GB2247087A - Perimetric test chart - Google Patents

Abstract

A new test chart has been developed as a quick, alternative and supplementary method of perimetric evaluation of the central 25 degrees of the visual field to test for the presence of relative and absolute scotomas as part of a routine eye and neurological examination. The result of a comparison of this test with formal perimetry in 107 patients are described and discussed. The chart provides a central target and surrounding targets of different colour. <IMAGE>

Description

RED COLOUR COMPARISON PERIMETRY CHART IN NEURO-OPHTHALMOLOGICAL EXAMINATION DESCRIPTION RED COLOUR COMPARISON PERIMETRY CHART The Chart has nine disc shaped test targets on both sides, one in the center and others in the surrounding periphery.

The si2e of the chart, diameters of each disc pattern and distances between the centre of the central disc pattern and centre of the each peripheral disc patterns together with the angles subtending between each pair of peripheral disc patterns are given on the technical drawing next page.

The centre of the chart is marked withal mm. black dot to be used as a fixation point.

rargets (discs) are made of a vivid red colour. The background is black on one side of the test chart and grey on the reverse side of the chart. Colour specifications are made according to the Munsell Book of Colours and given on the Technical Draving attached.

Introduction: Taken together with visual acuity and colour vision, perimetric tests can provide information essential to a clear understanding of the integrity of a patient's visual system.

Perimetry is a key aid to diagnosis of neurological conditions affecting the pothwey from the eye to the occipital cortex.

A proportion of neurologicol ond neurosurgical patients have difficulty in sustaining the necessary cooperation for accurate perimetry. Therefore, charting of the visual fields of such patients may sometimes be omitted. in other settings, formal perimetry is impractical or too time consuming to be used on routine clinical examination . A perimetric test chart based on red colour comparison technique has been designed to overcome these problems, and has been compared with conventional perimetry.

Method: The chart has nine disc shaped test targets on both sides, one in the centre and the others in the surrounding periphery Targets were made of a vivid red colour. The background was black on one side of the test chart, creating a 50% contrast gradient and grey on the reverse side of the card, creating a 75 % contrast gradient(Fig 1,2. Patent pending).

Target distribution was arranged to correspond to the central 25 degrees of the visual field when held at 30 cm distance from and parallel to the eye. Two test spots were positioned in each quadrant, avoiding the vertical and horizontal meridians. (Fig.s 3, 4). The centre of the chart was marked with a 1 mm. black dot to be used as a fixation point.

Patients referred to neuro-ophthalmolog clinic were tested with their best spectacle correction for distance, in a diffusely illuminated room with a constant level of illumination. Direct light sources behind and in front of the patient were avoided.

Each patient was first questioned to exclude congenital achromatopsla and had a full neuro-ophthalmic examination including colour vision testing with H-R-R plates. Incorrect identification of more than two plates was considered abnormal. The red comparison perimetry chart was then shown to the patient and explained. Each eye was tested with both the gray and black background. Right eyes were tested first. The patient was asked to fix on the central spot, central disc or at the approximate centre of the chart according to their visual acuity level and while fixation to the centre was continuously checked and encouraged, they were asked to indicate the total number of discs seen. Missing targets would imply the presence of an absolute scotoma. Cases reporting any missing targets were asked if blinking a few times caused the targets to reappear.They were then asked to indicate if any target(s) had washed-out colours (e.g. pale, pinkish, dark yellow, gray) compared to the others in order to identify relative scotomas.

All patients were subsequently examined with Bjerrum 2 m.

Screen perimetry by a second observer who was unaware of the previous findings. Fields to white and red targets were plotted.

Patients with congenital colour vision anomalies and normal fields were excluded from the study. Results in subjects with congenital achromatopsia and neurological field deficit were evaluated only with regard to the total number of disc patterns seen.

Results: 107 patients, 39 female and 68 male, aged between 19 and 80 years were examined. All had normal pupils sized 3-7 mm. 33 patients had Bjerrum screen visual field abnormalities.

Two patients who had glaucomatous field defects, one senile maculopathy case with central scotoma, one individual who was considered to have hysterical field examination findings (with normal chart result), one patient with poor cooperation and fixation and a patient with neurological field defect outside the central 20 degree (totally six patients) were excluded from the study. Among the remaining 27 patients listed in Table 1, 16 cases (26 eyes) had absolute, 7 cases (1 1 eyes} had relative and 4 patients (7 eyes) had combined relative and absolute field defects. 74 patients did not show any abnormal Bjerrum Screen findings. There were no differences in patient responses to grey and black test backgrounds, other than more frequent episodes of transient disappearance of the disc patterns on black background, due to fast local adaptation.

Case 10 and 22 in Table 1 had congenital achromatopsia.

The test had 92% sensitivity and 96% specificity with 4% false positive and 7.4S false negative results in detecting the presence of any field loss within the central 25 degrees when compared with 2 m. Bjerrum Screen testing. Positive and negative predictive values of the test were 90% and 97%, respectively.

Correlation between the actual extent of the defect found on Tangent Screen perimetry and reported abnormalities of the corresponding disc patterns on the chart were studied further. Patients with macular splitting on Tangent Screen perimetry usually described the central red disc as intact. This was attributed to the patients' possible tendency to extrafoveal fixation. The chart was found to be 89% sensitive and 95% specific in determining the boundaries of the Tangent Screen field defect with 4.8% false positive and 10.5% false negative findings and with positive predictive value of 93S and negative predictive value of 92%. Formal perimetry results and test chart findings of seven patients are shown on Table 2-8.

Discussion: A century of controversy has surrounded the concept of colour versus white targets in neurological perimetry.

In cases of pituitary adenoma, it was reported that red test stimulus demonstrated grater field loss when red and white spots were chosen to give equal isopters in unaffected regions of the visual field (1).

It has often been stated that defects to coloured test objects can be found at an earlier stage of compression of the intracranial visual pathway than to white test objects(2,3,4,5).

Others report that white objects give the same sensitivity, with a close correlation between chromatic and achromatic visual loss if minimum stimuli are used, or if achromatic and chromatic stimuli of equal size are matched for intensity (6,7).

In colour perimetry, each coloured object has two endpoints: target recognition (achromatic endpoint) and colour recognition (chromatic endpoint). The former always gives a larger isopter for a given colour as the stimulus threshold for colour recognition is several times higher than its visibility.

It has been suggested that this difference might relate to the sampling interval for magnocellular and parvocellular neurons in the human visual system(85. According to contemporary theories the magnocellular system ( P Alfa ganglion cells) is insensitive to colour contrast but has a high sensitivity to luminance contrast. Conversely, the parvocellular system (P Beta ganglion cells) is less sensitive to luminance contrast but processes colour information. Although colour can probably only be processed by the parvocellular system, visibility might conceivably be mediated by both systems (9).Positron emission tomographic scanning during visual stimulation with stationary and moving coloured and isoluminant achromatic patterns has demonstrated that two anatomically distinct areas of human prestriate cortex are involved in processing of colour and motion(10). Several cases of hemiachromatopsia have been described ( . Homonymous field defects can themselves introduce errors in colour arrangement tests such as the FM 100-hue test (123.

In patients with pronounced congenital colour defects or lack of appreciation of coloured stimuli due to an acquired lesion of the central nervous system, perimetry with chromatic targets is virtually meaningless (13, 14) in a relative scotive scotoma, visuai sensation is reduced because of a change in visual threshold associated with a subjective reduction of brightness. In colour comparison testing, subjective sense of brightness depends on how far above threshold the stimulus is. Thus, a stimulus can appear less bright, and of different colour, in a region where sensitivity is reduced because it's intensity exceeds the threshold stimulus value by a lesser amount than it does in the normal portion of the visual field.Differences in colour saturation are more easily appreciated than brightness(15). A red object, for instance, might seem maroon in the defective field area, and bright red in the adjacent normal area. This effect may be used to confirm the results of conventional perimetric methods. During colour comparison testing, the first response should receive the greatest attention and the colour difference should be instantly obvious to the patient. If a patient has to think about it, the test is unreliable(15). In order to reveal scotomas using the simultaneous comparison technique, patients are asked to compare red coloured stimuli located on multiple sites on the chart, both in the centre and in the surrounding area and report whether they are all of the same appearance or whether there are different or missing ones.

Confrontation technique employing white and red-headed hatpins was advocated by Kestenbaum in 1948 (16). Commonly encountered inadvertent surface reflection on the coloured sphere part of the pin is a major drawback of this widely used technique. Its modification by examining with a green or red coloured torch(17) has the disadvantage of a lack of background neutrality.

The ease, rapidity and sensitivity of the Amslergrid(18) for accurate detection of central scotomas is well established and specific responses to the Amsler grid test are most commonly seen in patients with macular lesions. One of the Amsler test plates is made up of red lines on a black surface for colour field testing. However, this grid has limitations when used to detect relative scotomas of neurological origin, except for prechiasmal visual pathway disorders causing a field defect very centrally. The red lines are so thin and dim on the dark background that even intelligent patients with normal visual fields and acuities miss them(14). This phenomenon is due to rapid local light adaptation (Troxler's phenomenon), which is inherent with eccentrically fixated white or coloured objects.When a small stationary target is carefully fixated by an observer, it is found that an object seen in the area surrounding the fixation point fades out after a few seconds and disappears completely. As the peripheral target disappears, its background seems to fill in the area it occupied. The steadier the fixation the more pronounced is Troxler's effect for a given observer, with a wide range of observer variation.

The Troxler phenomenon depends mainly on neural rather than photochemical action and the lateral geniculate body has been suggested as the seat of the effect 19}. The weaker the stimuli(smaller or dimmer), the more easily can the effect be demonstrated(20). The persistence time of the object apparently increases with the number of receptive cells excited by the stimulus, since the disappearance takes longer with increasing target size, stimulus border enhancement and temporal modulation at a given eccentricity(21,22). Once the target has disappeared, a short discontinuity of fixation restores its visibility.

For these reasons, our test charts were designed with large target sizes and two different contrast gradients between the targets and the background. Patients were asked to blink in order to minimise the local light adaptation effect.

Chiasmatic lesions may primarily effect only the decussating nasal- macular fibres, resulting in a " central bitemporal hemianopia". Only the area up to 10 degrees from fixation is involved with normal peripheral fields. Any lesion affecting the tip of the occipital lobe produces a defect involving only the central homonymous hemifields(23) with macular sparing (corresponding to the central disc pattern of the test chart which subtends 3 degrees, thus testing the blind zone of the Goldmann perimeter). We believe this chart is especially useful in detecting such lesions, in addition to optic tract and radiation defects.

Incongruous superior mid-peripheral "pie in the sky" quadrantopsia such as those produced by anterior temporal lobe lesions involving Meters loop, peripheral field defects caused by lesions of the upper calcarine fissure and some isolated .

paracentral scotomas would not be detected by these charts.

However, such lesions and their secondary perimetric changes are rarely encountered.

We have found the red colour comparison perimetry chart is a useful adjunct to conventional perimetry in routine neuro-ophthalmic examinations. In addition, reliable information may be obtained from patients who can not cooperate sufficiently to perform conventional perimetry.

References: 1. Bertolli F., Liuzzi L. Laser Perimetry: Diagnostic application in six cases of pituitary adenoma. Acte Ophthal.

1973,51:841-852.

2. Enoksson P. Perimetry in Neuro-Ophthalmological Diagnosis. Acta Ophthalmologica 1965, 43, Suppl. 82:1-54.

3. King-Smith PE, Lubow M, Benes SC . Selective damage to chromatic mechanisms in neuro-ophthalmic diseases. Docum.

Ophthal. 1984, 58: 3,241-250.

4. Bailey J.E. The status of colour fields today. J. Amer.

Optom. Ass. 1980.51: 843-847.

5. Hedin A, Verriest 6. Is clinical colour perimetry useful? Docum. Ophthal. Proc. Ser. 1981,26: 161-184.

6. Mindel JS. Visual field testing with red targets. Arch.

Ophthal. 1983, 101: 927-929.

7. Hart W.H., Burde R.M. Colour Contrast Perimetry.

Ophthalmology 1985, 92: 768-776.

8.Drasdo N, Thompson C.M. Do visibility and colour recognition isopters relate to the distribution of Pd and PI3 ganglion cells of the retina? Ophthal. Physiol. Opt. 1989, 9: 447-450.

9. Zeki S., Shipp S. The functional logic of cortical connections. Nature (London) 1988,335: 311-317.

10. Lueck C.J., Zeki S. Demonstration of functional specialisation in human prestriate cortex using positron emission tomography. The London Hospital, UK. Presented at 8th International Neuro-Ophthalmology Symposium, Winchester, England. June 1990.

11. Kolmel H.W. Pure homonymous hemiachromatopsia.

Findings with neuro-ophthalmic examination and imaging procedures. Eur. Arch. Psychiatry Neurol. Sci. 1988, 237: 237-243.

12. Zihl J. The influence of homonymous visual field disorders on colour sorting performance in the FM 100-hue test.

Neuropsychologia 1988, 26: 869-876.

13 Walsh T. J. Neuro-ophthalmology. Clinical Signs and Symptoms. 2nd Edition. Lea-Febiger, 1985.

14. Meadows J.C. Disturbed perception of colours associated with localized cerebral lesions. Brain 1974. 97: 615-632.

15. Anderson D. R. Perimetry with and without automation. 2nd edition, The C V Mosby Company, 1987.

16. Duke-Elder S. Investigation of Indirect Vision: The visual fields. System of Ophthalmology. Vol VII: 393-421.

Henry Kimpton, London. 1962.

17. Frisen L. A Versatile Color Confrontation Test for the Central Visual Field. Archives of Ophthalmology 1973,89:3-9.

18. Amsler M. Earliest Symptoms of the Diseases of the Macula. Br. J. Ophthal. 1953; 37: 521-537.

19. Clarke FJ, Belcher SJ. On the localization of the Troxler's effect in the visual pathway. Vision Res. 1962, 2: 53-63.

20.Cibis S. Zur pathologie der lokal adaptation. v. Grafes Arch. Ophth. 148,1-92: 216-257 21. Moses RA. Adler's Physiology of the Eye.Clinical Applioation.7th Edition.The CV Mosby Company, 1981.

22. Dawson WW, Michels M, Semple-Rowland SL. Results from a simple laser colour perimeter. Documenta Ophthal mologica, 1984, 57:181 - 186 23. Bajandas F.J., Kline L.B. Neuro-Ophthalmology Review Manual. Third Edition. Slack Incorporated, USA, 1989:1-23.

Legends: Figures 1 and 2 : Red colour comparison perimetry chart; gray and black background.

Figure 3 : Test spot positions superimposed on a Tangent Screen.

Figure 4 : Test spot positions superimposed on the retina.

VISUAL ACUITY COLOUR VISION DEFICIT PA AGE SEX A L R L PATHOLOGY FIELD DEFECT 1. 67 F 616 616 + + l. Temporo-OcCIPITAL SOL R. Sup. Homonymous Quadranlopsia 2. 74 M PL 6118 + Püuitary Adenoma R. Hemisnopiss 3. 73 M 616 616 + + Pituitary Adenoma L.Hemianopia ; R. Sup. Altitudinal Defect 4. 71 M 619 6112 + + Pituitary Adenoma BitemporafHemianopia 5. 20 F 616* 616 + + Pituitary Adenoma Bitemporal Supernor Quadrantopaia 6. 73 F CF 616 + - R.AION L.Interior Altitudinal Defect 7. 62 M 6g6 616 - - Occipital SOL L. Hornonymous Hemisnopie.

8. 80 F 619 619 - - Occipital Lobe Inforction L. Homonymous Hemianopia 9. 43 F 616 616 - - Empty Sea Syndrome R. Homonymous Hemianopia 10. 37 M 6160 616 + + lntemalCapsular lnfarct ? R.NassalHemianopia 11. 25 M 619 CF + + Muitidle Sclerosis R. lnfenorAltifudinalDefectandCentral scotoma 12. 28 F 6Z6 616 - - Multiple Sclerosis R. Sup. Temporal Quadrantopsia 13. 55 M 616 6136 ~ + L.ALON L. Sup. AltitudinalDefect 14. 33 M 616 616 ~ + EmptySellaSyndrome R. Sup. AltitudinalDefect L. lnf. AltitudinalDefect 15. 44 H 616 616 - - Occipitallobelnfarction R. HomonymousSup.Quadrantopsia 16 26 M 616 616 + + Craniopharynigioma L.Homonymouslncongrous D6fect 17 28 M 616 HM ~ + Craniopharyngioma R.Temporal Hemianopla L.Central Scatoma 18. 56 F 619 6160 + + Suprasellar SOL R.TemporalHemianopia L.Centtal Scotoma 19. 71 H - HH PituitaryAdenoma L.Temporal Hemianopia 20. 59 H 616 619 + + Occipital Lobelnfarct R.Homonymous Hemianopia 21. 60 H 6124 6,6 + - R. Posterior NAION R. Superior Altitudinal Detect 22. 71 H 6136 6136 + + Parietotemporallnfarct L.HomonymousHemianopia 23 27 F 619 615 + ~ R.Retrobulbar O.Neuritis R.Central Scotoma 24. 29 F 6112 615 + ~ R.Retrobulbar O.Neuritis R.Centrocecal Scotoma 25. 54 M 619 616 + + Pitutary Adenoma BitemporalHemianopia 26. 59 H 615 615 - - Occipital Lobelniarct Bilateral Paracentral Scotoma 27. 58 H 615 616 + + Occipital Skull Fracture Bilateral L. Sup. Quadraritopsia TABLE 1: List of patiants with visualfield defects.

SOL : Spaceoccupying lesion, ALON : Anterior ischaernic optic newropathy, NALON : Nonartenitie ischaemic optic neuropathy, Sup : superior, O : optic, R : right, L : left.)

Claims (1)

1. CLAIMS 1. A visual field test (perimetry) chart comprising a surface which is painted in an colour, and multiple test stimuli (targets) on this surface in any other colour(s) (including black. shades of grey and white) which are different, either darker or brighter in contrast. hue or tone than the chart surface colour.

   2. h visual field test (perimetry) chart as claimed in Claim

   1 wherein multiple test targets lstimuli) are situated as whe ilr-~t orle in th. centre oi the chart surface foi the purpose of maintenance of the steady @aze (fi@ation) of tile individual being tested and tile other test target or targets are distributed at different eccentricities in the surrounding reriDherv of the central test (fiXatiOn! target on the chart surface.

   A A visual field test lpesimetry) chart as claimed in Claim

   1 or Claim 2 wherein chart size and shape (geometry) as well as multiple test targets' (stimuli) size and shape (geometry) may vary and these may be redefined depending on the desired extent of the retinal area to be stimulated in each selected patient eye-chart test distance and eye test chart surface orientation.

   4. A visual field test (perimetry) chart as claimed in Claim l or Claim 2 or Claim 3 wherein test target (stimuli) distribution pattern, distribution eccentricities, distribution symmetries may vary and these may be re defined according to each selected patient eye-chart test distance and eye-test surface orientation.

   5. A visual field test (perimetry) chart as claimed in Claims 1-4 wherein multiple test stimuli (targets) can be created either: (i) by exposing the test targets through the holes on a front mask which is the test chart surface by means of sliding the mask on the front of a background surface and allowing the test stimuli to appear through the multiple holes at a number of prearranged locations anywhere on the chart's surface; or (ii) by allowing the test stimuli to appear through the multiple holes on a steady front mask which is the test chart surface; or (iii) by printing the multiple test stimuli on the test chart surface.

   6. A visual field test (per'ietry) chart as claimed in Claims 1-5 which can be hand-held or self-supporting on a desk by means of foldable flaps on the back of the chart.

   AMENDMENTS TO THE CLAIMS H AVE BEEN FILED AS FOLLOWS.

   1. A visual field test (perimetry) chart comprising a surface which is painted in any colour, and multiple stimuli (test targets) on this surface in any other colour (including black, shades of grey and white) which are different, either darker or brighter in contrast, hue or tone, than the chart surface colour.

   2. A perimetry chart as claimed in Claim 1, wherein a fixation point (fixation target) is located in the centre of the chart surface for the maintenance of the steady gaze(fixation) of the patient's eye during the test and other multiple stimuli which have well-defined distinct borders (square-wave stimulus) are distributed in the surrounding periphery of the central fixation point.

   3. A perimetry chart as claimed in Claim 1 and Claim 2 wherein a) the chart size and shape (geometry) and, b) the multiple square-wave type test targets' size and shape (geometry) may vary and may be redefined depending on the desired extent of the retinal area to be stimulated in any selected patient's eye-chart distance and eye-chart surface orientation.

   4. A perimetry chart as claimed in Claim 1 and Claim 2 and Claim 3 wherein the distribution pattern, symmetry and eccentricities of the stimuli may vary and may be redefined according to any selected eyechart distance and surface orientation.

   5. A perimetry chart as claimed in Claims 1,2,3 and 4 wherein the square-wave type multiple stimuli can be created either A) by exposing the test targets through the multiple holes on a front mask which is the test chart surface by means of radial or rotatory sliding of i) the mask in front of the steady background surface ii) the background surface behind the steady front mask; or B) by printing the stimuli on the chart surface.

   6. A perimetrx chart as claimed in Claims 1-5 which can be hand-held or sc-lf-supportin by means of foldable flaps on the the chart.