Visual Acuity Clinical Trial
Official title:
Evaluation of Letters Versus Numbers (ELEVEN) Study: ETDRS Visual Acuity Chart Performance in an English Alphabet Illiterate Population
This is a prospective randomised controlled trial to determine the performance of Best Corrected Visual Acuity (BCVA) scores using the ETDRS number chart were compared with ETDRS alphabet chart in healthy eyes of patients who do not recognise the English alphabet.
BACKGROUND: The measurement of visual acuity is important in the clinical setting to assess
visual function and treatment response, while in research to provide objective clinical
outcomes. The current gold standard for visual acuity measurement in most research studies,
including major clinical trials, is the Early Treatment Diabetic Retinopathy Study (ETDRS)
chart designed by Bailey and Lovie. However, this may not be suitable for participants who
are illiterate. Alternatives exist, including the ETDRS numbers chart, Landolt C chart and
Tumbling E chart. Existing studies show that the Landolt C and Tumbling E charts are
alternatives with agreement with ETDRS letters chart in healthy and diseased eyes. However,
the charts are limited by their 25% (if four orientations) or 12.5% (if eight orientations)
chance of guessing the orientation of the letter.
The ETDRS numbers chart may overcome this limitation, as it uses five unique numbers instead
of a single rotating letter. There are few studies evaluating the different types of visual
acuity measurement among those unfamiliar with the English alphabet. Though one study shows
high repeatability and agreement between the ETDRS letters and numbers charts in healthy and
diseased eyes of English literate individuals and shorter testing duration when using the
numbers chart, this finding has not been validated in individuals unfamiliar with the English
alphabet. This study aims to evaluate how the ETDRS letters and numbers charts compare in
individuals unfamiliar with the English alphabet.
METHODS: Eligible subjects were divided into 2 groups according to level of literacy.
Literacy was determined by self-reported exposure to the English alphabet and recognition of
the 10 Sloan letters (C, D, H, K, N, O, R, S, V, and Z). Subjects included were classified
into the 2 groups: group A, with no exposure to the English alphabet and recognition of <6/10
letters, and group B, with exposure to the English alphabet and recognition of ≥6/10 letters.
Testing: Each subject underwent 2 rounds of BCVA measurements using 2 types of ETDRS charts
in randomized sequence as follows: LN or NL (L = ETDRS letters chart, N = ETDRS numbers
chart) from Precision Vision® (PV). The randomization of the testing sequence was performed
by a study coordinator independent of study recruiter, optometrist or investigator.
Sequentially numbered, opaque and sealed envelopes were used for allocation concealment and
opened by the optometrist prior to testing.
The tests were performed and recorded by a single optometrist in the same testing room with
similar lighting conditions. For every round of testing, the right eye was examined first,
followed by the left eye. For the right eye, numbers chart (PV No. 2702A) and letters chart
(PV No. 2173) were used. For the left eye, the numbers chart (PV No. 2714A) and letters chart
(PV No. 2174) were used. Different charts (with the same optotypes but in different order)
were used for right and left eyes to minimize the effect of learning between consecutive
tests.
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