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CDI of Ophthalmic Artery Blood Flow in Patients with TIAs
Letters to the Editor
CDI of Ophthalmic Artery Blood Flow in Patients with TIAs Dear Editor: In "Color Doppler Imaging of the Ophthalmic Artery Blood Flow Spectra of Patients Who Have Had a Transient Ischemic Attack: Correlations with Generalized Iris Transluminance and Pseudoexfoliation Syndrome" (Ophthalmology 1995;102:1199-205), Repo and associates suggested that iris transillumination defects (TIDs) and pseudoexfoliation syndrome may be associated with impaired blood flow to the iris and ciliary body. Their first analysis showed that patients with transient ischemic attacks (TIAs) had a higher incidence of both TIDs and pseudoexfoliation than did an age- and sex-matched control group. They also performed color Doppler imaging (CDI) in both groups and demonstrated an increased resistivity index in the ophthalmic artery of patients with TIAs and iris TIDs. However, the omission of certain data correlations prompted us to write this letter. Color Doppler imaging of the ophthalmic artery may not be the appropriate technology to be used in diagnosing anterior segment ischemia. Direct measurements of the blood flow in the iris via optical means, such as in video capillaroscopy,' would yield a clearer picture of such localized pathology. The color Doppler unit used was an Ultramark 9 (Advanced Technology Laboratories, Bothell, WA) with a 5-MHz transducer, which limits spatial resolution to only 0.28 mm. Therefore, the reproducibility of CDI measurements may be less than that reported with higher (7.5 MHz) frequencies? Several factors influence orbital blood flow measurements with CDI, including blood pressure, blood viscosity, and age.' Blood pressure measurements were not reported by Repo et al. The authors compared a subgroup of patients with TIAs who had TIDs with a subgroup of controls without TIDs and found a significant difference in resistivity index. Significant occlusive carotid disease (internal carotid stenosis > 70%) is associated with decreased peak systolic and end diastolic velocities and increased resistivity indices of the ophthalmic, central retinal, and short posterior ciliary arteries (Costa VP, et al; presented as a poster at the American Academy of Ophthalmology Annual Meeting, Atlanta, Oct/Nov 1995). Repo et al did not perform cm analysis of the carotid function in the control group, but it has been shown that patients with TIAs have a high incidence (> 50%) of anatomically significant lesions of the internal carotid artery.v' Hence, if patients with TIAs have a higher chance of showing occlusive carotid disease, and occlusive carotid disease is associated with higher resistivity indices in the ophthalmic artery, then any subgroup of patients selected
in the TIA group probably would show a higher resistivity index in the ophthalmic artery compared with a control population (theoretically without occlusive carotid disease). It would have been interesting to compare the ophthalmic artery measurements of patients with TIAs with and without TIDs and control subjects with and without TIDs. We congratulate Repo et al on their excellent work, but we suggest consideration of more applicable hemodynamic assessment techniques and more careful attention to all possible factors that influence CDI measurements, with particular reference to carotid artery status. VITAL
P. COSTA, MD
ALaN HARRIS, PHD
sao Paulo, Brazil
References I. Arend 0, Wolf S, Harris A, et aI. Effects of oral contraceptives on conjunctival microcirculation. Clinical Hemorreology 1993; 13:435-45. 2. Harris A, Williamson TH, Martin B, et aI. Test/retest reproducibility of color Doppler imaging assessment of blood flow velocity in orbital vessels. J Glaucoma 1995;4:281-6. 3. Williamson TH, Lowe GDO, Baxter GM. Influence of age, systemic blood pressure, smoking, and blood viscosity on orbital blood flow velocities. Br J Ophthalmol 1995;79: 1722. 4. Rothrock JF, Lyden PD, Vee J, Wiederholt We. "Crescendo" transient ischemic attacks: clinical and angiographic correlations. Neurology 1988;38: 198-20 I. 5. The Amaurosis Fugax Study Group. Current management of amaurosis fugax. Stroke 1990;21 :20 1-8.
Author's reply
Dear Editor: Various methods, both invasive and noninvasive, have been devised to measure blood flow, oxygen saturation, and mean circulation time in ocular structures. The invasive methods used to measure the intraocular blood flow in laboratory animals are unsuitable for clinical use, whereas the noninvasive methods lend themselves more readily to clinical studies in humans. Color Doppler imaging (CDI) is a method of ultrasonography that allows simultaneous two-dimensional imaging of anatomic structures and blood flow. The color image is used as a guide to detect the blood vessels, and Doppler spectral analysis allows quantitative assessment of the blood flow velocities within the blood vessels. Pourcelot's resistive index is suitable to measure the resistance of blood flow
993
CDI of Ophthalmic Artery Blood Flow in Patients with TIAs Dear Editor: In "Color Doppler Imaging of the Ophthalmic Artery Blood Flow Spectra of Patients Who Have Had a Transient Ischemic Attack: Correlations with Generalized Iris Transluminance and Pseudoexfoliation Syndrome" (Ophthalmology 1995;102:1199-205), Repo and associates suggested that iris transillumination defects (TIDs) and pseudoexfoliation syndrome may be associated with impaired blood flow to the iris and ciliary body. Their first analysis showed that patients with transient ischemic attacks (TIAs) had a higher incidence of both TIDs and pseudoexfoliation than did an age- and sex-matched control group. They also performed color Doppler imaging (CDI) in both groups and demonstrated an increased resistivity index in the ophthalmic artery of patients with TIAs and iris TIDs. However, the omission of certain data correlations prompted us to write this letter. Color Doppler imaging of the ophthalmic artery may not be the appropriate technology to be used in diagnosing anterior segment ischemia. Direct measurements of the blood flow in the iris via optical means, such as in video capillaroscopy,' would yield a clearer picture of such localized pathology. The color Doppler unit used was an Ultramark 9 (Advanced Technology Laboratories, Bothell, WA) with a 5-MHz transducer, which limits spatial resolution to only 0.28 mm. Therefore, the reproducibility of CDI measurements may be less than that reported with higher (7.5 MHz) frequencies? Several factors influence orbital blood flow measurements with CDI, including blood pressure, blood viscosity, and age.' Blood pressure measurements were not reported by Repo et al. The authors compared a subgroup of patients with TIAs who had TIDs with a subgroup of controls without TIDs and found a significant difference in resistivity index. Significant occlusive carotid disease (internal carotid stenosis > 70%) is associated with decreased peak systolic and end diastolic velocities and increased resistivity indices of the ophthalmic, central retinal, and short posterior ciliary arteries (Costa VP, et al; presented as a poster at the American Academy of Ophthalmology Annual Meeting, Atlanta, Oct/Nov 1995). Repo et al did not perform cm analysis of the carotid function in the control group, but it has been shown that patients with TIAs have a high incidence (> 50%) of anatomically significant lesions of the internal carotid artery.v' Hence, if patients with TIAs have a higher chance of showing occlusive carotid disease, and occlusive carotid disease is associated with higher resistivity indices in the ophthalmic artery, then any subgroup of patients selected
in the TIA group probably would show a higher resistivity index in the ophthalmic artery compared with a control population (theoretically without occlusive carotid disease). It would have been interesting to compare the ophthalmic artery measurements of patients with TIAs with and without TIDs and control subjects with and without TIDs. We congratulate Repo et al on their excellent work, but we suggest consideration of more applicable hemodynamic assessment techniques and more careful attention to all possible factors that influence CDI measurements, with particular reference to carotid artery status. VITAL
P. COSTA, MD
ALaN HARRIS, PHD
sao Paulo, Brazil
References I. Arend 0, Wolf S, Harris A, et aI. Effects of oral contraceptives on conjunctival microcirculation. Clinical Hemorreology 1993; 13:435-45. 2. Harris A, Williamson TH, Martin B, et aI. Test/retest reproducibility of color Doppler imaging assessment of blood flow velocity in orbital vessels. J Glaucoma 1995;4:281-6. 3. Williamson TH, Lowe GDO, Baxter GM. Influence of age, systemic blood pressure, smoking, and blood viscosity on orbital blood flow velocities. Br J Ophthalmol 1995;79: 1722. 4. Rothrock JF, Lyden PD, Vee J, Wiederholt We. "Crescendo" transient ischemic attacks: clinical and angiographic correlations. Neurology 1988;38: 198-20 I. 5. The Amaurosis Fugax Study Group. Current management of amaurosis fugax. Stroke 1990;21 :20 1-8.
Author's reply
Dear Editor: Various methods, both invasive and noninvasive, have been devised to measure blood flow, oxygen saturation, and mean circulation time in ocular structures. The invasive methods used to measure the intraocular blood flow in laboratory animals are unsuitable for clinical use, whereas the noninvasive methods lend themselves more readily to clinical studies in humans. Color Doppler imaging (CDI) is a method of ultrasonography that allows simultaneous two-dimensional imaging of anatomic structures and blood flow. The color image is used as a guide to detect the blood vessels, and Doppler spectral analysis allows quantitative assessment of the blood flow velocities within the blood vessels. Pourcelot's resistive index is suitable to measure the resistance of blood flow
993