Threshold variability with an automated LED perimeter

Area of Science:

• Ophthalmology
• Visual Science
• Medical Device Technology

Background:

• The CooperVision Dicon AP 2000 perimetry uses light emitting diodes (LEDs) in a dark cavity, unlike traditional projection perimeters.
• This design can create a negative differential threshold (stimulus intensity lower than background) in highly sensitive retinal areas.

Purpose of the Study:

• To investigate the impact of the Dicon AP 2000's unique stimulus presentation on visual field testing.
• To identify factors contributing to variability in threshold measurements with this instrument.

Main Methods:

• Compared visual field visibility thresholds between the Dicon AP 2000 and projection perimeters.
• Analyzed threshold variability in sensitive retinal areas where negative differential thresholds occurred.
• Modified the Dicon AP 2000 by adding a diffuser and altering stimulus duration to assess impact on variability.

Main Results:

• Threshold visibility with the Dicon AP 2000 was generally comparable to projection perimeters.
• Increased threshold retesting variability was observed in sensitive areas exhibiting negative differential thresholds.
• Adding a diffuser to equalize background light or shortening stimulus duration significantly reduced this variability.

Conclusions:

• The Dicon AP 2000's design can lead to unreliable threshold measurements in specific retinal regions due to negative differential thresholds.
• Instrument modifications, such as adding a diffuser or reducing stimulus duration, can mitigate variability and improve test accuracy.
• These findings suggest potential improvements for perimetric instruments utilizing LED technology.