The cortical representation of gradient-adapted multiple-stimulus perimetry

Area of Science:

• Ophthalmology
• Visual Neuroscience
• Perimetry

Background:

• Isosensitivity profiles, achieved when stimuli are M-scaled (proportional to the reciprocal of inter ganglion cell receptive field separation), aid in detecting visual field abnormalities.
• Such profiles are crucial for efficient multiple stimulus perimetry.

Purpose of the Study:

• To determine if stimulus diameters required for an isosensitive perimetric profile are indeed M-scaled.
• To investigate the relationship between stimulus scaling and visual sensitivity across the visual field.

Main Methods:

• Sensitivity profiles were measured in 15 observers using the Friedmann Visual Field Analyzer (VFA) Mk II.
• Stimulus aperture diameters were measured and corrected for optical distortions.
• Apparent diameters were M-scaled using established equations and compared to observed diameters.

Main Results:

• An overestimation of M-scaled stimulus diameters compared to apparent diameters was observed.
• This overestimation increased with visual field eccentricity, reaching up to 3.5 times.
• The findings held true for all four cardinal meridians.

Conclusions:

• The observed overcompensation suggests that the cortical representation of perimetric targets is influenced by both retinal ganglion cell density and variations in ganglion cell characteristics with eccentricity.
• This has significant implications for the design of perimetric instruments, particularly at low photopic adaptation levels.