UCASH: A New Letter Chart for Super Acuity Investigation of Indigenous People

Abstract

Normal population has an average acuity of 6/6 or better, depending on age and other factors. However, super acuity phenomena have been frequently reported among indigenous people in numerous parts of the world. Up to now, far too little attention has been paid to develop specific letter charts to quantify super acuity. Most of the letter charts are fabricated to estimate recognition acuity up to 6/6. This paper describes a new letter chart for super acuity investigation of indigenous people with three distinct features. UiTM Chen-Azmir-Saiful-Hoe (UCASH) is a super-acuity letter chart designed to quantify the recognition acuity up to 3/0.5 or 6/1 Snellen Notation. UCASH is constructed using single letter display design for a 3-meter testing distance. Four neighbouring contour bars are incorporated to simulate crowding effect and control the accommodation during acuity measurements. Each acuity level of UCASH has an equal optotype combination that takes into consideration the optical blur from spherical, against-the-rule astigmatism; with-the-rule astigmatism; and oblique astigmatism defocus stimulation. UCASH involves two letters from 3/30 to 3/15 or 6/60 to 6/30 of Snellen Notations and five letters from 3/12 to 3/0.5 or 6/24 to 6/1 of Snellen Notations. UCASH is available in both hardcopy printout and electronic versions. The electronic option allows data to be automatically converted and formatted in spreadsheet outputs. The electronic mode saves chair-times and overcomes data loss, insufficient physical storage, and paper waste issues. UCASH is a useful super-acuity investigation tool for indigenous people who usually reside in extreme remote locations worldwide.