Training Children in Eccentric Viewing: A Case Study

Abstract

Eccentric viewing is a strategy that is used to ameliorate the impact of the loss of macular vision through the use of the viable peripheral retina as an alternative to the nonfunctional fovea or macula. The efficacy of this technique has been reported in relation to adults with age-related macular degeneration (AMD) (Fitzmaurice, Kinnear, & Chen, 1994; Goodrich & Mehr, 1986; Nilsson & Nilsson, 1994; Vukicevic & Fitzmaurice, 2005). However, a keyword search of a range of appropriate databases (PubMed, CINAHL, Current Contents, and Google Scholar) did not yield any articles that specifically reported the provision of training in eccentric viewing to children. Retinal adaptation to the loss of the foveal function has been well described in the literature, particularly in relation to strabismus. The choice of the fovea for fixation is based on the high quality of vision that is provided; the sensation of straight-ahead viewing; and the fact that the fovea is the zero point for the oculomotor system, thus maintaining fixation on the object of regard (Duke-Elder & Wybar, 1973). The extent to which an eccentric fixation point develops these characteristics determines whether the anomalous situation is eccentric fixation or viewing. Eccentric fixation occurs when the eccentric position provides the best-available vision and straight-ahead oculomotor reference. Eccentric viewing occurs when an eccentric position is used to improve vision, with oculomotor orientation remaining referenced to the fovea and the person being aware that he or she is not looking at the object of regard (von Noorden & Mackensen, 1962). When foveal vision is lost because of macula or optic nerve disease and a person looks beyond the object of regard to place the image on a viable area of the peripheral retina, it is considered eccentric viewing (Duke-Elder & Wybar, 1973; von Noorden, 1990). The natural development of the use of nonfoveal loci to improve potential sight in the presence of a central scotoma has been well described in the literature, with the anomalous fixation point described as a preferred retinal locus (Crossland, Sims, Galbraith, & Rubin, 2004; Fletcher & Schuchard, 1997; Macedo, Nascimento, Gomes, & Puga, 2007; Reinhard et al., 2007; Schuchard, 1995). Some researchers have described a trained retinal locus, a term that is generally used to indicate that training has been used to modify the position of the naturally selected preferred retinal locus (Deruaz et al., 2006; Nilsson, Frennesson, & Nilsson, 2003; Watson, Schuchard, De l'Aune, & Watkins, 2006). This research has predominantly been with adults with AMD and the use of the trained retinal locus to improve reading performance. The need for such training has been debated in the literature. Nilsson et al. (1998, 2003) advocated the advantages of providing training in eccentric viewing, whereas other authors have reported that research has not yet supported the use of such training (Fletcher, Schuchard, & Watson, 1999; Schuchard, 2005). There is some support for the use of training an eccentric locus to increase the stability of fixation, but it is not clear whether this training is successful because it raises awareness of the preferred retinal locus or if a new trained retinal locus has been developed (Crossland, Culham, & Rubin, 2004; Schuchard, 2005). Research has demonstrated that there is an exponential decrease in visual acuity with eccentricity from the fovea (Davson, 1990). Logically, the closer an eccentric viewing locus is to the nonfunctional fovea, whether a preferred retinal locus or a trained retinal locus, the better the potential visual outcome. The evidence to date is not clear that the spontaneous development of the preferred retinal locus that is associated with the loss of macula vision inevitably provides the best potential acuity. Eccentric viewing is predominantly discussed in relation to reading, but some researchers have noted the application of eccentric viewing to enhance the performance of activities of daily living (ADL) (Fitzmaurice et al. …