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Refractive Surgery | Sep 2009

Medicolegal Issues in Biometry

A postop refractive surprise does not necessarily constitute negligence.

A headline in the Daily Mail Online,1 the Web version of one of Britain's famed tabloid newspapers, read as follows: "Cataract op that means I can throw my glasses away." The article below that headline described how a certain new type of IOL "restores sight completely" after cataract surgery, without the need for reading glasses postoperatively.

In ophthalmic practice, as we know, the reality is often different. Patients may need glasses after cataract surgery for all sorts of reasons. But in the minds of many of our patients who are exposed daily to articles like the one in The Mail earlier this year, cataract surgery means throwing away your glasses.

Because of media influences, it is a common misconception in the United Kingdom and elsewhere that if a patient needs glasses after cataract surgery, by definition that constitutes negligence. On the contrary, however; negligence is not the same as not hitting the refractive target. Negligence occurs—and the potential for a successful suit arises—if the surgeon or biometrist does not perform good biometry and the patient ends up with the wrong refraction as a result.

This article reviews what constitutes negligence under English law and similar legal systems, how this relates to biometry, and how cataract surgeons can take steps to avoid negligence and defend themselves against charges of negligence in this crucial area of surgical planning.

In English law, there is a fourfold test to determine negligence:

  • First, it must be established that there is a duty of care between the patient and the physician—this would be a given in the case of cataract surgery. If a doctor is operating on a patient for cataract, he has a duty to make sure he takes all possible care.
  • Second, the plaintiff has to show that there was a breach of that duty of care. He has to show, for the purposes of this discussion, that the biometry was faulty or was inadequately or sloppily performed.
  • Third, it must be shown that this breach of the duty of care led to harm. Suppose biometry was performed poorly but by fluke the patient wound up with the right implant; there would be no negligence because no harm flowed from the breach of duty. For a negligence suit to be successful, harm must flow from the error.
  • Fourth, the cause of harm must not be too remote. Say bad biometry was performed, and the patient had to wear glasses, and the glasses broke and cut his face. If he decided to sue the surgeon because he now has a scar, that would probably be regarded as too remote a cause and thrown out of court.

These four tests, not the magnitude of the error, determine negligence. In the absence of these four elements, there is no negligence. It should be noted that under English law, the onus of proof lies with the plaintiff. It is not that the physician-defendant has to disprove that these four things have not taken place.

A patient presented to our practice 6 to 8 months ago for cataract surgery. At the preoperative examination, she was slightly hyperopic (0.75 D in the right eye; 0.25 D in the left). This patient could perform most distance activities without glasses, although she needed low-powered reading glasses. Postoperatively, she had a myopic result in each eye, as well as significant astigmatism in the right eye (-2.25 -1.50 X 15° in the right eye; -2.50 -0.25 X 175° in the left).

What happened? We reviewed our biometry and other operative data to see where the refractive error might have originated.

First, the postoperative astigmatism is a mystery. The IOL was implanted through a 1.7-mm incision (Figure 1), which should have been astigmatically neutral, and indeed the pre- and postoperative keratometry (K) readings were identical.

Let us set the cylinder aside for the purposes of this discussion and examine the biometry. Was there a breach of the duty of care that led to this refractive surprise?

The correct K readings were used, and the keratometer had been properly maintained and serviced. The axial length measurements were tightly grouped, with small standard deviations for anterior chamber and lens, vitreous, and overall length (Figure 2). The sound speeds used to calculate the distances were correct. The overall length (22.6 mm) was consistent with that of an average eye. All these measurements appear to have been correct, or at least as accurate as can be measured with ultrasound biometry. The fact that the anterior chamber depths were so similar in all the 10 readings, with a low standard deviation, strongly supports the contention that the eye was not being compressed.

The tracings produced by the machine were good, with high spikes indicating all the intraocular landmarks, so this was not a sloppy or careless reading. The SRK/T IOL power calculation formula was used, which is appropriate for an eye with this axial length. The A-constant used was correct for the IOL selected, and the correct IOLs were implanted in each eye. There were no intra- or postoperative complications.

In this patient, in other words, there was no breach of the duty of care. The test for negligence fails. We did the best we could do, and we still got the wrong result. This patient who never wore glasses for distance vision in the past now must do so. I do not know why she got a bad result; the reason is not apparent in any of the elements reviewed here. The biometrist did a perfectly acceptable job, and the fact that a refractive surprise resulted is not evidence of negligence.

Suppose, however, that in a similar case an incorrect sound speed was set for the vitreous (Figure 3). The previous patient had silicone oil in her eye, which requires a different setting, and the biometrist forgot to change the sound speed back to the normal vitreous setting. And suppose that this error resulted in a postoperative refractive error of 0.50 D.

If a suit were bought, the plaintiff in that case would have a claim in negligence, even though the refractive error is smaller than in the first case described. The crux is not the size of the error but whether or not good biometry was performed. Even though this resulted in a small refractive error, the surgeon could be unsuccessful in defending a claim in negligence.

It is crucial to inform patients that refractive errors can occur despite our best efforts to prevent them. In addition to our usual informed consent about the risks of surgical intervention, we must tell patients that an ametropic result is a possibility.

This sentence appears in the information brochure we give to all our cataract patients: "We cannot guarantee that patients will not depend on glasses in every case, even those patients who did not depend on glasses beforehand."

I always emphasize to patients that, contrary to what the Daily Mail may say, the primary purpose of cataract surgery is to restore vision—to prevent the patient from going blind. Emmetropia is a bonus that we make every effort to provide, but it is not the purpose of the intervention. The bottom line is: Contemporary biometry cannot guarantee emmetropia 100% of the time. Postoperative 2.00 D errors occur from time to time, and we do not always know what causes them.

It must be said that a different standard is upheld in a patient with a clear lens who desires refractive lens exchange. That is a refractive surgery procedure, not cataract surgery. Also, for patients who have previously undergone corneal refractive surgery, as well as any type of therapeutic corneal surgery, it is important to recognize that standard keratometry methods cannot be used. The figures generated by standard keratometry in a patient after LASIK would be useless, and the surgeon who used them would be automatically negligent. One or more of the published methods for calculating IOL power in eyes after corneal surgery should be used in these patients.

It is also worth noting that use of the IOLMaster (Carl Zeiss Meditec, Jena, Germany) does not grant immunity from biometry error. Although precise axial length measurement is possible with its partial coherence interferometry technology, this method is equally susceptible to error as ultrasound biometry. The biometrist must understand this piece of equipment and know how to get a good result.

In the United Kingdom, a technician or nurse typically perform the biometry. These staff members are sometimes concerned that they may be liable in negligence cases, but this is not usually the situation. The biometrist could theoretically be sued if he performed the examination wrong, but the court would look to the surgeon and wonder why he did not check the printout and spot the error. Usually in the United Kingdom, it is the employer—the surgeon or the hospital—who would be vicariously liable. There is a tenet, after all, in all law: Don't sue someone who doesn't have any money.

The most important point for surgeons and biometrists to remember regarding negligence is to keep careful notes.

Record all measurements clearly, making note of any difficulty in obtaining a measurement (ie, patient was unable to keep still and kept squeezing her eye); note any discrepancies (ie, have taken five K readings and can't get it consistent) The biometrist should tell the patient about any problems and note that he was told, and also tell the surgeon and note that he was told.

Keeping good notes on the biometry exam—not just the printout but comments such as how easy it was and how well the patient understood the process—can be your salvation in the case of a negligence suit in the future. Remember, questions in a court case may be asked 5 years after the patient was originally seen, not the next day. Memory at that great a remove is spotty at best. Better to have documentation to rely on. If the surgeon cannot verify that everything was done properly, the court may give the benefit of doubt to the patient.

John P. Bolger, DO, FRCS, is Founder and Director of The Cataract Clinic in London. Dr. Bolger states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +44 20 8445 8877; e-mail: eyelead@aol.com.

  1. Davis C. Cataract op that means I can throw my glasses away. Daily Mail Online. May 12, 2009. Available at: http://www.dailymail.co.uk/health/article-1180636/Cataract-op-means-I-throw-reading-glasses-away.html. Accessed July 1, 2009.