What is the utility and name of the device with holes, like the Bjerrum screen, used during eye exams?

The Tangent Screen (Bjerrum Screen) in Eye Examination

The tangent screen, also known as the Bjerrum screen, is a perimetry device used to detect and map central and paracentral visual field defects during eye examinations. 1, 2

Description and Physical Characteristics

• The tangent screen consists of a large black felt or cloth screen with a central fixation target
• It typically has concentric circles and radial lines marked on it
• The screen is usually positioned at 1 or 2 meters from the patient
• The examiner uses small white or colored test objects (often on a wand or stick) of varying sizes to test different areas of the visual field

Clinical Utility

Primary Functions

• Detection of central and paracentral visual field defects (within 20-30° of fixation)
• Particularly useful for identifying:
  • Glaucomatous visual field defects in the Bjerrum area 2, 3
  • Neurological visual field defects (such as in multiple sclerosis) 4
  • Scotomas (blind spots) in the visual field

Advantages

• Simple, portable, and inexpensive compared to automated perimetry
• Allows direct observation of patient fixation by the examiner
• Provides good sensitivity for detecting paracentral defects
• Can be used when automated perimetry is not available or practical

Examination Technique

1. Position the patient at the appropriate distance from the screen (typically 1-2 meters)
2. Occlude one eye and instruct the patient to fixate on the central target
3. Present test objects of appropriate size in different locations of the visual field
4. Ask the patient to report when they see the test object appear or disappear
5. Map areas where the patient cannot detect the stimulus (scotomas)
6. Pay particular attention to the Bjerrum area, where early glaucomatous defects often appear 2

Clinical Significance

• Particularly valuable for detecting early glaucomatous visual field defects, which characteristically appear in the Bjerrum area (10-20° from fixation) 2
• Can detect both focal and diffuse retinal damage in early glaucoma 5
• Useful in monitoring progression of visual field defects over time
• Can help differentiate between various causes of visual field loss

Modern Alternatives

While the traditional tangent screen remains clinically useful, newer technologies offer additional advantages:

• Automated perimetry (such as Humphrey Field Analyzer) provides standardized, quantitative assessment 1
• Tablet-based perimetry with eye-tracking technology offers portable alternatives 6
• Optical coherence tomography (OCT) complements visual field testing by providing structural information 7

Common Pitfalls and Limitations

• Requires good patient cooperation and sustained attention
• Examiner skill and technique significantly influence results
• Less standardized than automated perimetry
• Limited to central and paracentral visual field (typically 20-30°)
• Less sensitive for detecting shallow defects compared to automated static perimetry
• Patient fatigue can affect reliability during longer examinations

The tangent screen remains a valuable clinical tool for detecting visual field defects, particularly in settings where automated perimetry is unavailable or impractical, though modern automated techniques offer greater standardization and quantitative assessment capabilities.