- Email: [email protected]
Phacodynamics: An Aspiration Flow vs Vacuum Comparison
TABLE 2. Patient Characteristics and Circulation Time (⌬T50) Before and After Intravitreal tPA Injection in Five Patients
Case
Age
Gender
Duration (week)
Pre-logMAR VA
6-mo logMAR VA
Pre-⌬T50 (second)
Post-⌬T50 (second)
1 2 3 4 5
63 66 63 54 76
F M M M M
8 3 4 4 24
1.2 0.7 0.2 0.2 0.3
0.4 0.2 0.2 0.0 ⫺0.1
5.10 2.80 4.00 4.43 2.57
5.47 3.57 4.13 3.23 2.27
Duration (month) ⫽ duration from the onset of visual impairment to treatment; pre-VA ⫽ pretreatment visual acuity; six month VA ⫽ visual acuity at six months after treatment; Pre-⌬T50 ⫽ pretreatment ⌬T50; Post-⌬T50 ⫽ posttreatment ⌬T50.
and 0.359 ⫾ 0.319 (P ⬍ .05) at six months after intravitreal tPA administration (Table 1). The mean foveal thickness decreased significantly from 738 ⫾ 156 m to 253 ⫾ 164 m (P ⬍ .001) at six months (Table 1). The Figure shows a case in which there was substantial improvement after intravitreal tPA administration. Some cases of BRVO resolve spontaneously, and this is a consideration before treatment. Although several treatments have been reported, only grid-pattern photocoagulation by the Branch Vein Occlusion Study Group has shown any evidence of efficacy. To determine whether grid-pattern photocoagulation or intravitreal tPA injection is more efficacious, we are planning a randomized control trial. In addition, to evaluate the thrombolytic effects of tPA, the retinal circulation time (⌬T50) was calculated in five of 17 patients (Table 2). The ⌬T50 decreased in two eyes and increased in three eyes after treatment. Although the difference in the ⌬T50 between before and after treatment was not significant, we could not conclude that tPA has no thrombolytic effects and additional analysis is needed. Other mechanisms, such as posterior vitreous detachment (PVD) induced by intravitreal tPA6 and development of collateral vessels, might affect the VA improvement. In the current study, two complications developed in one eye each: a focal pigmentary alteration sparing the macula and a retinal hole after PVD induced by tPA, which was treated with photocoagulation and gas tamponade. Since toxicity associated with intravitreal tPA has been reported,7 electroretinograms were performed in eight of the 17 patients. The mean amplitudes of the A- and B-waves were not reduced after treatment (data not shown). However, patients should be carefully observed for tPA toxicity. In conclusion, intravitreal tPA injection might improve VA outcomes and induce resolution of ME. 320
AMERICAN JOURNAL
REFERENCES
1. Frangieh GT, Green WR, Barraquer-Somers E, Finkelstein D. Histopathologic study of nine branch retinal vein occlusions. Arch Ophthalmol 1982;100:1132–1140. 2. Lahey JM, Fong DS, Kearney J. Intravitreal tissue plasminogen activator for acute central retinal vein occlusion. Ophthalmic Surg Lasers 1999;30:427– 434. 3. Elman MJ, Raden RZ, Carrigan A. Intravitreal injection of tissue plasminogen activator for central retinal vein occlusion. Trans Am Ophthalmol Soc 2001;99:219 –221. 4. Ohashi H, Oh H, Nishiwaki H, Nonaka A, Takagi H. Delayed absorption of macular edema accompanying serous retinal detachment after grid laser treatment in patients with branch retinal vein occlusion. Ophthalmology 2004;111:2050 –2056. 5. Yamaji H, Shiraga F, Tsuchida Y, Yamamoto Y, Ohtsuki H. Evaluation of arteriovenous crossing sheathotomy for branch retinal vein occlusion by fluorescein videoangiography and image analysis. Am J Ophthalmol 2004;137:834 – 841. 6. Hesse L, Kroll P. Enzymatically induced posterior vitreous detachment in proliferative diabetic vitreoretinopathy. Klin Monatsbl Augenheilkd 1999;214:84 – 89. 7. Chen SN, Yang TC, Ho CL, Kuo YH, Yip Y, Chao AN. Retinal toxicity of intravitreal tissue plasminogen activator: case report and literature review. Ophthalmology 2003;110:704 –708.
Phacodynamics: An Aspiration Flow vs Vacuum Comparison Wesley Adams, MD, Jason Brinton, BA, Michael Floyd, BA, and Randall J. Olson, MD To compare actual flow and the vacuum necessary to generate that flow for the Advanced Medical
PURPOSE:
Accepted for publication Feb 27, 2006. From the Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah. Supported in part by a grant from Research to Prevent Blindness, Inc, New York, New York, to the Department of Ophthalmology and Visual OF
OPHTHALMOLOGY
AUGUST 2006
Optics Sovereign (Advanced Medical Optics, Santa Ana, California, USA) and the Alcon Legacy (Alcon, Fort Worth, Texas, USA) phacoemulsification machines. DESIGN: In vitro laboratory study. METHODS: Flow was collected and machine indicated vacuum noted from 12 ml/min to 40 ml/min in 2 ml/min steps (20-gauge). Nineteen and 20-gauge tips were also compared. Machine indicated vacuum was converted to actual tip vacuum. RESULTS: Legacy flow (102.4 ⴞ 3.8% of indicated) was significantly more than Sovereign (96.5 ⴞ 3.9%; P < .0001). 20-gauge flow was less than 19-gauge flow (96.1% vs 98.6% of indicated, P < .0001). Sovereign had less unoccluded vacuum (70.3 ⴞ 3.2 mm Hg) than Legacy (89.4 ⴞ 1.2 mm Hg) at 36 ml/min of flow (P < .0001 for 26 to 36 ml/min of flow). CONCLUSION: There is unoccluded vacuum at the phaco tip of these systems at 14 ml/min, of flow and at 40 ml/min, this was 112.0 mm Hg for the Legacy. (Am J Ophthalmol 2006;142:320 –322. © 2006 by Elsevier Inc. All rights reserved.)
L
TABLE 1. Flow as % of Machine Indicated for Alcon Legacy and AMO Sovereign Phacoemulsification Machines With 0.9 mm Tips Machine
Flow as % of Actual
Legacy Sovereign 1.1 mm tip* 0.9 mm tip*
102.4 ⫾ 3.81 96.5 ⫾ 3.91 98.6 ⫾ 3.12 96.1 ⫾ 3.42
*2 Legacy and 2 Sovereign machines in range 24 to 40 ml/min of flow 1. and 2. P ⬍ .0001. Flow was measured from 12 to 40 ml/min in 2 ml/min steps.
TABLE 2. Vacuum Necessary to Create a Specific Flow for Alcon Legacy and AMO Sovereign Phacoemulsification Machines Machine
Legacy
Sovereign
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
0 (0.5 ⫾ 0.7) 2.0 ⫾ 0.2 (3.4 ⫾ 0.2) 4.2 ⫾ 0.4 (7.0 ⫾ 0.7) 11.7 ⫾ 2.1 (17.6 ⫾ 3.1) 20.4 ⫾ 1.1 (2.5 ⫾ 1.4) 26.4 ⫾ 0.5 (30.3 ⫾ 0.6) 31.9 ⫾ 0.4 (36.9 ⫾ 0.4) 39.0 ⫾ 2.4 (45.0 ⫾ 2.7) 49.9 ⫾ 1.8 (56.2 ⫾ 2.0) 58.6 ⫾ 1.2 (61.7 ⫾ 1.3) 70.1 ⫾ 1.5 (73.8 ⫾ 1.6) 75.6 ⫾ 1.4 (79.6 ⫾ 1.5) 89.4 ⫾ 1.2 (88.8 ⫾ 1.2) 100.7 ⫾ 2.1 (99.3 ⫾ 2.0) 112.3 ⫾ 3.6 (107.0 ⫾ 3.0)
4.0 ⫾ 0.2 (7.5 ⫾ 0.4) 10.1 ⫾ 1.8 (14.3 ⫾ 2.6) 17.5 ⫾ 0.4 (14.3 ⫾ 2.6) 20.5 ⫾ 1.6 (27.5 ⫾ 2.2) 25.5 ⫾ 0.8 (33.8 ⫾ 1.0) 28.0 ⫾ 1.9 (37.4 ⫾ 2.6) 30.8 ⫾ 4.1 (38.5 ⫾ 5.2) 37.6 ⫾ 1.8 (45.9 ⫾ 2.2) 43.4 ⫾ 4.0 (54.4 ⫾ 5.2) 53.2 ⫾ 5.1 (59.2 ⫾ 5.4) 57.7 ⫾ 5.3 (71.3 ⫾ 6.8) 64.8 ⫾ 4.7 (75.2 ⫾ 6.8) 70.3 ⫾ 3.2 (85.1 ⫾ 6.2) 76.2* (89.4 ⫾ 3.2) 83.7* (95.5 ⫾ 4.4)
ITTLE HAS BEEN REPORTED ON ACTUAL FLOW/VACUUM
characteristics of phacoemulsification machines. This study specifically looks at the flow/vacuum relationships of the Advanced Medical Optics Sovereign (Advanced Medical Optics, Santa Ana, California, USA)(SOV) and the Alcon Legacy (Alcon, Fort Worth, Texas, USA) (LEG) phacoemulsification machines. Maximum vacuum was set at 300 mm Hg and bottle height at 70 cm. We started at a machine setting of 12 ml/min and each run was a minute long. The aspirate was collected in a graduated cylinder to measure the actual flow and the machine indicated vacuum maximum and minimum during the run were noted. Flow was increased in 2 ml/min increments to 40 ml/min. There were five runs at each setting using a 20-gauge (0.9 mm diameter) straight phaco needle. Also, two LEG and two SOV machines were similarly tested with 20- and 19-gauge (1.1 mm) phaco needles from 24 to 40 ml/min of flow in 2 ml/min increments. The mean aspiration flow and mean vacuum necessary to maintain that flow was determined. Flow was determined as a percent of actual. Vacuum was adjusted to actual measured flow and actual phaco tip vacuum. This has previously been measured with a calibrated vacuum gauge with the vacuum chamber isolated to the tip and correlated with machine indicated vacuum.1 Comparisons were by Student t testing with significance set at P ⬍ .05.
Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah. Dr Olson is a consultant for Advanced Medical Optics. Inquiries to Randall J. Olson, MD, Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, 50 North Medical Drive, Salt Lake City, Utah 84132; e-mail: [email protected]
VOL. 142, NO. 2
*Estimates because actual flow did not occur in this range. This shows actual tip vacuum in mm/Hg at actual flow with machine indicated values in parenthesis.
Aspiration flow as percent of indicated was LEG 102.4 ⫾ 3.8 and SOV 96.5 ⫾ 3.9% (P ⬍ .0001). Flow for a 0.9 mm tip was 96.1 ⫾ 3.4% and for a 1.1 mm tip 98.6 ⫾ 3.1% of machine indicated (P ⬍ .0001, Table 1). Vacuum was minimal at 12 ml/min and higher for LEG (89.4 ⫾ 1.2 mm Hg) than SOV (70.3 ⫾ 3.2 mm Hg) at 36 ml/min flow (P ⬍ .0001 for flow from 26 to 36 ml/min; Tables 2 and 3). A 19-gauge tip decreased average generated vacuum by 18% when compared with a 20-gauge tip (P ⬍ .0001). There may be no correlation between what flow rate is set and the actual flow with peristaltic pumps if a low vacuum limit is set. For instance, LEG with a vacuum limit of 60 mm Hg will generate no more than 30 ml/min of flow with a 20-gauge tip. A 19-gauge tip will increase this flow limit by approximately 18% and increase
BRIEF REPORTS
321
Homocysteine and Retinal Emboli: The Blue Mountains Eye Study
TABLE 3. A Comparison of Actual Vacuum Created for Actual Flow for the Range of 26 Through 36 ml/min in 2 ml/min Steps (0.9 mm tip) Machine
Comparative Value
Sovereign Legacy
1.00 ⫾ .07* 1.16 ⫾ .08*
Brian Chua, BSc, MBBS, MPH, Annette Kifley, MBBS, MAppStat, Tien Y. Wong, FRCS, MPH, PhD, and Paul Mitchell, MD, PhD, FRANZCO To examine the association between serum homocysteine and retinal emboli in a general older population. DESIGN: Cross-sectional population-based study. METHODS: Homocysteine level was determined from fasting venous blood collection at the second Blue Mountains Eye Study (BMES) (n ⴝ 3509, age >49 years, 1997 to 2000). Retinal emboli were graded from retinal photographs. Using logistic regression, we analyzed associations between serum homocysteine and retinal emboli adjusting for age, gender, hypertension, body mass index, and lipid levels. RESULTS: After multivariable adjustment, serum homocysteine was associated with presence of retinal emboli (odds ratio (OR) 1.2; 95% confidence interval (CI), 1.0 to 1.6 per standard deviation [4.8 mol/l] increase in serum homocysteine). CONCLUSION: Elevated serum homocysteine is weakly associated with increased odds of retinal emboli in this older population-based study. (Am J Ophthalmol 2006;142: 322–324. © 2006 by Elsevier Inc. All rights reserved.) PURPOSE:
*P ⬍ .0001. Sovereign was used as reference value of 1.0 for each 2 ml/min step.
the actual flow at any setting by approximately 2.5%. Furthermore, at over 30 ml/min of flow there can be a lot of active, unoccluded vacuum at the tip. While this has been theoretically recognized,2 many assume that only venturi systems have active unoccluded vacuum.3 While instantaneous vacuum may be an advantage for vitrectomy, many cataract surgeons have felt the lack of vacuum at the tip of peristaltic systems until after occlusion is a safety advantage if the iris or capsule is accidentally contacted. What this study shows is this differentiation disappears at the higher flow rates popular today. Bottle elevation would increase the flow without need for vacuum for all systems but would also increase the intraocular pressure. LEG must have either greater restriction than SOV in its normal flow path or a longer restricted area because of the considerably greater vacuum needed to create any specific flow rate when compared with SOV. Flow restriction also explains why a 20-gauge phaco tip requires more vacuum to create flow than a 19-gauge tip. All of these issues must be considered when comparing different phacoemulsification machines. Flow at low maximum vacuum levels may be much lower than indicated on the machine and marked unoccluded vacuum may be present at higher flows with peristaltic machines. This is because vacuum is necessary to maintain flow above 12 ml/min depending on bottle height, especially with a 20-gauge tip. This means, contrary to common belief, there may be active, high vacuum at the phaco tip in peristaltic systems without occlusion.
R
lesterol, fibrin-platelet, or calcium deposits arising from carotid arteries or cardiac valves. They have been associated with an increased risk of stroke and other vascular diseases.1,2 Previous clinic-based studies show that elevated serum homocysteine is an independent risk factor for retinal emboli and other retinal and vascular diseases.3–5 Whether homocysteine is a risk factor for retinal emboli has not been examined in population-based samples, and is assessed in this report. The mechanisms by which elevated homocysteine causes thromboembolic disease are not yet fully elucidated. Homocysteine has been proposed to cause endothelial dysfunction and atherothrombotic disease through (1) vascular inflammation and atherogenesis through proinflammatory cytokine release; (2) oxidative stress, from the production
REFERENCES
Accepted for publication Mar 16, 2006. From the Centre for Vision Research, Department of Ophthalmology, University of Sydney, Sydney, Australia (B.C., A.K., P.M.); and Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, Melbourne, Australia, and Singapore Eye Research Institute, National University of Singapore, Singapore (T.Y.W.). NHMRC Grant 211069. Inquiries to Paul Mitchell, MD, PhD, FRANZCO, University of Sydney Department of Ophthalmology (Centre for Vision Research), Eye Clinic, Westmead Hospital, Hawkesbury Rd, Westmead, NSW, Australia, 2145; e-mail: [email protected]
1. Payne M, Georgescu D, Waite A, Olson R. Actual vacuum pressure at the phacoemulsification tip: a comparison of four phacoemulsification devices. J Cataract Refract Surg. Forthcoming. 2. Seibel, BS. Phacodynamics, 2nd ed. Thorofare, New Jersey: Slack Inc, 1995:6. 3. Zacharias J, Zacharias S. Volume-based characterization of post occlusion surge. J Cataract Refract Surg 2005;31: 1976 –1982.
322
AMERICAN JOURNAL
ETINAL EMBOLI ARE DISCRETE INTRALUMINAL CHO-
OF
OPHTHALMOLOGY
AUGUST 2006
Case
Age
Gender
Duration (week)
Pre-logMAR VA
6-mo logMAR VA
Pre-⌬T50 (second)
Post-⌬T50 (second)
1 2 3 4 5
63 66 63 54 76
F M M M M
8 3 4 4 24
1.2 0.7 0.2 0.2 0.3
0.4 0.2 0.2 0.0 ⫺0.1
5.10 2.80 4.00 4.43 2.57
5.47 3.57 4.13 3.23 2.27
Duration (month) ⫽ duration from the onset of visual impairment to treatment; pre-VA ⫽ pretreatment visual acuity; six month VA ⫽ visual acuity at six months after treatment; Pre-⌬T50 ⫽ pretreatment ⌬T50; Post-⌬T50 ⫽ posttreatment ⌬T50.
and 0.359 ⫾ 0.319 (P ⬍ .05) at six months after intravitreal tPA administration (Table 1). The mean foveal thickness decreased significantly from 738 ⫾ 156 m to 253 ⫾ 164 m (P ⬍ .001) at six months (Table 1). The Figure shows a case in which there was substantial improvement after intravitreal tPA administration. Some cases of BRVO resolve spontaneously, and this is a consideration before treatment. Although several treatments have been reported, only grid-pattern photocoagulation by the Branch Vein Occlusion Study Group has shown any evidence of efficacy. To determine whether grid-pattern photocoagulation or intravitreal tPA injection is more efficacious, we are planning a randomized control trial. In addition, to evaluate the thrombolytic effects of tPA, the retinal circulation time (⌬T50) was calculated in five of 17 patients (Table 2). The ⌬T50 decreased in two eyes and increased in three eyes after treatment. Although the difference in the ⌬T50 between before and after treatment was not significant, we could not conclude that tPA has no thrombolytic effects and additional analysis is needed. Other mechanisms, such as posterior vitreous detachment (PVD) induced by intravitreal tPA6 and development of collateral vessels, might affect the VA improvement. In the current study, two complications developed in one eye each: a focal pigmentary alteration sparing the macula and a retinal hole after PVD induced by tPA, which was treated with photocoagulation and gas tamponade. Since toxicity associated with intravitreal tPA has been reported,7 electroretinograms were performed in eight of the 17 patients. The mean amplitudes of the A- and B-waves were not reduced after treatment (data not shown). However, patients should be carefully observed for tPA toxicity. In conclusion, intravitreal tPA injection might improve VA outcomes and induce resolution of ME. 320
AMERICAN JOURNAL
REFERENCES
1. Frangieh GT, Green WR, Barraquer-Somers E, Finkelstein D. Histopathologic study of nine branch retinal vein occlusions. Arch Ophthalmol 1982;100:1132–1140. 2. Lahey JM, Fong DS, Kearney J. Intravitreal tissue plasminogen activator for acute central retinal vein occlusion. Ophthalmic Surg Lasers 1999;30:427– 434. 3. Elman MJ, Raden RZ, Carrigan A. Intravitreal injection of tissue plasminogen activator for central retinal vein occlusion. Trans Am Ophthalmol Soc 2001;99:219 –221. 4. Ohashi H, Oh H, Nishiwaki H, Nonaka A, Takagi H. Delayed absorption of macular edema accompanying serous retinal detachment after grid laser treatment in patients with branch retinal vein occlusion. Ophthalmology 2004;111:2050 –2056. 5. Yamaji H, Shiraga F, Tsuchida Y, Yamamoto Y, Ohtsuki H. Evaluation of arteriovenous crossing sheathotomy for branch retinal vein occlusion by fluorescein videoangiography and image analysis. Am J Ophthalmol 2004;137:834 – 841. 6. Hesse L, Kroll P. Enzymatically induced posterior vitreous detachment in proliferative diabetic vitreoretinopathy. Klin Monatsbl Augenheilkd 1999;214:84 – 89. 7. Chen SN, Yang TC, Ho CL, Kuo YH, Yip Y, Chao AN. Retinal toxicity of intravitreal tissue plasminogen activator: case report and literature review. Ophthalmology 2003;110:704 –708.
Phacodynamics: An Aspiration Flow vs Vacuum Comparison Wesley Adams, MD, Jason Brinton, BA, Michael Floyd, BA, and Randall J. Olson, MD To compare actual flow and the vacuum necessary to generate that flow for the Advanced Medical
PURPOSE:
Accepted for publication Feb 27, 2006. From the Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah. Supported in part by a grant from Research to Prevent Blindness, Inc, New York, New York, to the Department of Ophthalmology and Visual OF
OPHTHALMOLOGY
AUGUST 2006
Optics Sovereign (Advanced Medical Optics, Santa Ana, California, USA) and the Alcon Legacy (Alcon, Fort Worth, Texas, USA) phacoemulsification machines. DESIGN: In vitro laboratory study. METHODS: Flow was collected and machine indicated vacuum noted from 12 ml/min to 40 ml/min in 2 ml/min steps (20-gauge). Nineteen and 20-gauge tips were also compared. Machine indicated vacuum was converted to actual tip vacuum. RESULTS: Legacy flow (102.4 ⴞ 3.8% of indicated) was significantly more than Sovereign (96.5 ⴞ 3.9%; P < .0001). 20-gauge flow was less than 19-gauge flow (96.1% vs 98.6% of indicated, P < .0001). Sovereign had less unoccluded vacuum (70.3 ⴞ 3.2 mm Hg) than Legacy (89.4 ⴞ 1.2 mm Hg) at 36 ml/min of flow (P < .0001 for 26 to 36 ml/min of flow). CONCLUSION: There is unoccluded vacuum at the phaco tip of these systems at 14 ml/min, of flow and at 40 ml/min, this was 112.0 mm Hg for the Legacy. (Am J Ophthalmol 2006;142:320 –322. © 2006 by Elsevier Inc. All rights reserved.)
L
TABLE 1. Flow as % of Machine Indicated for Alcon Legacy and AMO Sovereign Phacoemulsification Machines With 0.9 mm Tips Machine
Flow as % of Actual
Legacy Sovereign 1.1 mm tip* 0.9 mm tip*
102.4 ⫾ 3.81 96.5 ⫾ 3.91 98.6 ⫾ 3.12 96.1 ⫾ 3.42
*2 Legacy and 2 Sovereign machines in range 24 to 40 ml/min of flow 1. and 2. P ⬍ .0001. Flow was measured from 12 to 40 ml/min in 2 ml/min steps.
TABLE 2. Vacuum Necessary to Create a Specific Flow for Alcon Legacy and AMO Sovereign Phacoemulsification Machines Machine
Legacy
Sovereign
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
0 (0.5 ⫾ 0.7) 2.0 ⫾ 0.2 (3.4 ⫾ 0.2) 4.2 ⫾ 0.4 (7.0 ⫾ 0.7) 11.7 ⫾ 2.1 (17.6 ⫾ 3.1) 20.4 ⫾ 1.1 (2.5 ⫾ 1.4) 26.4 ⫾ 0.5 (30.3 ⫾ 0.6) 31.9 ⫾ 0.4 (36.9 ⫾ 0.4) 39.0 ⫾ 2.4 (45.0 ⫾ 2.7) 49.9 ⫾ 1.8 (56.2 ⫾ 2.0) 58.6 ⫾ 1.2 (61.7 ⫾ 1.3) 70.1 ⫾ 1.5 (73.8 ⫾ 1.6) 75.6 ⫾ 1.4 (79.6 ⫾ 1.5) 89.4 ⫾ 1.2 (88.8 ⫾ 1.2) 100.7 ⫾ 2.1 (99.3 ⫾ 2.0) 112.3 ⫾ 3.6 (107.0 ⫾ 3.0)
4.0 ⫾ 0.2 (7.5 ⫾ 0.4) 10.1 ⫾ 1.8 (14.3 ⫾ 2.6) 17.5 ⫾ 0.4 (14.3 ⫾ 2.6) 20.5 ⫾ 1.6 (27.5 ⫾ 2.2) 25.5 ⫾ 0.8 (33.8 ⫾ 1.0) 28.0 ⫾ 1.9 (37.4 ⫾ 2.6) 30.8 ⫾ 4.1 (38.5 ⫾ 5.2) 37.6 ⫾ 1.8 (45.9 ⫾ 2.2) 43.4 ⫾ 4.0 (54.4 ⫾ 5.2) 53.2 ⫾ 5.1 (59.2 ⫾ 5.4) 57.7 ⫾ 5.3 (71.3 ⫾ 6.8) 64.8 ⫾ 4.7 (75.2 ⫾ 6.8) 70.3 ⫾ 3.2 (85.1 ⫾ 6.2) 76.2* (89.4 ⫾ 3.2) 83.7* (95.5 ⫾ 4.4)
ITTLE HAS BEEN REPORTED ON ACTUAL FLOW/VACUUM
characteristics of phacoemulsification machines. This study specifically looks at the flow/vacuum relationships of the Advanced Medical Optics Sovereign (Advanced Medical Optics, Santa Ana, California, USA)(SOV) and the Alcon Legacy (Alcon, Fort Worth, Texas, USA) (LEG) phacoemulsification machines. Maximum vacuum was set at 300 mm Hg and bottle height at 70 cm. We started at a machine setting of 12 ml/min and each run was a minute long. The aspirate was collected in a graduated cylinder to measure the actual flow and the machine indicated vacuum maximum and minimum during the run were noted. Flow was increased in 2 ml/min increments to 40 ml/min. There were five runs at each setting using a 20-gauge (0.9 mm diameter) straight phaco needle. Also, two LEG and two SOV machines were similarly tested with 20- and 19-gauge (1.1 mm) phaco needles from 24 to 40 ml/min of flow in 2 ml/min increments. The mean aspiration flow and mean vacuum necessary to maintain that flow was determined. Flow was determined as a percent of actual. Vacuum was adjusted to actual measured flow and actual phaco tip vacuum. This has previously been measured with a calibrated vacuum gauge with the vacuum chamber isolated to the tip and correlated with machine indicated vacuum.1 Comparisons were by Student t testing with significance set at P ⬍ .05.
Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah. Dr Olson is a consultant for Advanced Medical Optics. Inquiries to Randall J. Olson, MD, Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, 50 North Medical Drive, Salt Lake City, Utah 84132; e-mail: [email protected]
VOL. 142, NO. 2
*Estimates because actual flow did not occur in this range. This shows actual tip vacuum in mm/Hg at actual flow with machine indicated values in parenthesis.
Aspiration flow as percent of indicated was LEG 102.4 ⫾ 3.8 and SOV 96.5 ⫾ 3.9% (P ⬍ .0001). Flow for a 0.9 mm tip was 96.1 ⫾ 3.4% and for a 1.1 mm tip 98.6 ⫾ 3.1% of machine indicated (P ⬍ .0001, Table 1). Vacuum was minimal at 12 ml/min and higher for LEG (89.4 ⫾ 1.2 mm Hg) than SOV (70.3 ⫾ 3.2 mm Hg) at 36 ml/min flow (P ⬍ .0001 for flow from 26 to 36 ml/min; Tables 2 and 3). A 19-gauge tip decreased average generated vacuum by 18% when compared with a 20-gauge tip (P ⬍ .0001). There may be no correlation between what flow rate is set and the actual flow with peristaltic pumps if a low vacuum limit is set. For instance, LEG with a vacuum limit of 60 mm Hg will generate no more than 30 ml/min of flow with a 20-gauge tip. A 19-gauge tip will increase this flow limit by approximately 18% and increase
BRIEF REPORTS
321
Homocysteine and Retinal Emboli: The Blue Mountains Eye Study
TABLE 3. A Comparison of Actual Vacuum Created for Actual Flow for the Range of 26 Through 36 ml/min in 2 ml/min Steps (0.9 mm tip) Machine
Comparative Value
Sovereign Legacy
1.00 ⫾ .07* 1.16 ⫾ .08*
Brian Chua, BSc, MBBS, MPH, Annette Kifley, MBBS, MAppStat, Tien Y. Wong, FRCS, MPH, PhD, and Paul Mitchell, MD, PhD, FRANZCO To examine the association between serum homocysteine and retinal emboli in a general older population. DESIGN: Cross-sectional population-based study. METHODS: Homocysteine level was determined from fasting venous blood collection at the second Blue Mountains Eye Study (BMES) (n ⴝ 3509, age >49 years, 1997 to 2000). Retinal emboli were graded from retinal photographs. Using logistic regression, we analyzed associations between serum homocysteine and retinal emboli adjusting for age, gender, hypertension, body mass index, and lipid levels. RESULTS: After multivariable adjustment, serum homocysteine was associated with presence of retinal emboli (odds ratio (OR) 1.2; 95% confidence interval (CI), 1.0 to 1.6 per standard deviation [4.8 mol/l] increase in serum homocysteine). CONCLUSION: Elevated serum homocysteine is weakly associated with increased odds of retinal emboli in this older population-based study. (Am J Ophthalmol 2006;142: 322–324. © 2006 by Elsevier Inc. All rights reserved.) PURPOSE:
*P ⬍ .0001. Sovereign was used as reference value of 1.0 for each 2 ml/min step.
the actual flow at any setting by approximately 2.5%. Furthermore, at over 30 ml/min of flow there can be a lot of active, unoccluded vacuum at the tip. While this has been theoretically recognized,2 many assume that only venturi systems have active unoccluded vacuum.3 While instantaneous vacuum may be an advantage for vitrectomy, many cataract surgeons have felt the lack of vacuum at the tip of peristaltic systems until after occlusion is a safety advantage if the iris or capsule is accidentally contacted. What this study shows is this differentiation disappears at the higher flow rates popular today. Bottle elevation would increase the flow without need for vacuum for all systems but would also increase the intraocular pressure. LEG must have either greater restriction than SOV in its normal flow path or a longer restricted area because of the considerably greater vacuum needed to create any specific flow rate when compared with SOV. Flow restriction also explains why a 20-gauge phaco tip requires more vacuum to create flow than a 19-gauge tip. All of these issues must be considered when comparing different phacoemulsification machines. Flow at low maximum vacuum levels may be much lower than indicated on the machine and marked unoccluded vacuum may be present at higher flows with peristaltic machines. This is because vacuum is necessary to maintain flow above 12 ml/min depending on bottle height, especially with a 20-gauge tip. This means, contrary to common belief, there may be active, high vacuum at the phaco tip in peristaltic systems without occlusion.
R
lesterol, fibrin-platelet, or calcium deposits arising from carotid arteries or cardiac valves. They have been associated with an increased risk of stroke and other vascular diseases.1,2 Previous clinic-based studies show that elevated serum homocysteine is an independent risk factor for retinal emboli and other retinal and vascular diseases.3–5 Whether homocysteine is a risk factor for retinal emboli has not been examined in population-based samples, and is assessed in this report. The mechanisms by which elevated homocysteine causes thromboembolic disease are not yet fully elucidated. Homocysteine has been proposed to cause endothelial dysfunction and atherothrombotic disease through (1) vascular inflammation and atherogenesis through proinflammatory cytokine release; (2) oxidative stress, from the production
REFERENCES
Accepted for publication Mar 16, 2006. From the Centre for Vision Research, Department of Ophthalmology, University of Sydney, Sydney, Australia (B.C., A.K., P.M.); and Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, Melbourne, Australia, and Singapore Eye Research Institute, National University of Singapore, Singapore (T.Y.W.). NHMRC Grant 211069. Inquiries to Paul Mitchell, MD, PhD, FRANZCO, University of Sydney Department of Ophthalmology (Centre for Vision Research), Eye Clinic, Westmead Hospital, Hawkesbury Rd, Westmead, NSW, Australia, 2145; e-mail: [email protected]
1. Payne M, Georgescu D, Waite A, Olson R. Actual vacuum pressure at the phacoemulsification tip: a comparison of four phacoemulsification devices. J Cataract Refract Surg. Forthcoming. 2. Seibel, BS. Phacodynamics, 2nd ed. Thorofare, New Jersey: Slack Inc, 1995:6. 3. Zacharias J, Zacharias S. Volume-based characterization of post occlusion surge. J Cataract Refract Surg 2005;31: 1976 –1982.
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