Glaucoma
Conditions
Keywords
Ocular Physiology, Brimonidine, Timoptic, Dorzolamide, ocular blood flow, Regional Blood Flow
Brief summary
Background Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. The existence of an effective autoregulation in the optic nerve circulation has been shown in animals and humans. The exact mechanism behind this autoregulation is still unknown. The motive for the investigation of optic nerve head (ONH) blood flow autoregulation is to enhance the understanding of pathologic eye conditions associated with ocular vascular disorders. To clarify the regulatory mechanisms of ONH microcirculation is of critical importance to understand the pathophysiology of glaucoma, because there is evidence that glaucoma is associated with optic nerve head ischemia. Several studies indicate that a disturbed autoregulation might contribute to glaucomatous optic neuropathy. Currently, five classes of intraocular pressure (IOP) reducing drugs are available for topical therapy in patients with glaucoma or elevated intraocular pressure. These drugs have also vasoactive properties, which may influence both the resting ocular circulation and the autoregulatory mechanisms of blood flow during changes in ocular perfusion pressure. Study objective To investigate the influence of common topical glaucoma therapy on ONH blood flow regulation during changes in IOP and systemic arterial blood pressure.
Interventions
DRUGTimolol (drug)
Timolol (0.5%, non-selective beta-blocker, Timoptic®, Merck Sharp & Dohme, Haarlem, Netherlands), dose 1 drop in one eye twice daily for two weeks
DRUGdorzolamide (drug)
Dorzolamide (2%, carbonic anhydrase inhibitor, Trusopt®, Laboratoires Merck Sharp & Dohme - Chibret, France), dose: 1 drop in one eye twice daily for two weeks
DRUGbrimonidine (drug)
Brimonidine (0.2%. alpha-2 adrenergic agonist, Alphagan®, Allergan Pharmaceuticals, Westport, Ireland), dose: 1 drop in one eye twice daily for two weeks
DEVICELaser Doppler flowmetry
blood flow measurements at the temporal neuroretinal rim of the optic nerve head, in total 4x 9 minutes on 2 study days
intraocular pressure measurements, in total 2x 5 measurements on two study days
PROCEDURESuction cup method
The IOP will be raised by an 11 mm diameter, standardized suction cup placed on the temporal sclera with the anterior edge at least 1 mm from the limbus; 4x 8 minutes on 2 study days
Sponsors
Medical University of Vienna
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
BASIC_SCIENCE
Masking
DOUBLE (Subject, Investigator)
Eligibility
Sex/Gender
ALL
Age
19 Years to 35 Years
Healthy volunteers
Yes
Inclusion criteria
* Men aged between 19 and 35 years, nonsmokers * Body mass index between 15th and 85th percentile * Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant * Normal ophthalmic findings, ametropia \< 1 Dpt.
Exclusion criteria
* Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study * Treatment in the previous 3 weeks with any drug * Symptoms of a clinically relevant illness in the 3 weeks before the first study day * Blood donation during the previous 3 weeks * Presence of intraocular pathology: ocular hypertension, glaucoma, retinal vasculopathy or other retinal diseases
Design outcomes
Primary
| Measure | Time frame |
|---|---|
| Ocular perfusion pressure - ONH blood flow relationship | on 2 study days |
Secondary
| Measure | Time frame |
|---|---|
| Composite measure: Blood pressure, heart rate | on 2 study days |
Countries
Austria
Outcome results
None listed