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Benedetto Falsini, Lucia Galli-Resta, Marco Piccardi, Lucia Ziccardi, Antonello Fadda, Angelo Maria Minnella, Dario Marangoni, Giorgio Placidi, Giovanni Resta; Inter-eye correlation in clinical measures of visual function in cone-rod dystrophy (CRD) patients. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1418. doi: https://doi.org/.
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To investigate inter-eye correlation in clinical measures of visual function in cone-rod dystrophy (CRD) patients and therefore the feasibility of clinical trial designs using monocular treatments and the untreated eye as an internal control
A retrospective study of the CRD patient database from the Ophthalmology Dept. of the Cattolic University in Rome. Baseline values were from 158 CRD patients. Follow-up measures from a subset of 46 CRD patients followed for 6.5 ± 3.2 years (2.5-13 years), with an average of 1 visit/year, and a minimum of 3 visits. Baseline age was 27± 16 years (9-67 years). Measures considered were: 1) best corrected visual acuity (BCVA, evaluated as minimal angle of resolution or MAR); 2) focal macular cone ERG (fERG) recorded in response to an 18 deg red central red field flickering at 41 Hz. This latter measure was chosen because it can detect early visual function decline in CRD, often anticipating BCVA loss of several years1
Inter-eye correlation at baseline was very high for both BCVA and fERG (Spearman coefficient 0,858 N=123, P<10-35 for BCVA; 0.819, N=158; P<10-7 for fERG). In the follow-up cohort stationary patients had stationary visual measures in both eyes (N= 23 ; stationary cutoffs: fERG: -35% - +56%; BCVA: ±20%MAR), while progressive patients experienced BCVA and fERG decay in both eyes (N=23). Global linear fitting of logfERG showed that fERG progression rate was consistent between the 2 eyes. Yearly fERG loss in fast progressing patients: OD 35,7% (95%CI: 26,9-43.4% N=10 pz, Adj R20,76); OS 33,7% (95%CI: 25,5-41.0% N=10 pz, Adj R2 0,81). Yearly fERG loss in slow progressing patients: OD 5.4%, (95%CI: 1.1-9.6% N=13 pz, Adj R2 0,78); OS 11,4% (95%CI: 8.4-13.6% N=13 pz, Adj R2 0,88). In both fast and slow progressing CRD patients OD vs OS rates are not significantly different (Wilcoxon matched-pairs signed rank test of individual fits: Fast progressors P=0,8; Slow progressors P=0,31).
Baseline values of BCVA and fERG, as well as progression modality and rates of fERG loss show high inter-eye correlation in CRD patients. These data support the design of clinical trials involving unilateral treatment with the use of the fellow eye as internal control. 1Galli-Resta, L., M. Piccardi, L. Ziccardi, et al., Invest Ophthalmol Vis Sci 2013; 54(10): 6560-9
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