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E. L. Lamoureux, J. F. Pallant, K. Pesudovs, G. Rees, J. E. Keeffe; A Self-Assessment Instrument Designed to Assess Restriction of Participation in People With Low Vision: Generalizability to Patients With Age-Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2007;48(13):1182.
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© ARVO (1962-2015); The Authors (2016-present)
An appropriate instrument is necessary to assess the impact of AMD on quality of life (QoL) across the spectrum of the disease. In this study, we assessed if the Impact of Vision Impairment (IVI) was a valid instrument to measure participation in daily activities and QoL in patients with AMD with varying levels of visual impairment.
Participants were recruited from a public eye hospital and low vision rehabilitation centres across Victoria (Melbourne). The IVI data and its three subscales were assessed for fit to the Rasch model. Dimensionality, item fit, response category performance, differential item functioning (DIF) and targeting of items to patients were assessed.
220 patients (mean age=83.5 yr) were recruited and the majority (70%) were females. 22.3%, 47.5 % and 28.8% of the participants had mild (6/12-6/18), moderate (<6/18-6/60) and severe vision loss (<6/60), respectively. The 28-item IVI and its three subscales i.e., ‘mobility and independence’, ‘reading and accessing information’ and ‘emotional well-being’ displayed ordered thresholds indicating that the respondents had no difficulty differentiating between the response options of the scale. There was no evidence of person and item misfit, DIF or multidimensionality. Internal reliability was substantial ranging between 0.89 and 0.95. The IVI scale and its three subscales recorded mean person values ranging between -0.2 and 0.1 which indicate effective person-item targeting for this AMD population. The overall IVI scale and its three subscales recorded non-significant probability values (p=0.1-0.6) when fitted to the Rasch model which indicate that ordering of the IVI items is consistent across all levels of participation in daily living and QoL.
The 28-item IVI is an appropriate and valid scale to assess overall and three specific aspects of participation in daily activities in patients with AMD. Importantly, the IVI has the potential to assess QoL outcomes across a range of visual acuity loss in patients with AMD.
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