Learning Center
Glossary
Every term the Learning Center uses, defined in one plain sentence, with the articles that explain it in context.
Back to the Learning Center- Accommodation
- The eye using its focusing power to sharpen a near object.
- Explained in: Dilating drops: why they are needed and how to prepare your child, Vergence: how the eyes adjust together for near and far
- Adherence
- How much of the prescribed treatment is actually carried out.
- Explained in: Why is eye patching so hard? Ways to make it easier, Can games treat lazy eye?, Keeping motivation up through months of treatment, The evidence for dichoptic treatment: where we stand today
- Ambient light
- The general lighting in the room; it directly affects screen glare and eye comfort.
- Explained in: Setting up home sessions: distance, light and timing
- Amblyopia
- The medical name for lazy eye.
- Explained in: The 20 questions parents ask most, Lazy eye: myths and facts, Just told your child has lazy eye: what to do in the first week, How to explain lazy eye to your child, The lazy eye guide: signs, causes and treatment options, What is lazy eye (amblyopia)?
- Anaglyph
- The century-old technique of delivering a separate image to each eye with red and blue filters.
- Explained in: How do red-blue therapy glasses work?
- Anisometropia
- A marked difference in refractive error (prescription) between the two eyes.
- Explained in: Anisometropia: why a difference in prescription between the eyes matters, The lazy eye guide: signs, causes and treatment options
- Anisometropic amblyopia
- Amblyopia arising from a difference in refractive error between the eyes.
- Explained in: Patient selection and follow-up in dichoptic treatment: a practical frame
- Astigmatism
- The cornea is not equally curved in every direction, so light focuses along a line rather than at a point, affecting both distance and near.
- Explained in: Myopia, hyperopia and astigmatism: what each one means
- Atropine
- A medicine that temporarily paralyses the focusing muscle of the eye it is placed in, blurring that eye's near vision.
- Explained in: Atropine drops: the alternative to the patch
- Atropine drops
- An alternative to the patch that temporarily blurs the strong eye's near vision.
- Explained in: Why is eye patching so hard? Ways to make it easier
- Axis
- An angle between 0 and 180 stating the orientation of an astigmatism. It is a direction, not a severity.
- Explained in: How to read an eyeglass prescription
- Binocular diplopia
- Double vision that appears only with both eyes open and vanishes when one is covered.
- Explained in: Double vision (diplopia): why it happens, and why children rarely report it
- Binocular disparity
- The slight difference in where the same object falls on each eye's retina; the raw data the brain uses to compute depth.
- Explained in: Stereopsis: how depth perception is built, and what its loss costs
- Binocular rivalry
- When each eye is shown images too different to merge, perception alternates back and forth between them.
- Explained in: Binocular rivalry: what happens when each eye sees something different
- Binocular treatment
- An approach working both eyes together to target suppression and binocular function.
- Explained in: The evolution of amblyopia treatment: from patching to binocular approaches
- Binocular vision
- The images from both eyes becoming one single, whole picture in the brain.
- Explained in: Binocular vision: how two eyes build one picture
- Brock string
- A simple training tool, a string with colored beads, that makes the meeting point of the two eyes visible.
- Explained in: Classic orthoptic exercises: the Brock string, pencil push-ups and the rest
- Classroom adjustment
- Small changes such as seating, print size or extra time that keep a lesson accessible.
- Explained in: Does lazy eye affect reading and school?
- Congenital cataract
- A clouding of the lens present from birth, blocking light from passing through.
- Explained in: Deprivation amblyopia: when the image is blocked from the start
- Contrast
- The difference between light and dark areas of an image; the key variable in dichoptic settings.
- Explained in: How do red-blue therapy glasses work?
- Contrast balancing
- Lowering the contrast shown to the strong eye so the weaker eye's signal gains room in perception.
- Explained in: What is dichoptic training? How it differs from patching, Contrast sensitivity: the vision the chart does not measure
- Contrast sensitivity
- The smallest difference in brightness needed to tell an object from its background. The smaller the difference you can catch, the higher the sensitivity.
- Explained in: Contrast sensitivity: the vision the chart does not measure
- Convergence
- The eyes turning inward when looking at something near.
- Explained in: Classic orthoptic exercises: the Brock string, pencil push-ups and the rest, Convergence insufficiency: the reason behind eyes that tire while reading, Vergence: how the eyes adjust together for near and far
- Convergence insufficiency
- The eyes not sustaining that inward turn well enough at near, creating difficulty with close work.
- Explained in: Convergence insufficiency: the reason behind eyes that tire while reading
- Cover test
- Briefly covering and uncovering each eye in turn to assess alignment and which eye is preferred.
- Explained in: How suppression is detected: the methods used at an exam, What happens at your child's eye exam?
- Critical period
- The early-childhood window in which the visual system develops fastest and is most open to experience.
- Explained in: Neuroplasticity: how the brain relearns to see, Lazy eye in adults: is it really too late?, The critical period: the years vision is built in
- Crowding
- The difficulty of recognising a target when other objects surround it. It is markedly stronger in amblyopia.
- Explained in: Crowding: one letter is readable, a row of them is not
- Cycloplegic exam
- An exam using drops that temporarily relax focusing, revealing the true prescription.
- Explained in: Dilating drops: why they are needed and how to prepare your child, Anisometropia: why a difference in prescription between the eyes matters, What happens at your child's eye exam?
- Cycloplegic refraction
- A measurement taken after drops relax the focusing muscles, which is how a child's true prescription is revealed.
- Explained in: Can glasses alone treat lazy eye?
- Deprivation amblyopia
- Lazy eye that develops because the image is physically prevented from reaching the retina.
- Explained in: Deprivation amblyopia: when the image is blocked from the start
- Dichoptic presentation
- Showing each eye its own image, achieved with filter glasses or special displays.
- Explained in: Binocular rivalry: what happens when each eye sees something different, How do red-blue therapy glasses work?
- Dichoptic setup
- An arrangement where content is split between the eyes and the task needs both.
- Explained in: Can games treat lazy eye?
- Dichoptic training
- Showing each eye a different part of the same scene; the task completes only with both eyes contributing.
- Explained in: What is dichoptic training? How it differs from patching, What is lazy eye (amblyopia)?
- Dichoptic treatment
- An approach that presents a different image to each eye in order to reduce suppression and recover binocular function.
- Explained in: The evidence for dichoptic treatment: where we stand today
- Digital eye strain
- The dryness, burning and strain that follow long periods of close screen work.
- Explained in: Screen time worries: is the therapy screen harmful too?
- Dioptre
- The unit of a lens's focusing power. Prescription values are written in it, and the sign shows which way the error runs.
- Explained in: How to read an eyeglass prescription
- Diplopia
- Perceiving a single object as two separate images.
- Explained in: Double vision (diplopia): why it happens, and why children rarely report it, Fusion: how the brain turns two images into one, Suppression: why the brain ignores one eye
- Eccentric fixation
- Holding a target with a region offset from the sharpest point of the retina rather than with that point itself. It occurs in some patterns of amblyopia.
- Explained in: Fixation instability: the gaze is never truly still
- Experience-dependent plasticity
- The reorganisation of neural connections according to incoming input. It is strongest during the critical period and declines afterwards without disappearing.
- Explained in: The critical period: the years vision is built in
- External reward
- Motivation that comes from something given for the behaviour rather than from the behaviour itself. Useful at the start, not durable on its own.
- Explained in: Keeping motivation up through months of treatment
- Eye dominance
- The brain's tendency to prefer one eye when a task needs a single eye; normal in healthy vision.
- Explained in: Eye dominance: what a dominant eye is, and why it is not lazy eye
- Eye strain
- The feeling of visual fatigue that follows close work.
- Explained in: Doing vision exercises safely at home: what to watch for
- Filter glasses
- Glasses that deliver a different image to each eye, worn over prescription glasses.
- Explained in: Setting up home sessions: distance, light and timing
- Filter-based test
- Using glasses that send a different image to each eye to check which eye is reaching perception.
- Explained in: How suppression is detected: the methods used at an exam
- Fixation
- Holding the gaze on a target so its image falls on the sharpest region of the retina.
- Explained in: Fixation instability: the gaze is never truly still
- Fusion
- The two eye images merging into one perception in the brain.
- Explained in: Which kind of work targets which visual skill?, Fusion: how the brain turns two images into one, Binocular vision: how two eyes build one picture, What strabismus surgery does, and what it does not
- Fusion test
- A test showing whether the separate images seen by each eye merge into one perception in the brain.
- Explained in: Depth and fusion tests: how the eyes' teamwork is measured
- Gamification
- Making a task sustainable through rewards, levels and variety.
- Explained in: Can games treat lazy eye?
- Hand-eye coordination
- Guiding the movement of the hand by what the eyes report. Reduced depth perception can make these tasks harder.
- Explained in: Does lazy eye affect reading and school?
- Hyperopia
- The image focuses behind the retina. In children the focusing muscle can mask part of it.
- Explained in: Myopia, hyperopia and astigmatism: what each one means
- Interocular difference
- The difference in visual acuity between the two eyes. In follow-up it is often more informative than the absolute value.
- Explained in: Outcome measures in amblyopia: what to track, and when
- Latent deviation
- A misalignment that only shows under certain conditions and is not always visible.
- Explained in: Strabismus and lazy eye: how the two connect
- Linear optotypes
- Letters presented together as a row. In amblyopia this reflects real performance more accurately than a single symbol does.
- Explained in: Crowding: one letter is readable, a row of them is not
- Maintenance
- The phase in which treatment continues at reduced intensity to hold the gains.
- Explained in: After treatment: do the gains hold, and can it regress?, A vision training roadmap: what to expect week by week
- Microsaccade
- A very small involuntary flick made during fixation. It is normal machinery that keeps the image from fading.
- Explained in: Fixation instability: the gaze is never truly still
- Monocular deprivation
- Depriving one eye of its image during development. It is the experimental method that established the existence of the critical period.
- Explained in: The critical period: the years vision is built in
- Monocular depth cues
- Distance clues available to one eye alone, such as shadow, objects overlapping each other, size and perspective.
- Explained in: Stereopsis: how depth perception is built, and what its loss costs
- Monocular diplopia
- Doubled or ghosted vision in one eye that persists even when the other eye is covered.
- Explained in: Double vision (diplopia): why it happens, and why children rarely report it
- Monocular treatment
- An approach exercising the weaker eye alone; patching is the typical example.
- Explained in: The evolution of amblyopia treatment: from patching to binocular approaches
- Motor fusion
- The eyes constantly fine-tuning their alignment so the two images can be brought on top of each other.
- Explained in: Fusion: how the brain turns two images into one
- Myopia
- Short sight, a refractive error that can progress during childhood.
- Explained in: Screen time worries: is the therapy screen harmful too?, Myopia, hyperopia and astigmatism: what each one means
- Near point of convergence
- The closest distance at which a single image can be held; measured at an exam.
- Explained in: Convergence insufficiency: the reason behind eyes that tire while reading
- Neuroplasticity
- The brain's ability to reorganize its connections in response to experience and repetition.
- Explained in: Neuroplasticity: how the brain relearns to see, Lazy eye in adults: is it really too late?
- Non-inferiority trial
- A trial design intended to show that a new method is not meaningfully worse than the established one.
- Explained in: The evidence for dichoptic treatment: where we stand today
- Objective dose monitoring
- Measuring delivered treatment time from device records rather than from self-report. Occlusion dose monitors do this for patching, usage logs for digital treatments.
- Explained in: The evidence for dichoptic treatment: where we stand today
- Optic nerve
- The nerve carrying signals from the retina to the brain.
- Explained in: The visual cortex: where seeing actually happens
- Orthoptic exercise
- Exercises aimed at the eyes' teamwork and focusing skills, done under the guidance of a doctor or orthoptist.
- Explained in: Classic orthoptic exercises: the Brock string, pencil push-ups and the rest
- Patching
- Covering the strong eye for set periods so the weaker one has to be used.
- Explained in: Why is eye patching so hard? Ways to make it easier
- Penalisation
- The treatment logic of deliberately degrading the strong eye's image so the brain turns to the other one: patching and atropine both belong here.
- Explained in: Atropine drops: the alternative to the patch
- Photoscreening
- A device-based check that estimates refractive error and misalignment risk from a photograph-like measurement, usable at ages too young for a letter chart.
- Explained in: When should a child's eyes be checked?
- Plateau
- A stretch where progress pauses; a natural part of the process.
- Explained in: A vision training roadmap: what to expect week by week, Outcome measures in amblyopia: what to track, and when
- Ptosis
- A drooping upper eyelid, which can cover part of the field of vision.
- Explained in: Deprivation amblyopia: when the image is blocked from the start
- Pursuit movements
- The eyes following a moving target smoothly.
- Explained in: Which kind of work targets which visual skill?
- Reading fluency
- Reading a text accurately, quickly and without stumbling. It can be affected by visual factors and by language-based ones alike.
- Explained in: Does lazy eye affect reading and school?
- Red reflex test
- Assessment of the light reflected back from the retina. In babies it catches conditions such as cataract that block the image early.
- Explained in: When should a child's eyes be checked?
- Refractive adaptation
- The initial period observed with optical correction alone, during which acuity gains are expected.
- Explained in: Patient selection and follow-up in dichoptic treatment: a practical frame, Can glasses alone treat lazy eye?
- Refractive error
- Focusing deviations such as short sight, long sight and astigmatism; corrected with glasses.
- Explained in: Lazy eye: myths and facts, Dilating drops: why they are needed and how to prepare your child, Anisometropia: why a difference in prescription between the eyes matters, Can glasses alone treat lazy eye?
- Regression
- Part of the gains achieved during treatment slipping back afterwards.
- Explained in: After treatment: do the gains hold, and can it regress?
- Residual deviation
- The misalignment that remains after surgery. Muscles respond differently from person to person, so full alignment in a single operation is not always achievable.
- Explained in: What strabismus surgery does, and what it does not
- Retina
- The thin layer at the back of the eye that turns light into electrical signals.
- Explained in: The visual cortex: where seeing actually happens
- Reverse amblyopia
- A drop in acuity in the previously strong eye when penalisation runs too long or too hard. It is uncommon and is caught at follow-up visits.
- Explained in: Atropine drops: the alternative to the patch
- Routine
- Doing something at the same time and in the same order every day. It removes the need to make the decision afresh each time.
- Explained in: Keeping motivation up through months of treatment
- Seconds of arc
- The unit of depth perception sensitivity; a smaller number means finer differences in depth are being distinguished.
- Explained in: Depth and fusion tests: how the eyes' teamwork is measured
- Sensory fusion
- The brain merging the two aligned images into a single perception.
- Explained in: Fusion: how the brain turns two images into one
- Single optotype
- A letter or symbol presented alone on the chart. With nothing beside it, crowding does not come into play.
- Explained in: Crowding: one letter is readable, a row of them is not
- Snellen chart
- The classic eye chart with letters that shrink from top to bottom.
- Explained in: How visual acuity is measured, and what the numbers mean
- Spatial frequency
- How fine the detail in a pattern is. Contrast sensitivity is not one number but a curve drawn across coarse to fine detail.
- Explained in: Contrast sensitivity: the vision the chart does not measure
- Sphere
- The SPH column of the prescription: a plus value means hyperopia, a minus value means myopia.
- Explained in: How to read an eyeglass prescription
- Stereo test
- A depth perception test viewed through special glasses, in which certain shapes appear to stand out.
- Explained in: Depth and fusion tests: how the eyes' teamwork is measured
- Stereoacuity
- The smallest disparity in depth that can be discriminated, in seconds of arc. It is a direct measure of binocular function.
- Explained in: Outcome measures in amblyopia: what to track, and when
- Stereopsis
- True depth and 3D perception, born from the small difference between the two eyes' viewpoints.
- Explained in: Binocular vision: how two eyes build one picture, Stereopsis: how depth perception is built, and what its loss costs
- Strabismic amblyopia
- Amblyopia arising from a misalignment of the eyes.
- Explained in: Patient selection and follow-up in dichoptic treatment: a practical frame
- Strabismus
- The eyes not pointing at the same spot; one eye turning in, out, up or down.
- Explained in: Strabismus and lazy eye: how the two connect, The lazy eye guide: signs, causes and treatment options
- Strabismus surgery
- An operation that aligns the visual axes by moving where the eye muscles attach or by changing their tension.
- Explained in: What strabismus surgery does, and what it does not
- Suppression
- The brain pushing one eye's image into the background.
- Explained in: The 20 questions parents ask most, How suppression is detected: the methods used at an exam, Strabismus and lazy eye: how the two connect, Binocular rivalry: what happens when each eye sees something different, Eye dominance: what a dominant eye is, and why it is not lazy eye, Suppression: why the brain ignores one eye, The lazy eye guide: signs, causes and treatment options, What is dichoptic training? How it differs from patching, What is lazy eye (amblyopia)?
- Treatment plan
- The program set by the doctor, defining which method is used, how often and for how long.
- Explained in: Just told your child has lazy eye: what to do in the first week
- Tumbling E test
- A vision test for children who cannot read, in which they indicate which way the E points.
- Explained in: How visual acuity is measured, and what the numbers mean
- Vergence
- The two eyes turning toward or away from each other according to how far the target is.
- Explained in: Vergence: how the eyes adjust together for near and far
- Vision exercise
- Planned work targeting the eyes' teamwork, focusing, or the easing of suppression.
- Explained in: Doing vision exercises safely at home: what to watch for
- Vision screening
- A quick check designed to single out children at risk rather than to diagnose. It does not give an answer, it points to a full examination.
- Explained in: When should a child's eyes be checked?
- Vision training
- Work built on regular repetition, aimed at the eye and brain functioning together.
- Explained in: How to explain lazy eye to your child
- Visual acuity
- How much fine detail an eye can resolve; it directly affects seeing the board.
- Explained in: Talking to school and teachers: what helps in the classroom, Which kind of work targets which visual skill?, How visual acuity is measured, and what the numbers mean, Suppression: why the brain ignores one eye, What happens at your child's eye exam?
- Visual cortex
- The area at the back of the brain where signals from the eyes are processed into seeing.
- Explained in: The visual cortex: where seeing actually happens, Neuroplasticity: how the brain relearns to see, Binocular vision: how two eyes build one picture
- Visual fatigue
- The strain that follows long close work, most noticeable while reading.
- Explained in: Talking to school and teachers: what helps in the classroom