Central perimetric sensitivity estimates are directly influenced by the fixation target

Area of Science:

• Ophthalmology
• Visual Neuroscience
• Medical Imaging

Background:

• Perimetry is crucial for assessing central visual field sensitivity.
• The central visual field (0°, 0°) is vital for many visual tasks.
• Fixation targets may interfere with central sensitivity measurements.

Purpose of the Study:

• To investigate the impact of fixation targets on central visual field sensitivity measurements.
• To quantify the reduction in sensitivity at the central (0°, 0°) location due to masking.
• To assess the variability and clinical implications of this effect.

Main Methods:

• Retrospective analysis of microperimetry data from 60 healthy subjects.
• Prospective study on 15 healthy subjects using a cross-shaped test pattern with and without a fixation target.
• Comparison of central sensitivity to adjacent locations and assessment of fixation stability.

Main Results:

• Central sensitivity was significantly lower (median 2.0-2.8 dB) with the fixation target present.
• The reduction was comparable to a 60-100% increase in stimulus luminance.
• Variability in the effect was observed, with no clear link to fixation stability.

Conclusions:

• Fixation targets in perimetry cause a measurable reduction in central visual sensitivity.
• This masking effect necessitates cautious interpretation of central perimetric data.
• Clinical management, especially for patients with visual diseases, should consider this artifact.