Your Child’s Randot Stereo Test: What the Score Actually Means
Your Child's Randot Stereo Test Score at a Glance
The Randot test checks how well your child's eyes work together to see depth. The score is a number in 'seconds of arc.' A lower number is better. It means the eyes can spot smaller differences in depth.
One score is a snapshot, not a label. A depth perception test checks whether a child sees in three dimensions, is painless and needs no special preparation, and can help find lazy eye and crossed eyes early when they are easier to treat.1
A single Randot number does not diagnose anything by itself. It tells the eye doctor how your child's eyes are teaming up today, and it points to whether a closer look is needed. Young children especially can score lower than their true ability simply because the task is new or they are tired. What matters is the whole picture: the score, the eye exam, and any repeat testing.
Your child's eye doctor or orthoptist interprets the score in the context of the full exam. They compare it to what is typical for your child's age, check it against how the eyes align and focus, and decide whether to reassure you, repeat the test, or look further. The sections below explain what the number measures, how the test is done, and what different scores can mean.
What the Randot Stereo Test Actually Measures
The Randot test measures stereoacuity, which is the finest depth difference the two eyes can detect when they work as a pair. The unit, seconds of arc, is just a way of describing how small that detectable difference is. A smaller number means the eyes can pick up finer depth, so on this test lower is better, the opposite of a school grade.
Good depth perception depends on both eyes sending matching pictures that the brain fuses into one 3D view. Testing binocular depth perception is used as a screening test for amblyopia in some offices, but it should not substitute for visual acuity testing, and it is often difficult for children under 5 to perform.2 That is why the Randot result is read alongside the rest of the exam, never on its own.
Randot is short for 'random dot.' The pictures are hidden inside fields of scattered dots, so a shape only pops out in 3D when both eyes are working together and the brain fuses the two views. This design makes it hard to guess or fake the answer using one eye, which is what makes it a useful check of true binocular teaming rather than one-eyed cleverness.
How to Prepare Your Child for the Test
You do not need to change anything before this test. A depth perception test needs no special preparation and has no risks or side effects.1 If your child normally wears glasses, bring them, because the test is usually done with the child's regular correction on so the result reflects everyday vision.
The best preparation is a calm, rested child. It can help to describe it as a picture game where they wear special sunglasses and point to shapes that seem to float. A hungry, sleepy, or nervous child may not give their best effort, and that alone can lower the score. If your child is having an off day, it is reasonable to ask whether the test can be repeated another time.
What Happens During the Test
Your child wears lightweight polarized glasses, similar to 3D movie glasses, over any regular glasses. The tester holds a booklet of dot patterns, and your child either points to a shape that appears to stand out or names simple pictures that look 3D. The glasses let each eye see a slightly different image, which is what creates the depth effect when the eyes team up.
The test is quick, usually just a few minutes, and it feels like a game rather than a medical procedure. The tester starts with easier, more obvious shapes and moves to finer ones until your child can no longer see the hidden picture. The last level your child gets right is recorded as the score. There is no bright light, no drops, and nothing that touches the eye.
What Your Child's Score Actually Means
The Randot Preschool version reports the score at set steps. The Randot Preschool stereotest measures depth perception at set levels of 800, 400, 200, 100, 60 and 40 seconds of arc, where a lower number means finer depth perception and 40 is the best score, and nearly all children aged 5 and older who are not stereoblind reach 40.3 So a score of 40 is the strongest result, and larger numbers mean coarser depth perception.
Normal depends heavily on age, because depth perception is still maturing in the preschool years. Younger children often score in the middle of the range and improve as they grow, while most school-age children reach the finest level. That is why an eye doctor compares your child's number to age norms rather than to an adult standard, and why a 3-year-old's score is read very differently from a 7-year-old's.
It is normal for the number to move between visits without anything changing in the eyes. Repeat Randot testing in children can vary by roughly a factor of four between sessions even when vision has not changed.3 So a one-step difference on a retest is usually just normal test-to-test wobble, not a decline, which is another reason a single score is never the whole story.
A consistently high number, or not seeing the shapes at all, can be a clue that the eyes are not teaming well. A depth perception test can help detect lazy eye and crossed eyes early, when they are easier to treat.1 A worrying score does not confirm any of these on its own; it tells the doctor to examine further.
If a closer exam does point to lazy eye, the reassuring part is that it usually responds well to treatment, especially when caught early. Treatment for amblyopia (lazy eye) includes glasses, patching the stronger eye, and atropine eye drops.4
A good Randot score is reassuring, but it is not a clean bill of health for the whole eye. It does not measure how sharply each eye sees on its own, it does not check eye health at the back of the eye, and a young child's low score can reflect attention rather than vision. This is exactly why the result is paired with visual acuity testing and a full eye exam instead of standing alone.
Risks and What the Result Means Going Forward
The Randot test is one of the gentlest parts of an eye exam. There are no drops, no bright lights, and nothing touches your child's eye, so there is nothing to recover from and your child can go straight back to normal activities. The only real limitation is cooperation: the score is only as good as the effort your child gives on the day.
A strong result is a good sign that the eyes are teaming well, though it is read together with the rest of the exam rather than as a guarantee. Up to 3 of every 100 children have amblyopia, and it is treatable, especially when it is found and treated early.5 If your child's score prompts a closer look, that early attention is the whole point of testing, and it is what gives treatment its best chance to work.
When to Call Your Child's Eye Doctor
The test result itself is not urgent, but some vision changes are worth a same-day or prompt call whatever a past score showed. Contact the eye doctor promptly if you notice a new eye turn or wandering eye, if your child suddenly closes or covers one eye, complains of double vision, holds things very close, or has a sudden drop in vision, since these can signal a problem that needs a timely look. Trust your own observations at home; they are valuable information for the doctor.
If the eye doctor recommends a recheck or a referral, keep it even if your child seems fine day to day, because early teaming problems are easy to miss without testing. A general eye doctor may handle the follow-up, or your child may be sent to a pediatric eye specialist or orthoptist if the exam points to lazy eye, an eye-alignment problem, or a need for closer monitoring.
Common Questions Parents Ask
No. A single higher number is a reason to look more closely, not to panic. Scores are affected by age, attention, tiredness, and simply how new the task is, and they can vary from visit to visit. Your eye doctor reads the number alongside the full exam and may repeat the test before drawing any conclusion. If a real teaming problem is found, it is usually treatable, especially when caught early.
A score of 40 seconds of arc is the best result on this test and shows the eyes are teaming well for depth. It is genuinely reassuring, but it measures depth perception only. It does not tell you how sharply each eye sees on its own or whether the eyes are healthy inside, which is why a full eye exam still includes acuity testing and a look at eye health. Think of 40 as one strong green light, not the whole dashboard.
Seconds of arc is a unit for a very small angle, used here to describe the tiniest depth difference your child's eyes can detect. You do not need the math: just remember that a smaller number means the eyes can sense finer depth. That is why 40 is better than 400 on this test. It is one of the few scores in life where lower is the goal.
Some change between visits is expected and usually harmless. Repeat testing can shift by about one step in either direction even when a child's vision is unchanged, because effort, attention, and the newness of the task all affect the result. A one-level difference on its own is rarely meaningful. Your doctor looks for a pattern across visits and the rest of the exam, not a single number, before deciding anything has truly changed.
The random-dot design makes guessing hard. The hidden shapes only appear in 3D when both eyes work together, so a child using one eye alone simply cannot see them. That is a strength of the Randot test: it checks genuine binocular teaming rather than letting a sharp single eye cover for a weaker one. A child can score low from lack of cooperation, but they cannot fake a good score.
Not necessarily. Depth perception testing is often difficult for children under 5, and some simply are not ready to point reliably or sit still for it yet. That is a normal developmental limit, not automatically a vision problem. The eye doctor may try a simpler version, retest at the next visit, or rely more on other parts of the exam. Being untestable at a young age is common and does not by itself mean anything is wrong.
More Questions Parents Ask
It helps, but it is not the only check. Reduced depth perception can be an early clue to lazy eye or an eye-alignment problem, which is why stereo tests are used in screening. However, the test should not replace measuring how sharply each eye sees, so it is used together with acuity testing rather than instead of it. A normal Randot score lowers the odds of a significant teaming problem but does not rule out every eye condition.
They are close cousins. Titmus, Randot, and TNO are all stereo tests that measure depth perception using special glasses and hidden 3D images. The Randot uses random-dot patterns, which are harder to guess than some older tests. The exact score can differ a little from one test to another, so what matters most is comparing your child's result to the age norms for the specific test that was used.
That depends on the result and the rest of the exam, so follow your eye doctor's advice. A clearly normal score in an older child may just be noted at routine visits, while a borderline or low score, or a child being treated for lazy eye or an eye turn, may be rechecked more often to track progress. Keeping the recommended follow-up visits is the reliable way to catch any change early.
- Is my child's score normal for their age?
- Was the test done with my child's glasses on?
- Do you want to repeat the test, and if so, when?
- Does this score change what other eye tests my child needs?
- What signs at home should make me call you sooner?
- If a follow-up is needed, who will my child see?
- Cleveland Clinic (2023). Depth Perception Test: What It Is & How It Works.
- American Academy of Ophthalmology (2023). Testing of binocular depth perception.
- PLOS ONE (2019). Characterizing the Randot Preschool stereotest: Testability, norms, reliability, specificity and sensitivity in children aged 2-11 years.
- American Association for Pediatric Ophthalmology and Strabismus (AAPOS) (2024). Amblyopia.
- National Eye Institute (NIH) (2024). Amblyopia (Lazy Eye).