Risk Management

Failure to Diagnose Toxic Optic Neuropathy

Digest, Winter, 1995

Allegation

Insured ophthalmologist allegedly failed to diagnose ethambutol toxicity.

Disposition

Lawsuit was settled on behalf of the insured ophthalmologist. Co-defendant pulmonologist also settled for an undisclosed amount.

Background

Ophthalmologists should be alert to the potential visual side effects of the non-ophthalmic medications their patients use and be prepared to include even rare toxic conditions in their differential diagnoses.

Case Summary

The plaintiff was a 67-year-old male with a long-standing history of bronchiectasis and non-tuberculosis mycobacterial infection. In 1991, the patient’s pulmonologist added 1000 mg. per day of ethambutol to the medication regimen. Although ethambutol is associated with liver damage and ophthalmic toxicity, the pulmonologist only screened the patient for liver complications. He did not perform any ophthalmic testing or refer the plaintiff to an ophthalmologist for monitoring.

Approximately six months after the plaintiff had started on ethambutol, he presented to the insured ophthalmologist complaining of a heavy feeling in his eyes, diplopia, and esophoria. Visual acuity was measured at 20/25 +/- OU with pinhole at 20- and 20. Mild cataracts OU were noted. The insured indicated in his notes that the plaintiff might need a prism if the double vision increased. A medication history was recorded and included ethambutol.

Four months later, the plaintiff returned to the insured’s office with continued complaints of heaviness in the right corner of his right eye, blurry vision, and occasional horizontal diplopia. At this visit, the plaintiff’s visual acuity was 20/25 OU. The insured noted 1-2+ cataracts bilaterally. Media clarity was documented as 20/25. The diagnosis was possible ptosis and cataracts, and the plaintiff was advised to return in three weeks for further evaluation. When the plaintiff returned as instructed, visual acuity OD had decreased to 20/40, and he continued to complain of infrequent diplopia at night. The insured recommended cataract removal. Over the next several weeks, the plaintiff’s vision deteriorated rapidly to 20/200 OD. Cataract surgery was performed in late 1992 without complication. Postoperatively, the plaintiff’s visual acuity OD was count fingers. The insured documented in his notes that he did not understand why the plaintiff did not have better vision. A month after the surgery, the plaintiff was demonstrating visual loss in the left eye as well. Concerned about the continued vision loss in the left eye, the insured ordered an MRI. The results were normal. At this point, the insured referred the plaintiff to a neuro-ophthalmologist.

The neuro-ophthalmologist suspected toxic optic neuropathy resulting from ethambutol and recommended that the pulmonologist immediately take the plaintiff off the drug. The plaintiff continued to be treated by the neuro-ophthalmologist. Over time, his visual acuity improved to 20/200 OD and 20/50 OS, and his central scotomas and much of his color vision problems were resolved.

Analysis

Defense experts identified several issues that made defense of the case difficult. First, the medical records did not clearly reflect a recognition of the potential for ethambutol to cause toxic optic neuropathy. Second, there was no visual field testing performed. Even if visual fields do not assist in specifically diagnosing ethambutol toxicity, abnormal results might suggest the need for further evaluation or referral to a specialist. Third, the inconsistency between the degree of visual loss and the severity of the cataracts suggests looking for an alternative explanation for the patient’s problems.

Defense experts who consulted on the case did point out, however, that ethambutol toxic optic neuropathy is a very rare phenomenon and not one typically seen in a general ophthalmologist’s practice. This allowed the defense to argue during settlement negotiations that the insured was justified in pursuing more common explanations for the plaintiff’s visual problems (i.e., cataracts) before considering unusual conditions.

Risk Management Principlesand Commentary

An ophthalmologist’s vigilance concerning medications should extend beyond the prevention of classic medication errors that can arise in clinical settings. It should extend to evaluating the impact of medications prescribed by other treating physicians on the health of the patient’s eyes. General ophthalmologists serving an elderly population are so accustomed to cataracts being the major cause of visual problems among their patients that they may forget to document the possibility of other explanations, such as drug toxicity, in their differential diagnosis. If a lawsuit ensues, the lack of such documentation makes it difficult to argue that the physician was proceeding in an orderly fashion to rule out possible causes of the patient’s visual deterioration.