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Code to Generate Latin and Canadian Aboriginal Syllabics (CAS) Visual Acuity (VA) Charts

Adapted from https://github.com/manu-mannattil/vachart

This repository contains a LaTeX file and a Python script for making random Snellen charts. PDFs with Latin and CAS charts, meant to be kept at a distance of 3 m, have been included with this repository. To generate the TeX commands for new charts, run VA_Chart.py. Then, edit CAS.tex or Latin.tex and change the distance \factor if required. To compile the file, run make or compile using XeLaTeX. We recommend using Overleaf for generating PDFs.

Background

The Snellen chart consists of a series of optotypes (usually the Latin letters C, D, E, F, L, O, P, T, and Z) in different sizes. We have developed here a visual acuity chart using Canadian Aboriginal Syllabics (CAS) using the optotypes of ᐱ, ᑎ, ᑭ, ᒧ, ᒋ, ᒥ, ᑯ, ᒧ, and ᔨ.

Using elementary trigonometry, the equation that relates the optotype width (or height) w, the subtended angle φ, and the distance to the chart d, is w = 2d tan(φ/2)

A person's vision is considered normal (i.e., 6/6 or 20/20 vision) if he or she can delineate 1-arcminute-wide features of an optotype that has an angular width of 5 arcminutes. Conventionally, the Snellen chart is kept at a distance of 6 m. This means that the optotype width must be

w = (12 m) × tan(π/4320) = 8.73 mm.

Further reading

R. J. Kolker, Subjective Refraction and Prescribing Glasses (American Academy of Opthalmology, San Francisco, CA, 2014).

A. R. Elkington, H. J. Frank, M. J. Greaney, Clinical Optics, 3rd ed. (Blackwell Science, Oxford, 1999).

Disclaimer and License

This repository is for informational purposes only and do not constitute medical advice. It is not intended to replace the advice of a qualified health provider or a licensed optometrist.

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Canadian Aboriginal Syllabics Visual Acuity Chart

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