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The Structure-Function Relationship in Eyes With Glaucomatous Visual Field Loss That Crosses the Horizontal Meridian
Catherine Boden, PhD;
Pamela A. Sample, PhD;
Andreas G. Boehm, MD;
Christiana Vasile, MD;
Radha Akinepalli, BS;
Robert N. Weinreb, MD
Arch Ophthalmol. 2002;120:907-912.
ABSTRACT
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Objective To evaluate the relationship between visual field loss and glaucomatous
optic discs in eyes in which field loss spreads across the horizontal meridian.
Subjects and Methods Ninety-six patients with glaucoma (9 advanced, 60 moderate, and 27 early)
with 2 successive abnormal fields were included. Standard achromatic automated
perimetry defects were identified with a nerve fiber bundle map to identify
abnormal sectors. Crossover was present if the superior and inferior sectors
at the horizontal meridian (nasal, central, or temporal) were both abnormal.
Optic disc damage was assessed by masked grading of simultaneous stereophotographs.
Results Only 30% (29) of glaucomatous eyes showed crossover, and only 2 of those
eyes had early loss. The most frequent pattern of visual field loss (41% of
eyes) was single hemifield damage with defects in contiguous sectors. Regardless
of the pattern or severity of visual loss, most eyes (66 [69%] of 96) had
both superior and inferior optic disc damage.
Conclusions Early glaucomatous visual field loss rarely crosses the horizontal meridian,
but defects in both hemifields at the horizontal meridian are more common
in more advanced field loss. In 26 (90%) of 29 eyes with crossover, it could
be explained by changes at the optic nerve head.
INTRODUCTION
IT IS COMMONLY THOUGHT that visual loss does not progress across the
horizontal meridian until the later stages of glaucoma.1
That is, visual loss is believed to spread within a hemifield until the disease
is more advanced. To our knowledge, no studies employing automated static
threshold tests have explicitly addressed how often visual field loss spreads
across the horizontal meridian in patients with glaucoma.
Visual field loss correlates with the appearance of the optic disc and
retinal nerve fiber layer,2-9
and functional defects are topographically related to these structural changes.10-15
Simultaneous stereophotographs are commonly used in the clinical setting to
evaluate optic disc integrity and monitor progression of glaucomatous optic
neuropathy. Optic disc damage identified by stereophotographs correlates with
functional loss,2, 4 and field
defects have been predicted based on optic disc photographs.5
The purpose of the present study was to determine the frequency of visual
field defects that cross at the horizontal meridian on standard automated
perimetry and to relate this pattern to optic disc abnormalities on stereophotographs
in eyes with early, moderate, and advanced glaucoma.
SUBJECTS AND METHODS
SUBJECTS
We performed a retrospective analysis of visual field data from a prospective
longitudinal study of patients with primary open-angle glaucoma at the University
of California, San Diego, Glaucoma Center. All patients gave informed consent
to participate in this research, and the study was approved by the University
of California, San Diego, Human Subjects Committee and conformed to the Declaration
of Helsinki.
Each subject underwent a complete ophthalmological examination, which
included a review of the relevant medical history, best-corrected visual acuity,
slitlamp biomicroscopy (including gonioscopy), applanation tonometry, dilated
funduscopy, and fundus photography. Patients had to have a best-corrected
visual acuity of 20/40 or better, a spherical refraction within ±5.0
diopters (D), and a cylinder within ±3.0 D. Patients were excluded
if they had a history of intraocular surgery (except uncomplicated cataract
surgery), other intraocular diseases, other diseases affecting the visual
field (pituitary lesions, demyelinating diseases, acquired immunodeficiency
syndrome, or diabetes mellitus), a "generalized depression" or "sensitivity
too high" result on the Glaucoma Hemifield Test, or problems other than glaucoma
affecting color vision.
Standard automated perimetry with a Goldmann size III (0.43°) stimulus
on a 31.5-apostilb background was performed. The Humphrey 24-2 program (Humphrey-Zeiss,
Dublin, Calif) was used for perimetric testing. Of the 256 patients with glaucoma,
96 eyes from 96 patients had 2 successive abnormal and reliable standard visual
fields and met the inclusion and exclusion criteria outlined above. Visual
fields were reliable if they had false-positive, false-negative, and fixation
losses of 25% or less. A visual field was designated abnormal if the corrected-pattern
SD was outside 95% or the Glaucoma Hemifield Test was outside 99.5% of age-specific
norms. Except when otherwise stated, the results are based on the first 2
abnormal fields to show spread of visual loss across the horizontal meridian.
When crossover was not present, we used the first 2 abnormal visual fields
available from each patient. The mean ± SD number of years between
the 2 visual field tests was 0.89 ± 0.77. We determined the severity
of visual loss on the first of the 2 fields included in the study for each
patient. There were 27 early, 60 moderate, and 9 advanced cases (Table 1). Age ranged from 29 to 88 years
with a mean ± SD of 63.7 ± 12.0 years.
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Table 1. Criteria Defining Early, Moderate, and Advanced Visual Field
Defects
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PROCEDURE
For each visual field, we identified which field sectors were abnormal
on a perimetric nerve fiber bundle map described by Weber et al13-14
(Figure 1). This map was derived
empirically from the analysis of a large number of patients with localized
nerve fiber layer and wedge defects. Visual field locations corresponding
to the same retinal nerve fiber bundle are grouped into sectors. The map was
slightly modified from the original by combining adjacent sectors containing
single visual field locations (labeled sectors 1/2, 9/10, 12/13, and 20/21).
This reduced the overemphasis on sectors with only 1 field location. Sectors
with only 2 visual field locations (ie, sectors 20/21, 1/2, 3, 19, and 18)
had to have at least 1 of the visual field locations at a pattern deviation
of less than 5% for the sector to be abnormal. For the remaining sectors,
2 or more visual field locations within the sector with a pattern deviation
of less than 5% were necessary for the sector to meet the criteria for abnormality.
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Figure 1. Perimetric nerve fiber bundle
map. Each bundle is demarcated by solid lines on a representation of the visual
field. Sectors 1 and 2, 9 and 10, 12 and 13, and 20 and 21 were combined for
this study. Each visual field location for the 24-2 program (Humphrey-Zeiss,
Dublin, Calif) has been given a number to denote which sector it belongs to.
Adapted with permission from Weber et al.13
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Characterizing the Pattern of Visual Loss
After mapping the visual field defects, we determined whether visual
loss had spread across the horizontal meridian (hereafter referred to as crossover).
Crossover was present if (1) both the superior and inferior sectors adjacent
to the horizontal meridian were abnormal in the nasal (sectors 8 and 14),
central (sectors 9/10 and 12/13), and/or temporal regions (sectors 20/21 and
1/2) (Figure 2) and (2) crossover
was repeated in the same region on both fields. We also determined whether
additional areas of field defects were in adjacent perimetric nerve fiber
bundles or spatially separated regions of the field. We identified 5 patterns
of visual loss (Figure 3): A, crossover
with contiguous defects; B, no crossover with contiguous defects; C, crossover
with noncontiguous defects; D, no crossover with noncontiguous defects; and
E, no confirmed defects.
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Figure 2. A schematic of crossover [ie,
visual loss had spread across the horizontal median] in the nasal (A), central
(B), and temporal (C) regions without any additional defects.
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Figure 3. Examples of visual field loss
from patients with glaucoma that illustrate 4 patterns of visual loss. The
pattern deviation plots (left) from the Humphrey Statpac 2 (Humphrey-Zeiss,
Dublin, Calif) analysis. Squares indicate test locations outside normal limits.
Visual field sectors are designated as abnormal (right) based on the pattern
deviation plot. A, The patient has crossover [ie, if visual loss had spread
across the horizontal median] in the nasal region, and all the defective sectors
are contiguous. B, The patient does not show crossover, and all the defects
are contiguous. C, The patient has crossover in the nasal region with additional
noncontiguous defects. D, The patient does not show crossover, and defects
are noncontiguous. Noncontiguous defects may occur in opposite hemifields
(as in section D) or in the same hemifield. Shaded areas indicate visual field
loss.
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Optic Disc Stereoscopic Photographs
Simultaneous stereoscopic photographs (Topcon Simultaneous Stereo Camera
TRC SS; Topcon America Corp, Paramus, NJ) were obtained for all patients and
reviewed with a simultaneous stereoscopic viewer. Masked simultaneous stereophotographs
closest to the visual field date were examined independently for excavation,
focal, and diffuse rim-thinning and nerve fiber layer defects by at least
2 experienced reviewers (C.V. and A.G.B.). In cases of disagreement, consensus
was reached by 2 graders. The superior and/or inferior optic discs were designated
abnormal if excavation, rim-thinning, and/or nerve fiber layer defects were
present in that hemifield. The decisions of the senior grader were employed
in cases of disagreement about the location of the abnormality. This was necessary
in only 6 of 96 eyes. The mean ± SD number of years from the date of
the stereophotographs to the date of the field used was 0.38 ± 0.51
years.
RESULTS
Overall, visual field defects spread across the horizontal meridian
in only 29 (30%) of 96 eyes (Figure 4).
Crossover was rare in eyes with early loss (2 [7%] of 27) and relatively more
common in eyes with moderate (21[35%] of 60) and advanced (6 [67%] of 9) visual
loss. When visual loss did spread across the horizontal meridian, 20 (69%)
of 29 eyes had crossover in the nasal region and 18 (62%) of these eyes had
contiguous defects (Table 2).
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Figure 4. The subdivision of patients according
to whether they had crossover [ie, if visual loss had spread across the horizontal
median] (crossover or no crossover) and whether they had contiguous visual
defects (contiguous or noncontiguous) or no confirmed defects. The number
of patients with early, moderate, and advanced visual field loss is provided
for each of the 5 resulting categories.
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Table 2. Region of Crossover in 29 Eyes With Confirmed Crossover*
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The most common pattern of loss among the 96 eyes was a pattern of defects
in contiguous sectors that did not cross the horizontal meridian (39 eyes;
41%) (Figure 3B). Each of the 4
remaining patterns was represented by a small number of patients. There were
12 eyes (13%) in which no sectors were confirmed abnormal, although the fields
were abnormal by the Glaucoma Hemifield Test and/or corrected-pattern SD.
Sixteen eyes (17%) had no crossover with noncontiguous defects (Figure 3D), 11 eyes (11%) had crossover with noncontiguous defects
(Figure 3C), and only 18 eyes (19%)
had crossover with defects in contiguous sectors (Figure 3A).
A pattern of crossover with contiguous defects might be expected to
be associated with both superior and inferior optic disc changes. Analysis
of the stereophotographs revealed rim thinning and/or excavation in both superior
and inferior segments of the optic disc in all but 2 (11%) of these 18 eyes
(Table 3). Of those 2 eyes, 1
had a normal stereophotograph, and 1 had primarily an inferior field defect
and inferior rim thinning of the optic disc. The eye with a primarily inferior
field defect was also the only case of early visual loss in this group. The
majority of eyes (14 [78%]) had moderate loss, whereas 3 eyes (17%) had advanced
loss.
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Table 3. Relationship Between Presence or Absence of Contiguous Defects
and Structural Damage in 29 Eyes With Crossover*
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Similarly, a pattern of crossover with noncontiguous defects (pattern
C) might be expected to be associated with damage to both superior and inferior
optic discs. Damage was present in both the upper and lower optic discs of
these eyes (Table 3). Three of
the remaining eyes had normal stereophotographs. One eye had defects in both
superior and inferior visual fields but only inferior optic disc damage. One
eye showed primarily an inferior visual field defect but superior optic disc
damage. This patient had early visual loss. Most of these eyes (7 [64%] of
11) had moderate visual loss.
Twelve (13%) of the 96 eyes had normal stereophotographs. Eyes with
a pattern of noncontiguous defects with crossover (Figure 3C) had a higher frequency of normal stereophotographs than
the other patterns (27% of eyes) (Table
3 and Table 4).
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Table 4. Relationship Between Presence or Absence of Contiguous Defects
and Structural Damage in 55 Eyes Without Crossover*
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COMMENT
It is rare for defects to spread across the horizontal meridian in early
glaucoma (only 2 [7%] of 27 eyes had early visual loss). Of the 2 eyes with
early visual loss and crossover, 1 eye had a primarily inferior field defect
with inferior optic disc damage, and 1 eye had a primarily inferior field
defect with superior optic disc damage. Even in the group as a whole, crossover
was relatively uncommon in the patients with glaucoma (30% of eyes). When
visual loss did spread across the horizontal meridian, crossover typically
occurred in the nasal region and was associated with damage to both superior
and inferior optic discs, and defects were often also in contiguous perimetric
nerve fiber bundles. It should be noted that we specifically chose visual
fields that showed crossover if this pattern was evident on any of the patient's
visual fields. Our results will reflect this selection process.
The most common pattern of visual loss showed defects in contiguous
sectors that did not cross at the horizontal meridian. Defects in field locations
testing arcuate and nasal nerve fiber bundles were most frequent in these
eyes, reflecting the classic glaucomatous arcuate, paracentral, and nasal
step defects.16-20
As previously reported, defects near the horizontal meridian in the temporal
visual field were relatively uncommon, and field loss was more common in the
upper than the lower hemifield for eyes with this pattern of loss.1, 20 Damage to the nasal side of the disc
(temporal visual field) might be more likely to affect vision above and below
the horizontal meridian because of the configuration of the nerve fiber bundles.
Temporal visual field defects were relatively uncommon, and the 24-2 test
pattern only tests 4 locations in the temporal field, so there were fewer
opportunities for observing crossover. With the other patterns of loss, superior
and inferior field defects were equally frequent.
Previous studies have noted that optic disc abnormalities precede visual
field loss.21-22 Because all eyes
in this study had confirmed visual field loss, we cannot address this issue
directly. However, in the present study, 13% of eyes with confirmed abnormal
visual fields had normal stereophotographs. Glaucomatous changes may be apparent
on visual fields prior to structural changes in some patients. For instance,
Emdadi et al23 noted that 7 (18%) of 39 eyes
with early focal visual field loss had no detectable optic nerve damage by
confocal scanning laser ophthalmoscopy.
It has been proposed that progressive field loss may sometimes be due
to additional retinal ganglion cell death by secondary factors resulting from
the death of neighboring ganglion cells,24-29
although not everyone agrees.30 In this case,
one might expect early visual field loss near the horizontal meridian to more
readily progress to the adjacent hemifield. Crossover might then be associated
with damage only to the superior or inferior optic disc. It should be noted
that atrophy at the optic disc following secondary degeneration of retinal
ganglion cells is difficult to distinguish from primary loss at the optic
disc. Only 1 patient showed this pattern of loss, and the patient had early
visual loss. There was, therefore, little evidence in the present study of
the effects of retinal secondary neurodegeneration on the standard automated
perimetry fields. With current visual field techniques, secondary degeneration
might be hard to detect against the background of primary loss. A visual function–specific
test, such as short-wavelength automated perimetry or frequency-doubling technology,
which is more sensitive than standard automated perimetry,31
may detect visual loss due to retinal secondary neurodegeneration. However,
10% of stereophotographs from eyes with crossover were classified as normal.
The sensitivity and specificity of observers identifying early glaucomatous
optic disc changes from stereoscopic photographs has been estimated at 71%
to 78% and 60% to 95%, respectively.32-35
Additional cases may be detected with a more sensitive measure of optic disc
damage. For instance, diffuse optic disc changes may be difficult to detect
with stereophotographs. Another technique, such as confocal scanning laser
ophthalmoscopy, may more objectively quantify optic nerve damage.
In conclusion, visual field loss that spreads across the horizontal
meridian is rare in early glaucoma and occurs with greater frequency in more
advanced glaucoma, although it is still not very common. When visual loss
does cross over at the horizontal meridian, it is typically accompanied by
both upper and lower optic disc damage.
AUTHOR INFORMATION
Submitted for publication September 26, 2001; final revision received
January 14, 2002; accepted March 20, 2002.
This study was supported by grant EY08208 from the National Institutes
of Health, Bethesda, Md (Dr Sample).
Corresponding author and reprints: Pamela A. Sample, PhD, Department
of Ophthalmology, University of California, San Diego, 9500 Gilman Dr, La
Jolla, CA 92093-0946 (e-mail: psample{at}eyecenter.ucsd.edu).
From the Glaucoma Center and the Visual Function Laboratory, Department
of Ophthalmology, University of California, San Diego (Drs Boden, Sample,
Boehm, Vasile, and Weinreb and Ms Akinepalli), and the Department of Ophthalmology,
University of Dresden, Dresden, Germany (Dr Boehm).
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