Accurate visual acuity testing at near distances is critical in eye care, yet the most widely used near testing tool, the Rosenbaum card, is known to be unreliable. This problem was highlighted in a landmark 1997 paper by Jonathan C. Horton, MD, PhD, and Matthew R. Jones, MD. They reviewed Rosenbaum cards from different manufacturers and found dramatic inconsistencies in the sizing of optotypes (the letters or symbols used for testing), often resulting in misleading acuity measurements. The study showed that most commercially available cards were not scaled properly to the standard Snellen system and could lead to over- or underestimation of visual acuity.
Where Rosenbaum Cards Fall Short
- Inconsistent Scaling: Most Rosenbaum cards lack accurate scaling. In some cases, the numbers on a "20/25" line were the same size as those on a "20/30" line, making them unreliable for visual acuity testing.
- No Standardized Font: Rosenbaum cards frequently use Times New Roman-type fonts, which do not align with the standardized Sloan optotypes used in modern research and clinical practice.
- Manufacturing Variability: No official standard existed for making Rosenbaum cards, so companies produced millions of cards with inconsistent sizing and spacing.
Introducing My Call Bag's Vision Testing Tool
The My Call Bag app solves every one of these problems using a precision-based approach to near and intermediate vision testing. Watch a demo of the My Call Bag vision test.
1. Screen-Aware Calibration
My Call Bag detects the specific iPhone model being used, including screen size and resolution, and automatically adjusts the optotype size to the standardized measurement needed for accurate acuity testing.
2. Credit Card Calibration Option
In case of screen modifications or magnification changes, My Call Bag offers a built-in calibration option using a standard-size credit card to confirm the device's display scale.
3. Standardized Sloan Letters
Unlike Rosenbaum cards, My Call Bag uses Sloan optotypes, the same typefaces used in ETDRS (Early Treatment Diabetic Retinopathy Study) charts, making visual acuity testing more reliable and repeatable.
4. TrueDepth Camera Integration
The most advanced feature of My Call Bag is its use of the iPhone's TrueDepth camera. It measures the distance from the device to the user's eye in real time and adjusts the optotype size based on this distance. Whether testing at 14 inches or at arm's length, the app automatically recalibrates the chart for accurate visual acuity measurement.
5. Adaptive Chart Display
Based on viewing distance, My Call Bag automatically switches between near, intermediate, or distance visual acuity charts. This removes the need to manually change anything and ensures users always get the right test for the right distance.
A Needed Modern Upgrade
Near vision testing has relied on an outdated printed card system for decades, even though its flaws have been well documented. My Call Bag modernizes this process by integrating calibration, precision typography, and real-time distance measurement using TrueDepth technology.
Whether you're testing vision at the bedside, in clinic, or out in the field, My Call Bag delivers accurate, device-calibrated visual acuity results every time.
Try the future of vision testing
My Call Bag makes it simple and accurate, right from your iPhone.