Makindo Medical Notes

Related Subjects: |Anatomy the Medulla Oblongata |Anatomy of the Midbrain |Anatomy of the Pons

Introduction

Approximately 30% of stroke patients experience post-stroke visual impairment. Common symptoms include hemianopia, visual neglect, diplopia, reduced visual acuity, ptosis, anisocoria, and nystagmus. Homonymous hemianopia is seen in about 8% of stroke patients, some of whom may still be driving.

Aetiology

• Homonymous hemianopia is the loss of the same (homo) right or left halves (hemianopia) of the visual field in both eyes. It typically results from a stroke affecting the optic radiation or visual cortex in the occipital lobe, most commonly due to middle or posterior cerebral artery involvement. The occipital lobe tip may receive dual blood supply (PCA and MCA), potentially sparing the macular portion of the visual field, resulting in macular-sparing hemianopia.
• Quadrantanopia can also occur, presenting as: Superior quadrantanopia: Damage to the optic radiation inferiorly in the temporal lobe. Inferior quadrantanopia: Damage to the parietal lobe optic radiation

Range of Field Losses

Left Homonymous Hemianopia (Patient's Perspective)

Visual Neglect

Visual neglect is a form of spatial inattention, often affecting the left side in dominant parietal lobe lesions. Patients may not recognize objects or aspects on the neglected side, impacting activities like shaving or eating. Occupational therapy can help patients learn compensatory techniques.

Hemianopic Alexia

Hemianopic alexia, often caused by a stroke in the left hemisphere, impairs reading as it disrupts the right visual field used for planning eye movements. This reading deficit is common post-stroke and can be debilitating.

Driving and Visual Field Defects

Complete hemianopia impacts peripheral vision, posing risks if the individual continues to drive. It’s crucial that stroke patients with visual field loss refrain from driving until a full assessment. Current guidelines for driving with visual impairment can be found at the DVLA.

Minimum Standards for Field of Vision - All Drivers

For Group 1 driving, the minimum visual field requirement includes:

• A field of at least 120° horizontally, with 50° left and right extension
• No significant binocular defect encroaching within 20° of central fixation
• Homonymous or bitemporal defects close to fixation are generally unacceptable for driving

If a DVLA visual field assessment is necessary, it will include:

• A binocular Esterman field test (standard)
• Monocular full field charts in specific cases
• Exceptionally, Goldmann perimetry with strict criteria

Management of Visual Field Defects

• A team approach with education, risk identification, and adaptive techniques is essential.
• Useful resources, like the Patient Information Sheet, provide guidance.
• Ophthalmologists, orthoptists, physicians, and occupational therapists collaborate for individualized management.
• Prism lenses may help shift images from the non-seeing to the seeing field.
• Prognosis is unpredictable; formal reassessment at 2-3 months is recommended.

References

• [1] Gilhotra JS, Mitchell P, Healey PR, et al. Homonymous visual field defects and stroke in an older population. Stroke 2002;33:2417-20.
• [2] Visual field defects after stroke. Reprinted from Australian Family Physician Vol. 39, no. 7, July 2010
• [3] DVLA Minimum standards for field of vision - all drivers