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RehabMeasures Instrument

Dynamic Visual Acuity Test - Non-Instrumented

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Purpose

The DVAT-NI provides a “low-tech”, objective, behavioral measure of vestibulo-ocular reflex (VOR) function in response to examiner generated (i.e., “passive”) rotational head movement stimuli. The DVAT NI provides a functional, low-cost assessment of gaze stability that can be administered in any clinical environment. This measure is used to screen for and characterize the severity of gaze instability (quantified as “lines lost” on an eye chart) and is commonly administered in conjunction with other “bed-side” clinical tests of vestibular function like the Head Impulse Test or the Head Shaking Nystagmus Test in the absence of more sophisticated assessment techniques.

Acronym DVAT-NI

Area of Assessment

Vestibular
Vision & Perception

Assessment Type

Performance Measure

Administration Mode

Computer

Cost

Free

Key Descriptions

  • The non-instrumented Dynamic Visual Acuity Test (DVAT NI) assesses gaze stability during sinusoidal, examiner mediated head rotations relative to head-stationary visual acuity.
  • To administer this test, visual acuity is first assessed under static head movement conditions (i.e.: no head movement).
  • The patient is instructed to wear prescription lenses if needed for distance viewing and then seated a specified distance before an optometric eye exam chart (e.g., 4 meters for the commonly used Early Treatment of Diabetic Retinopathy Study (ETDRS) chart or 20 feet for a standard optometric Snellen Chart).
  • The patient is instructed to read the lowest line recognizable and to keep reading until he or she can no longer identify all the letters on a given line.
  • The examiner should take note of the last line where all letters were correctly identified and the total number of letters correctly identified.
  • For the dynamic component of the test, the examiner should stand behind the patient and firmly grasp the patient’s head with both hands just above the ears.
  • For testing in the yaw plane, the patient’s head should be flexed forward ~ 30 degrees to bring the horizontal semicircular canals into the plane of testing (i.e., the horizontal plane).
  • Next, the examiner will oscillate the head at a magnitude of 20-30 degrees from mid line about a vertical axis taking care to restrict range for patients with corrective lenses.
  • Frequency of rotation should occur at 2 Hz (i.e., 2 cycles per second) to achieve adequate stimulus intensity to drive a hypofunctional vestibular end organ into inhibitory cutoff.
  • The patient will read the letters on the lowest line of the eye chart possible until he or she can no longer correctly identify them.
  • The examiner should note this line and record the number of optotypes incorrectly identified.
  • A loss of three or more lines of visual acuity relative to one’s static visual acuity is regarded as clinically significant and suggestive of possible vestibular dysfunction.

Equipment Required

  • Eye Chart (e.g., ETDRS, Lighthouse, E, or Snellen)

Time to Administer

3 minutes

Required Training

Reading an Article/Manual

Age Ranges

Preschool Child

2 - 5

years

Child

6 - 12

years

Adolescent

13 - 17

years

Adult

18 - 64

years

Elderly Adult

65 +

years

Instrument Reviewers

Matthew R Scherer PT, PhD, NCSJennifer L. Stoskus, PT, MSPT, DPT.

Body Part

Head
Neck

ICF Domain

Body Structure
Body Function

Measurement Domain

Motor
Sensory

Considerations

  • Patient should be cleared of vascular and orthopedic contraindications (i.e. vertebral artery integrity and cervical stability) and demonstrate full, pain-free active range of motion in the plane of testing.
  • Use of a metronome (traditional or digital) to standardize frequency of passive sinusoidal head rotations is recommended to improve reliability and to facilitate adequate visual stimulus intensity during testing. Yaw oscillation of at least 1.5 Hz is recommended to achieve sufficient stimulus intensity (Dannenbaum 2005).

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Vestibular Disorders

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Normative Data

Loss of <3 lines of visual acuity during dynamic testing conditions is considered “within normal limits”. Loss of 3 or more lines is suggestive of potential vestibular dysfunction. (Herdman, 2008)

Loss of > 2 lines during dynamic visual acuity using Illegible E-test is considered abnormal (Longridge and Mallinson, 1984 and 1987)

Test/Retest Reliability

Children with Bilateral Vestibular Hypofunction (BVH) (Rine et al, 2003; n = 76 typically developing children; mean age = 7 years; n = 26 adults; mean age = 32 years; n = 11 children with BVH).

Passive Yaw Head movements (hDVA): n = 30 (reliability sub-analysis), mean age = 25 years for reliability component of study.

  • Excellent test—retest reliability ICC(2,2) r = 0.94

Passive Pitch Head movements (vDVA): n = 11, mean age 25 years (reliability sub-analysis). Note: Vertical DVA was “poorly tolerated” by participants.

  • Excellent test-retest reliability r = 0.88

Interrater/Intrarater Reliability

Children with Bilateral Vestibular Hypofunnction (Rine et al, 2003)

  • Excellent inter-tester reliability ICC(3,2) = 0.84

Criterion Validity (Predictive/Concurrent)

Predictive Validity, Yaw Passive

Children with BVH vs. Adults and Typically Developing Children (Rine et al 2003);

  • Excellent Sensitivity: 100%
  • Excellent Specificity: 100%
  • Excellent Positive Predictive Value: 100%
  • Excellent Negative Predictive Values: 100%
    Predictive Validity, Pitch Passive

Though statistical differences have been found between known groups (TD vs. BVH), observed differences were not clinically significant (all achieved DVA scores < 2 lines). The vertical dynamic acuity test was not tolerated by most children, precluding its usefulness (Rine et al, 2003).

Longridge and Mallinson, 1984 (n normals = 80)

·  All control subjects demonstrated normal calorics and < 1 row of deterioration during illegible E-test.

·   82.5% demonstrated no deterioration in reading ability during head motions; 17.5% demonstrated 1 row deterioration.

Longridge and Mallinson, 1987 (n normal= 30)

·     All control subjects demonstrated normal calorics and < 1 row of deterioration during illegible E-test.

94% demonstrated no deterioration in reading ability during head motions; 6% demonstrated 1 row deterioration.

Face Validity

Unilateral Vestibular Hypofunction (Dannenbaum et al 2005, n = 41, 10 with UVH mean age = 49.4(15.5); range 19-70 years.

·      The frequency of head motion has an impact on clinical DVA scores in subjects with UVH. DVAT- NI scores significantly decreased as head movement frequency increased from 0.5 to 1.0 Hz and from 1.0 to 1.5 Hz, during horizontal (yaw) and vertical (pitch) movements, and with both vision charts (p < .001).

·      Study results suggest that DVAT-NI be administered with horizontal and vertical rotational head movements of at least 1.5 Hz with the E-chart.

Unilateral Vestibular Hypofunction (Dannenbaum 2009, n = 10, mean age 58.8 (16.3) range = 40-83, patients with UVH s/p acoustic neuroma resection.

DVAT-NI had week correlation with degree of vestibular deficit established by bithermal calorics. Spearman correlation analyses revealed low-correlation coefficients between percentage of vestibular paresis at the caloric test and DVA scores (horizontal direction: r = 0.31, p = 0.38 for Snellen chart and = -0.33, p = 0.35 for the E-chart; vertical: = 0.05, p = 0.91 for the Snellen chart and r = -0.28, p = 0.50 for the E-chart).

Bibliography

Dannenbaum, E., Paquet, N., et al. (2009). "Clinical evaluation of dynamic visual acuity in subjects with unilateral vestibular hypofunction." Otol Neurotol 30(3): 368-372. Find it on PubMed

Dannenbaum, E., Paquet, N., et al. (2005). "Optimal parameters for the clinical test of dynamic visual acuity in patients with a unilateral vestibular deficit." J Otolaryngol 34(1): 13-19. Find it on PubMed

Herdman, S. J. (2007). Vestibular Rehabilitation, F. A. Davis Company. Longridge, N. S. and Mallinson, A. I. (1984). "A discussion of the dynamic illegible "E" test: a new method of screening for aminoglycoside vestibulotoxicity." Otolaryngol Head Neck Surg 92(6): 671-677. Find it on PubMed

Longridge, N. S. and Mallinson, A. I. (1987). "The Dynamic Illegible E-test: A Technique for Assessing the Vestibulo-ocular Reflex." Acta Otolaryngol 103(5-6): 273-279. Find it on PubMed

Rine, R. M. and Braswell, J. (2003). "A clinical test of dynamic visual acuity for children." Int J Pediatr Otorhinolaryngol 67(11): 1195-1201. Find it on PubMed

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