What medications can affect gaze and how should they be managed?

Medications Affecting Gaze and Their Management

Several medications can significantly affect eye movements and gaze, with ethambutol, opioids, anticholinergics, and psychotropic medications being the most concerning due to their potential to cause permanent vision damage. Management requires prompt recognition, medication discontinuation, and ophthalmologic monitoring.

Medications That Affect Gaze

1. Antimicrobials

• Ethambutol
  • Causes retrobulbar neuritis manifesting as decreased visual acuity or red-green color discrimination 1
  • Risk is dose-related (minimal at 15 mg/kg daily, higher at >30 mg/kg daily)
  • Higher risk in patients with renal insufficiency
  • Can lead to permanent vision loss if not detected early

2. Psychotropic Medications

• Phenothiazines (e.g., chlorpromazine, thioridazine)

  • Cause mydriasis, accommodation problems, and potential angle-closure glaucoma 2
  • Can lead to retinopathy with high doses over prolonged periods
  • May cause ocular dystonias affecting eye movements

• Tricyclic Antidepressants (TCAs)

  • Cause mydriasis that can promote angle closure in susceptible patients 2
  • Produce transient blurred vision in up to one-third of patients
  • Can trigger angle-closure glaucoma in patients with narrow angles

• SSRIs

  • May cause mydriasis and rarely ocular dystonias 2
  • Lower risk than TCAs but still require caution in patients with narrow angles

3. Anticholinergics

• Scopolamine and other anticholinergics
  • Can cause mydriasis and cycloplegia (paralysis of accommodation)
  • May precipitate angle-closure glaucoma in susceptible patients 3
  • Affect pupillary responses and accommodation

4. Opioids

• Cause transient downbeat nystagmus and saccadic intrusions 4
• Decrease gain of smooth pursuit eye movements
• Produce vertical pursuit with upward velocity offset

5. Other Medications

• Topiramate

  • Associated with acquired myopia and angle-closure glaucoma 2
  • Can cause ocular dystonias affecting gaze

• Benzodiazepines

  • Frequently cause disturbances in eye movements 2

• Hydroxychloroquine

  • Risk of QT prolongation when combined with other medications 1
  • Can cause ocular toxicity requiring monitoring

Management Approach

1. For Ethambutol

• Baseline assessment before starting therapy:

  • Visual acuity testing (Snellen chart)
  • Color discrimination testing (Ishihara tests)

• Regular monitoring:

  • Monthly questioning about visual disturbances
  • Monthly testing of visual acuity and color discrimination for:
    • Patients on doses >15-20 mg/kg
    • Treatment duration >2 months
    • Any patient with renal insufficiency 1

• Patient education:

  • Instruct patients to report any vision changes immediately

• Management of toxicity:

  • Discontinue ethambutol immediately and permanently if any signs of visual toxicity 1
  • Refer to ophthalmology for comprehensive evaluation

2. For Psychotropic Medications

• Pre-treatment assessment:

  • Identify patients with narrow angles or other risk factors
  • Consider baseline ophthalmologic exam for high-risk patients

• Monitoring:

  • Regular assessment of visual symptoms
  • Prompt ophthalmology referral for any visual complaints

• Management of toxicity:

  • Dose reduction or medication switch for mild symptoms
  • Discontinuation for severe symptoms or evidence of retinopathy

3. For Anticholinergics

• Avoid in patients with known narrow angles or glaucoma 3
• Monitor for symptoms of blurred vision, eye pain, or headache
• Discontinue if signs of angle closure develop (eye pain, headache, nausea)

4. For Opioids

• Recognize transient nature of eye movement abnormalities
• Monitor for resolution (typically within 10-15 minutes) 4
• Consider alternative analgesics in patients with pre-existing vestibular disorders

Special Considerations

High-Risk Patients

• Pre-existing glaucoma - particularly susceptible to medication-induced angle closure
• Narrow anterior chamber angles - at risk with anticholinergics, TCAs, and phenothiazines
• Renal insufficiency - requires dose adjustment for ethambutol 1
• Elderly patients - more susceptible to medication side effects
• Patients with high myopia - increased risk of medication-induced glaucoma 3

Common Pitfalls

1. Failure to perform baseline assessment before starting high-risk medications
2. Inadequate monitoring during treatment
3. Delayed recognition of early symptoms
4. Continuing medication despite visual symptoms
5. Not adjusting doses in patients with renal impairment

Emergency Management of Acute Angle Closure

If a medication triggers acute angle closure:

1. Immediate ophthalmology referral
2. Discontinue the offending medication
3. Administer IOP-lowering medications as directed by ophthalmologist
4. Document the reaction to prevent future re-exposure

By carefully selecting medications, performing appropriate baseline assessments, and implementing regular monitoring, clinicians can minimize the risk of medication-induced gaze abnormalities and prevent permanent vision loss.