Near Visual Acuity - N notation chart
- Subhabrata Bhattacharya
- Mar 29, 2022
- 4 min read
Updated: Mar 21
In an earlier article Decoding Snellen Chart In 4 Mins https://www.quickguide.org/post/decoding-snellen-s-chart-in-4-mins we have touched upon the science behind Snellen Chart for measuring distance visual acuity with near vision chart chart. It may be important here to now focus on the science behind measuring near visual acuity. In many countries, we largely represent patient's near visual acuity in terms of N notation chart -N6, N8, N10, etc. It is time to look into the science behind such numbers, how they are derived and what this means for the patient.
In 1951, FW Law published Standardization of Reading Types in the British Journal of Ophthalmology. The aim was to standardize near acuity test reading charts that was found wanting unlike the distance acuity Snellen charts that was well established by then. He found the Jaeger notation that was widely practiced for recording near acuity as highly obsolete and without standardization of the reading fonts. He proposed, that the Times New Roman font ( a name derived from the famous The Times paper) as a standard font for reading charts. This would ensure standardization of style, length, and height of the fonts across the reading chart. Thus the N-notation represents the record of what the patient reads as per the font size (point size).
Different fonts differ in height, despite the same point. For example, on your computer/laptop if you select the Arial with 10 point, it will be of a different height than that of Times New Roman with the same point. Therefore Times New Roman was selected as the standard.
