Summary

Summary Visual Fields 2 PeG

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Module
Optometry (PEG)

Institution
Aston University, Birmingham (Aston)

Themes: • Differentiating types of perimetry (kinetic vs. static). • Visual field defects and their clinical relevance. • Test grids and their specific applications. • Factors affecting test reliability and patient outcomes.

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Written Notes

Visual Fields 2: Key Techniques and Concepts
1. Types of Perimetry
a) Kinetic Perimetry

● Stimulus: Moved from non-seeing to seeing areas.
● Instrument: Goldmann Perimeter.
● Key Features:
○ Forms isopters (contours of equal sensitivity).
○ Good for detecting deep focal losses and monitoring residual fields.
○ Dependent on reaction time.
● Limitations: Shallow defects may be missed due to peripheral detection of moving
stimuli.

b) Static Perimetry

● Stimulus: Fixed position; brightness gradually increased or decreased.
● Instruments: Manual (time-consuming) or Automated (more sensitive).
● Key Features:
○ Independent of reaction time.
○ Sensitive to shallow focal losses and small scotomas.
○ Generates a map of sensitivity (dB).
● Two Types:
○ Full Threshold Perimetry: Quantifies the visual field.
○ Suprathreshold Perimetry: Screens for visual field defects.

2. Perimetry Concepts
Threshold Determination

● Threshold: Minimum light needed for a visual response.
● Expressed in: Decibels (dB).
○ 0 dB = Brightest stimulus.
○ Higher dB = Lower luminance.
● Short-term Fluctuation (SF): Variability in threshold measurements.

Strategies for Threshold Testing

● Full Threshold Strategy (4-2 dB Staircase):
○ More accurate, small threshold errors, reproducible.
○ Time: ~13 min/eye.
● Fast Threshold Strategy:
○ Faster but less accurate, greater variability.
○ Time: ~8 min/eye.

Suprathreshold Testing

● Tests for visual field defects quickly.
● Gradient Adapted Strategy: Accounts for decreased sensitivity with eccentricity.

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