(Carotid Patency Evaluation, Ocular Pressures)
Oculoplethysmography (OPG) is used to detect the presence of a blockage in the carotid arteries. These arteries, located on each side of the neck, deliver oxygenated blood from the heart to the brain. If the carotid arteries are blocked or narrowed due to fatty deposits, the brain can become deprived of oxygen and stroke (damage to the brain tissue due to lack of blood flow) can occur.
OPG may be used to monitor the success of a carotid endarterectomy, a surgical procedure that treats narrowing of the carotid artery.The OPG test indirectly measures the blood flow in the ophthalmic artery, which branches off the carotid artery and supplies blood to the eye. Suction cups are placed on the eyes for the recording and sensors are placed on the earlobes.
If the pulse arrives at the ophthalmic arteries and the earlobes at the same time, this usually means that the carotid arteries are free of blockage. In contrast, if the pulse arrives at the eyes and the earlobes at different times, this may mean that blood flow in these arteries is restricted.
OPG only estimates the extent of blockage that may be present. If the results are abnormal, than a more precise test called angiography (x-ray evaluation of the artery after injection with an opaque dye) may be necessary.
As a result of ultrasound technology that can assess blood flow in the carotid artery much more easily, OPG is rarely performed anymore.
OPG is often conducted in conjunction with a test called oculopneumoplethysmography (OPPG; OPP-Gee). Like OPG, OPPG can detect a narrowing or blockage of the carotid artery and is given for the same reasons, but the procedure is slightly different.
For OPPG, suction cups resembling contact lenses are placed on the eyes and a stronger vacuum than that used for OPG is applied (about 300 mmHg versus 50 mmHg for OPG). The strong suction temporarily halts the pulses in the ocular artery. When the force of the suction is reduced, the pulses reappear and are recorded. Blood pressure in the arm is also taken. Together, these measurements can be used to determine blood flow through the carotid artery.
Other related procedures that may be performed to evaluate the carotid artery and its branches are cerebral arteriogram and carotid artery duplex scan. Please see these procedures for more information.
Your physician may recommend OPG if you experience ataxia (inability to coordinate muscle movement), syncope (fainting due to lack of blood flow to the brain), or stroke. OPG may also be used to determine blood flow after a carotid endarterectomy (removal of a blockage in the carotid artery).
There may be other reasons for your physician to recommend OPG.
OPG is associated with a risk of corneal abrasion (scratches on the surface of the eye). Not rubbing the eyes or inserting contact lenses immediately after the test can reduce this risk.
OPG should not be performed on persons who have had eye surgery within the previous two to six months or in those with cataracts, conjunctivitis (pinkeye), diabetes mellitus, uncontrolled glaucoma, lens implantation, or a history of retinal detachment.
The test is usually not performed on persons allergic to local anesthetics.
Anesthetic eye drops used for the procedure may cause temporary blurred vision and a mild burning sensation when applied.
OPPG is contraindicated in patients using anticoagulant (blood-thinning) medications, due to the increased risk for conjunctival hemorrhage (bleeding that causes the white part of the eye to become red). OPPG may cause a temporary loss of vision.
There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.
Certain factors or conditions may interfere with the results of the test. These include, but are not limited to, the following:
OPG may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician's practices.
Generally, OPG follows this process:
Once the test is complete, you will be observed for any eye discomfort or light sensitivity, which may indicate corneal abrasion. You will also be instructed not to rub your eyes or insert contact lenses for a few hours.
Your vision may be temporarily blurred. However, once you are home you should contact your physician if blurred vision or any burning or discomfort continues.
Your physician may give you additional or alternate instructions after the procedure, depending on your particular situation.
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