Risk Management

Reduce the Risks of Mapping the Visual Field

By Ralph Z. Levene, MD

Argus, May, 1993

Next to acuity, the visual field is the most important determinant of visual function. Mapping the field has become increasingly complex during the past decade. The variety of instruments, methods and strategies to choose from, as well as the sea of numbers, can be overwhelming. Confusion over which instrument to buy and how to set up a visual field protocol may be eased by talking to an expert.

Even before technology offered so many choices, visual fields often were the source of many malpractice suits. Faulty technique, misinterpretation of results, failure to test or to follow up on tests often were to blame. The following risk management considerations can help you avoid these and other liability problems related to visual field testing.

First, ask yourself how your office performs in technique and interpretation. Do you or your technician need a refresher course? Are fields interpreted shortly after they are done? Are all interpreted fields filed together in the correct chart? An unread or misplaced field is not a legal defense.

What is your protocol on routine screening? Some ophthalmologists perform a screening on all new patients and periodically on regular patients, following up with a definitive field if the screening is suspicious. Others prefer to perform a definitive test when there are suspicious clinical circumstances. Both strategies can be legally and ethically correct.

However, delaying or failing to follow up on suspicious or puzzling clinical circumstances is a frequent factor in malpractice suits involving visual fields. In a case from the OMIC files, a physician notes a suspicious pale optic disc and an acuity of 20/20, but misses a pituitary tumor. He schedules the patient for a return visit in one year by which time the tumor has become inoperable.

In another case, a physician notes a suspicious cupped optic disc, visual acuity of 20/20, and pressures of 16. He schedules the patient for a return visit in six months. The patient fails to keep the appointment and the physician does not follow up. When the patient finally returns two years later with frank glaucomatous disc and visual field changes, the diagnosis of low tension glaucoma has been significantly delayed.

Does the defect fit the diagnosis? An ophthalmologist takes over the care of a patient being treated with a topical beta-blocker for glaucoma. Many of the patient’s visual fields have a vertical midline defect and pressures of 10 to 12. Relying on the previous diagnosis of glaucoma, the ophthalmologist misses a brain tumor.

Do you recognize artifacts and evaluate the reliability of each field? Some patients never yield a reliable field and others do so intermittently. The newer static methods are more sensitive to detecting defects but probably are more prone to artifacts. When in doubt or in unusual circumstances, repeat the field.

Is the defect progressive? This is a critical point in patient management. Apart from artifact, variations from test to test often are underestimated with consequent errors in interpretation. Case in point: an ophthalmologist has been treating a patient with an advanced case of glaucoma and a stable field defect. On a recent visit, a visual field, performed with reasonable reliability, shows an apparent change and is incorrectly interpreted as a significant progression. The ophthalmologist suggests surgery. The patient seeks a second opinion. A repeat field shows a previous stable defect. Unnecessary surgery, with the potential for a lawsuit, is avoided. The change interpreted by the first ophthalmologist as significant was actually a normal variation from one test to another.

Another factor to consider when evaluating results is whether there has been a change in technique. Switching from tangent or Goldman instruments to newer computer assisted methods can skew results. Discuss ambiguous results with an expert or refer the patient for a second opinion. Don’t be afraid to ask for help.