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Comanagement Q&A
The Pressure is On!Edited by Paul C. Ajamian, O.D.Submit a question to Dr. Ajamian
Answer: We all know that IOP is but one risk factor in diagnosing and managing glaucoma. Nevertheless, it’s one of the most important indicators we have of whether a particular medication is working, and whether the patient is complying. Performing Goldmann applanation tonometry—the standard of care for measuring IOP—is as much an art as a skill. We must do this carefully and consistently. Expect varied results if untrained technicians take the pressures. Whenever possible, insist that the same person checks the pressure each time for the same patients, and make sure that person records the time she takes the pressure. There are also some other tips that will help you and your staff achieve consistency. First, be sure the illumination on the tonometer tip is optimal. Too dim a light will not allow for accurate viewing of the mires. For ideal visualization, dim the room lights and set the magnification to 16x. Second, the amount of fluorescein that’s used dramatically affects the mires and the end result. Many practitioners still use too much dye, particularly if they use a pre-made anesthetic/fluorescein combination in a bottle. Too much fluorescein leads to mires that are too wide or thick, causing a reading that will be higher than the actual IOP. The opposite is true as well. Mires that are too thin lead to false low readings. You can obtain an ideal amount of dye by touching a small dry fluorescein strip to the lower cul-de-sac. There is no need to paint it onto the lower bulbar conjunctiva. If you apply too much, simply irrigate it out.
Answer: Patients who have had LASIK tend to have lower Goldmann tonometry measurements, says optometrist Paul Karpecki of the Hunkeler Eye Centers, Kansas City, Mo. He says that two extensive studies have shown that LASIK lowers IOP by 2.8mm Hg on average.1,2 “Originally this was thought to be due to flattening of the cornea after the procedure, but it appears to be due to the change in corneal thickness,” Dr. Karpecki says. “In fact, patients who have not had LASIK but simply have abnormally thin corneas will also have lower IOP measurements.” How do you take an accurate reading? “If you’re concerned about the pressure comparison, simply add 3mm Hg to the IOP reading,” Dr. Karpecki says. “That approximates the result you’d get if you used the complex formulas found in the studies to modify pressure.” This rule should apply to all LASIK patients, he says, “since most surgeons understand they should not leave less than 250µ of tissue under the flap, or [achieve] a final pachymetry measurement of 410µ or more.”
Answer: In about 3-4 months, a new hand-held tonometer should be available for patients to self-administer home tests. The patient touches the device to the superior nasal aspect of the closed eyelid, and applies just enough pressure until he or she sees a “pressure phosphene”—a perception like a lighted bull’s-eye. The pressure phosphene tonometer appears to provide comparable results to Goldmann. Bausch & Lomb plans to market the device as the Proview. This instrument may also be helpful in measuring the pressure in-office in situations where getting a Goldmann reading is difficult. Non-contact tonometry and Tonopen instruments can also be used in these situations, but are more expensive. u |
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Q&A? Have a question for Comanagement Q&A? E-mail it to reviewofoptometry@jobson.com , fax it to (610) 492-1049 or send it to: CMQA, Review of Optometry 11 Campus Blvd., Suite 100 Newtown Square, PA 19073 |
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Review of Optometry OnLine December 15, 2000 |
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