Eccentricity and speed of adaptation in the mesopic range

JUAN ANTONIO APARICIO; ALEJANDRO GLORIANI; BEATRIZ MATEZANZ; PABLO BARRIONUEVO; ISABEL ARRANZ; LUIS ISSOLIO; SANTIAGO MAR

Winchester

Simposio; The 22nd Symposium of the International Colour Vision Society; 2013

International Colour Vision Society

The mesopic range is an interval of luminances where cones and rods work simultaneously. The great spatial gradients in the photoreceptors distribution across the retina, the different temporal features of both types of photoreceptors and the different cone-rod interactions existing in the mesopìc, make the comprehension of the adaptation mechanisms a difficult task in this range of luminances. In this work, we present the experimental results of threshold luminance measurements LtLA performed with a two Maxwellian view optical system on the temporal retina of the right eyes of four individuals. We considered mesopic luminances (0.05-5 cd/m2), in retinal eccentricities from 0º to 15º, under steady (LA) and transient (SOA300) adaptation fields. Spatiotemporal characteristics of the adaptation field and stimulus used were 1.05º with 500 ms and 0.45º with 40 ms respectively. The light source employed was a halogen incandescent lamp (T=3000 K). The log(LtLA/LtSOA300) was used as an index of the sensitivity recovery 300 ms after the onset of an adapting beam and therefore of the speed of adaptation. At high mesopic adaptation luminances (5 cd/m2) this speed of adaptation increases with eccentricity up to 6 deg and then decrease. However at low mesopìc luminances (0.05 cd/m2), speed of adaptation remains constant with eccentricity and is slightly lower than at 5 cd/m2. At this time we are modelling the different mechanisms explaining these results. As a preliminary conclusion, we could say that, beyond the different contribution of rods and cones with eccentricity and luminance, results might also show the changing nature of rod cone interactions along this range of eccentricities and luminances.