LEA Numbers Low Vision Book Has Advantage Over Feinbloom Chart
A recently published research article by David Lewerenz, OD; Nick Hardgrave; and Jonathan Harley of the Oklahoma College of Optometry at Tahlequah, Oklahoma, reported a slight advantage of the LEA Numbers Low Vision Book over the Feinbloom visual acuity chart.
First . . . the backstory.
William Feinbloom, according to the authors, was an optometric pioneer who believed individuals with visual impairment should have special testing methods. The Feinbloom chart, introduced in the first half of the 20th century with number optotypes in larger sizes, was the first chart designed to use specifically with visually impaired individuals.
The authors stated that, while the Feinbloom chart includes large optotype sizes, is portable, and can be used at any distance, disadvantages include inconsistent optotype width-to-height ratios and irregular progression of optotype sizes.
The LEA Numbers Low Vision Book is also handheld and portable. However, this visual acuity test was developed to overcome some of the chart design disadvantages of the Feinbloom chart. For example, the numbers were calibrated against the Landolt C, the international reference optotype; numerals 5, 6, 8, and 9 are used to meet one of the national/international guidelines for standardized eye chart design (optotypes should be approximately equal in legibility or discriminability); and optotypes progress systematically in 0.1 logMAR units.
Hardgrave, Harley, and Lewerenz designed a study to determine which handheld book would provide visual acuity measurements more similar to the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart, considered the gold standard for measuring visual acuity, and which provided the most repeatable measure of visual acuity in visual impaired individuals.
Distance visual acuities were taken with the LEA Numbers Low Vision Book, the Feinbloom chart, and the ETDRS chart. Measurements were repeated 15 to 30 minutes later. Participants were nine visually impaired children ages 8 to 19 years and nine visually impaired adults ages 35 to 88 years. The authors stated that the small number of participants is typical of a pilot study and recommends further research using a larger sample size.
Both charts were evaluated for correlation to ETDRS. The LEA Numbers Low Vision Book showed closer correlation with ETDRS.
Conclusions were: “The results of our study indicate that there is a slight advantage, in terms of agreement with ETDRS, of LNLVB over the Feinbloom chart when testing visually impaired patients. The two tests proved nearly identical in terms of repeatability in a low-vision setting. Both handheld charts measured slightly worse acuity than the ETDRS chart, but overall proved to be suitable alternatives when the ETDRS chart is not available or practical in certain clinical situations.” Refer to the article for suggested reasons regarding why both handheld charts measured slightly worse acuity than the ETDRS chart.
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