RESUMO
Retinal image slip promoted by fixational eye movements prevents image fading in central vision. However, in the periphery a higher amount of movement is necessary to prevent this fading. We assessed the effect of different levels of retinal image slip in peripheral vision by measuring peripheral visual acuity (VA), with and without crowding, while modulating retinal image slip by using gaze-linked stimuli. Measurements were carried out at four isoeccentric positions at 5 and at 10 degrees eccentricity. Gaze position was monitored throughout using an infrared eyetracker. The target was presented for up to 500 msec, either with no retinal image slip, with reduced retinal slip, or with increased retinal image slip. Without crowding, peripheral visual acuity improved with increased retinal image slip compared with the other two conditions. In contrast to the previous result, under crowded conditions, peripheral visual acuity decreased markedly with increased retinal image slip. Therefore, the effects of increased retinal image slip are different for simple (noncrowded) and more complex (crowded) visual tasks. These results provide further evidence for the importance of fixation stability on complex visual tasks when using the peripheral retina.
Assuntos
Fixação Ocular/fisiologia , Retina/fisiologia , Acuidade Visual/fisiologia , Campos Visuais , Adulto , Humanos , Estimulação Luminosa/métodosRESUMO
Patients with scotomas due to macular disease may use more than one preferred retinal locus (PRL) for fixation. We have developed and evaluated an objective, quantitative technique to determine the number of PRLs used during an episode of fixation and the extent of each locus. In five of eight adults with macular disease our techniques consistently indicated the presence of multiple PRLs. Patients with multiple PRLs were more likely to have suffered recent vision loss in the tested eye. Our technique describes fixation more fully than the traditional method of calculating a single bivariate contour ellipse area.
