Foveal

About: Foveal is a research topic. Over the lifetime, 2652 publications have been published within this topic receiving 94120 citations.

Landmark-driven fundus perimetry using the scanning laser ophthalmoscope.

Abstract: Visual field measurement provides important information regarding the diagnosis, progression, and management of many ocular diseases. Most notably, visual fields are extremely important in glaucoma to diagnose and evaluate the progression of disease, in neuroophthalmologic disorders to aid in the determination of the site of involvement in the eye, optic nerve, or brain, and in some retinal diseases, such as retinitis pigmentosa, to assess the extent of involvement and visual disability. These evaluations are well served by our current methods of visual field determination, herein referred to as conventional visual field testing, which include Goldmann kinetic perimetry, Humphrey static perimetry, and similar techniques. However, conventional visual field determination is inadequate for the accurate evaluation of macular disorders or any retinal disorder in which foveal vision is compromised and the patient may have unstable fixation or extrafoveal fixation. Accuracy of the conventional visual field relies on the assumption that fixation is foveal and stable. If fixation is not foveal, the conventional visual field will still be mapped as though fixation is at the center (0°) of the field, so that all points tested will be shifted relative to their true retinal location. (A perimeter that uses the blind spot to test fixation may register fixation losses, but it is unable to correct for these.) If central fixation is unstable and there is significant eye movement during testing, scotoma size will be incorrect. Often, eccentric fixation and unstable fixation coexist, and there is a combination of these errors in scotoma location and size. In addition, there is often perceptual “filling in” of the area of the scotoma so that even the Amsler grid, used as a screening test for changes in central vision, may not detect the presence of a scotoma.1,2 Pericentral fixation lines to facilitate a patient’s centering on the fovea often still result in eccentric fixation. 3,4 Fundus perimeters are devices that provide for visualization of the fundus and the precise location of the stimulus on it. One can then see the exact test site on the retina and can correlate visual field defects to their true retinal positions.5 Several fundus perimeters have been designed and used in the past 30 years.6–14 The scanning laser ophthalmoscope (SLO) is the most recent and well-known fundus perimeter. It has allowed us to gain new information regarding the nature of visual loss in various macular diseases, including age-related macular degeneration and macular holes.1,6,7,15–25 However, because of difficulties in dealing with the additional data provided by SLO testing, methods of performing fundus perimetry have not used and have even ignored the advantage of viewing the fundus during testing. These difficulties include how to evaluate data correctly when the stimulus does not fall on the desired retinal location because of eye movement, how to ensure that the desired retinal areas are tested, and how to summarize the data. An additional problem is how to test for scotomas that might not correspond to observable lesions rather than simply testing over or at borders of retinal lesions. A number of investigators have shown that in diabetes26–28 and other macular diseases,29 scotomas may be present that do not correspond to observed retinal lesions; this is undoubtedly true in other retinal diseases, and these areas would be missed by testing only over observed retinal lesions. Finally, there must be a reliable method to test over the same retinal points when testing is repeated, even if fixation has shifted, to assess change over time.

Eye movement control during reading: foveal load and parafoveal processing.

Abstract: We tested theories of eye movement control in reading by looking at parafoveal processing. According to attention-processing theories, attention shifts towards word n+1 only when processing of the fixated word n is finished, so that attended parafoveal processing does not start until the programming of the saccade programming to word n+1 is initiated (Henderson & Ferreira, 1990; Morrison, 1984), or even later when the processing of word n takes too long (Henderson & Ferreira, 1990). Parafoveal preview benefit should be constant whatever the foveal processing load (Morrison, 1984), or should decrease when processing word n outlasts an eye movement programming deadline (Henderson & Ferreira, 1990). By manipulating the frequency and length of the foveal word n and the visibility of the parafoveal word n+1, we replicated the finding that the parafoveal preview benefit is smaller with a low-frequency word in foveal vision. Detailed analyses, however, showed that the eye movement programming deadline hypothesis...

The comparison of small-size rectangle and checkerboard stimulation for the evaluation of delayed visual evoked responses in patients suspected of multiple sclerosis

Abstract: The use of foveal small-size rectangle stimulation to elicit visual evoked responses was compared with VERs elicited by the standard checkerboard pattern. Foveal stimulation achieved a significantly better discrimination of optic nerve lesions in the early diagnosis of multiple sclerosis. Sources of misdiagnosis due to different neurological disorders are discussed.

Impairing the useful field of view in natural scenes: Tunnel vision versus general interference

Abstract: A fundamental issue in visual attention is the relationship between the useful field of view (UFOV), the region of visual space where information is encoded within a single fixation, and eccentricity. A common assumption is that impairing attentional resources reduces the size of the UFOV (i.e., tunnel vision). However, most research has not accounted for eccentricity-dependent changes in spatial resolution, potentially conflating fixed visual properties with flexible changes in visual attention. Williams (1988, 1989) argued that foveal loads are necessary to reduce the size of the UFOV, producing tunnel vision. Without a foveal load, it is argued that the attentional decrement is constant across the visual field (i.e., general interference). However, other research asserts that auditory working memory (WM) loads produce tunnel vision. To date, foveal versus auditory WM loads have not been compared to determine if they differentially change the size of the UFOV. In two experiments, we tested the effects of a foveal (rotated L vs. T discrimination) task and an auditory WM (N-back) task on an extrafoveal (Gabor) discrimination task. Gabor patches were scaled for size and processing time to produce equal performance across the visual field under single-task conditions, thus removing the confound of eccentricity-dependent differences in visual sensitivity. The results showed that although both foveal and auditory loads reduced Gabor orientation sensitivity, only the foveal load interacted with retinal eccentricity to produce tunnel vision, clearly demonstrating task-specific changes to the form of the UFOV. This has theoretical implications for understanding the UFOV.