The 20-Step Eye Exam on the NIDEK RT-6100 — Why It Takes 20–30 Minutes

What Is the Difference Between a 2-Minute Machine Reading and the 20-Step Exam?

Stage 1 (Steps 1–3): Data Entry — Knowing Where You Start From

1. Enter the autorefractor (AR) readings — the objective draft mentioned above, transmitted straight into the phoropter over the local network; nothing is copied by hand, so nothing gets garbled in transcription.
2. Measure uncorrected visual acuity in each eye and with both eyes — the "nothing corrected yet" baseline.
3. Measure your old glasses on a lensmeter, then test your vision through those same old glasses — the "what you are used to" baseline. This is the data that becomes decisive in Stage 3, which is why bringing your old glasses to the exam matters so much.

Stage 2 (Steps 4–15): Fine-Tuning Each Eye — the Heart of the Exam

Each eye goes through the same 6 steps in turn (with the other eye covered):

1. Input check: with the machine's numbers dialed in, the eye must be able to read medium-sized letters — if not, the draft data has a problem that must be resolved before moving on.
2. Red–green test, round 1: the machine adds +0.50D to blur your vision slightly (fogging) to relax accommodation, then steps it back down while asking whether the letters on the red or the green background look clearer — the chromatic dispersion of light helps reveal whether the current numbers are under-corrected or over-minused. Details here: over-minused glasses and the red–green test.
3. Refine the astigmatism axis with the Jackson Cross Cylinder: the famous "which is clearer, 1 or 2?" question series — the machine rotates the axis in steps as small as 1° when astigmatism is high. Why the axis must be set before the power: see the secret of the cross cylinder.
4. Refine the astigmatism power, also with the cross cylinder, once the axis is correct.
5. Red–green test, round 2: changing the cylinder power shifts the focal point, so the sphere must be rechecked — this sphere → cylinder → sphere loop is exactly what makes the exam take time.
6. Lock in maximum acuity at "maximum plus": the classic principle — choose the most plus (least minus) power that still gives maximum acuity; for a nearsighted person, that means the lowest possible prescription — a higher number is not automatically better.

Stage 3 (Steps 16–18): Both Eyes Together — Where Quick Exams Cut Corners

1. Binocular balance: polarized lenses split the image into two rows of letters, one row for each eye; the machine fogs both slightly, then adjusts until the two rows look equally clear. Each eye being right on its own is not enough — the two eyes being slightly out of balance is enough for an all-day headache, as analyzed in glasses with the right prescription that still strain your eyes.
2. Stereo (depth) check: four marked bars, and you say which bar appears to "pop out" closer — confirming that the two eyes are truly working together as one system, with neither eye being "abandoned" by the brain.
3. Deciding the wearing prescription: the step that turns "maximum power" into "a glasses prescription". The machine has its own algorithm (NIDEK calls it FinalFit) that cross-checks the result against your old glasses and your capacity to adapt — for nearsighted eyes, unless truly necessary, both the increase over the old glasses and the difference between the two eyes are kept within roughly ~0.75D — and then the technician asks how it feels to you and adds or subtracts the final notch. This is why "three places give three different numbers": the difference is not the machine, it is whether this step is done at all.

Stage 4 (Steps 19–20): Near Vision — for Those Over 40 or Doing Lots of Close Work

1. Measure the near addition (ADD): the machine suggests a starting number based on age, then it is fine-tuned with a grid chart at your actual working distance (reading a book, a screen, or a sewing table — every occupation has its own distance). Why you cannot just "add by age": see presbyopia exams: ADD cannot be added by age.
2. Verify with a real near reading chart: you read small print at your real working distance before the prescription is finalized.

For complex cases, the technician may add measurements beyond the standard program (near point of convergence, amplitude of accommodation...) — these are not part of the default 20 steps and are used only when symptoms suggest them.

After 20 Steps You Are Still Not Done: From Prescription to Actual Glasses

More About the Equipment

Frequently Asked Questions

Q: How long does the 20-step exam take?

A: Usually 20–30 minutes for a standard case; longer with high astigmatism, a large difference between the two eyes, or a first progressive-lens fitting. A 2-minute machine reading covers only Stage 1 of the protocol.

Q: If I answer "1 or 2" wrong, will the result be wrong?

A: No need to worry. The machine repeats the questions over multiple rounds with progressively smaller steps precisely to filter out the noise from hesitant answers; "they look the same" is also a valid answer and is often a signal that the adjustment is already correct.

Q: Why can another place produce a prescription in 5 minutes?

A: A 5-minute prescription is usually the automated machine's number plus experience-based tweaks. For easygoing eyes, the result may be acceptable; for eyes with astigmatism, a large difference between the two eyes, sensitive wearers, or anyone over 40, skipping the subjective steps is the origin of glasses that are "the right numbers but uncomfortable".

Q: Can children go through this protocol?

A: Sitting behind a phoropter and answering consistently usually requires late-kindergarten to elementary-school age (roughly 5–6 years and up). Younger children, children whose prescription is increasing quickly, or those with fluctuating measurements should see an eye doctor for age-appropriate objective methods, with cycloplegic (accommodation-paralyzing) eye drops considered before measuring.

Q: How long is a prescription valid?

Q: Does the exam hurt, or involve any eye drops?

A: No. All 20 steps consist of looking through trial lenses and answering questions. Cycloplegic drops are used only when a doctor prescribes them at a medical facility — they are not part of a routine glasses exam.

Summary

References

• NIDEK CO., LTD. — Operator's Manual Refractor RT-6100 (Programmed Refraction chapter, Standard Program A; Power Adjustment/FinalFit) and the product page Intelligent Refractor RT-6100.
• StatPearls / NCBI Bookshelf — Subjective Refraction Techniques.