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Traci E Clemons, Emily Y Chew, Tunde Peto, Ferenc Sallo, MacTel Study Group; Responsiveness and the minimal clinically important difference for the NEI VFQ-25 in patients with Macular Telangectasia Type 2 (MacTel Type 2). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1360.
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© ARVO (1962-2015); The Authors (2016-present)
To provide a detailed reporting of the responsiveness to change in visual acuity and minimal clinically important differences (MCID) of the NEI VFQ-25 and its subscales in patients with MacTel Type 2.
MacTel Type 2 affects both eyes and is characterized by retinal opacification, vascular telangiectasis, right-angle venules, intraretinal crystalline deposits, foveal thinning, retinal pigment epithelial hypertrophy, and, in some cases, intra-/sub-retinal neovascularization. A total of 259 patients followed as part of the Natural History Study of Macular Telangiectasia (MacTel Study) had two years of follow-up NEI VFQ-25 and best corrected visual acuity (BCVA) measurements. Responsiveness to change in the NEI VFQ-25 over a 2 year period was assessed using an outcome of best corrected visual acuity (BCVA) change (≥ 10 letters loss). Responsiveness was measured for the overall NEI VFQ-25 and subscales using a distribution based index, the Effect Size Index (ESI), and a criterion based index, Guyatt’s Responsiveness Index (GRI). Generalized linear models (GLM) were also used to compare the responsiveness of the NEI VFQ-25 and subscales to change in BCVA. Criterion and distribution based methods were also employed for estimating the MCID for the overall NEI VFQ-25 and subscales.
Subgroups categorized by BCVA change ( ≥ 10 letters lost [N=49] or < 10 letters lost [N=210]) differed significantly in mean change in overall NEI VFQ-25 (GLM=P<0.0004) and were moderately responsive to change (ESI=0.41; GSI=0.62) over a 2 year period. Seven subscales (General Vision, Ocular Pain, Near Activities, Distance Activities, Mental health, Dependency and Peripheral vision) also moderately responsive to change in BCVA over 2 years in patients with MacTel Type 2. MCID estimates were similar using distribution and criterion based methods. The MCID for the overall NEI VFQ-25 was between 4-6 points.
These data support the use of the NEI VFQ-25 as a responsive measure of vision-related function in patients with MacTel Type 2. Based on these data a 4- to 6-point change in the overall NEI VFQ-25 score represents a MCID corresponding to a 10-letter change in BCVA in patients with MacTel Type 2.
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