Optometry Visual Field Testing Overview

Visual Field Testing Overview

• Visual field testing evaluates pathological eye conditions, particularly those affecting retinal function.
• Modern perimeters generate complex printouts that require careful interpretation.

Importance of Knowledge in Optometry

• Knowledge is equated with sight in optometry, emphasizing the importance of understanding visual field data.

Apostilbs and Decibels

• Luminance in perimetry is measured in apostilbs, an absolute unit.
• Decibels (dB) measure sensitivity on a relative scale and vary by device; 0 dB signals the brightest stimulus.

WANDER Interpretation Scheme

• WANDER aids in systematically interpreting visual field reports:
  • What was done?: Identify test area and strategy.
    • Test areas: 10°, 24°, 30°, 60°.
    • Strategies: Full Threshold, Screening, Fast Test (e.g., SITA FAST, Top).
  • Fixation Loss: Measures patient’s engagement with the test. Should be less than 33% for reliability.
  • False Positive: Indicates when a patient responds to an audible cue rather than visual stimuli.
  • Short-term Fluctuation: Normal range is 1-2 dB; >2 dB suggests poor reliability.

Evaluating Normal vs. Abnormal Fields

• Assess the field's normality by analyzing gray scale and numerical values.
• Gray Scale: Provides a visual impression but is not fully reliable due to limited test points.
• Numerical Values: Reflect retinal sensitivity relative to age. The normal decay rate of sensitivity is 0.5 to 1.0 dB per decade.

Total and Pattern Deviations

• Total Deviation: Compares patient's retinal sensitivity to age-corrected norms.
• Pattern Deviation: Adjusts measured thresholds based on generalized changes to assess localized defects.
• Pattern Deviation Probability (PDP): Visualizes deviations beyond expected norms for age.

Global Indices for Interpretation

• Developed by perimeter manufacturers to aid clinicians in interpreting results:
  • Mean Deviation (MD).
  • Pattern Standard Deviation (PSD).
  • Corrected Pattern Standard Deviation (CPSD).
  • Short-Term Fluctuation (SF).

Clinical Significance of Mean and Pattern Deviations

• Mean Deviation: Represents the overall height of the visual field.
• Pattern Standard Deviation: Reflects the shape of the field.
• Thresholds:
  • Normal MD and PSD indicate an intact visual field.
  • Abnormal findings can suggest generalized depression or localized defects, with specific thresholds indicating severity of depression.

Summary of Findings Interpretation Table

• MD and PSD combinations help determine field health:
  • Normal MD and PSD: Normal visual field.
  • Abnormal MD with normal PSD: Generalized depression; no focal defects.
  • Normal MD with abnormal PSD: Localized defects present.
  • Abnormal MD and PSD: Severe localized defects.

These notes encapsulate key concepts and procedures related to visual field testing that are crucial for understanding and interpreting results in optometry.