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Original ArticleOpen Access
The Thai Logarithmic Visual Acuity Chart
Ruamviboonsuk Pa 
,
Tiensuwan M
,
Tiensuwan M PAISAN RUAMVIBOONSUK, M.D.*,
MONTIP TIENSUW AN, Ph.D.**
Objective
: To evaluate visual acuity scores from the Thai and the standard logarithmic
visual acuity chart.
Design
: Comparative non-randomized clinical study.
Participants and Method
: 153 subjects, calculated from sample size estimation, without
any ocular disease and aged between 18 and 80 years old who could read English and at least 3 out
of 5 letters of the largest line of both charts were enrolled to use only their right eyes to read the
Thai and the standard logarithmic visual acuity chart without any refractive correction. 27 subjects
came back for second measurements of visual acuity in the same manner as the first a week later.
Main Outcome Measurement:
The visual acuity scores were divided into the Snellen or
the whole line score and the ETDRS or the letter-by-letter score. The former was compared by
weighted Kappa and the latter was compared by the paired t-test.
Results.
: There was high agreement in weighted Kappa between the Snellen scores from
the Thai and standard chart (k = 0.7375). There was also high agreement in weighted Kappa be-
tween the Snellen scores from the first and second reading of the Thai chart (k = 0.7304) and the
standard chart (k = 0.7282). A high correlation was observed between the ETDRS scores from the
Thai and standard charts (r = 0.947). Also there was a high correlation between the ETDRS scores
of the first and second reading of both the Thai chart (r = 0.962) and the standard chart (r = 0.952).
There was a significant difference between the ETDRS scores from the Thai and standard chart
(p
MONTIP TIENSUW AN, Ph.D.**
Objective
: To evaluate visual acuity scores from the Thai and the standard logarithmic
visual acuity chart.
Design
: Comparative non-randomized clinical study.
Participants and Method
: 153 subjects, calculated from sample size estimation, without
any ocular disease and aged between 18 and 80 years old who could read English and at least 3 out
of 5 letters of the largest line of both charts were enrolled to use only their right eyes to read the
Thai and the standard logarithmic visual acuity chart without any refractive correction. 27 subjects
came back for second measurements of visual acuity in the same manner as the first a week later.
Main Outcome Measurement:
The visual acuity scores were divided into the Snellen or
the whole line score and the ETDRS or the letter-by-letter score. The former was compared by
weighted Kappa and the latter was compared by the paired t-test.
Results.
: There was high agreement in weighted Kappa between the Snellen scores from
the Thai and standard chart (k = 0.7375). There was also high agreement in weighted Kappa be-
tween the Snellen scores from the first and second reading of the Thai chart (k = 0.7304) and the
standard chart (k = 0.7282). A high correlation was observed between the ETDRS scores from the
Thai and standard charts (r = 0.947). Also there was a high correlation between the ETDRS scores
of the first and second reading of both the Thai chart (r = 0.962) and the standard chart (r = 0.952).
There was a significant difference between the ETDRS scores from the Thai and standard chart
(p
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