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Water Drinking Test for IOP Resurfaces
Sometimes clinical advances require physicians to dust off an old test and put it to a new use. Just such a transformation has happened with the “water drinking test” (WDT) of intraocular pressure. A quarter century after the WDT failed as a diagnostic test, it is regaining attention—this time as a low-tech tool for identifying patients at risk for progression because of undetected, daily spikes in IOP.
The one-hour test provides a surrogate marker of whether an eye’s aqueous outflow system is allowing IOP to climb dangerously and undetectably during the patient’s daily activities, said Remo Susanna Jr., MD, leader of a Brazilian team that began looking at peak pressure and the WDT a decade ago. Studies by his group and others have shown that the peak IOP recorded during the test correlates directly with diurnal peak pressure and is associated with higher risk of progressive visual field loss.
The WDT can tell ophthalmologists whether patients need further intervention despite having achieved target pressures, said Dr. Susanna, who is professor and head of ophthalmology at the University of São Paulo. “Pressure is crucial to the course of glaucoma, but between 40 percent and 60 percent of peak pressures are not detected during an office visit.” Often, the true peak in a patient’s daily pressures is missing from diurnal tension curves and long-term records of the patient’s IOP because the tonometry is not frequent enough or begins too late in the morning, he said. “We have found the water drinking test to be very useful in evaluating these undetected rises in pressure and the speed of the eye’s recovery.”
Dr. Susanna and colleagues conducted a two-year study of open-angle glaucoma patients whose baseline IOP was less than 17 mmHg. Results showed peak pressures on the WDT averaged 1.9 mmHg higher in those whose disease progressed than for those with stable visual fields (p = 0.001).1
Another study led by Dr. Susanna found that in bilateral glaucoma patients the worse-affected eyes had higher pressure peaks, with greater percentage of change, than the contralateral eyes (p < 0.001).2
Recently, the WDT has been gaining greater acceptance as a clinical tool, Dr. Susanna said. In fact, the American Journal of Ophthalmology ran an editorial that characterized the WDT as a way to “enhance the effectiveness of our treatment of some of our most challenging patients.”3
“Knowing the highest pressure that a glaucoma eye experiences diurnally is important,” said Ivan Goldberg, MBBS, coauthor of the AJO editorial. Comprehensive ophthalmologists to whom he spoke at the Academy’s Joint Meeting last fall appeared eager to learn about this inexpensive test that might help them improve patient outcomes, said Dr. Goldberg, an Australian glaucoma subspecialist who is clinical associate professor of ophthalmology and eye health at the University of Sydney and chief of the glaucoma unit at Sydney Eye Hospital. “We have found the water drinking test to be very useful in looking after patients. We are actually modifying our treatment based on the results of the test,” Dr. Goldberg said. “If you have a patient who appears to be progressing despite therapy, or if the patient already has enough damage that they cannot afford to lose any further vision, those are the patients for whom you want to get this WDT information early.”
Dr. Susanna uses the WDT with every glaucoma patient, yet he cautioned against overinterpretation. “There is no positive or negative result of this test. It is just a stress test. It detects whether the peak pressure during the day exceeds the target pressure,” he said. So, if the target pressure is 22 mmHg, and if IOP during the test peaks at 22, then the patient will not progress, he said. But if the target pressure is 15, and if IOP rises to 22 during the test, then similarly large spikes in IOP are occurring throughout the day—indicating a need to reevaluate the treatment plan, due to higher risk of progression, he said.
The biggest skeptics about the WDT’s value usually are ophthalmologists who, like Dr. Goldberg, were in training during the 1960s and 1970s as the water drinking test was being discredited for diagnosis, Dr. Goldberg said.
“It’s normal to have some skepticism when something new is proposed,” said Dr. Susanna. “But when you have more than 30 papers done by different authors at different times and reaching the same result, it’s difficult to say that this is not a useful way to monitor patients over time.”
1 Susanna, R. et al. Br J Ophthalmol
2 Susanna, R. et al. Invest Ophthalmol Vis Sci
3 Goldberg, I. and C. I. Clement. Am J Ophthalmol
A WDT How-To
|No liquids for two hours before the test.
|Measure pre-test IOP.
|Patient drinks 800 to 1,000 ml of water in five minutes.
|Measure IOP 15, 30 and 45 minutes later.
|Compare the highest IOP to the pre-test figure. (In 65 percent of patients, peak occurs at 30 minutes.)
|Repeat test when therapy is changed or if better assessment of IOP is necessary.
|SOURCE: Remo Susanna Jr., MD
New Findings on Feeding and ROP Exams
Pediatric ophthalmologists in Canada have found that feeding premature infants one hour before a retinopathy of prematurity examination may reduce stress in the infants, as measured by decreased crying time, and does not increase the incidence of vomiting or other gastric side effects.1 These findings are contrary to the usual practice in many neonatal intensive care units of withholding feeding from premature infants before ROP examinations in the belief that this reduces gastrointestina distress.
Thirty-four infants were enrolled in the prospective, randomized, single-masked study, with a total of 57 eye exams conducted. In 25 cases the infants were fed one hour before the exam, and for 32 exams they were fed two hours or more beforehand. In the one-hour feeding group, crying occurred 19 percent less often than in the two-hour feeding group. Similarly, infants in the one-hour group had three times less vomiting, fewer gastric side effects and lower diastolic blood pressure.
“This is the first study to examine how feeding schedules affect preterm infants’ stress and gastrointestinal responses to ROP exams,” said lead author Yi Ning J. Strube, MD, assistant professor of pediatric ophthalmology and strabismus at Queen’s University in Kingston, Ontario. “Our results suggest that feeding infants before the exam may provide them comfort. Ophthalmologists conducting ROP exams can now reassure parents and nurses that they can feed their baby according to the infant’s usual feeding schedule prior to the ROP exam.”
Other researchers have reported that neonatal pain may cause increased sensitivity to pain and changes in neurological development. This study emphasizes the importance of managing and reducing neonatal pain during procedures such as the ROP exam and provides new feeding guidelines for infants in neonatal intensive care units that could have beneficial health effects over the infant’s lifetime.
1 Strube, Y. N. et al. J AAPOS
The iPhone May Be the Next Step in Telemedicine
Can the iPhone step in for the standard computer monitor display when it comes to evaluating diabetic retinopathy images?
The answer appears to be yes, according to researchers at the University of Pittsburgh. In a poster presentation at the Academy’s Joint Meeting in Chicago, Robert J. Noecker, MD, MBA, and his colleagues presented the results of their study about the use of an iPhone to transmit fundus photos of 55 patients (110 eyes) who had not been previously diagnosed with DR.1
In comparing the iPhone and standard computer images, the researchers found absolute agreement of 85 percent on such issues as “the presence of macular edema, the presence and degree of any DR, the presence of other findings, such as macular degeneration or glaucoma, image quality and recommended follow-up,” said Dr. Noecker, professor and vice chairman of ophthalmology at the university.
Agreement with regard to clinical diagnosis was higher, at 94 percent. “The images looked the same on the iPhone as on the computer monitor,” said Dr. Noecker.
Overall, Dr. Noecker’s instinct is that portable devices like the iPhone and iPad will become players in telemedicine. “The government wants to improve care, especially specialty care in underserved areas, and this is one way to keep the cost down on the receiving end. It also frees up the receiving doctor to roam about and do other things while interpreting results.”
However, he said, “We need to figure out if it is just trendy to support this, or if it’s clinically worthwhile. It seems promising so far, but it requires new infrastructure [on the IT side], and there are associated support costs.”
1 Noecker, R. J. et al. Poster #38. Presented at the American Academy of Ophthalmology Joint Meeting, Sunday, Oct. 17, 2010. Find it at www.aao.org/2010
Scientists Report Gene Associated With Myopia
The first report of a genome-wide association for common myopia and refractive error was made by a team of researchers led by Terri L. Young, MD, professor of ophthalmology, pediatrics and medicine and a researcher in the Center for Human Genetics at Duke University. Until now, no individual genes had been associated with myopia.
The discovery could lead to screening for susceptibility to myopia and even manipulation of the gene to prevent this ocular disorder, which affects as many as 35 percent of U.S. adults and as many as 80 percent of some Asian populations. Severe myopia can lead to eventual vision loss, said Dr. Young, “not today or tomorrow, but yes.” The eye is a good candidate for gene therapy because it’s small and self-contained, she said. Also, its accessibility allows for noninvasive treatments.
Dr. Young has been following myopia’s genetic trail since 1996, when she began creating linkage maps in families with high-grade myopia and discovered a number of chromosomal locations where genes for the disorder reside. With a team of collaborators she also discovered a gene for myopia in a Chinese population, and genes for primary open-angle glaucoma in Caucasians.
Her recent discovery identified single-nucleotide polymorphisms, or SNPs, of the gene RASGRF1, which lives on chromosome 15q25.1 These SNPs, or alterations in the gene sequence, are related to susceptibility to refractive error. The RASGRF1 gene, associated with focusing errors, is highly expressed in neurons and the retina, and therefore is crucial to retinal function and visual memory consolidation.
The findings were based on Dr. Young’s database of more than 4,000 Caucasian Australian and English twins (the database was developed with collaborators from each country), and corroborated by studying DNA from 9,000 twins from Rotterdam.
Since the RAS gene may be influenced by environmental factors, Dr. Young hopes to discover whether manipulating environmental conditions, such as light and dark, might induce myopia in animal models. “Myopia is not a direct gene-disease issue,” she said. “Just as is the case for AMD and POAG, common average degrees of myopia have now been associated with susceptibility genes.”
1 Hysi, P. G. et al. Nat Genet
Dr. Young’s study was funded by the NIH.
EyeNet thanks Susan Bressler, MD, K. David Epley, MD, and Stephen I. Rosenfeld, MD, for their help with this issue’s
News in Review.