REALIZATION OF SEMI-AUTOMATED KINETIC PERIMETRY WITH THE INTERZEAG OCTOPUS 101 INSTRUMENT

ULRICH SCHIEFER,1 STEPHAN RAUSCHER,1 A. HERMANN,1

K. NOWOMIEJSKA,1,2 JENS PAETZOLD1 and JAN SCHILLER1

1Department II, University Eye Hospital Tübingen, Tübingen, Germany; 2Tadeusz Krwawicz Chair of Ophthalmology and 1st Eye Hospital, Medical University, Lublin, Poland

Introduction

Kinetic perimetry is the method of choice in cases of advanced visual field loss (e.g., altitudinal defects, quadrantanopia, hemianopia, or concentric constriction), in patients with poor compliance, and in examinations dealing with expert opinion or other topics of social ophthalmological relevance. However, the quality of examinations with the conventional Goldmann perimeter can be considerably impaired by examiner-related shortcomings: for example, unintended variation or instability of stimulus velocity; reduced spatial resolution within the central (15°) visual field, and insufficient, or even missing, assessment of patient-related quality control criteria, such as response times, response variability, and fixation stability.

The aim of this study was to overcome most of the above-mentioned shortcomings by developing a largely examiner-independent kinetic perimetric test procedure using a (modified) conventional bowl perimeter, and additionally to provide age-related normative values.

Methods and subjects

Using a redesigned mirror unit and a revised user interface, which can be integrated into all Octopus 101 perimeters, a smooth, constant stimulus motion with angular velocities up to 80°/sec in any direction within the entire (almost) 90° cupola area, can be realized (Fig. 1). The examination procedure is controlled via a conventional computer mouse or a combined video display unit and touch pad with stylus (CintiQ 15X, interactive pen display, WACOM Europe GmbH, Krefeld, Germany). The examiner

Address for correspondence: Prof. Dr. med. Ulrich Schiefer, University Eye Hospital Tübingen, Department II, Schleichstrasse 12–16, D-72076 Tübingen, Germany. Email: ulrich.schiefer@unituebingen.de

Perimetry Update 2002/2003, pp. 233–238

Proceedings of the XVth International Perimetric Society Meeting, Stratford-upon-Avon, England, June 26–29, 2002

edited by David B. Henson and Michael Wall

© 2004 Kugler Publications, The Hague, The Netherlands

Fig. 1. Combined video display unit and touch pad with stylus (CintiQ 15X, interactive pen display, WACOM Europe GmbH, Krefeld, Germany) for controlling the entire perimetric examination procedure (background: Octopus 101 perimeter, Haag-Streit Inc., Koeniz, Switzerland).

can choose any arbitrary origin, direction, and length of a so-called ‘vector’, along which the pre-defined stimulus is moved by the computer program, with a selected constant angular velocity.1-3 By pressing a response button, the patient stops stimulus presentation. Presentations can be repeated in order to estimate the scatter (standard deviation or other adequate parameters characterizing dispersion) of local responses. Presentations within the intact visual field are used to assess, and optionally correct for, subjects individual response time characteristics (for further details, see Schiefer et al.4; S. Rauscher et al., This Volume, pp. 353-358).

Age-correlated normative data (Goldmann stimulus III 4e) were obtained in 12 ophthalmologically healthy subjects per decade of life with an angular velocity of 5°/sec, using six centripetal stimulus presentations in random order along each of the eight cardinal meridians. The results of left eyes were mirrored and could thus be superimposed on those of right eyes.

Normal individuals had to meet the following inclusion criteria:

•normal ophthalmological history (i.e., no intraocular trauma or inflammation; no eye surgery – except for cataract surgery with uncomplicated intraocular lens implantation; no history of either squint, amblyopia, patching, penalization, or nystagmus; no hints of visual pathway lesion – especially with regard to glaucoma, optic neuritis, anterior ischemic optic neuropathy (AION), other optic neuropathies, retinal diseases, intracerebral space occupying lesions, and stroke);

•normal general history (especially no diabetes mellitus; no current arterial hypertension – blood pressure < 180/< 90 mmHg; no hint of intracerebral pathology, such as tumor, stroke, vascular malformation, seizure, or multiple sclerosis; no drugs potentially affecting reaction time; no alcohol, nicotine, caffeine within two hours of perimetric examination);

•normal ophthalmological examination (maximum spherical ametropia ± 6 D, maximum cylindrical ametropia ± 2 D, normal Lang(-I) stereo test, no manifest squint (strabismus), normal ocular motility, no double vision, no relative afferent pupillary defect (RAPD), no anisocoria, normal anterior segments, no relevant opacities of the central refractive media, normal fundus examination with undilated pupils, intraocular pressure (IOP) < 22 mmHg (air pulse, after perimetry);

•distant visual acuity:

≥20/20 for age group < 60 years

≥16/20 for age group 60 to 69 years

12/20 for age group > 69 years

• near visual acuity (→ reading performance):

Birkhäuser text ≥ 1.0 for age group < 60 years Birkhäuser text ≥ 0.8 for age group 60-69 years Birkhäuser text ≥ 0.6 for age group > 69 years

• rested, relaxed condition.

The examinations were performed according to the tenets of the Helsinki declaration, and informed consent was obtained from each patient.

Results

‘Kinetic thresholds (eccentricities)’ along the nasal horizontal meridian for the abovementioned stimulus conditions (III 4e, 5°/sec, six centripetal stimulus presentations) are given as a typical example: 53.7 ± 6.8° (Mean ± SD), and 54.4 ± 8.0°, for the second and seventh age decade, respectively. Taking account of individual response times, these values increase to 56.8 ± 6.5°, and 57.3 ± 7.9°, respectively.

Figure 2 shows normative data for all eight cardinal meridians in the age group ten to 19 years. Figure 2a presents the original data without correction for individual response time (RT), whereas correction for RT in Figure 2b leads to an expansion of the isopter – even in these young normal subjects!

As expected, ‘kinetic thresholds’ show maximum eccentricity in the temporal region of the visual field. There might be a small ‘ceiling effect’ due to mechanical and geometrical factors (chin/forehead rest, cupola geometry, etc.).

Inter-individual scatter is greatest in the inferior nasal region, most probably due to anatomical variations of noses. Scatter turns out to be smallest in the inferior temporal region. Again, variability of the temporal horizontal meridian may be reduced by the above-mentioned instrument-related ‘ceiling effect’.

An age-corrected (smooth) mathematical model, considering target luminance, size, velocity, and vector location is being developed.

Discussion

One of the major reasons for developing automated static perimeters was to exclude/ reduce examiner-related sources of variability, which seemed to be unavoidably linked with conventional manual kinetic perimetry. However, static grid perimetry is an

Fig. 2. Results of the age-related normative study with the following experimental conditions: Goldmann stimulus III 4e (i.e., ~26’, 320 cd/m2), angular velocity 5°/sec, six centripetal stimulus presentations in random order along each of the eight cardinal meridians; age group 10–19 years (error bars indicating Mean ± SD of 12 ophthalmologically healthy subjects). Results for right eyes are shown; data of left eyes were mirrored. (RT = reaction time)

exhaustive procedure making high demands of the patient. According to the experience of one of the authors (US), up to one-third of neuro-ophthalmological patients cannot be examined properly with this technique. This is especially true in cases of advanced visual field loss (e.g., hemianopic or altitudinal field defects, concentric constriction). Kinetic perimetry is the method of choice in these patients, since the presentation of targets may be efficiently focussed on regions of interest, i.e., scotoma borders, steps, etc. Since body or gaze movements induce a retinal shift of the image, even in case of stationary obstacles, kinetic perimetry seems in general to be closer to reality than static perimetric methods. This is one of the reasons why, for example, in Germany, final decisions in expert opinions or aptitude tests are based on kinetic perimetry.

Goldmann made outstanding contributions with regard to standardization of the kinetic examination procedure by creating a cupola perimeter with defined, homogeneous background luminance level, by standardizing target characteristics, and by proposing adequate angular stimulus velocities.5,6 However, this procedure is dependent on the examiner’s skills and is also more or less irreproducible, since, for example, neither stimulus angular velocity nor stimulus approach towards the assumed scotoma border are controlled or documented. Factors such as these are a major drawback with regard to quality control and reproducibility, thereby limiting the value of this method, especially for follow-up purposes.

Automated kinetic procedures have been developed to solve some of the abovementioned problems.7-9

By means of the standardized, semi-automated kinetic perimetry (SKP) procedure, which is presented in this paper, the examiner can choose any arbitrary origin, direction, and length of a so-called ‘vector’, along which the predefined stimulus is moved by the computer program with a pre-selected constant angular velocity.1-3 Stimulus presentation is stopped by the response of the patient. Each vector is stored, is optionally shown on the examination monitor, and is also documented in the perimetric record. Thus, origin and direction of the stimulus (perpendicular towards the scotoma border) can be checked at any time. The set of vectors, together with the selected stimulus characteristics, is stored for follow-up purposes. Examiner-related effects should be minimized by this procedure.

The instrument chosen for this normative study (Octopus 101, Haag-Streit Inc., Koeniz, Switzerland) seems to be well suited for the task, since it allows target movements in all directions (for example, exactly perpendicularly crossing the vertical meridian within the central visual field in order to check for macular splitting/sparing with kinetic targets).

Angular velocity of the stimulus is an important and critical parameter of kinetic perimetry: low speed results in longer examination duration and may inadequately stimulate the ‘motion channels’ of the visual system. High velocities may induce systematic measurement errors, especially if the response time is not considered, with scotoma borders shifting towards the direction of the target motion by an extent dependent upon target velocity.12 It is especially important to consider response times in patients with neurological disorders and/or of advanced age.2,4,10 The above-men- tioned problems can be reduced by taking account of individual response times (S. Rauscher et al., This Volume, pp. 353-358). Schiefer et al.4 recently demonstrated that, even in ophthalmologically healthy individuals, subject-related factors had a larger impact on response time than target-related ones. This is likely to be even more pronounced in patients suffering from neuro-ophthalmological diseases.

Static stimuli along the vectors chosen for SKP will additionally allow assessment of stato-kinetic dissociation (SKD) in the same instrument, and even within the same session19 (see also: J. Schiller et al., This Volume, pp. 75-81).

Although kinetic perimetry has been used for a long time, age-corrected normative data are rare.6,12,20 To our knowledge, this is the first study to consider response times and interas well as intra-individual scatter, in a semi-automated procedure. Further evaluation of the complete dataset will help to model an age-corrected normative ‘kinetic hill of vision’, which may then serve as a reference.

Despite the importance of kinetic perimetry, its routine application seems to have declined over the past decade: a few years ago, less than 50% of German general ophthalmologists had access to a kinetic perimeter.21 Now perimeters are available that can perform both automated static grid perimetry and kinetic perimetry, there seems to be a renaissance of this technique. Unfortunately, kinetically skilled staff have become a ‘threatened species’. Therefore, special teaching programs, with builtin ‘artificial visual field defects’ and quality control, are needed (J. Paetzold et al., This Volume, pp. 69-73). The vector-based approach of the SKP strategy, presented in this paper, clearly demonstrates any flaws in an examination (i.e., ‘vector positioning’), and should therefore help less experienced examiners to improve their performance.

Acknowledgment

Supported by: Haag-Streit Inc., Koeniz, Switzerland; Steinbeis-Zentrum (StZ) Biomedizinische Optik, Tübingen, Germany.

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