July 2015
The Story of the MNREAD Chart
Measuring Reading Acuity, Critical Print Size, and Maximum Reading Speed
In a continuation of our “Behind the Test” series, this month the PV Marketing Team traveled to Minneapolis, Minnesota to meet with the renowned Dr. Gordon Legge of the University of Minnesota to get a closer look at the MNREAD Chart—the continuous-text platform designed to simultaneously evaluate reading acuity, critical print size, and maximum reading speed.
In this featured video briefing, Dr. Legge deep dives into the scientific origins of the test, its widespread applications across low-vision patient mapping, and shares an exciting technical announcement regarding the new iPad version of the test currently navigating its closed Beta testing phase.
Dr. Gordon Legge, Minnesota Laboratory for Low Vision Research
Video Briefing: Dr. Gordon Legge walks through the functional development of MNREAD
Join Us at BVA in Louisville
Precision Vision will be exhibiting at the Blinded Veterans Association Annual Meeting this August 18th–19th in Louisville, Kentucky. Join our technical representatives live at our booth to explore our newly awarded supply schedule contract with the Department of Veterans Affairs (click here for more contract details).
If you want to evaluate a particular hardware system live at the meeting, simply click on this link to send an email request. We will do everything in our power to arrange logistics to fulfill your request.
Each issue we take a look at some of the most frequently asked questions that we receive and feature a regulatory Q&A below:
Q: Dear PV, is it more meaningful to measure threshold parameters or sustainable performance profiles?
To address this core architectural framework, we asked world-renowned expert and low-vision consultant, Dr. August Colenbrander, to provide a structural breakdown:
A: The question of whether it is more meaningful to measure threshold or sustainable performance cannot be answered without knowing what the precise objective of the measurement is.
Clinicians and researchers who want to know how the EYE functions as a biological sensory organ need standardized, clinical measurement techniques capable of detecting small changes that can be reliably repeated across different times and locations. Threshold measurements are ideally suited for this purpose.
For patients, however, it is far more important how the PERSON functions during the execution of Activities of Daily Living (ADL). Unless navigating elite athletic competition, everyday functional tasks rarely demand absolute peak threshold resolution. For typical ADL profiles, sustainable performance over extended durations is highly critical. This requires supra-threshold stimuli, although the testing parameters are less easily standardized.
The difference between threshold and sustainable parameters is easily demonstrated with classic visual acuity measurements. The task Snellen chose for his original letter chart was the recognition of isolated single black letters on an empty white background, providing an easily reproducible test with robust test-retest reliability. The scoring criterion is a classic threshold parameter: identifying "more than half" (e.g., 3 out of 5 letters) on a given row.
Compare this to real-world ADL tasks, where environmental objects are rarely as perfectly black as chart print, and backgrounds are dark or highly patterned instead of white and empty. When reading a book, a person cannot pause to resolve each letter separately; recognizing half of the words is an entirely unsatisfactory performance tier. Patients demand the capacity to read comfortably for hours, meaning reading speed is just as important as minimum print size.
Snellen defined 20/20 as a letter size “easily recognized” by healthy eyes. By definition, 20/20 means resolving 1M text (average newsprint) at a 1-meter viewing distance. However, we normally read newspapers at roughly 40 cm—placing the visual demand at least 2.5x above threshold (a 4-line margin on a logarithmic chart). This is a massive functional cushion.
As Gordon Legge noted, reading acuity (the smallest print size resolved) is a pure threshold metric; critical print size (the smallest font size read at maximum fluent reading speed) is a metric of sustainable performance. When prescribing optical magnifiers, the calculation should always be based on the latter sustainable metric. These differences apply across all modern reading tests. Similar critical differences exist within contrast sensitivity measurements (click here for details).
In conclusion: The choice between threshold and sustainable tracking is not a zero-sum, either/or scenario. The two metrics directly supplement each other because they isolate separate clinical endpoints. Letter charts are excellent for defining threshold limits. But for sustainable ADL performance mapping, words are better than isolated letters, and standardized sentences (as found on low vision reading cards) are vastly superior to disconnected word lists. Extended paragraphs—such as those on the IReST platform—are best. Precision Vision manufactures them all.
Standardized Multilingual Reading Test Collections
Precision Vision carries the world’s most trusted line of geometrically calibrated Reading Cards. Review the core applications of each system to choose the ideal tool for your lane:
Continuous Text Near Vision Card
Continuous text layouts realistically simulate the everyday near-vision demands patients encounter, such as reading newspapers or prescription labels. This is highly important because it captures the primary component of daily visual experience. Testing with continuous passages enables practitioners to establish an objective mathematical basis for computing the exact magnifier additions or refractive power offsets required to restore patient comfort.
MNREAD Chart
This highly acclaimed continuous-text chart is engineered to map both normal and low-vision thresholds. Developed at the Minnesota Laboratory for Low Vision Research at the University of Minnesota, it incorporates highly specific geometric text progressions where sentence length, line width, and typographic layout are rigidly locked, ensuring an accurate and predictable real-world testing environment.
Radner Reading Chart
The Radner chart operates as a highly standardized, multi-disciplinary reading test system engineered for clinical practice and international research trials. Developed via deep collaboration across global universities involving cognitive psychologists, linguists, statisticians, and ophthalmologists, it presents highly validated sentence difficulties. It delivers exceptional test-retest reliability across numerous languages.
SK Read Test
The SK Read Test Two-Card Set was engineered specifically to evaluate word recognition performance in adult individuals suffering from central or paracentral scotomas (visual field defects). The text passages intentionally utilize words that can be easily confused to facilitate the verbalization of mistakes. Analyzing the specific pattern of reading errors helps differentiate between left-sided and right-sided visual field interference.
International Reading Speed Texts (IReST)
The premier tool for evidence-based near vision research, providing perfect reproducibility, comparability, and successful data documentation across 17 distinct languages! Each testing booklet includes ten long text paragraphs, all highly calibrated against one another and cross-calibrated across all available language editions.
The system is incredibly easy to use, easy to handle, and easy to measure via simple stopwatch timing, featuring pre-calculated normal values and formula matrices. By providing standardized passages of identical length, linguistic complexity, and typographical difficulty, the IReST represents the gold standard for tracking natural, continuous newspaper-print reading under everyday living conditions.
To discover more about these configurations or explore our custom clinical solutions, connect with our specialists via online chat or email us directly.
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