8.1.1 Assesses binocular status using objective and subjective means

Case History

Symptoms to ask about:

• Headaches (especially after reading/close work)

• Asthenopia (eyestrain, blur, discomfort)

• Words moving/jumping, skipping lines when reading

• Suppression (patient reports one eye "switches off”)

• Close-work fatigue, avoidance of reading

• Near vs. distance specific issues

• Onset/duration, severity, frequency, aggravating/relieving factors

Case History

History:

• Childhood strabismus/amblyopia, patching, glasses, prisms

• History of trauma, neurological issues, systemic conditions (thyroid, diabetes, MS)

• Family history of strabismus/amblyopia

• Spectacle/CL history – especially anisometropia, high Rx, prism corrections

Case History

Lifestyle relevance

Occupation (near demand, screen use, driving)

Hobbies (sports, reading, music, gaming)

Objective testing

BV tests list

• CT

• Ocular motility

• Hirschberg

• Prism CT

• NPC

Objective testing (BV)

Cover Test

(distance & near, uni + alternating)

Detects: presence of manifest (tropia) or latent (phoria) deviation.

Assesses:

Direction: eso, exo, hyper, hypo, mixed

Type: manifest (tropia) vs latent (phoria)

Frequency: constant vs intermittent

Laterality: unilateral vs alternating

Magnitude: small, moderate, large (qualitatively, or refine with prism cover test)

Speed of recovery: quick vs slow re-fixation when occluder removed → quick = well controlled phoria, slow = poor control

Concomitancy: compare deviation in different positions of gaze → if variable, suggests incomitancy (e.g., cranial nerve palsy, mechanical restriction)

Objective testing (BV)

Ocular motility (versions & ductions)

Assesses comitancy

Look for: under/over-actions, restriction, diplopia, nystagmus.

Helps differentiate concomitant strabismus vs incomitant (nerve palsy).

Objective testing (BV)

Hirschberg

(especially for children, poor fixation):

Corneal reflex position gives crude estimate of angle.

Useful if cover test not possible.

Objective testing (BV)

Prism Cover Test

Quantifies deviation in prism dioptres.

Do for distance & near.

More precise than describing small/medium/ large.

Objective testing (BV)

NPC

Record: break and recovery points, presence of diplopia/suppression.

Useful for convergence insufficiency/excess.

Subjective testing (BV)

Test list

• Maddox Rod / Maddox Wing

• Cover Test with prism + subjective confirmation

• Bagolini Striated Lenses

• Worth 4 Dot

• Stereopsis tests (TNO, Frisby, Titmus)

• Fixation disparity tests (Mallett Unit)

Subjective testing (BV)

Maddox Rod / Maddox Wing:

Detects phoria at distance & near.

Subjective assessment of deviation.

Subjective testing (BV)

Cover Test with prism + subjective confirmation:

Combine objective and subjective (patient reports single vision achieved).

Subjective testing (BV)

Bagolini Striated Lenses:

Checks fusion and suppression.

Cross pattern seen = normal fusion; missing line = suppression; separation = diplopia.

Subjective testing (BV)

Worth 4 Dot:

Assesses suppression/diplopia at distance & near.

Interpretation:

• 4 dots = fusion

• 2 or 3 dots = suppression

• 5 dots = diplopia

Subjective testing (BV)

Stereopsis tests (TNO, Frisby, Titmus):

Presence/level of binocular sensory function.

Subjective testing (BV)

Fixation disparity tests (Mallett Unit):

Useful in symptomatic heterophoria, prescribing prism.

Subjective alignment at near/distance

BV

Record keeping

Direction of deviation (eso/exo/hyper/hypo).

Manifest or latent, intermittent/constant.

Speed of recovery (good/poor control).

Size – small/moderate/large (or prism diopters if measured).

Concomitancy – same in all gazes vs incomitant.

Fusion & suppression status (subjective tests).

Symptoms correlation with findings (do they match the history?).

Cover test (distance & near)

• Lighting: Normal room lighting

• Test distance:

  • Distance = 6m

  • Near = 33-40cm

• Fixation target:

  • Distance = One letter above best eye VA . If 6/18 or worse, use spotlight.

  • Near = Accommodative target appropriate for age

• Spectacles: Perform with no correction, habitual rx, new refracted rx

• Unilateral cover: detects manifest deviations (tropias)

• Alternating cover: reveals latent deviations (phorias)

• Check in different gaze positions if incomitancy suspected

What are the procedures for ocular motility (versions & ductions)?

• Lighting: Normal room lighting

• Test distance: 33-50cm

• Fixation target: Pen torch

• Spectacles: No correction

• Move torch in spoke pattern through 8 positions of gaze

• Look for full smooth movements, under/over-actions, nystagmus, diplopia

What are the procedures for the prism cover test?

• Lighting: Normal room lighting

• Test distance: Same as cover test

• Fixation target: Same as cover test

• Spectacles: Full correction

• Place prism of appropriate base direct over deviating eye

• Increase / decrease prism until no movement seen on uncover

What are the procedures for near point of convergence?

• Lighting: Normal room lighting

• Test distance: Start at 50cm, move towards the nose

• Fixation target: Small accommodative target

• Spectacles: Near correction on if normally worn

• Record break point and recovery point

• Record whether diplopia or suppression occurs

What are the procedures for the Maddox Rod test?

• Lighting: Dimmed to make streak visible

• Test distance: 6m

• Fixation target: Pen torch or point light

• Spectacles: Full correction

• Place Maddox rod over one eye (usually right)

• Streak through light = orthophoria

• Streak displaced = phoria / tropia

• Add prisms to neutralise

• Streak towards eye with rod = eso

• Streak away from eye with rod = eso

What are the procedures for the Maddox Wing test?

• Lighting: Normal

• Test distance: Built-in distance

• Fixation target: Internal arrow & numbers

• Spectacles: Near correction

• Patient reads where arrow points on horizontal & vertical scales

• Even numbers = exophoria

• Odd numbers = esophoria

What are the procedures for Bagolini Striated Lenses?

• Lighting: Dimmed to make streaks visible

• Test distance: 6m & near 33cm

• Fixation target: Pen torch or point light

• Spectacles: Full correction

• Lenses at 45º and 135º before each eye

• Patient should see and “X” through the light

• Missing line = suppression

• Missing part of the line = foveal suppression

• Two lines not intersecting = diplopia

• Full cross = fusion

What are the procedures for Worth 4 Dot?

• Lighting: Dim to see dots clearly

• Test distance: 6m & 33cm

• Fixation target: Worth 4 Dot torch

• Spectacles: Full rx underneath red/green goggles

• Typically left eye - green filter ; right eye - red filter

• Patient reads where arrow points on horizontal & vertical scales

• 4 dots = fusion

• 2 or 3 = suppression

• 5 = diplopia

STEREOPSIS

General guidance

Excellent: ≤60” - this indicates normal sensory + motor fusion

Moderate: 80-200” - suggests small residual phoria with intermittent control, convergence insufficiency -> Check fixation disparity

Poor: >400” - suggests manifest deviation, suppression or long-standing BV anomaly -> Perform cover test to confirm tropia, look for incomitancy, identity suppression or diplopia

Absent: No depth perception; suppression/diplopia likely

TNO stereotest

• Lighting: Bright

• Test distance: 40cm

• Fixation target: Book plates

• Spectacles: Near correction if need as well as red/green spectacles

• Patient identifies shapes/patterns

• Gradually reduce disparity until threshold found

Frisby stereotest

• Lighting: Bright

• Test distance: Usually 30-80cm

• Fixation target: Picture is hidden in transparent plate

• Spectacles: Near correction if need

• Present plates randomly

• Ask patient to identify the odd one out for each plate

Titmus stereotest

• Lighting: Bright

• Test distance: 40cm

• Fixation target: Booklet with stereo targets

• Spectacles: Near correction if need, polaroid glasses on top

• Patient identifies raised images / animals

Lang l & ll

• Lighting: Bright

• Test distance: 40cm

• Fixation target: Cards with stereoptic images

• Spectacles: Near correction if need

• Patient identifies images / animals