Operant measurement of subjective visual acuity in non-verbal children.

Macht (1971) taught five non-verbal kids with intellectual disability to press a lever when a Snellen E card matched a sample.

The lever press worked like a yes. Correct presses earned candy. Wrong presses meant no candy.

After training, the kids pressed more when the E was clear and less when it was tiny. The curve gave a visual-acuity score.

All five kids learned the game. Their acuity curves lined up with later eye-doctor checks.

Two kids got new glasses because the test showed their old lenses were too weak.

Taras et al. (1993) later used the same lever-press idea to teach daily-living skills to visually impaired teens. They added hand-over-hand help and step-by-step talk. The method still worked after ten months.

Lanza et al. (2024) looked at 69 papers and found most vision tests need words. The 1971 lever test fills that gap for kids who can’t speak.

Tang et al. (2003) used single-case operant methods like Macht (1971) but hunted for sensory reinforcers instead of acuity. Both show one lever can answer many questions.

You now have a cheap, fast way to check if a non-verbal client needs glasses. No words, no waiting for eye-clinic time. Train the lever-press game, run a quick curve, and share the number with the optometrist. Start next session with one Snellen E card and a candy dish.