Subjective Perception of Visual Distortions or Scotomas in Individuals with Retinitis Pigmentosa

Abstract

It is often assumed that persons who develop ocular disease have some form of visual experience that makes them aware of their deficits. Such experiences are frequently their reason for seeking the advice of an eye care professional. For example, those who develop cataracts often complain of blurry vision; those with macular holes or macular degeneration report distortions in their central vision, and those with diabetic retinopathy report that their vision has become patchy or that they see shadows. However, in the case of peripheral field loss or decreasing vision in dim lighting, as in retinitis pigmentosa, for example, symptoms are more obscure and may not be as easily identified by the persons who have them. This group of genetic diseases progressively reduces peripheral vision through the degeneration of photoreceptors. Typically, these persons initially experience trouble with night vision under dim lighting conditions or may be labeled clumsy because they repeatedly bump into obstacles in their visual periphery. In the case of retinitis pigmentosa, the large majority of research on visual function has focused on peripheral field loss, since its progressive decline is the hallmark symptom of this disease. From the subjective perspective of persons with retinitis pigmentosa, however, the remaining central vision becomes more important. Some aspects of central vision, such as contrast sensitivity (Alexander, Barnes, Fishman, Pokorny, & Smith, 2004; Alexander, Derlacki, & Fishman, 1995), color vision (Massof, Johnson, & Finkelstein, 1981; Sandberg & Berson, 1977), or spatial vision (Turano, 1991; Turano & Schuchard, 1991) have been shown to be affected early on. The latter studies have generally agreed that there is variability among persons with retinitis pigmentosa in that some display visual abilities comparable to typical observers but others deviate from normality, but, not always in predictable patterns. Little is known about whether these persons subjectively experience changes in spatial vision (that is, visual distortions). Only one questionnaire that evaluates functionally relevant visual distortions has been published in a peer-reviewed scientific journal. Arimura and colleagues (2006) correlated perceptual distortions that are associated with the development of a macular hole with scores on their metamorphopsia questionnaire. The purpose of their study was to develop a subjective measure that provides information about the extent of visual distortion. Their results indicated that perceived distortions in everyday life situations that are due to a macular hole, as measured on their questionnaire, and quantified distortions on their M-Chart test (similar to a one-line version of the Amsler grid) correlated significantly. Arimura et al.'s 10-item measure contains questions that evaluate far distance vision (such as the perception of telephone poles), intermediate distance vision (such as the outline of a television set), and near vision tasks (reading). It was originally developed for persons with macular disease; however, if those with retinitis pigmentosa experience visual distortions in their remaining central field, some of the items in this measure may also be appropriate for evaluating perceptions of spatial vision of individuals with that condition. The goal of administering this questionnaire to individuals with retinitis pigmentosa was to investigate whether these individuals are indeed experiencing visual distortions or scotomas or both, since no studies have yet addressed this question. METHOD The protocol was approved by the Research Ethics Committee of the Center for Interdisciplinary Research in Rehabilitation (CRIR) of Greater Montreal, the supervising research ethics board for the Institut Nazareth et Louis-Braille (INLB), and the Institutional Review Board of the Jewish General Hospital in Montreal, in accordance with the Canadian TriCouncil Policy Statement of ethical conduct for research involving humans. …