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Elizabeth Tschosik, Nancy Kline Leidy, Miriam Kimel, Chantal Dolan, Eric Souied, Rohit Varma, Neil M Bressler; Quantifying functional reading independence in geographic atrophy: the FRI Index. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4789. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Visual acuity (VA) does not fully capture impact of geographic atrophy (GA) on vision function. Thus, this study evaluated measurement properties of the Functional Reading Independence (FRI) Index and quantified difficulties with functional reading reported by GA patients, in anticipation of using the FRI Index in clinical trials of GA treatments.
Data were analyzed from MAHALO, a multi-center, randomized, single-masked, sham-controlled, phase 2 trial that evaluated lampalizumab for GA secondary to age-related macular degeneration (AMD). Subjects received injections of sham or lampalizumab in one eye monthly or every other month for 18 mo. The FRI Index, a measure of self-reported independence performing everyday reading activities, was interviewer-administered every 6 mo. Treatment arms were collapsed for psychometric analyses (n=100), which included the application of item response theory (IRT) and tests of reliability, validity and responsiveness to change in lesion size.
The 7-item FRI Index scores range from 1 (unable to do) to 4 (totally independent); mean score (SD) was 2.5 (0.8) at baseline (n=94) and worsened to 2.2 (0.9) at month 18 (n=81). The proportion of subjects at Level 1 (unable to do) increased from 17% at baseline to 30% at month 18 (difference: 13%). FRI Index internal consistency (IRT marginal reliability) was 0.90. Test-retest reliability (intraclass correlation coefficient) in subjects who remained stable on the National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25) from baseline to month 6 was 0.86 (n=27). FRI Index scores were correlated with NEI VFQ-25 (r=0.66; P<0.001) and GA lesion size (r=−0.26, P=0.02). No relationship was found with high contrast best-corrected VA (r=0.16; P=0.11). The FRI Index showed a trend in mean (SD) known-groups validity based on GA lesion size of <4 disc areas (<10mm2) vs ≥4 disc areas (≥10mm) (2.9 [0.8] vs 2.4 [0.8]; P=0.06). Scores were sensitive to within-subject change in GA lesion size over time, with those having an increase in lesion size over 18 mo (≥0.94mm2) showing greater FRI deterioration than those whose lesion was stable (<0.94mm2) (−0.3 vs −0.1, P=0.02).
Patients with GA in MAHALO experienced impairment in functional reading independence that worsened by 18 mo. This study supports the use of the FRI Index as a tool to assess functional reading independence in patients with GA secondary to AMD.
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