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					Threshold Amsler Grid                                          Testing
Cross-Polarizing Lenses Enhance Yield
Michael   Wall, MD, Alfredo      A.   Sadun, MD, PhD


   \s=b\ The Amsler grid is a commonly used           tive field defects may not be detected
test for evaluation of the 10\s=deg\of visual field   with a suprathreshold stimulus (Fig
surrounding fixation. The Amsler grid is a            1). We therefore decided to use a
suprathreshold stimulus and thus may not              stimulus barely suprathreshold in an
detect relative scotomas. Therefore, we
                                                      attempt to increase the yield of visual
had ten patients with optic neuropathies              field defects detected with Amsler
view the grid through cross-polarizing fil-
                                                      grid testing.
ters that created low luminance condi-                    Contrast is a function of the differ¬
tions in which the grid was barely percep-            ence   in luminance between target and
tible. The patients were also surveyed                                                                Fig 1.—Sagittal section of visual island as
                                                      background; thus, decreasing the                would be plotted by static perimetry. Relative
with a 2-m tangent screen protocol and                luminance of the white Amsler grid to
threshold automated perimetry. The                    the level at which the grid can just be         scotoma is shown with diagonal lines. Supra¬
threshold Amsler grid technique in-                                                                   threshold standard Amsler grid (SA) stimulus
                                                      seen would enable one to test the 10°
creased both the number of defects found                                                              may survey island at too great a depth and
                                                      surrounding fixation at only slightly           miss relative scotoma found with threshold
and the total area of these defects by                above threshold. To accomplish this, a          Amsler grid testing (TA).
approximately a factor of 5. Two thirds of            device consisting of cross-polarizing
the defects found were confirmed by one               filters was used to vary the luminance
of the other screening techniques.                    of the white grid. The device employed
Threshold Amsler grid testing is a rapid,             was developed by one of us (A.A.S.) to
inexpensive, and sensitive technique for              test   brightness-sense (Fig 2).4
the evaluation of the central 10\s=deg\of the            Patients with optic neuropathies
visual field.                                         were evaluated with routine and
   (Arch Ophthalmol 1986;104:520-523)                 threshold Amsler grid testing, static
                                                      and kinetic 2-m tangent screen exami¬
                                                      nation, and threshold automated
Oince its introduction in 1947, the                   perimetry. These tests were compared
^ Amsler grid has become important                    for their yield, reliability, and cost
in the evaluation of the 10° of visual                efficiency in screening for visual field
fieldsurrounding fixation.1·2 Patients                defects in the central 10° of visual
report   abnormalities representing                   field. In particular, we studied wheth¬
metamorphopsia, scotomas, and de¬                     er visual defects detected at near
pressions of the central field when                   threshold levels were being over¬
viewing this grid. The field defects                  looked by routine Amsler grid testing           Fig 2.—Top, Polarized filters have been
noted have been confirmed with kinet¬                 and other visual field screening meth¬          affixed to four blank trial lenses and placed in
ic and static perimetry.3                             ods. Normal subjects also underwent             standard trial frame. Bottom, Custom-built
   It is not uncommon, however, for                   routine and threshold Amsler grid               device containing pairs of polarized filters in
                                                                                                      each ocular. Front filter can be rotated. In both
there to be defects present in the                    testing to evaluate false-positive
central 10° even when results of                      responses.                                      instruments, ocular that would be placed
                                                                                                      before patient's left eye shows reduced trans¬
Amsler grid testing are normal. Rela-                         MATERIALS AND METHODS                   mission of light, measured by rotation of front
                                                                                                      filter.
  Accepted for publication Nov 8, 1985.                  Twenty subjects from two institutions
  From the Departments of Ophthalmology and           were studied; ten patients with optic nerve
Neurology, Tulane University School of Medi-          disease and ten normal (control) subjects       lenses have been fixed in each of the ocu¬
cine, New Orleans (Dr Wall) and the University        were chosen. Threshold Amsler grid test¬        lars (Fig 2). For each eye, the luminance
of Southern California School of Medicine, Los
Angeles (Dr Sadun).                                   ing was performed by having the subject         was slowly diminished until the subject

   Reprint requests to Department of Neurology        view a white Amsler grid while wearing          could no longer see the grid. Luminance
and Psychiatry, Tulane Medical Center, 1415           the specialized glasses. The device consists    was then increased by changing the
Tulane Ave, New Orleans, LA 70112 (Dr Wall).          of a trial frame in which a pair of polarized   amount of polarization 1° at a time until




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                                                                          Central and Paracentral Scotomas Found by Tests*
                                                                                                                                           Scotomatous
                                                                                                                                                Area,
                                                                                                                                           sq min of Arc
                                                     Patient
                                                      No.        Eye      Diagnosis        TA     SA    TK     TS      32,34     61        TA            SA
                                                                OD      Normal
                                                                OS      Optic   neuritis
                                                                OD      Optic   neuritis                                                 23.400
                                                                OS      Normal
                                                                OD      Optic neuritis                                                    10,400
                                                                OS      Normal
                                                                OD      Optic   neuritis                                                118,300         63,700
                                                                OS      Normal

Fig 3.—Two-meter tangent screen strategy.                       OD      Normal?                                                          14,300
Kinetic targets (arrowheads) were used that                     OS      Optic neuritis                                                   45,500
surveyed isopters at 2.5°, 5°, and 10°. Static                  OD      Pseudotumor
targets (dots) were projected just inside their                           cerebri
associated kinetic target.
                                                                OS      Same                                                             36,400
                                                                OD      Optic   nerve                                                     15,600
                                                                           drusen
the subject was barely able to perceive the
grid. The subject then drew any manifest                        OS      Same                                                               5,200
defects on Amsler recording chart paper.                        OD      Optic   neuritis
Standard white Amsler grid testing was                                  Normal
                                                                OS
performed in the usual fashion, as
described by Amsler.12                                          OD      Optic   neuritis                                                 49,400         10,400
   Each of the subjects examined by means                       OS      Same                                                             31,200
of the standard white and threshold Amsl¬                       OD      Normal
er grid testing also underwent complete
                                                                OS      Optic neuritis                                                  107,900         23,400
neuro-ophthalmologic examination. In ad¬
dition, threshold automated perimetry                 Total             (N 20 eyes)
                                                                           =
                                                                                           23            6                       10     525,200      97,500
(OCTOPUS) was performed with two pro¬                *TA indicates threshold Amsler grid testing; SA, standard Amsler grid testing; TK, tangent screen, kinetic;
grams. The central 30° was surveyed at 6°         TS, tangent screen, static; 32,34, threshold automated (OCTOPUS) perimetry, programs 32 or 34 (central
intervals (programs 32 or 34) and the cen¬        30°); and 61, OCTOPUS perimetry, program 61 (central 6°).
tral 6° was tested at 3° intervals (program
61). Kinetic and static tangent screen test¬
ing was performed at 2 m using targets to
survey  2.5°, 5°, and 10° isopters (see Fig 3
for the algorithm used). The defects found
on threshold Amsler grid testing were not
specifically looked for with the tangent
screen protocol. The results for each
screening method were compared for each
subject.
                  RESULTS
   The Table shows the results of the
testing on the patients. Normal sub¬
jects occasionally reported that they
could not see one or more corners of
the grid when the threshold Amsler
grid testing was done. They did not
report other field defects. Conse¬
quently, we ignored these defects
when they were reported by patients.
Twenty-three scotomas were found by
threshold Amsler grid testing where¬
as five scotomas were found by stan¬
dard Amsler testing.
   Patient 5 is an example of a 31-
year-old man who presented with
optic neuritis in the left eye. Visual
acuity was 20/13 OD and 20/15 OS.
Confrontation visual fields were nor¬
mal and color plate testing results
were normal. There was questionable
disc pallor in the left eye. Results of           Fig 4.—Results of threshold Amsler grid testing, tangent            screen   examination, and threshold
standard white Amsler grid testing in             automated perimetry for patient 5 (optic neuritis).




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                                                                                                  revealed a small right inferior para¬
                                                                                                  central scotoma. The results of the
                                                                                                  OCTOPUS 61 program were normal.
                                                                                                     Patient 6 was a 29-year-old woman
                                                                                                  with pseudotumor cerebri. Snellen
                                                                                                  visual acuity was 20/20 OU and con¬
                                                                                                  frontation visual fields were normal.
                                                                                                  Chronic bilateral papilledema was
                                                                                                  present with no apparent spread of
                                                                                                  edema into the macular region.
                                                                                                  Results of standard Amsler grid test¬
                                                                                                  ing were normal in both eyes. Results
                                                                                                  of the polarized grid testing, 2-m tan¬
                                                                                                  gent screen examination, and OCTO¬
                                                                                                  PUS 61 program were normal in the
                                                                                                  right eye. In the left eye, however,
                                                                                                  there was an inferior nasal paracen¬
                                                                                                  tral scotoma found on all three tests
                                                                                                  (Fig 5).
                                                                                                     The area of each scotoma was esti¬
                                                                                                   mated by calculating the number of
                                                                                                   square minutes of arc of the scotoma.
                                                                                                   The total area of scotomas detected by
                                                                                                  standard testing of the ten patients
                                                                                                   with optic neuropathies was 97,500 sq
                                                                                                   minute. Threshold testing on these
                                                                                                   same ten patients resulted in a total
Fig 5.—Results of three types of central visual field testing for case 6 (pseudotumor cerebri).    scotoma area of 525,200 sq minute of
Paracentral scotoma found in left eye was detected by threshold Amsler grid testing but not by     arc (Table and Fig 6).
standard Amsler grid testing.                                                                         The relative yield of the total num¬
                                                                                                   ber of scotomas by the various tests is
                                                                                                   shown in Fig 6. Threshold Amsler grid
                                                                                                   testing had the highest yield with 23
                                                                                                   scotomas. Static tangent screen exam¬
                                                                                                   ination at 2 m revealed 15 scotomas.
                                                                                                   Kinetic tangent screen examination
                                                                                                   detected six defects. There were 18
                                                                                                   defects found on tangent screen exam¬
                                                                                                   ination combining the static and
                                                                                                   kinetic strategies. Threshold Amsler
                                                                                                   grid testing was therefore superior to
                                                                                                   the tangent screen protocol combining
                                                                                                   static and kinetic examination.
                                                                                                     Threshold automated perimetry
                                                                                                  with the OCTOPUS apparatus was
                                                                                                  performed using programs 32 or 34
                                                                                                  and program 61. Ten scotomas were
                                                                                                  found with program 61 and five
                                                                                                  defects were detected with the 30
                                                                                                  series programs.
                                                                                                     Of the 23 defects found by threshold
                                                                                                  Amsler grid testing, six defects were
                                                                                                  confirmed by both tangent screen
                                                                                                  examination and OCTOPUS perime¬
                                                                                                  try. Seven defects were confirmed
                                                                                                  only by tangent screen examination
                                                                                                  and two areas of loss only by thresh¬
                                                                                                  old automated testing. Of the 23
     Fig 6.—Comparisons of yields of visual field screening methods used in this study.           defects, 15 were confirmed by at least
                                                                                                  one other test. There were three
                                                                                                  defects found on tangent screen exam¬
both eyes were normal. The results of             6°. Findings from the tangent screen            ination and two defects on OCTOPUS
the polarized Amsler grid testing are             examination of this eye were normal.            testing that were not present on
shown in Fig 4. In the asymptomatic               In the left eye a superior temporal             threshold Amsler grid testing.
right   eye,   a   paracentral   scotoma   was    paracentral scotoma was found with                            COMMENT
found using the polarized grid with a             an associated area of depression on
similar scotoma found with the                    2-m tangent screen examination. The               It is well established that various
OCTOPUS 61 program for the central                tangent screen examination also                 sensory visual functions may be dif-



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ferentially affected by disease of the       ly above threshold detection of the             Amsler grid testing. We have also
optic nerve. Patients with optic neuri¬      grid, there was a fivefold increase in          found threshold Amsler grid testing
tis may have normal Snellen visual           yield in total number of scotomas and           of use for detection of relative scoto¬
acuity despite having significant color      a   fivefold increase in total scotoma          mas in diseases of the macula. We
vision defects. Quigley and associates5      area.                                           recommend that this test be added to
have shown that histologie assess¬              Of the 23 defects found on threshold         the clinician's battery of visual exam¬
ment of the optic nerve in glaucoma          Amsler grid testing, 15 were con¬               inations for the detection, character¬
suspects with normal findings from           firmed by either tangent screen exam¬           ization, and monitoring of diseases of
kinetic visual field examination may         ination, threshold automated perime¬            the optic nerve and retina affecting
have a loss of up to 40% of the retinal      try, or both tests. The 2-m tangent             the central 10° of visual field.
ganglion cell axons. Frisen and Fri¬         screen strategy used in this study
                                                                                                                 References
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                                                 In this                                     in cataract patients. Acta Ophthalmol 1981;59:57\x=req-\
it is analogous to mapping the visual                  study of patients with vari¬          63.
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get. This is shown diagrammatically          perceived luminance of the grid great¬          et al: Scanning laaser ophthalmoscopy: Clinical
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