Orthoptics Evaluation

1. History Taking

• Chief complaint: diplopia (double vision), headaches, reading difficulty, squint noticed by others
• Onset and duration (sudden vs. gradual)
• Constant vs. intermittent symptoms
• Associated neurological symptoms (suggests cranial nerve palsy, multiple sclerosis, stroke)
• Relevant past ocular, medical, and family history
• Current spectacle correction

2. Visual Acuity (VA)

• Measure with best refractive correction in place
• Test each eye uniocularly (monocularly), then binocularly
• Use standard LogMAR or Snellen charts for adults
• Use Cardiff cards, Teller acuity cards, or preferential looking for infants/pre-verbal children
• Test near VA as well, especially in accommodative disorders, nystagmus, and amblyopia treatment monitoring
• If a head posture is present, test vision both with and without it

3. Cover Test (CT)

Cover-Uncover Test

• Detects a manifest deviation (tropia/strabismus)
• Cover one eye; watch the uncovered eye for a re-fixation movement
• No movement = no manifest deviation
• Movement indicates the uncovered eye was not fixating (i.e., it was the deviating eye)
• Repeat for both eyes

Alternate Cover Test

• Detects a latent deviation (phoria) by dissociating binocular vision
• Rapidly alternate the cover between eyes; watch for refixation movements when each eye is uncovered
• Adduction on uncover = exophoria; abduction on uncover = esophoria
• Performed at near (1/3m), distance (3-6m), and far distance (>6m)
• Always test with and without spectacles - a 10 prism dioptre (PD) difference between measurements indicates an accommodative deviation
• Test in the primary position and with compensatory head posture if present

Abbreviations Commonly Used

4. Measurement of Deviation

Hirschberg Test

• A rough, objective estimate of strabismus angle
• Shine a light at the patient's eyes and observe the corneal light reflex position
• Central reflex = orthophoria; reflex near the pupil border ≈ 10-15°; near the limbus ≈ 40°
• Useful when formal testing is not possible (young children, non-cooperative patients)

Krimsky Test

• Like Hirschberg, but prisms are added until corneal reflexes are centered
• Useful in young children and non-cooperative patients

Prism Cover Test (PCT)

• The gold standard for measuring the angle of deviation in prism dioptres (PD)
• Perform the alternate cover test while increasing prism strength (using a prism bar) until no refixation movement is seen
• Prism base is placed opposite to the direction of deviation (e.g., base-out for esotropia)
• The end-point is when movement is neutralized; confirm by going just past (reversal) then reducing back
• Performed in primary position, all 9 positions of gaze (important for paretic squints), near and far

Maddox Rod

• Dissociates the eyes by converting a point of light into a streak
• Used to detect and measure heterophoria (latent deviations)
• Red glass rod in front of one eye; patient states whether the streak passes through the light (orthophoria), or is displaced (phoria)
• Measures both horizontal and vertical deviations

Maddox Wing

• Used to measure near heterophoria (at 1/3m)
• Right eye sees arrows, left eye sees numbers
• Patient reports which number the arrow points to for horizontal, vertical, and cyclophoria

5. Ocular Motility (OM)

• Assesses muscle function and eye movement disorders
• Patient fixes on a light held ~50 cm away; head is kept stationary
• Follow the light into 8 positions of gaze (right, upper-right, upper, upper-left, left, lower-left, lower, lower-right)

Key point: In neurological (paretic) conditions, the duction movement is greater than the version; in mechanical restriction, the degree of movement is equal.

6. Binocular Single Vision (BSV) Status

Worth Four-Dot Test

• Uses red-green glasses to dissociate the two eyes
• Patient views 4 lights (1 red, 2 green, 1 white)
• 4 lights seen = BSV present
• 2 red lights = right eye suppression
• 3 green lights = left eye suppression
• 5 lights = diplopia
• Alternating = alternating suppression

Bagolini Striated Glasses

• A natural viewing test for BSV, anomalous retinal correspondence (ARC), or suppression
• Lenses placed at 45° and 135° before each eye; each eye sees a streak at 90° to the other
• An "X" crossing at the centre = BSV (if eyes are straight) or harmonious ARC (if strabismus present)
• Single streak only = suppression

Convergence (Near Point of Convergence)

• A target is slowly moved toward the patient's nose; note the point at which one eye diverges (breaks) and when it recovers
• Normal: convergence maintained to ~6 cm
• Convergence insufficiency: fails before 6 cm and may not recover easily

7. Sensory Fusion and Stereopsis

• Randot / TNO / Lang stereotest (at 40 cm)
• Frisby stereotest

8. Prism Fusion Range (PFR)

• Measures motor fusion - the ability to maintain BSV while making vergence movements
• Performed with prism bars: horizontal (base-out and base-in) and vertical (base-down and base-up)
• Recorded in prism dioptres
• Extended vertical fusion range suggests a long-standing 4th nerve palsy (vs. recently acquired)

9. Detection of Anomalous Retinal Correspondence (ARC)

• Subjective angle (where the patient perceives images to align)
• Objective angle (measured by cover test / corneal reflex)

• Bagolini glasses
• 4-prism dioptre base-out test (for microtropia)

10. Additional / Specialist Tests

• Hess chart - maps the field of action of each extraocular muscle; invaluable for diagnosing and monitoring paretic squints and tracking progression
• Lancaster red-green test - similar purpose to Hess chart
• Bielschowsky head-tilt test - for suspected 4th nerve palsy; the hypertropia increases when the head is tilted toward the affected side
• Forced duction test - passive movement of the eye under topical anaesthesia; distinguishes paresis from mechanical restriction
• Parks-Bielschowsky three-step test - systematic identification of a paretic vertical muscle

Summary Sequence

1. History
2. Visual acuity (distance + near, each eye + binocular)
3. Cover test (cover-uncover + alternate cover, near + distance, with/without glasses)
4. Measurement of deviation (PCT, Hirschberg/Krimsky if needed)
5. Ocular motility (versions + ductions, 8 positions)
6. Binocular status (Worth four-dot, Bagolini, convergence)
7. Fusion + stereopsis (synoptophore, Randot, TNO)
8. Prism fusion range
9. Specialist tests as indicated (Hess chart, head-tilt test, etc.)