Prospective, multicenter determination of visual acuity agreement between the standard Early Treatment of Diabetic Retinopathy Study (ETDRS) chart and a handheld ETDRS equivalent

Abstract

 

Purpose

 

To characterize agreement in visual acuity measurement between a standard back-illuminated EDTRS chart and a handheld internally illuminated ETDRS chart.

 

Methods

 

Multicenter, prospective study enrolling 134 eyes (70 patients) between October 2012 and August 2013. Visual acuity in patients with retinal disease was measured using both the ETDRS chart and the handheld ETDRS device by masked, independent examiners after best protocol refraction. Examination was performed in the same room under identical illumination and testing conditions. The primary outcome measured in this trial was agreement between the two methods as measured in individual letter units.

 

Results

 

The mean number of letters seen was 63.0 (standard deviation (SD): 19.8 letters) and 61.2 letters (SD: 19.1 letters) for the ETDRS chart and handheld ETDRS device, respectively. Mean difference per eye between the methods was found to be 1.8 letters. A correlation coefficient (r) of 0.95 demonstrated a positive linear correlation between the standard ETDRS chart and handheld acuities. Intraclass correlation coefficient (ICC) was performed to assess the reproducibility of the measurements made by different observers measuring the same quantity, and was calculated to be 0.95 (95% confidence interval: 0.93, 0.96). Bland-Altman plot revealed no systematic bias between the two methods, showing a relatively symmetric distribution of values around the zero difference line.

 

Conclusions

 

The strong correlation between the standard ETDRS chart and handheld ETDRS equivalent suggests they may be used interchangeably, with accurate measurements. Potential benefits of this portable device include the ability to use one device in multiple locations, as well the ability to test ETDRS visual acuity without a dedicated testing lane.

 

 

Scatter plot demonstrating the number of letters read by the standard Early Treatment Diabetic Retinopathy Study (ETDRS) chart (x-axis) vs. the handheld ETDRS device (y-axis).

 

 

Bland-Altman plot demonstrating visual acuity measurement discrepancy between the standard ETDRS chart and the handheld ETDRS device. The x-axis displays the mean between the standard ETDRS and the handheld ETDRS letter score (standard ETDRS + handheld ETDRS)/2. The y-axis displays the difference between measurements by both charts (standard ETDRS - handheld ETDRS).

 

Keywords: 754 visual acuity • 468 clinical research methodology • 465 clinical (human) or epidemiologic studies: systems/equipment/techniques