
nerve damage is unknown. Both physiological and mechanical mechanisms are thought to play a
role. Previous authors have reported structural changes in the connective tissue of optic
nerves of eyes with glaucoma. Structural changes in the optic nerve head which affect the
mechanical compliance of the nerve may be significant in the cause of glaucomatous nerve
damage. This study aims to assess the compliance of the optic disc in subjects with and
without glaucoma. We would test compliance by imaging the optic discs of participants before
and during a brief (less than two minutes) increase in intra-ocular pressure. We would aim
to repeat the tests on the same subjects 3 years later to see how compliance changed. We
would also seek to correlate other important parameters such as corneal thickness and visual
field changes with our findings
Clinical Details
Official title: Optic Nerve Compliance Study
Study design: Allocation: Non-Randomized, Endpoint Classification: Safety Study, Intervention Model: Single Group Assignment, Masking: Open Label
Primary outcome: Optic Disc ChangeVisual Field Progression
Secondary outcome: Visual Acuity Change
Detailed description:
Chronic glaucoma is one of the leading causes of blindness and visual loss in the developed
world (the following reference gives rate of visual impairment/blindness caused by glaucoma
in one cross-section of an older Australian population as 6% - Foran S, Wang JJ, Mitchell P.
Causes of visual impairment in two older population cross-sections: the Blue Mountains Eye
Study. Ophthalmic Epidemiol. 2003 Oct;10(4):215-25). Glaucoma is a condition where long term
exposure to high eye pressures (intra-ocular pressure) damages the nerve fibres in the eye.
The exact mechanism of how the high intra-ocular pressure causes nerve damage is unknown
(Albon J, Purslow PP, Karwatowski WS, Easty DL. Age related compliance of the lamina
cribrosa in human eyes. Br J Ophthalmol. 2000 Mar;84(3):318-23). Both physiological and
mechanical mechanisms are thought to play a role. Previous authors have reported structural
changes in the connective tissue of optic discs of eyes with glaucoma, and postulated that
this may contribute to changes in the compliance of the optic nerve head (Pena JD, Netland
PA, Vidal I, Dorr DA, Rasky A, Hernandez MR. Elastosis of the lamina cribrosa in
glaucomatous optic neuropathy. Exp Eye Res. 1998 Nov;67(5):517-24). Structural changes in
the optic nerve head which affect the mechanical compliance of the nerve may be significant
in the cause of glaucomatous nerve damage. This study aims to assess the compliance of the
optic disc in subjects with and without glaucoma. We would test compliance by imaging the
optic discs of participants before and during a brief increase in intra-ocular pressure. We
would aim to repeat the tests on the same subjects 3 years later to see how the optic nerve
compliance changed. We would also look to correlate changes with other ocular parameters
such as corneal thickness and visual field defects.
1. Non-glaucoma group
Inclusion criteria:
Age over 18
Exclusion criteria:
Previous eye surgery Best corrected visual acuity <6/9 Chronic eye disease (including
glaucoma) Glaucomatous optic disc Ocular perfusion abnormalities (e. g. previous retinal
artery or vein occlusion; or abnormal vasculature including those whose retinal
circulation might be compromised by pressure on the eye).
2. Glaucoma group
Inclusion criteria:
Age over 18 Diagnosis of glaucoma (visual field proven) Stable, well controlled glaucoma
Exclusion criteria:
Secondary glaucoma (eg uveitis, neovascular glaucoma, etc) Advanced or fixation-threatening
visual field changes Previous eye surgery Chronic eye disease (not including glaucoma)
Ocular perfusion abnormalities (e. g. previous retinal artery or vein occlusion; or abnormal
vasculature including those whose retinal circulation might be compromised by pressure on
the eye).
Two different groups of participants will be studied, those with glaucoma, and those without
glaucoma. Participants will have a routine eye examination performed by an experienced
doctor. Information such as visual acuity, intra-ocular pressure, corneal thickness, and
optic nerve appearance will be obtained. Then participants will have their optic nerves
imaged by a Heidelberg retinal tomograph (HRT). The intra-ocular pressure will then be
artificially raised to approximately 50 mmHg for approximately two to four minutes using a
suction cup oculopressor. The optic nerve will be imaged again by the HRT during that time.
From the HRT images we will calculate the optic nerve compliance using measures such as mean
position of the disc, and optic cup area and volume. This data will then be analysed
statistically to look for a significant difference in the optic nerve compliance of the two
groups. Participants will then undergo the same testing procedure 3 years later to see how
their optic nerve compliance has changed. We will then examine these changes to see how they
correlate with changes in their vision. These changes would include: development of
glaucoma; decreased visual acuity; reduced visual field.
Clinical methods – history and examination. Visual field testing (in those with glaucoma)
using an automated visual field testing machine.
Intra-ocular pressure measurement using a Goldmann tonometer. Corneal thickness measurement
using a “Pachmate”, pachymeter. Optic disc images using a Heidelberg retinal tomograph (a
confocal scanning diode laser ophthalmoscope).
There is a theoretical risk that a short term rise in intra-ocular can compromise the blood
supply to the optic nerve and cause optic nerve damage. However a previous study looking at
optic nerve compliance found no side-effects after a short term rise in intraocular pressure
induced with a suction cup (Augusto, A., Harris, A., Cantor, L., Abreu, M., & Weinland, M.
Effects of short term increase of intraocular pressure on optic disc cupping. British
Journal of Ophthalmology. 1998. 82, 880-883). Also a recent study has shown that a short
term rise in intra-ocular pressure does not alter the response of retinal and optic nerve
head blood flow (Garhofer, G., Resch, H., Weigert., Lung, S., Simader, C. & Schmetterer, L.
Short-term increase of intraocular pressure does not alter the response of retinal and optic
nerve head blood flow to flicker stimulation. Investigative Ophthalmology & Visual Science.
2005. 46(5), 880-883). We also know from clinical experience that patients with short term
rises in intra-ocular pressure caused by vitreo-retinal surgery and acute angle closure
glaucoma do not have long term side effects from raised pressure for hours.
To further reduce the risk of side-effects we will exclude those with advanced or fixation
threatening glaucoma changes. We will also exclude those whose retinal circulation is seen
to be compromised by digital pressure on the eye during examination.
Eligibility
Minimum age: 18 Years.
Maximum age: N/A.
Gender(s): Both.
Criteria:
Inclusion Criteria:
- Age over 18, Diagnosis of glaucoma (visual field proven), Stable, well controlled
glaucoma
Exclusion Criteria:
- Previous eye surgery, Best corrected visual acuity <6/9, Chronic eye disease
(including glaucoma, Secondary glaucoma (eg uveitis, neovascular glaucoma, etc),
Advanced or fixation-threatening visual field changes, Ocular perfusion abnormalities
(e. g. previous retinal artery or vein occlusion; or abnormal vasculature including
those whose retinal circulation might be compromised by pressure on the eye).
Locations and Contacts
Capital Vision Research Trust, Wellington 6001, New Zealand
Additional Information
Starting date: March 2006
Last updated: October 16, 2006
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