Low Vision Rehabilitation Intervention for People with Ring Scotomas

Abstract

Central scotomas--areas of the nonseeing retina within the central 20 degrees of the visual field--are present in approximately 90% of vision rehabilitation patients (Fletcher & Schuchard, 1997). They vary in size and shape and can be small or large, symmetrical or asymmetrical, round or irregularly shaped. Most central scotomas border fixation on one side and can be overcome with magnification and sometimes eccentric viewing. However, these strategies seldom suffice in the case of ring scotomas (see Figure 1), which border three or four sides of fixation and have been present in 20%-47.5% of patients with eye conditions that affect central vision (Fletcher & Schuchard, 1997; Messias et al., 2007; Mogk, 2009). Patients with ring scotomas generally have near-normal acuity (Maguire & Vine, 1986; Moil et al., 2001; Rotenstreich, Fishman, & Anderson, 2003), which does not reflect their functional impairment in reading and activities of daily living (Fletcher & Schuchard, 1997; Sarks, Sarks, & Killingsworth, 1988; Sunness et al., 1999; Sunness, Rubin, Zuckerbrod, & Applegate, 2008). They display a characteristic slow-fast-slow reading pattern when performing tests such as the MNREAD acuity chart (Legge, Ross, Luebker, & LaMay, 1989; Sunness, 2008). They read the largest print slowly, speed up with the middle print sizes as more letters fit within the central island of vision, and then slow again when the print drops below the size they can discern (Fletcher & Schuchard, 2006; Fletcher, Schuchard, Walker, & Raskauskas, 2008). Most patients with ring scotomas fixate centrally even for targets that are larger than the central island (Messias et al., 2007; Mori et al, 2001), possibly because reorganization of cortical visual processing only occurs in the absence of foveal vision (Baker, Dilks, Peli, & Kanwisher, 2008). Three principles characterize the approach to intervention for patients with fovealsparing scotomas: education about the scotoma, supporting the use of the limited central vision, and maximizing the potential to use the peripheral retina. AWARENESS OF THE SCOTOMA The most essential issue for successful intervention for ring scotomas is that both the clinician and the patient are aware of the visual pattern and its clinical significance. Ring scotomas can be confusing and nonsensical to patients. Training may include increasing awareness of the difficulty of reading large print and of the negative impact of substantial magnification that causes the target to fall on the scotomatous area. Education about the nature of the ring scotoma can prepare patients to learn effective reading strategies and engage in vision rehabilitation. Families and caregivers may think that the patient's description of his or her vision seems illogical, leading to distrust and doubt about the patient's visual function and performance of activities. Education can avoid such misunderstandings (Cimarolli & Boerner, 2005) and thus support optimal functioning by improving the patient's social environment. One of the most concrete methods for successful education is providing a visual image of the ring scotoma with either a Scanning Laser Ophthalmoscope (SLO; SLO-101, Rodenstock, Dusseldorf, Germany) or California Central Visual Field Test (CCVFT; Mattingly, California), defining the scotoma in lay terms (for example, a doughnut-shaped blind spot), and then discussing precisely how the patient's scores on reading acuity tests changed with the print size. [FIGURE 1 OMITTED] USING THE CENTRAL ISLAND OF VISION The second step is to evaluate and support the use of the central island when it is functional. Practitioners need to determine the size, visual acuity, and contrast sensitivity of the seeing central area, the extent of the surrounding scotoma, and the nature of the patient's habitual fixation. Does the patient consistently fixate centrally or shift to eccentric fixation when viewing larger images? …