Risk Management

Faulty A-Scan Readings Present Potential Liability

By Jean Hausheer Ellis, MD

Argus, April, 1994

A-scan Biometry, used to measure axial length in calculating intraocular lens power, presents potential liability hazards for the ophthalmologist. Axial length measurement is one of several important factors influencing the accuracy of intraocular lens power calculation. Myopia or Hyperopia induced because of inaccurate measurements are unpleasant postoperative surprises, unacceptable to patients and ophthalmologists.

Current ultrasound techniques allow better pre-op measurements with a possible accuracy or reproducibility to within 0.1 mm or less in axial length measurement. An error of 0.1 mm in axial length measurement preoperatively has been known to cause a postoperative refractive error of 0.25 diopters. The current standard of care calls for performing preoperative ultrasound and axial biometry rather than using a “standard lens power” based only on the preoperative refractive error.

Thanks to improvements in ultrasound technology and equipment over the years, the trained ophthalmic assistant or the ophthalmologist can more reliably and more predictably perform this test in the office or the hospital. Advancements in intraocular lenses require increased precision in axial length measurements, especially with multifocal intraocular lens designs. As ophthalmologists continue to closely track their postoperative refractive results and compare these to the desired preoperative refraction, they must pay closer attention to techniques, data interpretation, instrumentation and bilaterality of axial length measurements, as well as to which examiner is the most reliable, precise and reproducible tester.

A frequent risk management question is, who should perform the ultrasound and axial length measurements, the ophthalmologist or trained staff? As “captains of the shop,” ophthalmologists are responsible for staying current in their knowledge and understanding of this area. They typically oversee the work of their staff, check for errors (before the wrong lens implant is inserted in the eye), and are proficient at repeating the measurements in difficult eyes or when results are questionable.

It is wise to develop a “check and balance” system for taking and interpreting these measurements so they can be double-checked and rated as to their “ease” or “difficulty.” One suggestion is that the examiner record each individual measurement and rate each as “easy,” “medium” or “difficult” (A, B or C) in the patient record to better assure selection of the best one. In borderline cases, with difficult eyes, or when test results appear unusual, the measurements can be repeated by another individual and the results compared.

Should ultrasound and axial length measurements always be taken bilaterally? The answer is “yes” with only a few exceptions-one-eyed patients and pseudophakic second eyes. In pseudophakes whose previous measurements were taken elsewhere, attempts can be made to obtain previous biometry information and compare preoperative values for the two eyes. While reviewing a patient’s previous axial measurements can be helpful, you should perform your own ultrasound and axial length measurements to ensure reliability and reproducibility. Do not accept someone else’s measurements at face value. Even if you checked these measurements on the same patient several years ago, it is prudent to repeat the test as a quick check of yourself, your staff and your equipment. It is far less costly to retest the patient at no charge and to find that an error was made in the previous measurements than to have an unacceptable postoperative refractive error based on faulty measurements-a result that may lead to a malpractice suit.

If you are thinking about upgrading your equipment, consider a water immersion probe. It will not compress the cornea and, when combined with a standard contact probe, allows more flexibility. Since the ophthalmologist is ultimately responsible for thoroughly reviewing all measurements and ultrasonic data, look for equipment that can photograph test results. This serves as a useful guide and monitor, both pre- and postoperatively. Multiple readings are best, with the ophthalmologist choosing the ultimate test result. Creating a system for double-checking this information as it is entered into the lens implant calculation is well advised, again to reduce the chance for human error.

Ultimately, the ophthalmologist needs to be fully aware of who is performing these important measurements. Some hospital facilities routinely used trained staff members to perform these tests. While most will be accurate and reliable, your patient is best served when tested by someone who is experienced and not by someone who is new or in-training, without your prior knowledge or consent. Occasionally, the referring optometrist may perform and bill for preoperative ultrasound and axial measurements. Depending on the optometrist’s experience, it may be prudent for the ophthalmologist to repeat these measurements.

Good supervision, attention to detail, and routine checks and balances should be the rule when performing ultrasonic testing and biometry measurements. Periodically review the literature for current medical standards to increase the likelihood of a positive surgical outcome and to minimize or prevent malpractice claims.