Sensory and Motor Function Tests

Key Points at a Glance

Key Points of This Disease

• Sensory and motor function tests are a set of examination methods to evaluate eye misalignment (strabismus) and abnormalities of binocular vision.
• Motor function tests evaluate eye movements (versions and ductions) and eye alignment, while sensory function tests evaluate fusion and stereopsis.
• Sensory function tests should be performed before dissociative examination techniques (such as monocular occlusion or cover test).
• In the Hirschberg test, a 1 mm deviation of the corneal reflex corresponds to approximately 15 prism diopters.
• The three-step test (Parks-Bielschowsky) is useful for identifying the paralyzed muscle in acquired superior oblique palsy.
• In children, it is important to select examination methods according to age and developmental stage.

1. What are sensory and motor function tests?

Sensory and motor function tests are a series of examination methods to evaluate eye misalignment (strabismus) and abnormalities of binocular vision.

• Motor function tests: Evaluate eye movements (versions and ductions) and eye alignment.
• Sensory function tests: Evaluate fusion status and binocular vision (stereopsis and presence of suppression).

Sensory function tests should be performed before dissociative examination techniques (such as monocular occlusion or cover test) ¹⁾. Assessment of stereopsis is an important component of binocular alignment testing, and high-grade stereopsis is associated with normal eye alignment ¹⁾.

In pediatric ophthalmology, it is necessary to select examination methods according to age and developmental stage. Examinations that can be performed in infants include the red reflex test (Brückner test), refraction test, pupillary response, fixation and pursuit testing, and ocular alignment and motility testing.

Q Which should be performed first, sensory function tests or motor function tests?

A

Sensory function tests (such as stereopsis test and Worth 4-Dot test) should be performed first. Since dissociative tests like the cover test may disrupt fusion, sensory function should be evaluated before them.

2. Main symptoms and clinical findings

Subjective symptoms (symptoms that prompt examination)

• Diplopia: Binocular diplopia is most important. It increases in the direction of the paretic muscle.
• Impaired depth perception: Abnormal sense of depth.
• Eye strain and frequent headaches: In intermittent strabismus, the effort to maintain phoria causes significant eye strain.

Clinical Findings (Findings Detected by Examination)

• Deviation of eye position: Esotropia, exotropia, hypertropia, hypotropia, intorsion, extorsion
• Abnormal head posture: Face turn, head tilt
• Nystagmus
• Ptosis
• Fixation abnormality: Recorded as “central, steady, and maintained (CSM)“¹⁾
• Aversion reflex: A reflex indicating dislike of covering one eye, suggesting a difference in visual acuity between eyes.

Q If an infant has a deviation of eye position, how long can observation be continued?

A

In infants, small-angle exotropia may be transient and usually resolves by 4–6 months of age. If the deviation persists beyond this period, further evaluation is necessary. Note that the causes of sensory strabismus in infants include diseases requiring early diagnosis, such as retinoblastoma, so caution is needed.

3. Causes and Risk Factors

The main diseases indicated for sensory and motor function testing are listed below.

• Comitant strabismus: Intermittent exotropia, infantile esotropia, accommodative esotropia
• Paralytic strabismus: Congenital superior oblique palsy (most common cause of vertical strabismus in children), cranial nerve palsy, myasthenia gravis, thyroid eye disease
• Mechanical strabismus: Orbital floor fracture, Duane syndrome, Brown syndrome
• Amblyopia: refractive amblyopia, strabismic amblyopia, form deprivation amblyopia¹⁾

In congenital superior oblique palsy, abnormal head posture (head tilt) is often the main complaint.

Advice for parents

• If your child’s eyes appear crossed, they squint one eye, or tilt their head, please see an ophthalmologist.
• Early detection of strabismus in infancy is important. Have regular eye check-ups.

4. Diagnosis and examination methods

Patient history

Determine the characteristics of the deviation (which eye deviates in which direction and how often), duration, presence at distance or near, and age of onset. Inquire about double vision, depth perception problems, eye strain, and headaches.

Ocular motility examination

Versions

Method: Present a target 50 cm in front of the eyes and move it left, right, up, and down from the center. Observe smooth pursuit and any lag. Hold at the final position to check for limitation and end-position nystagmus.

Nine-gaze positions: Systematically evaluate movement limitations in each direction. Record motility on a 0–4 scale (0 = normal, - = underaction, + = overaction).

Note: Overaction is commonly seen in the inferior oblique and superior oblique muscles. It is important to examine with the head in the correct position.

Ductions and convergence

Ductions: Cover one eye and have the patient follow the target with the other eye. Normal range: on lateral gaze, the corneal limbus reaches the outer canthus; on medial gaze, the inner edge of the pupil reaches the lacrimal punctum line. If there is limitation on versions but not on ductions, it is judged as no restriction.

Convergence test: Use a ballpoint pen or finger (penlight is inappropriate). Slowly bring it from 50 cm in front of the eyes toward the tip of the nose.

Infants and young children: Versions and ductions should be tested in all infants and children¹⁾. The doll’s head maneuver can also be used for assessment¹⁾.

Choice of target

A penlight allows observation of corneal reflections but makes diplopia difficult to detect. A finger or ballpoint pen is advantageous for fixation and subjective diplopia. Holding the target vertically for horizontal movements and horizontally for vertical movements makes diplopia easier to perceive.

Ocular alignment tests

Hirschberg test

Use a penlight at a distance of 1/3 m and evaluate the symmetry of corneal reflections.

Corneal reflection displacement	Estimated deviation
1 mm	Approximately 7 degrees (approximately 15Δ)
Pupillary margin	Approximately 30Δ
Mid-iris	Approximately 60Δ
Limbus	Approximately 90Δ

If the reflection is displaced nasally, it indicates exotropia; if displaced temporally, it indicates esotropia.

Krimsky test: Prisms are used to correct the displacement of the corneal reflection. Use BI for exotropia, BO for esotropia, BD for hypertropia, and BU for hypotropia.

Angle kappa: The angle between the visual axis and the pupillary axis. A positive kappa angle simulates exotropia, while a negative kappa angle simulates esotropia. Important for differentiating pseudostrabismus.

Brückner test: In a dark room, use the ophthalmoscope lens set to “0” and shine light onto both eyes from a distance of 45 to 75 cm. Perform before pupil dilation ¹⁾.

Q In the Hirschberg test, how many prism diopters does a 1 mm displacement of the corneal reflection correspond to?

A

A 1 mm displacement of the corneal reflection corresponds to approximately 7 degrees (about 15 prism diopters). It is estimated to be about 30Δ at the pupillary margin, 60Δ at the mid-iris, and 90Δ at the limbus. However, these are approximations; for accurate measurement of deviation, use the prism cover test.

Cover tests

• Cover-uncover test: Detects manifest strabismus. Cover one eye for 1-2 seconds and observe the movement of the uncovered eye. Requires adequate visual acuity and cooperation ¹⁾
• Prism cover test: Measures only the angle of manifest deviation
• Alternating cover test: Measures the total deviation (manifest + latent deviation)

Fixation evaluation

Fixation is recorded using CSM (central, steady, and maintained) ¹⁾. In the induced tropia test, fixation behavior is observed using a 10-20Δ prism ¹⁾. The aversion response is a reaction of disliking occlusion of one eye, suggesting a difference in visual acuity between the eyes.

Three-step test (Parks-Bielschowsky)

Used to identify the paretic muscle in acquired hypertropia. The three-step test narrows down the paretic muscle from eight cyclovertical muscles. In the Bielschowsky head tilt test, the head is tilted to observe changes in hypertropia.

Q Can a positive three-step test be caused by conditions other than muscle palsy?

A

Dissociated vertical deviation (DVD), skew deviation, and myasthenia gravis can also yield a positive three-step test, so caution is needed in interpreting results. Clinical judgment should integrate other findings.

Upright and Supine Test

Used to differentiate skew deviation. A reduction of 50% or more in deviation when supine is considered positive, with reported sensitivity of 80% and specificity of 100%.

Sensory Function Tests

• Titmus/Randot Stereo Test: Quantifies stereopsis. Fly ≈ 3,000 seconds of arc, 9th circle ≈ 40 seconds of arc
• Worth 4-Dot Test: Assesses sensory fusion ¹⁾
• 4Δ Base-Out Test: Detects central suppression scotoma
• Prism Bar: Evaluates fusional vergence ¹⁾

5. Standard Treatment

Based on sensory and motor function test results, the following treatments are selected.

Optical Correction and Amblyopia Treatment

Refractive Correction: Full correction glasses are basic for esotropia. In accommodative esotropia, glasses alone may improve eye alignment.

Amblyopia Treatment: Optical correction, occlusion therapy, atropine penalization ¹⁾.

Prism therapy: Useful for mild paralytic strabismus. Glasses can correct up to 4 prism diopters (Δ); membrane prisms can achieve higher powers but may cause visual discomfort. Cyclotropia of up to 7° can be corrected with prisms; beyond 8°, surgery is indicated.

Surgical Treatment

Surgery for concomitant strabismus: For esotropia, bilateral medial rectus recession is the first choice; for exotropia, bilateral lateral rectus recession. Intermittent exotropia is considered for surgery after age 4 or when it becomes constant.

Congenital superior oblique palsy: Does not resolve spontaneously and requires surgery.

Nystagmus blockage syndrome: Medial rectus Faden operation (in children, 11–12 mm from the insertion) is performed.

Caution in Interpreting Test Results

Results of cover tests and prism measurements may vary depending on patient cooperation, fixation status, fatigue, etc. Especially in children, repeated evaluation and observation of changes over time are important.

Q When should intermittent exotropia be operated on?

A

Generally, surgery is considered after age 4. Indications include constant exotropia, worsening stereopsis, and poor control (deterioration of clinical control score). During follow-up, changes in deviation at distance and near and the ability to maintain fusion should be regularly assessed.

6. Pathophysiology and Detailed Mechanisms

Hering’s Law

Hering’s law (law of equal innervation) states that equal innervation is sent to the antagonist muscles of both eyes during conjugate movements. Due to this law, in paralytic strabismus, the deviation when looking in the direction of the paretic muscle (secondary deviation) is greater than the primary deviation.

Skew Deviation

Skew deviation is a vertical misalignment of the eyes caused by imbalance in otolithic input, occurring with lesions from the peripheral vestibular system to the brainstem. The upright-supine test uses changes in gravitational input to otolithic function to differentiate skew deviation from peripheral lesions.

Pathophysiology of Superior Oblique Palsy

In congenital superior oblique palsy, hypoplasia of the superior oblique tendon is observed, and MRI studies have confirmed trochlear nerve absence in over 70% of cases.

Sensorimotor fusion

Normal sensorimotor fusion integrates binocular coordination and binocular vision; amblyopia, strabismus, and refractive errors impair this fusion function ¹⁾.

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7. Latest research and future prospects (research-stage reports)

For patients: Please read carefully

The following content is currently at the research stage or under clinical trial and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Handheld optical coherence tomography (OCT)

Gurnani et al. (2025) reported that handheld SD-OCT (HH-SDOCT) is useful for imaging the retina and optic nerve in children and can aid in diagnosing infantile nystagmus syndrome and retinal dystrophies ²⁾. It can be performed even in infants who cannot cooperate with conventional tabletop OCT.

New amblyopia treatments

Dichoptic digital therapy (a treatment that presents different images to each eye using a tablet or VR headset) is being studied as a new approach for amblyopia treatment ¹⁾.

Intermittent occlusion therapy using liquid crystal shutter glasses is also being developed, which is expected to solve compliance issues with traditional eye patch occlusion therapy ¹⁾.

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8. References

1. American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Preferred Practice Pattern Panel. Amblyopia Preferred Practice Pattern. San Francisco, CA: American Academy of Ophthalmology; 2024.
2. Gurnani B, Kaur K, Khurana A, et al. Nystagmus in children. Clin Ophthalmol. 2025;19:1617-1637.