Background: Almost 2 million people in the UK are blind or partially sighted and this number is expected to double by 2030. Of this number, approximately 85% have residual vision (low vision) that can be used effectively for daily activities with appropriate visual aids. Bilateral macular disease is one of the leading causes of visual impairment especially in the elderly. In advanced age related macular degeneration (AMD) patients develop a scotoma at the fovea, the most sensitive central area of the field of view. In order to read or recognise faces most patients with AMD adopt an eccentric fixation locus (the preferred retinal locus or PRL) that acts as a pseudo-fovea and is used as a reference point for the patient’s oculomotor system. The PRL is placed upon parafoveal or extrafoveal retina depending on the scotoma size and location. Patients use one or more PRLs, depending on the task they are performing. PURPOSE. To investigate how visual function varies with retinal eccentricity, to determine how visual function at the PRL compares to other retinal locations of comparable eccentricity, and to determine whether a more suitable eccentric retinal location could be found for the patient to be trained to use as their PRL. Methods: 24 patients with AMD and 19 normal vision subjects (8 young and 11 similar in age to the patients) were recruited. All AMD patients were tested on a Rodenstock scanning laser ophthalmoscope to identify the PRL location in their better eye. A SMI EyeLink eyetracker was used to assess peripheral visual acuity contrast sensitivity in both groups. 15 AMD patients and 11 normal vision subjects (6 young and 5 similar in age to the patients) were further tested on the SMI Eyelink eyetracker to assess peripheral sustained attention and reading speed with Rapid Serial Visual Presentation (RSVP). Results: In normal vision subjects, visual acuity, contrast sensitivity, attention and reading speed declined with increasing retinal eccentricity, and varied with polar angle. For visual acuity, attention and reading speed performance was best along the horizontal meridian. Young normal vision subjects performed better in the retinal periphery for all tasks compared to the age-similar normal vision subjects. All AMD patients performed best at their PRL in the visual acuity, attention and reading speed tasks, but not in the contrast sensitivity task. Even at the PRL, AMD patients performed worse on all tasks than the age-similar normal vision control subjects at a similar eccentricity. Reading speed was poorly predicted by visual acuity and contrast sensitivity but well predicted by sustained attention. Conclusions: For the visual functions measured in these experiments, it appears that most AMD patients found the area best suited for their PRL. It is the area with best acuity and reading performance, and most easily attended to. This implies that visual rehabilitation training should utilize the patient's selected PRL rather than training a new PRL. However, visual function at the PRL is generally worse than would be expected for healthy retina at that eccentricity. It is not clear whether this is because the peripheral retinal is not functioning normally or that patients are not making full use of this area. The ability to deploy attention at the PRL appears to be important in reading, however more clinical research is needed in this area. These data provide important information about the optimal eccentric retinal area for text presentation to achieve maximal reading rate and may be useful for developing new training programmes to help patients make best use of eccentric fixation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:505212 |
| Date | January 2008 |
| Creators | Rees, Angela Lynn |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/15951/ |
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