This card is scientifically designed using the Bailey-Lovie format. It uses Sloan letters and features a geometric (or logarithmic) progression of font sizes. The lines change size in 0.1 log-unit steps so the line above a given line is 1.26 times larger than the line below. What this means is that you can use this card at any distance using M notation. The letters are roughly equal in legibility. The rows are marked in M notation and in 20 ft equivalent acuities. They are 20 ft equivalent acuities if the card is held at 40 cm (16 in).
There is a number chart on the card for use with very young children or illiterates. There is also a reading chart for assessment of reading ability. The font used is Times New Roman, a typical font used in newspapers & books. Remember that reading acuity is not necessarily the same as single –letter chart acuity. The stroke widths are not 1/5 of the height of the letter like they are in the single-letter chart. Patients with macular lesions (e.g., AMD) may have a reading acuity that is significantly worse than their single-letter acuity. Thus this is used in evaluating visual impairment or functional acuity rather than visual acuity. The reading card is designed using principles similar to those used for the Minnesota Low-vision Reading test (MN-READ).
The card is pocket sized and features a notched ruler and half moon ruler for measuring pupil size.
Review - 6/16/17
"The shortened length of lines with a full array of letters or numerals which are usually found spread across the whole chart width, creates “crowding phenomenon”. This is an important distinction in managing Amblyopia recovery. In diagnosing and remediating Amblyopia it is important to distinguish whether BEST acuity is the ability to identify an isolated single letter or the ability to distinguish individual letters in a line of print. Activated retinal edge detector discrimination, and intra-retinal ganglion cell processing are some of the neurological processes necessary for the recovery of “acuity” in Amblyopia. Isolated single letter acuity is a measurement taken in a limited environment. Patient fluency in identifying individual optotypes, in proper order, in a crowded line of print indicates functional improvement."
- Douglas G Smith, OD