Abstract
Objective
To compare the oscillopsia sensation in vestibular defective patients, using a specific handicap questionnaire and a specific Visual Analog Scale, with objective measure of the vertical vestibulo-ocular reflex efficiency in the pitch plane, using the computerized Dynamic Visual Acuity (DVA) test and Gaze Stabilization Test (GST).
Design
Controlled retrospective study.
Setting
Day hospital in ENT Rehabilitation Unit.
Subjects
Sixty-five subjects: 35 controls (12 men and 23 women; mean age, 50.77 ± 13.39 years) and 30 patients with chronic dizziness: 18 with unilateral vestibular hypofunction (7 men and 11 women; mean age, 55.50 ± 12.72 years) and 12 with bilateral hypofunction (7 men and 5 women; mean age, 57.25 ± 9.18 years).
Main measures
Computerize vertical DVA and GST; subjective Visual Analog Scale, Oscillopsia Score questionnaire.
Results
Instrumental tests had different means between subject groups; vertical DVA results and subjective measures were significantly correlated.
Conclusions
Vertical DVA and GST test in up and down direction are able to separate healthy and vestibular patients. Moreover, the DVA test in down direction differentiates patients with unilateral vestibular hypofunction and with bilateral vestibular hypofunction. These results show that vertical DVA test can be used for the assessment of the visual field instability referred to as disabling.
1
Introduction
Oscillopsia is the illusion of movement of the visual surroundings, usually due to the eyes not remaining steady onto the visual target .
The vestibulo-ocular reflex (VOR) is the primary mechanism for gaze stability. During movements of the head, the VOR stabilizes gaze (eye position in space) by producing eye movements of equal velocity and in opposite direction to the head movement.
Patients suffering with oscillopsia often report the surroundings to bounce up and down as well as vertical shimmering of images during walking; this suggests a defective VOR, predominantly in the vertical plane, as the cause of the disease .
In most of the daily activities, head movements reach very high velocities and frequencies; for example, during running, velocities are up to 90° per second, with predominant frequencies up to 2.7 Hz for yaw and 8.2 Hz for pitch . Therefore, it is important to asses vertical head movements as representative of everyday activities such as walking or running . Until now, it has been complicated to relate oscillopsia to the vestibular function since it was difficult to objectively evaluate the fixation capacity during head movements which is the main vestibular function.
Several tests of Dynamic Visual Acuity (DVA), the acuity obtained during relative motion of either optotype or observer, have been reported as the means of assessing the impact of impaired vestibular function. The clinical version of this test is carried out by measuring the static visual acuity of the patient sitting at a predefined distance in front of an optotype table; the test is then repeated by moving the patient’s head on the horizontal plane at a frequency of 2 Hz. A decrease greater than 2 lines in the letter identification indicates a reduction in the patients’ ability in focusing a target with the head moving, meaning a deficit in VOR gain . However, in this clinic DVA, test it is difficult to maintain correct head velocity and especially to avoid central pre-programming phenomena; thus, it is impossible to offer a really random presentation of the visual stimulus .
Recently, a computerized DVA test has become available as a new diagnostic instrument allowing a rapid dynamic visual acuity test for evaluating VOR efficiency. This test quantifies the impact of the impairment of VOR system on the patient’s capacity to perceive objects accurately while moving the head at a given velocity on a given axis. Computerized DVA test provides a direct measure of VOR impairment in terms of visual loss measured in logarithm of the Minimum Angle of Resolution (logMAR) , which is a reference measure for the assessment of visual acuity.
The Gaze Stabilization Test (GST), which is performed with the same DVA device, measures visual acuity of the subjects at different head velocities, assessing the VOR efficiency in terms of maximum head velocity at which the subject still maintains fixation of a stable optotype at a specified level of visual acuity . To the best of our knowledge, only a few publications have utilized both DVA and the Oscillopsia Score (OS) to asses oscillopsia but without significant relationship between subjective and objective measures of oscillopsia . There are no studies analyzing the relationship between oscillopsia sensation and GST.
Computerized DVA and GST tests in the yaw plane have been demonstrated to be good vestibular rehabilitation outcome measures . Therefore, we think that these tests in the pitch plane could also be used as rehabilitation outcome measures if proven to be related with oscillopsia sensation.
The aim of this study is to compare the oscillopsia sensation in vestibular defective patients, using a specific handicap questionnaire and a specific Visual Analog Scale (VAS) , with objective measures of the vertical VOR efficiency in the pitch plane, using the computerized DVA-GST tests.
2
Materials and methods
2.1
Subjects
Sixty-five subjects were recruited for the study from the ENT Rehabilitation Unit, San Raffaele Pisana Scientific Institute, San Raffaele s.p.a., Rome, Italy, during 2007. Thirty-five control subjects (12 men and 23 women; mean age, 50.77 ± 13.39 years) and 30 patients with chronic dizziness: 18 unilateral vestibular hypofunction (UVH) subjects (7 men and 11 women; mean age, 55.50 ± 12.72 years) and 12 bilateral vestibular hypofunction (BVH) subjects (7 men and 5 women; mean age, 57.25 ± 9.18 years).
Table 1 outlines the classification of patients.
| Classification | Diagnostic criteria | No. |
|---|---|---|
| N | Normal response at caloric test | 35 |
| UVH | Labyrinthine prevalence in the caloric test >50% | 18 |
| BVH | No significant bilateral labyrinthine responses obtained by bitermal energy stimulation | 12 |
Patients exclusion criteria were cognitive deficits, not corrected severe visual acuity loss, joint replacement, degenerative neurological disease, whiplash injury, post-traumatic vertigo, and benign paroxysmal positional vertigo. The institutional internal review board approved the study. All subjects gave written informed consent for participation.
2.2
Instruments
The inVision (Neurocom, Clackamas, Oregon) system was used to perform computerized DVA and GST tests. Detailed descriptions of the DVA-GST test have been reported previously . In brief, the test is performed at a distance of 1.5 meters with the subject seated; first of all the Static Visual Acuity (SVA) test on the horizontal plane is performed. The correct SVA test is then based on the least optotype rightly recognized by the subject: for this reason the optotype “E” is shown on the computer monitor with random spatial orientation (up, down, right, or left) and with random showing time. The starting size of the optotype, determined by the machine in relationship with the distance of the subject from the monitor, is equal to a visual acuity of 20/20 according to Snellen or to a 0.00 logMAR (logarithm of the minimum resolution angle).
2.3
DVA test
A given optotype size appears in a random spatial orientation a maximum of 5 times. If the patient responds incorrectly to 3 of 5 possible presentations of a given optotype size, the optotype size is increased 1 level until the patient accurately identifies 3 of the 5 possible presentations . Subsequently the DVA is assessed on the pitch plane; the patient wears a rate sensor mounted on the headband, which is used to monitor the velocity and direction of the head movements.
Even if the instrument instructions advises to let the patient move the head actively, it was decided to move the subjects’ head passively to avoid learning and central preprogramming phenomena . Patient’s head is moved in the pitch plane (up and down) at a minimum speed of 120° per second; under this limit, the optotype is not shown. Once the required velocity is achieved during a trial, the system randomly selects the direction of the head movement during which the optotype is to be presented. This avoids subject identifying the optotype during a fixation period and that the pursuit system is used in order to minimize the retinal slip . This test is carried out at a constant speed; in the beginning, the optotype is shown 3 sizes bigger than the patient’s SVA and is gradually reduced whenever the patient identifies the right orientation of at least 3 out of 5 sequential showings. When the patient cannot clearly distinguish the optotype anymore, the assessment is finished.
The analysis system compares the DVA with SVA and reports the change as DVA loss in logMAR units. This difference (large or small) is the fixation ability of the subject and then the VOR efficiency.
2.4
GST
The GST protocol quantifies the maximum velocity in degrees per second of the head movement at which the patient is able to maintain a specified level of visual acuity. During the GST, patient is asked to look at the optotype “E” which remains at a constant size (the patient’s SVA) while moving passively his/her head in the pitch plane. Patient’s head velocity is increased according to the accuracy of their response to the orientation of the E, As in the DVA test, once the required velocity is achieved during a trial, the system randomly selects the direction of the head movement during which the optotype is to be presented. When the subject can no longer accurately recognize the orientation of the optotype, the test is complete.
2.5
Subjective measures
The Italian version of a specific “questionnaire” on oscillopsia was used . This questionnaire is aimed at detecting the presence of oscillopsia and at assessing if patients experienced symptom as disabling. The questionnaire consists of 12 items relating to difficulties experienced in everyday tasks. Each item is scored from 1 (no difficulty) to 4 (cannot do). The OS ranges from 12 (no handicap) to 48 (higher level of handicap) . The last part of the questionnaire consists of 3 items about the possible limitations in daily life and a free question about the presence of disabling symptoms. The list of symptoms was not shown to patients to avoid influencing them and to obtain unconditional answers.
To measure oscillopsia we used an OS and a 10-cm vertically oriented VAS. Word cues representing the extreme of the oscillopsia sensation: “as bad as it could be” or “I can see clearly” were at the top and bottom of the line.
Subjects were instructed to walk straight ahead at a freely chosen speed for a distance of 10 meters while looking in front of them. During this exercise the patients were asked to rate the amount of visual blurring or motion they experienced in the environment by marking along the 10-cm line .
2.6
Statistical analysis
Means of the 3 groups to determine if at least 1 group mean was different from the other data were analyzed by 1-way analysis of variance after all the variables were checked for normality (with Skewness Normality of Residuals test) and for equal variance (with Modified-Levene Equal-Variance Test). Post hoc Bonferroni test was performed as multiple comparison procedure. Pearson correlation coefficients ( ρ ), with 2-tailed test of significance, were computed to analyze the correlations between all possible pairs of variables. Variables were considered well correlated if |ρ| ≥ .60.
2
Materials and methods
2.1
Subjects
Sixty-five subjects were recruited for the study from the ENT Rehabilitation Unit, San Raffaele Pisana Scientific Institute, San Raffaele s.p.a., Rome, Italy, during 2007. Thirty-five control subjects (12 men and 23 women; mean age, 50.77 ± 13.39 years) and 30 patients with chronic dizziness: 18 unilateral vestibular hypofunction (UVH) subjects (7 men and 11 women; mean age, 55.50 ± 12.72 years) and 12 bilateral vestibular hypofunction (BVH) subjects (7 men and 5 women; mean age, 57.25 ± 9.18 years).
Table 1 outlines the classification of patients.
