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Classification of Visual Field Abnormalities in the Ocular Hypertension Treatment Study

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Classification of Visual Field Abnormalities in the Ocular Hypertension Treatment Study CLINICAL SCIENCES Classification of Visual Field Abnormalities in the Ocular Hypertension Treatment Study John L. Keltner, MD; Chris A. Johnson, PhD; Kimberly E. Cello, BSc; Mary A. Edwards, BSc; Shannan E. Bandermann, MA; Michael A. Kass, MD; Mae O. Gordon, PhD; for the Ocular Hypertension Treatment Study Group Objectives: (1) To develop a classification system for Main Outcome Measures: A 97% interreader hemi- visual field (VF) abnormalities, (2) to determine inter- field agreement. reader and test-retest agreement, and (3) to determine the frequency of various VF defects in the Ocular Hy- Results: The average hemifield classification agree- pertension Treatment Study. ment (between any 2 of 3 readers) for 5018 hemifields was 97% and 88% for the 1266 abnormal VFs that were Methods: Follow-up VFs are performed every 6 months reread (agreement between the first and second and are monitored for abnormality, indicated by a glau- classifications). Glaucomatous patterns of loss (partial coma hemifield test result or a corrected pattern SD arcuate, paracentral, and nasal step defects) composed outside the normal limits. As of January 1, 2002, 1636 the majority of VF defects. patients had 2509 abnormal VFs. Three readers inde- pendently classified each hemifield using a classifica- Conclusion: The Ocular Hypertension Treatment tion system developed at the VF reading center. A Study classification system has high reproducibility and subset (50%) of the abnormal VFs was reread to evalu- provides a possible nomenclature for characterizing VF ate test-retest reader agreement. A mean deviation was defects. calculated separately for the hemifields as an index to the severity of VF loss. Arch Ophthalmol. 2003;121:643-650 HE OCULAR Hypertension confirmed on the next retest.7 Originally, Treatment Study (OHTS) is the OHTS criterion for reproducibility of a randomized clinical trial a visual field abnormality was 2 consecu- to evaluate the safety and tive abnormal visual fields with the ab- efficacy of topical hypoten- normality in the same location and on the Tsive medication in delaying or prevent- same index. However, in June 1997, the ing the onset of primary open-angle glau- abnormality criterion was changed to 3 coma (POAG) in participants with ocular consecutive abnormal fields with the ab- hypertension. The onset of POAG is de- normality in the same location and on the fined as either the development of repro- same index. In this article, we describe a ducible visual field loss (as determined by novel system for classifying the types of From the Visual Field Reading the visual field reading center) and/or re- visual field defects (glaucomatous and non- Center, Department of producible optic nerve damage (as deter- glaucomatous; reproducible and not re- Ophthalmology, University of California–Davis (Dr Keltner mined by the optic disc reading center) at- producible) and report the frequency of and Mss Cello, Edwards, and tributed to POAG. The OHTS Endpoint these defects during follow-up in the OHTS Bandermann); Discoveries in Committee determines POAG and is by their classification. Sight, Devers Eye Institute, masked to the participant’s randomiza- A number of investigators have devel- Portland, Ore (Dr Johnson); tion assignment. A detailed description of oped systems for classifying the severity and and the Department of the OHTS protocol and manual of proce- pattern of glaucomatous visual field loss.8-22 Ophthalmology and Visual dures1-3 as well as the baseline visual field Although these classification systems are Science, Washington University characteristics for the OHTS4 partici- typically based on cross-sectional data, they School of Medicine, St Louis, pants have been previously published. Re- contain the implicit assumption that glau- Mo (Drs Kass and Gordon). cent articles by Kass et al5 and Gordon et comatous visual field loss progresses from For a complete list of authors, 6 refer to the Ocular al have been published regarding the out- small, shallow deficits to large, deep de- Hypertension Treatment come of the OHTS. In addition, we have fects according to a particular sequential Study Web site: http://www reported that 86% of first-occurring ab- pattern. Some of these classification sys- .vrcc.wustl.edu. normal visual fields in the OHTS were not tems have been developed to characterize (REPRINTED) ARCH OPHTHALMOL / VOL 121, MAY 2003 WWW.ARCHOPHTHALMOL.COM 643 Downloaded from www.archophthalmol.com at Washington University - St Louis, on March 26, 2009 ©2003 American Medical Association. All rights reserved. the frequency, location, and shape of initial glaucoma- deviation plots; (2) 3 adjacent points (cluster) beyond normal lim- tous visual field deficits.10-12,14 By using inclusion/ its (PϽ.05) and at least 1 point worse than the .01 probability exclusion criteria that restrict the study sample to indi- level on the total and/or pattern deviation plots (a cluster is de- fined as Ն2 horizontally or vertically contiguous abnormal points viduals with small, shallow visual field deficits, some Ͻ investigations have assumed that these visual field de- with P .05); and (3) 3 or more clustered points worse than the .05 probability level on the total and/or pattern deviation plot. fects represent early glaucomatous visual field loss. For all 3 classification evaluations, the pattern of loss has to be Unlike other studies, the OHTS provides a unique consistent with ocular visual field abnormalities. Thus, for a hemi- opportunity to examine the characteristics of initial glau- field to be classified as normal, it must not meet any of the afore- comatous visual field loss in a longitudinal study. There mentioned criteria for hemifield abnormality. are many reports that use quantitative methods for de- The procedures for hemifield classification are as fol- scribing progressive visual field loss. However, quanti- lows: (1) The superior and inferior hemifields of visual fields tative methods may not capture information on the pat- that meet the OHTS abnormality criteria are evaluated sepa- tern and location of visual field loss that may be more rately, with the superior hemifield being classified first. Hemi- helpful in tracking the progression of glaucoma. field classifications are separated by a slash. If a defect straddles To be eligible for the OHTS, each eye was required the horizontal midline, only a single designation is given and to have 2 sets of normal and reliable visual fields at en- no slash is presented. (2) In general, the pattern on the devia- try in addition to other eye-specific and patient-specific tion plot (“total” or “pattern”) showing the greater number of abnormal points is used to determine the appropriate classifi- eligibility criteria. Follow-up visual fields were then ob- cation for a hemifield abnormality. However, the other devia- tained at 6-month intervals. The purpose of this report tion plot as well as the gray scale are evaluated to confirm the was to characterize visual field defects in OHTS partici- appropriateness of the classification. Abnormal points that are pants observed during follow-up. To accomplish this, it extraneous to the salient pattern are considered less impor- was necessary to develop a classification system and to tant for the determination of the hemifield classification. Thus, use trained readers to perform these classifications with the most predominant pattern is classified. high interreader agreement (agreement between read- Between February 28, 1994, and January 1, 2002, 38328 ers for a given reading) and high test-retest reader follow-up visual fields were evaluated in this report, which in- agreement (agreement between the first and second cluded 2509 that met the OHTS criteria for abnormality (glau- reading). comatous and nonglaucomatous; reproducible and not reproducible). Hemifields were not evaluated for the second- ary definition of abnormality unless the visual field first met METHODS the OHTS criteria for abnormality. Approximately 94% (2345/ 2509) of the abnormal visual fields classified in this report were The procedures employed by the OHTS and the baseline char- reliable, and only 6% (164/2509) were unreliable. acteristics of OHTS participants have been previously de- In 1990, 2 of us (J.L.K. and C.A.J.) began characterizing scribed.2 Briefly, 1636 participants were randomized in the OHTS the types and severity of visual field defects in the Optic Neu- at 22 participating clinical centers. To be eligible for the OHTS, ritits Treatment Trial (ONTT).23,24 As with ONTT, the authors participants were required to have an intraocular pressure be- developed a classification system for the OHTS in 1997 to iden- tween 24 and 32 mm Hg in one eye and between 21 and 32 tify glaucomatous visual field abnormalities in patients with ocu- mm Hg in the fellow eye. Visual fields were performed using lar hypertension. The categories included patterns of visual field Humphrey (Carl Zeiss Meditech, Dublin, Calif) 30-2 full- loss that were characteristic of glaucoma, patterns that were threshold, white-on-white, static perimetry. To meet visual field characteristic of other ocular and neurologic diseases, and pat- eligibility criteria, individuals completed a minimum of 2 and terns that were associated with testing artifacts. In the devel- a maximum of 3 visual field tests. Two of the 3 tests had to meet opmental stages of the classification system, each of the read- reliability criteria of less than 33% false positives, less than 33% ers evaluated a subset of 129 abnormal visual fields. These fields false negatives, and less than 33% fixation losses. Two of the 3 were subsequently included in the final set of the 2509 abnor- visual fields had to be judged normal by the visual field read- mal fields. Each reader’s classification from this training set was ing center, requiring a STATPAC II (Carl Zeiss Meditech) global compared and discussed to refine and standardize the criteria indices for corrected pattern SD (CPSD) within the 95% age- for developing the 17 mutually exclusive categories presented specific population norm, and a glaucoma hemifield test re- in Table 1.
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