[ODCOP1] Ocular Dominance & Interpupillary Distance

Ocular Dominance

Ocular Dominance (OD)

• Refers to the tendency of one eye to be preferentially used or relied upon by the visual system over the other

• NOT simply which eye has better visual acuity

  • Two patients can have equal VA and still have clear ocular dominance

Ocular Dominance

Clinically relevant in:

• Spectacle and contact lens prescribing (monovision; multifocal CLs)

• Refractive surgery planning (LASIK monovision; LASIK full correction eye selection)

• Binocular vision assessment

• Sports performance and visual training

Sighting (Motor) Dominance

Sensory Dominance

2 clinically recognized types of ocular dominance

Sighting (Motor) Dominance

• The eye used as the preferred “lead eye” when:

  • Aligning at a target

  • Aiming at a target

• The eye instinctively used when:

  • Sighting through a small aperture

  • Pointing at a target

Sighting (Motor) Dominance

• Also called motor dominance — it reflects the motor behavior of preferentially aligning the dominant eye with the visual axis to a target

• It is the most commonly tested form of ocular dominance in routine optometry

• Relatively stable and consistent within individuals — right eye dominance is indicated in approximately 71% of the population

Hole in a Card Test

Porta / Triangle / Ring Test (Miles Test)

Tests for sighting dominance

Hole in a Card Test

• Purpose:

  • Identify the sighting dominant eye

  • Patient aligns a small aperture with a distant target

  • Both eyes remain open

• Materials:

  • Card with a small circular hole

    • Approximately 3–5 cm diameter

  • Held at arm’s length

  • Or a commercially prepared target

Hole in a Card Test

Procedure

1. Ask the patient to hold a card with a central hole in both hands at full arm’s length.

2. Identify a small target at 4–6 m

   • Example:

     • A letter on the VA chart

     • A door handle

3. Instruct the patient:

   • “With both eyes open, look through the hole at the target.”

4. Observe which eye is naturally aligned with the hole and the target from in front of the patient.

5. Confirm by alternately occluding each eye

   • The dominant eye is the one that, when occluded, causes the target to disappear from the aperture.

6. Perform 3 consecutive trials

   • Record each result.

Recording

• ☐ OD dominant

• ☐ OS dominant

• ☐ Equal/Undetermined

Porta / Triangle / Ring Test

Purpose:

• A second sighting dominance test using the patient's own hands

• Should be consistent with the Hole in a Card result

Porta Test / Ring Test

Procedure

1. Ask the patient to:

   • Extend one arm

   • Form a ring using the thumb and index finger of that hand

2. Ask the patient to:

   • Look at a distant target through the ring

   • Keep both eyes open

3. Alternately occlude each eye

   • Dominant eye: keeps the target centered in the ring

   • Non-dominant eye: causes the target to shift out of the ring

Triangle / Miles Test

Procedure (Alternative)

• Ask the patient to:

  • Extend both arms

  • Overlap the thumbs and index fingers

  • Form a small triangular aperture

• Ask the patient to:

  • Look at the distant target through the triangle

  • Keep both eyes open

• Ask the patient to:

  • Slowly bring the triangle toward their face

  • The aperture naturally drifts toward the dominant eye

• Observe:

  • Which eye the aperture lands in front of

Recording

• ☐ OD dominant

• ☐ OS dominant

• ☐ Equal/Undetermined

Sensory Dominance

Refers to the eye to which the brain gives processing priority when both eyes are receiving information simultaneously

Sensory Dominance

• It is the eye whose input the brain favors when the two eyes are in competition.

• When the two eyes receive slightly different images:

  • The dominant eye's image is more strongly represented in conscious perception.

• Important Distinction:

  • (BLANK) dominance and (BLANK) dominance do not always agree

  • In one study:

    • 41% of participants showed a different dominant eye by (BLANK) testing compared to sighting testing.

Sensory Dominance

(BLANK) is Particularly Important for:

• Monovision contact lens and spectacle fitting

• Multifocal CL optical zone selection

• Refractive surgery monovision planning

• Binocular vision suppression assessment

+1.50 D Blur Test (Resistance to Blur Test)

Test for Sensory Dominance

+1.50 D Blur Test

Principle

• The dominant eye resists blur more strongly

  • It is harder for the brain to suppress clear vision from the sensory dominant eye.

• Placing a (BLANK) blur over the dominant eye:

  • Causes more noticeable visual disturbance than the same lens over the non-dominant eye.

• The sensory test, also called “resistance to blur,” allows for the determination of the “strength” of ocular dominance.

+1.50 D Blur Test

Procedure

1. Ensure the patient is wearing their best distance correction

   • Or is uncorrected if emmetropic

2. Ask the patient to view a line of letters on the distance VA chart

   • Approximately 2 lines above their best VA

   • With both eyes open

3. Place a +1.50 D lens over the RIGHT eye only

   • Ask:

     • “Does the chart look blurred or different now?”

     • “On a scale of 1 to 5, how bothersome is this blur?”

   • Record response.

4. Remove the lens and place +1.50 D over the LEFT eye only

   • Repeat the same question.

5. Ask:

   • “Which was more noticeable — the blur over the right or the left?”

6. The eye over which the blur is more noticeable and bothersome =

   • Sensory dominant eye

7. Repeat 2–3 times for reliability.

Recording

• ☐ OD sensory dominant

• ☐ OS sensory dominant

• ☐ Equal

Clinical Significance of Ocular Dominance

Monovision correction

Multifocal CL fitting

Refractive surgery

Sports

Documentation

Interpupillary Distance

The distance, in millimetres (mm), between the centres of the two pupils

Phoropter / Trial Frame

Spectacle Lenses

2 Primary Clinical Reasons for Measuring PD

Incorrect PD measurement

optical centres misaligned → unwanted prismatic effect → symptoms including asthenopia, headaches, diplopia, and reduced VA — especially significant in high-powered prescriptions

Distance (Far) PD

Near PD

Intermediate PD

Monocular PD (half-PD)

Binocular PD

Types of Interpupillary Distance

Distance (Far) PD

Definition: Separation between visual axes of both eyes when fixating a distant object (at optical infinity)

When Used: Measured for distance spectacle prescription; routine for most patients

Near PD

Definition: Separation between visual axes at the plane of the spectacle lenses when fixating at the near working distance

When Used: Separation between visual axes at the plane of the spectacle lenses when fixating at the near working distance

Intermediate PD

Definition: Separation between visual axes at an arm's-length working distance (approximately 60–80 cm)

When Used: Measured for computer or intermediate spectacles; progressive lens fitting

Monocular PD (half-PD)

Definition: Distance from either the right OR left visual axis to the center of the bridge of the nose

When Used: Essential for progressive addition lens dispensing; asymmetric faces; any case where precise monocular centration is required

Binocular PD

Definition: Total distance PD measured across both eyes simultaneously

When Used: Routine screening; standard spectacle orders

Women

Distance PD most commonly 55–65 mm (Average Values)

Men

Distance PD most commonly 60–70 mm (Average Values)

Young children

PDs as low as 45 mm (Average Values)

Near PD at 40 cm

• Near PD = Distance PD − 3–4 mm

• The eyes converge inward for near tasks.

• Therefore:

  • Distance PD is usually 3–4 mm greater than the near PD at 40 cm

  • Reason:

    • Both eyes rotate nasally (converge)

    • This brings the visual axes closer together when fixating on a near target.

63–65 mm

Average adult binocular distance PD

Interpupillary Distance

• Clinical Importance

  • The PD is one of the most clinically critical measurements in spectacle dispensing

  • It determines exactly where the optical centre of each lens is positioned relative to the patient's visual axis

• Correct Optical Centre Alignment

  • When the optical centre of a lens is correctly aligned with the visual axis:

    • Light passes through the lens without deviation

    • The patient experiences the full corrective effect of the prescription

    • There is no unwanted prismatic disturbance

• Effect of Prescription Power

  • The higher the prescription power, the more clinically critical the PD measurement becomes

  • Low prescription:

    • A small PD error causes negligible prismatic deviation

  • High prescription:

    • The same PD error induces clinically significant prism

Prentice's Rule

• governs the relationship between PD error and induced prism:

  
  

• Δ = F × c

• Where:

  • Δ = prism in prism dioptres

  • F = lens power in dioptres

  • c = decentration in centimetres

PD Too WIDE

(Optical centres are further apart than the patient's visual axes)

• The patient is looking through the nasal portion of each lens

• This induces base-out (BO) prism in each eye

  • An opposing prismatic force that fights the eyes' natural convergence

• Symptoms:

  • Eyestrain and fatigue

  • Difficulty maintaining single vision at near

  • Headaches

  • Blurred or unstable vision

  • Diplopia in severe cases

  • Discomfort wearing the glasses for extended periods

  • Patient reporting:

    • “I keep wanting to take them off”

PD Too NARROW

(Optical centres are closer together than the patient's visual axes)

• The patient is looking through the temporal portion of each lens

• This induces base-in (BI) prism in each eye

  • A convergent prismatic force

• Symptoms:

  • Blurred or double vision

  • Reduced depth perception

  • Spatial distortion

  • Headaches

  • Nausea in severe cases

  • Patient feeling:

    • “Pushed forward”

  • Perceiving the world as different in depth

Single vision distance

Single vision near (reading)

Bifocal / Multifocal

Progressive Addition Lenses (PALs)

High minus or plus lenses

Lens Type

Single vision distance

PD Error Consequence: Base-out or base-in prism depending on direction of error; generally tolerated in low Rx but symptomatic in high Rx

Why It Is Especially Critical: Higher power = more prism per mm of error (Prentice's Rule)

Single vision near (reading)

PD Error Consequence: Same as above PLUS misalignment at the specific convergence demand of near tasks — patient cannot sustain comfortable reading

Why It Is Especially Critical: Near tasks require sustained convergence — even small amounts of opposing base-out prism cause rapid fatigue

Bifocal / Multifocal

PD Error Consequence: If distance PD is wrong, both zones are misaligned; if near PD (seg inset) is wrong, reading zone is misaligned even if distance zone is correct

Why It Is Especially Critical: Must measure AND correctly incorporate BOTH distance and near PD

Progressive Addition Lenses (PALs)

PD Error Consequence: Monocular PD error causes the patient's visual axis to miss the progressive corridor entirely — they cannot find the clear intermediate or near zones

Why It Is Especially Critical: (BLANK) are the most PD-sensitive lens type — monocular PD must be precise to within ±0.5 mm ideally

High minus or plus lenses

PD Error Consequence: Significant induced prism from even small PD errors; also prismatic jump at the lens edge

Why It Is Especially Critical: Any prescription ≥ ±4.00 D warrants pupillometer measurement for maximum accuracy

Progressive Addition Lenses (PALs)

Provides a gradual change in lens power from distance → intermediate → near without visible segment lines.

Progressive corridor

The narrow, usable zone through which the lens power progressively changes from distance toward near.

Monocular PD

What measurement is used to position the progressive corridor during PAL manufacturing?

PD Is Measured Correctly

• Light passes through the optical centre of each lens

• Results in:

  • No unwanted prism

  • Full corrective effect of the prescription

  • Comfortable, stable vision

PD Is Measured Incorrectly

Consequences in order of severity:

1. Mild error in low Rx

   • Usually no noticeable symptoms

   • Patient adapts

2. Moderate error in medium Rx

   • Asthenopia

   • Headaches

   • Fatigue

   • Particularly at near

3. Significant error in high Rx

   • Diplopia

   • Spatial distortion

   • Nausea

   • Inability to wear the glasses

4. Any error in PAL

   • Loss of clear corridor

   • Swimming/rocking sensation

   • Progressive lens intolerance

   • Can occur even with a correct prescription

Anatomical PD Measurement (PD Ruler)

What It Measures

• The distance between the anatomical centres of the pupils

  • The geometric centre of each pupil

Clinical Use

• The most widely used method in routine clinical optometry worldwide

• Requires only a millimetre ruler

  • No specialist equipment

• Repeatability of anatomical binocular PD measurements is similar to that of a pupillometer

Anatomical PD Measurement (PD Ruler)

• Advantages: quick; inexpensive; no special equipment; usable by any trained clinician; reliable for binocular PD in most patients

• Disadvantages: slightly less accurate for monocular PDs than a pupillometer; susceptible to parallax error (particularly when the examiner's PD differs significantly from the patient's); requires the examiner to be binocular

Between the center of 2 pupils

Right temporal pupil margin to left nasal pupil margin

Right temporal limbus to left nasal limbus

Anatomical PD Procedure

Monocular PD Measurement

Why (BLANK) Matters

• Many patients have asymmetric faces

  • The nose bridge is not perfectly centered

  • This makes the right and left monocular PDs unequal

• Progressive addition lens dispensing requires monocular PDs

  • If binocular PD is used for both lenses in an asymmetric face:

    • The optical centres will be misaligned

Monocular PD Measurement

Procedure (Elliott, 2007)

1. Use the centre of the pupil as the reference point

   • Not the margin

2. Align the zero mark with the centre of the patient's RIGHT pupil

   • Read the distance to the centre of the nose bridge

   • This is the right monocular PD (OD PD)

3. To find the LEFT monocular PD:

   • Subtract the OD monocular PD from the total binocular distance PD

Monocular PD Measurement

Formula

• OS monocular PD = Total distance PD − OD monocular PD

Most Common Errors

Monocular PD Measurement

Catoptric / Physiologic PD (monocular)

Photographic PD Measurement

ANATOMICAL PD METHODS

Catoptric / Physiologic PD (Monocular)

What It Measures

• Measures the distance between the corneal light reflexes

  • Rather than the anatomical pupil centres

• Measures the visual axes (physiologic PD)

  • Rather than the lines of sight (anatomical PD)

Pupillometer

• The (BLANK) uses a light source directed at the cornea

• The corneal reflex of each eye is aligned with reference markers in the instrument

Catoptric Method

• Comes from the Greek katoptron, meaning mirror

• Refers to the use of corneal reflections as the measurement reference

Physiologic PD

• Distance between the two principal corneal reflexes

• This locates the visual axes of the eyes

Anatomical PD

• Distance between the anatomical pupil centres

• This locates the lines of sight (optical axes)

Pupillometer

How it Works

• A light source illuminates both corneas simultaneously.

• The examiner aligns reference markers with the corneal reflexes of each eye using a single viewing aperture.

  • Monocular measurement

  • No parallax error

• Digital pupillometers give a direct readout of:

  • Binocular PD

  • Monocular PDs

Advantages

• More accurate for monocular PD measurements than the anatomical method (Holland & Siderov, 1999).

  • Particularly beneficial for progressive addition lens dispensing

• No parallax error

  • Examiner uses one eye only.

• Quick and simple

  • Can be performed by a clinical assistant.

• Considered the gold standard instrument for routine IPD measurement (Chu, 2024).

Limitations / Important Considerations

• The PD measured with a corneal reflection pupillometer is typically 0.5–1.0 mm smaller than the anatomical PD.

  • Because it measures the physiological PD (visual axes), not the anatomical PD (optical axes).

• Inaccuracies can occur if the pupillometer sits higher or lower on the bridge than the intended spectacle frame.

Photographic PD Measurement

What It Measures

• The inter-pupillary distance (IPD) estimated from a calibrated photograph of the patient's face.

How It Works

1. Take a calibrated photograph of the patient's face

   • A known reference scale is placed in the same plane as the patient's pupils during the photograph.

   • Examples:

     • Ruler

     • Reference card of known width

     • Frame dimensions

2. Measure the pupil-to-pupil distance

   • The center-to-center pupil distance is measured from the photograph.

3. Calculate the scaling factor

   • The known reference scale is used to convert the measured pixel or millimetre distance on the photograph into the patient's true PD in millimetres.

Photographic PD

PD estimated from a calibrated facial photograph using a known reference scale.

Anatomical

Instrument: PD ruler (mm ruler)

Measures: Pupil centres; lines of sight

Clinical Use: Routine binocular PD for most patients

Key Limitation: Parallax error; less accurate for monocular PD

Catoptric / Physiologic

Instrument: Pupillometer (corneal reflex)

Measures: Corneal light reflexes; visual axes

Clinical Use: Monocular PD; progressive lenses; high Rx

Key Limitation: PD ~0.5–1.0 mm smaller than anatomical; instrument positioning Positioning of the corneal reflex (light)

Photographic

Instrument: Camera / smartphone app

Measures: Pupil centres from image

Clinical Use: Online ordering; remote measurement

Key Limitation: Lens distortion; reference scale accuracy; not reliable for high Rx

Gerstmann's Three-Quarters Rule

What It Is

• A clinical calculation rule for determining the near segment inset per eye and therefore the near PD when:

  • Direct near PD measurement is not possible, or

  • The working distance is non-standard.

The Rule

• For every diopter of dioptric demand, the optical centre of each reading lens or the geometrical centre of each bifocal addition should be inset 0.75 mm (three-quarters of a mm) from the distance optical centre.

Segment Inset per Eye

(Gerstmann's Three-Quarters Rule)

Dioptric Demand

(Gerstmann's Three-Quarters Rule)

Near PD

(Gerstmann's Three-Quarters Rule)

Recording PD

PD: distance PD / ne ar PD (in mm) (binocular)