Which symptom requires immediate reporting by a client taking ethambutol (Myambutol)?

Ethambutol is an antibiotic primarily used to treat tuberculosis, and one of its significant side effects is the potential for ocular toxicity, particularly affecting color vision. The symptom of difficulty with red-green discrimination indicates that the patient may be experiencing such adverse effects on their eyesight. This condition, known as optic neuropathy, can lead to permanent vision loss if not addressed promptly.

Immediate reporting is critical because it allows healthcare providers to assess the situation, potentially adjust the medication regimen, and prevent further complications. Other symptoms, such as dizziness, loss of appetite, and nausea, while they may also warrant discussion with a healthcare provider, do not present the same level of urgency or potential for irreversible harm as changes in vision do. Thus, the correct answer highlights the importance of vigilance regarding ocular side effects when a patient is receiving ethambutol.