Ocular blood flow analysis
Buscemi, Philip M
Part one of a two-part series.
My life-long friend says, “When you’re stuck in one of life’s rivers, go with the flow.” Well, treating glaucoma can sometimes feel like the Amazon. Fortunately, we now know that patients with high intraocular pressures (IOPs) don’t always have glaucoma and that folks with normal or even low pressures can have the disease.
Many current theories revolve around the diagnosis and treatment of glaucoma. One of these makes quite a bit of empiric sense.
Basically, it states that by measuring the ocular blood flow in addition to traditional testing for glaucoma, we can objectively determine the status of the health of the optic nerve and more accurately monitor the efficacy of treatment.
The better the blood flow, the healthier the eye from a glaucomatous standpoint. The greater the increase in blood flow from the baseline, the more efficacious the treatment.
The new diagnostic tools
Paradigm Medical Industries Inc. and Canon USA, Inc. are currently marketing devices with FDA approval to monitor intraocular blood flow. Because of the uniqueness of these instruments, and because I believe they’ll have a significant impact on future clinical practice in treating systemic and ocular diseases, I’ll cover them both in a two-part series.
This month, I’ll focus on Paradigm’s Blood Flow Analyzed and next month I’ll talk indepth about the Canon Laser Blood Flowmeter.
This month’s feature unit
Paradigm’s unit is priced at around $9,000 and is most easily used by mounting it on a slit lamp. It’s basically an electronic ophthalmody– namometer, which indirectly measures overall retinal blood flow. This is accomplished by electronically measuring the expansion and contraction of the globe with a sensor that rests on an anesthetized cornea.
When you view Goldmann mires during applanation tonometry, you can see the expansion and contraction of the cornea with the heartbeat. This event is essentially used to measure the amount of blood that passes through the retina with each heartbeat. The unit also delivers pulse rate and IOPs.
Applying the technique
I found these data clinically useful, which I’ll demonstrate in the following case scenario:
Imagine that a 23-year-old female presents with pressures of 20 mm Hg and is on latanoprost (Xalatan) q.d. There’s no obvious cupping or field loss, but she has a history of elevated pressures. You take her off medication for 6 weeks and follow her pressures, which rise to 23 mm Hg.
Now consider the Blood Flow Analyzer with the same patient. You evaluate her retinal blood flow, and it’s within the normal range. Stop the latanoprost on a trial basis to see what happens. If you see the same increase in IOP, but no significant change in blood flow, keep her off meds and monitor her.
On the other hand, if on the initial evaluation the patient has good blood flow, but you stop meds and her retinal blood flow decreases to an abnormal range, you’d keep her on meds with periodic evaluation.
Uses in glaucoma detection
The Blood Flow Analyzer is a great tool for borderline patients. But where it’s really useful is in evaluating patients with normal tension glaucoma, which can comprise anywhere from 16% to 60% of the population diagnosed with glaucoma, depending on race. In the United States, this figure is thought to be around 20%.
So the question then arises, “Who do you screen for normal tension glaucoma?” From start to finish, Paradigm’s unit takes at least 5 minutes so you may need to build in some extra time if you intend to perform screening on every patient. You should certainly consider screening any patient whom you suspect of having any form of glaucoma, especially low-tension.
When we perform tonometry on every patient to screen for glaucoma, we knowingly will miss 20% who have normal tension glaucoma without further testing. For this reason, I always perform a Humphrey FDT on every patient who’s able to undergo the test. But am I still slighting those patients with low-tension glaucoma whom I may diagnose at a later stage in the disease process?
It’s been shown that in diabetics, blood flow slows prior to any evidence of background retinopathy and that these patients will frequently have areas of nonperfusion requiring photocoagulation. Patients with macular degeneration and arteriolar sclerotic disease show similar reductions.
Beyond this, reduced ocular blood flow is a significant predictor of systemic diseases related to arteriolar sclerotic changes.
Features to consider
The Blood Flow Analyzer is moderately easy to use and is sensitive to changes. It has a simple-to-read printout on transparent film with a sticky backing, which is great for easy insertion into a patient chart.
The exam is reimbursable under the procedure code for ophthalmodynamometry. It serves well in a screening capacity for glaucoma suspects and really adds significantly to your ability to confidently initiate or decline treatment. If you actively treat glaucoma in your practice, you should take a look at this unit.
My biggest issue about Paradigm’s system relates to its variations in ocular rigidity and globe size. Also, laser– assisted in situ keratomileusis (LASIK) thins the cornea and can create the impression of greater blood flow than actually exists because of greater expansion and contraction of the cornea. I could see that these variables might affect the readings from the instrument.
Overall, I give the Blood Flow Analyzer a big thumbs up because it’s inexpensive and clinically useful.
For more information, call Paradigm at (801) 977-8970 or visit www.paradigm-medical.com.
Tune in next month for part two – a look at Canon’s Laser Blood Flowmeter. You may not be able to afford this one, but you’ll definitely want a test ride!
Copyright Boucher Communications, Inc. Oct 2000
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