Cataract
Flomax vs. Uroxatral: Time to Switch?
Elderly cataract patients who take a newer alpha1 antagonist, alfuzosin, for benign prostatic hyperplasia (BPH) will reduce their risk for intraoperative floppy iris syndrome compared with tamsulosin (Flomax), a Canadian study has found.
“Although IFIS can definitely occur in association with nonspecific alpha antagonists, such as terazosin (Hytrin), doxazosin (Cardura) and alfuzosin (Uroxatral), our experience has always been that the frequency and severity of IFIS is much greater with tamsulosin,”1-3 said David F. Chang, MD, clinical professor of ophthalmology at the University of California, San Francisco, and a private practice ophthalmologist in Los Altos, Calif. “Because Flomax so dominates the pharmaceutical market for BPH in the United States, however, it has been difficult to compare rates of IFIS associated with the other alpha blockers in clinical trials.” Dr. Chang was the lead author on the study that first reported IFIS.
The Canadian study,4 at a tertiary care hospital in Chicoutimi, Quebec, is a welcome contribution to what is known about the cause of IFIS, said Dr. Chang.
“In Canada, alfuzosin has a greater penetration of the pharmaceutical market for BPH, although it is still only about 20 percent,” Dr. Chang said. “This is therefore the first study to include enough patients taking alfuzosin and tamsulosin to make a valid statistical comparison of their association with IFIS.”
The retrospective study looked at the records of cataract surgery performed on 64 men (92 eyes) with BPH and found 22 men who had been treated exclusively with tamsulosin and 13 who had received only alfuzosin.
The difference in IFIS rates between the groups was strikingly large—86.4 percent for tamsulosin and 15.4 percent for alfuzosin. The adjusted odds ratio of IFIS in patients who had taken tamsulosin compared with patients who had taken alfuzosin was 32.15 (95 percent confidence interval 2.74 to 377.11).
IFIS eyes in the study also had a greater risk of surgical complications such as focal iris stromal atrophy, transient postoperative hypertension, major iris trauma, posterior capsule break with vitreous loss, zonular dehiscence and postoperative cystoid macular edema (P < 0.001). This confirms the experience reported by Dr. Chang and others.
The nonspecific alpha antagonists, terazosin and doxazosin, are associated with postural hypotension because of their effect on vascular smooth muscle. Tamsulosin minimizes this risk because it is specific for the alpha1A receptor subtype, which predominates in the prostate but not in vascular walls, according to Dr. Chang. “Alfuzosin was the newest alpha1 blocker to be FDA approved for BPH,” he said. “Although it is not a subtype-specific alpha antagonist, it does exhibit more uroselectivity than either terazosin or doxazosin.”
According to Dr. Chang, both alfuzosin and tamsulosin are similar in terms of cost. Alpha blockers to treat BPH symptoms are often prescribed by internists and primary care physicians.
“Because Flomax has been around much longer and is such a well-recognized brand, it continues to dominate this market,” he explained. “However, both drugs appear to be equally effective with a similar safety profile, with respect to postural hypotension.”5
“Knowing that alfazosin is less likely to cause IFIS,” Dr. Chang said, “I personally would try this drug first if I had BPH symptoms. Only if it was not effective would I then switch to tamsulosin.”
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1 Chang, D. F. and J. R. Campbell.
J Cataract Refract Surg 2005;31(4):664–673.
2 Chang, D. F. and J. R. Campbell (Letter)
J Cataract Refract Surg 2005;31:2239; author reply 2239–2340.
3 Chang, D. F. and J. R. Campbell (Letter) J Cataract Refract Surg 2005;31:2241; author reply 2241.
4 Blouin M. C. et al.
J Cataract Refract Surg 2007;33:1227–1234.
5 AUA Practice Guidelines Committee.
J Urol 2003;170:530–547.
Refractive Update
Anticipating Ectasia Risk in LASIK Patients
A recent scientific paper published online in Ophthalmology suggests a new way for LASIK surgeons to predict which patients will exhibit corneal ectasia after surgery.
Clinical researchers at Emory University did a meta-analysis of nine years of published results (1997 to 2005) related to corneal ectasia after LASIK. After culling 221 studies down to the 48 most relevant studies with the necessary level of case detail, and after adding in the unreported ectasia cases at Emory, they had 171 cases of corneal ectasia to assess. (A control group consisted of patients with uncomplicated LASIK performed at Emory.)
After analyzing the risk profiles of these cases, they assigned numerical scores to various risk factors for corneal ectasia (see table). The surgeon would add the numbers to reach an individual score, for which the researchers recommend specific actions:
- 0 to 2—Low risk. Proceed with LASIK or surface ablation.
- 3—Moderate risk. Proceed with caution, and consider special informed consent. The safety of surface ablation in these patients has not been established.
- 4 or above—High risk. Do not perform LASIK. The safety of surface ablation has not been established
The evolution over the last decade in the types of ectasia cases reported, as well as other study limitations, might have skewed the results, the researchers admit. “Therefore, it would be ideal to validate this model externally using a large unbiased sample of unpublished ectasia cases that were not part of this analysis,” they write.
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1 Randleman, J. B. et al.
Ophthalmology. Published online July 9, 2007.
| POINTS |
| PARAMETER | 4 | 3 | 2 | 1 | 0 | | Topography pattern
| Forme fruste
keratoconus | Inferior
steepeing/
skewed
radial axis |
| Asymmetric bowtie
| Normal/
symmetric bowtie | | Residual stromal bed
thickness (µm) | <240 | 240-259 | 260-279 | 280-299 | >300 | | Age (years) | | 18-21 | 22-25 | 26-29 | >30 | | Preop corneal thickness (µm) | <450 | 451-480 | 481-510 | | >510 | | Preop
spherical equivalent
manifest refraction (D) | >-14 | >-12 to -14 | >-10 to -12 | >-8 to -10 | -8 or less | | SOURCE: Randleman, J. B. et al. Ophthalmology. Published online July 9, 2007. | | PREDICTING ECTASIA. Patients with a score of 2 or lower are at low risk for ectasia after LASIK or suface ablation. | |
Retina Update
High-Glycemic Foods May Play a Role in AMD
A new potential villain has joined the long list of genetic, environmental and lifestyle factors linked to initiating age-related macular degeneration: the human sweet tooth.
An analysis of data from the Age-Related Eye Diseases Study (AREDS) found an association between AMD and consuming foods such as doughnuts, pancakes and even soda—that is, those with a high glycemic index.
Because simple sugars metabolize quickly, such foods raise blood glucose and insulin levels much higher in the two hours after consumption than do complex carbohydrates. High-glycemic eating has been identified as a contributor to blood-lipid abnormalities and cardiovascular diseases.
The AMD researchers reported their findings on 8,125 eyes in the American Journal of Clinical Nutrition.1 Led by Allen Taylor, PhD, who is chief of the Laboratory for Nutrition and Vision Research at Tufts University, the team used the AREDS food-frequency questionnaires from more than 4,000 elderly people with various stages of macular degeneration to look for connections between AMD stage and dietary glycemic index (dGI). Each person’s dGI was weighted to reflect portion size, glycemic index, total carbohydrate content and frequency of consumption.
After calculating mean dGI values for each AMD risk group and adjusting them for coexisting risk factors such as obesity, the researchers found that high dGI increased the risk of large drusen. Their study put this risk at about 40 percent higher in the highest-dGI quintile than in the lowest.
In subjects with a dGI higher than the median for their gender, they calculated a 49 percent higher risk of advanced disease (geographic atrophy plus neovascularization; P for trend < 0.001). The 95 percent confidence interval for the odds ratio was wide, between 1.19 and 1.85. Still, the researchers estimated that 20 percent of the prevalent AMD cases would have been eliminated if the AREDS subjects had a dGI below the median.
In 2006, when a similar, smaller study in female nurses hinted that lower dGIs might reduce the prevalence of AMD, an accompanying editorial pointed out that any apparent effect might instead be caused by a better diet overall.2
The current study is “provocative,” but it still has not resolved possible confounding factors, said one of that editorial’s authors, Julie A. Mares, PhD, professor of ophthalmology and visual sciences at the University of Wisconsin, Madison.
“It is likely that diets influence the retina over many years, and this study evaluated only recent diets,” Dr. Mares noted. “Therefore, questionnaires do not necessarily accurately estimate the intake of other protective aspects of diet over the decades that diet could influence AMD development.
“Also, people who have higher glycemic index scores may have other unhealthy lifestyles that promote chronic disease processes—such as low physical activity—that have not been accounted for adequately,” she added.
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1 Chiu, C. J. et al.
Am J Clin Nutr 2007;86:180–188.
2 Mares, J. and S. Moeller.
Am J Clin Nutr 2006;83:733–734.
Cornea Report
Estrogen-Ectasia Link?
What about estrogenic weakening of the cornea as a reason for ectasia? A German research group thinks that a reduction in the cornea’s biomechanical stiffness from estrogen might be to blame for some cases of ectasia after refractive surgery.1
When the group at the University of Dresden cultured bovine corneas, the corneal tissue became 12 percent thicker in the presence of estrogen, as opposed to controls cultured without estrogen, which became 6.4 percent thicker. And compared with controls, the biomechanical stiffness of the estrogen-exposed corneas fell by 36 percent.
Corneas are known to thicken from hydration when exposed to estrogen. However, the tissue did not thicken enough to account for the entire decrease in stiffness, the researchers write. “If estrogen would produce only a simple swelling process, we would expect a decrease of the stress value of about 6 percent. However, we found a reduction of the stress of 36 percent, which means that estrogen induces further, more complex, and deeper biomechanical changes than swelling,” they write.
Their explanation? That estrogen alters the types of genes being expressed by keratocytes. This changes the composition of proteins in the extracellular matrix and leads to a degradation of type I-collagen, resulting in increased distensibility and reduced stiffness, which might set the stage for ectasia.
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1 Spoerl, E. et al.
Br J Ophthalmol. Published online June 25, 2007.
