Situation: A public health nurse at a Rural Health Unit (RHU) manages clients enrolled in the National Tuberculosis Program (NTP). Many of them live in crowded urban households. In the 6th week of treatment with 2HRZE, a 50-year-old client says that his vision has become blurred and that red and green now look alike to him. What should the nurse do?

Blurred vision and loss of red-green color discrimination suggest optic neuritis caused by ethambutol. The drug must be stopped and the change reported at once, because early withdrawal allows recovery while continued use can cause permanent visual loss.

Clinical situation
A client in the 6th week of the intensive phase of tuberculosis treatment (2HRZE) reports blurred vision and loss of red-green color discrimination. These are classic early signs of ethambutol-induced optic neuritis, a serious and potentially irreversible adverse drug reaction ^[1][2].

Why this is ethambutol toxicity
Ethambutol is a first-line anti-tuberculosis drug included in the intensive phase regimen. Its most important and serious side effect is optic neuritis, which causes progressive, painless vision loss, reduced visual acuity, and color vision defects ^[1][2]. The client’s description of red and green appearing similar reflects red-green dyschromatopsia, a hallmark of ethambutol-related optic nerve damage ^[1]. The risk is dose- and duration-related; although the client is only in the sixth week, early toxicity can still occur, especially in individuals with impaired renal excretion or higher weight-based dosing ^[2].

Immediate nursing action
The correct response is to hold ethambutol and refer the client to the physician the same day. Ethambutol-induced optic neuritis is generally reversible if the drug is stopped early, but continued use can lead to permanent visual loss ^[1][4]. Reassuring the client that the symptom is harmless, continuing the drug until the end of the phase, or delaying reassessment to the next visit all increase the risk of irreversible optic nerve damage. Pyridoxine is used for isoniazid-induced peripheral neuropathy, not for ethambutol ocular toxicity, so it does not address the underlying problem.

Pathophysiology and clinical monitoring
Ethambutol exerts a toxic effect on the optic nerve, producing cecocentral scotomas and impaired color perception ^[1]. Visual changes may be subtle initially, and some patients develop blue-yellow rather than red-green defects, which can be missed by standard Ishihara plates and require more sensitive testing such as the Farnsworth Panel D-15 Hue test ^[4]. This underscores the importance of baseline and periodic visual acuity and color vision assessment for every client receiving ethambutol ^[4].

Key comparisons for exam preparation

Clinical finding	Most likely drug	Nursing action
Blurred vision, red-green color loss	Ethambutol	Stop drug, refer to physician immediately
Peripheral numbness, tingling	Isoniazid	Give pyridoxine as prescribed
Orange-red body fluids	Rifampicin	Reassure; harmless discoloration
Joint pain, hyperuricemia	Pyrazinamide	Monitor uric acid, report to physician

Watch out! Do not confuse ethambutol optic neuritis with the harmless orange discoloration caused by rifampicin. Visual changes are never a benign, expected effect of ethambutol and require immediate drug discontinuation and physician evaluation ^[1].

Key point! Early withdrawal of ethambutol allows visual recovery; delayed recognition can result in permanent blindness ^[1][4]. In any client on ethambutol who reports blurred vision or altered color perception, the priority nursing action is to hold the medication and secure same-day medical referral .