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
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.
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.
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.
Boden C, Sample PA, Boehm AG, Vasile C, Akinepalli R, Weinreb RN. The Structure-Function Relationship in Eyes With Glaucomatous Visual Field Loss That Crosses the Horizontal Meridian. Arch Ophthalmol. 2002;120(7):907-912. doi:10.1001/archopht.120.7.907
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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).
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.
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: firstname.lastname@example.org).