How do you diagnose homonymous hemianopsia?

Testing for Homonymous Hemianopia

Confrontation visual field testing is the primary method for detecting homonymous hemianopia, which should be performed by comparing the patient's peripheral vision in all four quadrants to the examiner's own visual field.

Confrontation Visual Field Testing Techniques

Standard Confrontation Method

1. Position yourself approximately 1 meter in front of the patient at eye level
2. Ask the patient to fixate on your eyes or nose
3. Bring a target (finger, pen, or other small object) from the periphery into the patient's visual field in all four quadrants
4. Compare the patient's ability to detect the target with your own visual field
5. Test both eyes simultaneously to identify homonymous defects

Finger Counting Method

1. Have the patient fixate on your face
2. Present 1-2 fingers in each quadrant of the visual field
3. Ask the patient to count the number of fingers shown
4. Test all four quadrants in both eyes

Red Target Method

1. Use a red target (pin or small red object)
2. Test each quadrant and ask if the patient can see the color red
3. This helps detect subtle defects as color perception may be affected before form perception 1

Formal Visual Field Testing

For definitive diagnosis and documentation, formal perimetry should be performed:

1. Automated Perimetry:

   • Standard automated perimetry (SAP)
   • Short-wavelength automated perimetry (SWAP) - can detect subtle hemianopic defects even when SAP is normal 2

2. Goldmann Kinetic Perimetry:

   • Particularly useful for patients who cannot maintain fixation for automated testing
   • Allows for testing of the entire visual field including peripheral regions

3. Scanning Laser Ophthalmoscope (SLO) Perimetry:

   • Provides direct visualization of the retinal fixation locus
   • Can differentiate true visual field sparing from scanning eye movements
   • Helps confirm whether apparent sparing is due to compensatory eye movements 3

Clinical Characteristics to Document

When testing for homonymous hemianopia, document the following:

• Completeness of the defect (complete vs. incomplete)
• Pattern of the defect (quadrantanopia, scotomatous defects, macular sparing)
• Congruity (whether the defect is identical in both eyes)
• Associated neurological deficits 4

Additional Assessment Components

1. Reading Assessment:

   • Observe the patient reading text to identify difficulties finding the beginning of lines
   • Note if the patient misses words on the affected side 5

2. Visual Scanning Evaluation:

   • Assess the patient's ability to scan the environment
   • Note any bumping into objects on the affected side
   • Evaluate awareness of the visual field defect (anosognosia) 6

3. Neurological Examination:

   • Perform a complete neurological assessment using the National Institutes of Health Stroke Scale (NIHSS)
   • Document any associated deficits (aphasia, hemiparesis, neglect) 1, 5

Common Pitfalls and How to Avoid Them

1. Failure to Detect Subtle Defects:

   • Always test all four quadrants systematically
   • Use multiple testing methods (finger counting, red target)
   • Consider SWAP when standard perimetry is normal 2

2. Confusing Compensatory Eye Movements with Intact Fields:

   • Strictly monitor fixation during testing
   • Repeat testing when eye movements are detected
   • Consider SLO perimetry to differentiate true sparing from scanning artifacts 3

3. Missing Associated Neglect:

   • Test for extinction (simultaneous stimulation in both visual fields)
   • Assess awareness of the visual field defect 5

4. Inadequate Documentation:

   • Document the specific pattern and extent of the visual field defect
   • Note congruity between eyes
   • Record associated neurological findings 4

By following these systematic testing approaches, clinicians can accurately diagnose homonymous hemianopia and distinguish it from other visual field defects, leading to appropriate management and rehabilitation strategies.