Eyeworld

EW NEWS & OPINION 18 New non-invasive approach for identifying dry eye A new tear stability analysis system (TSAS) offers an accurate, non-invasive al- ternative for evaluating tear dysfunction, accord- ing to Stephen C. Pflugfelder, M.D., professor of ophthalmology, Baylor College of Medicine, Hous- ton. Outcomes from the July 2010 e- published issue of Investigative Ophthalmology and Visual Science in- dicate that the TSAS is a useful de- vice for evaluating dry-eye disease and tear stability. Non-invasive appeal Part of the potential appeal of the TSAS system is the fact that it is a non-invasive test, with measure- ments made using the RT-7000 Auto Refractor-Keratometer (Tomey, Nagoya, Japan). "I think that every- one is looking for better ways of evaluating tear stability, especially in a non-invasive manner," Dr. Pflugfelder said. Typically fluores- cein staining is used here. After it is instilled in the eye, the patient is asked to blink to disperse the dye. Practitioners then count the number of seconds that it takes for the tears to break up. They determine this by looking for discontinuities in the fluorescein stained tear film. "The problem is that it's pretty variable," Dr. Pflugfelder said. "Because you're looking at the cornea, it might be difficult for the observer to detect subtle changes in one area versus an- other." The TSAS system, on the other hand, is an objective digital analysis involving 360-degree rings in the eye. It reflects such rings off the cornea similarly to corneal topogra- phy. "However, rather than taking a single image it takes a series of im- ages," Dr. Pflugfelder said. "Then it analyzes the brightness points on the ring." One image is taken each second for 6 seconds. The TSAS sys- tem then sums up the number of bright spots for each second and plots the changes in brightness. "In a normal eye over the 6 seconds there is a very minimal increase in the number of bright spots," Dr. Pflugfelder said. "But in a dry eye there is a linear increase over the 6 seconds in the number of bright spots, indicating more tear film ir- regularity." In the recent study on the TSAS system, investigators stratified dry- eye participants into three different groups. Included in level one were 23 patients who were complaining of irritation and who had rapid tear breakup but no other dry-eye symp- toms. In level two were 11 patients who were starting to get staining at the ocular surface and on their cornea and conjunctiva. The third group included 11 of the more se- vere level three and four patients. In addition, 25 control subjects with no dry-eye signs and symptoms were included. Effectively identifying dry eye Investigators found the TSAS system to be very reliable. "Those with dry eye clearly had much more corneal surface irregularity that increased over the 6 seconds than the control, which was pretty stable," Dr. Pflugfelder said. The TSAS system also considers the number of bright- ness spots and how much time it takes after the blink to cross the 20- spot dry-eye threshold. "All of the dry-eye groups, including level one, reached that threshold significantly faster than the normal group," Dr. Pflugfelder said. In addition, each of the dry-eye levels was found to have significantly more irregularity than the previous one. Dr. Pflugfelder sees these results as promising. "It does appear that by looking at the change in brightness over the 6 seconds and by plotting it out, we might have a good parame- ter for evaluating improvement in the ocular surface from therapies," he said. "The take-home message is that this appears to be a useful clini- cal test." He stressed, however, that the TSAS system is still evolving. There were no parameters initially provided with the instrumentation to evaluate. "This gives investigators a preliminary means of interpreting the results and perhaps ways to uti- lize the data to compare different groups and treatment," Dr. Pflugfelder said. "It appears to be a useful test that is still in evolution." However, Dr. Pflugfelder views this instrumentation as more geared to clinical trials. "Right now I think that it would be a way of saying that the tears are unstable," he said. "Whether or not it's worth it for the average practitioner to purchase this instrument to use in the clinic, I'm not sure. I don't know that it would be that much more valuable than the fluorescein breakup." For those doing clinical trials, however, it would be a different story. "It would be helpful because it provides a lot more data and it looks February 2011 by Maxine Lipner Senior EyeWorld Contributing Editor Patrolling dry eye with the TSAS system TSAS readout for a mild dry-eye patient Source: Stephen C. 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