A Comparative Validation Study of Near Visual Acuity Assessment Using Different Handheld Acuity Charts

Abstract

Objective: To develop a conversion table and compare the cross-validity of 3 types of widely utilized near vision charts: the ETDRS near chart, the N-notation chart, and the Rosenbaum chart.

Design: A prospective, cross-sectional, comparative validation study.

Participants: Aged ≥40 years.

Methods: A conversion table for the 3 types of near charts was created using objective character sizing based on vertical height captured using a surgical microscope with a 10× magnification. Eligible presbyopic patients had their near vision tested sequentially with 3 near charts in a randomized order.

Main outcome measures: Pearson correlation coefficient (r) for the relationship among the near visual acuity charts. The consistency between the different charts was evaluated by Bland-Altman diagrams.

Results: A total of 204 participants (129 women, 63.2%) were recruited for the study (mean age, 58.9 ± 7.1 years). For correlation, r ranged from 0.596 to 0.836 (all P < 0.001). The Rosenbaum chart had the smallest range of difference against the ETDRS chart (standard deviation [SD] = 0.12), followed by the N-notation chart (SD = 0.15). Most of the converted logarithm of the minimum angle of resolution (logMAR) values from the N-notation and Rosenbaum charts were between 0.0 and 0.1 higher than the ETDRS logMAR equivalent (range: 0.07-0.11), with a tendency for both the N-notation and Rosenbaum charts to overestimate logMAR at more positive values.

Conclusions: We have developed a conversion table for 3 types of commonly used near vision charts. When compared with the ETDRS near chart, the Rosenbaum chart had a smaller range of difference than the N-notation chart. Both the Rosenbaum and N-notation charts tended to underestimate near vision at worse vision.

Financial disclosures: The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Keywords: ETDRS near chart; N-notation chart; Near visual acuity; Presbyopia; Rosenbaum chart.

Figure 1

Objective grading of various reading charts with a surgical microscope. The reticule centers on the character being used for objective measurement: (A) 20/200 character on the ETDRS chart by Alcon; (B) 20/200 character on the ETDRS chart by Bausch & Lomb; (C) J16 character on the Rosenbaum chart; and (D-E) N24 characters on the alphabetical and numerical N-notation charts, respectively.

Figure 2

Bland−Altman plots of N-notation and Rosenbaum charts against ETDRS-A and ETDRS-BL as reference. Various Bland−Altman plots depicting comparisons between (A) ETDRS-BL against ETDRS-A, (B) ETDRS-A against N-notation chart letters, (C) ETDRS-A against N-notation chart numbers, (D) ETDRS-A against Rosenbaum chart numbers, (E) ETDRS-BL against N-notation chart letters, (F) ETDRS-BL against N-notation chart numbers, and (G) ETDRS-BL against Rosenbaum chart numbers. ETDRS-A = ETDRS chart by Alcon; ETDRS-BL = ETDRS chart by Bausch & Lomb; logMAR = logarithm of the minimum angle of resolution.

Figure S1

A photo of 2 optotypes from the N6 row of the N-notation chart taken from the microscope. Due to printing ink variability, the heights of these optotypes are not uniform the bases of the optotypes are not horizontal.