Repeatability of the Glaucoma Hemifield Test in Automated Perimetry

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1 Repeatability of the Glaucoma Hemifield Test i Automated Perimetry Joae Katz,*-\ Harry A. Quigley,^ ad Alfred SommerX Purpose. To examie the cocordace of the Glaucoma Hemifield Test ad other global visual field idexes betwee two cosecutive automated visual field tests. Methods. Normal subjects, subjects with ocular hypertesio, ad subjects with glaucoma had two automated visual field tests o the Humphrey Field Aalyzer. The Glaucoma Hemifield Test results, mea deviatio, ad corrected patter stadard deviatio of the two cosecutive visual field tests were compared. Results. Forty-oe ormal subjects were tested withi ad years of each other. Four hudred seve subjects with ocular hypertesio ad 95 subjects with glaucoma were tested year apart. The proportio of ormal subjects who met a criterio for abormality o two cosecutive tests was.%. The proportio of subjects with glaucoma with ormal results of two tests was 0.5%. The specificity of automated visual field testig was improved from 80.8% to 89.9%, with a modest loss of sesitivity if two rather tha oe abormal test result was required for etry ito a cliical trial erollig patiets with glaucomatous field loss. Similarly, specificity icreased from 8.% to 89.5% if two ormal tests were required for etry ito a ocular hypertesive cliical trial. Amog subjects with more closely spaced tests, the agreemet betwee cosecutive tests was similar for tests spaced versus moths apart. Coclusios. Although mere is cocordace of Glaucoma Hemifield Test results o cosecutive testig, there is eough disagreemet to result i improved specificity from the use of a secod test i a cliical trial settig. Ivest Ophthalmol Vis Sci. 995; 36: J. he defiitio ad diagosis of glaucoma depeds o visual field testig as a method of idetifyig ad quatifyig optic erve damage. Several studies have used automated perimetry to estimate the variability of mea sesitivity ad sesitivity at idividual locatios i the field over relatively short periods of time. " 8 These studies have foud substatial variability, particularly amog subjects with glaucoma ad those at high risk for glaucoma. The magitude of variability is importat for defiig limits beyod which true disease progressio is thought to have occurred. However, researchers ad cliicias ofte eed to make From the * Departmet of Iteratioal Health, Johs Hopkis School of Hygiee ad Public Health; the \Daa Ceter for Prevetive Ophthalmology, Wilmer Istitute, Johs Hopkis School of Medicie; ad the %Dea's Office, Johs Hopkis School of Hygiee ad Public Health, Baltimore, Marylad. Supported by grats EY0930, EY03605, ad RR0060 from the Natioal Istitutes of Health, Bethesda, Marylad. Submitted for publicatio October, 99; revised February 8, 995; accepted March, 995. Proprietary iterest category: C3, Cc. Reprit requests: Joae Klz, Departmet of Iteratioal Health, Johs Hopkis Uiversity, School of Hygiee ad Public Health, Room 555, 65 N. Wolfe Street, Baltimore, MD decisios about whether oe or more visual fields are ormal or abormal to make treatmet decisios or for regulatig etry ito cliical trials of treatmets with the potetial to slow the progressio of field loss. However, the results of two or three tests may differ. This report examies the cocordace of the results of two cosecutive visual field tests usig a commercially available algorithm, the Glaucoma Hemifield Test, that is widely available for classifyig idividual fields as ormal or abormal. 9 " We selected the Glaucoma Hemifield Test because it is readily available o the visual field pritout ad has bee show to have comparable sesitivity ad specificity to other algorithms i the classificatio of visual field tests as ormal or glaucomatous. We also examied the differeces betwee the commercially available global visual field idexes of mea deviatio (MD) ad corrected patter stadard deviatio (CPSD) of two cosecutive visual field tests to provide iformatio o the magitude of fluctuatios i these idexes from oe test to aother. To examie the repeatability of the Glaucoma 658 Ivestigative Ophthalmology & Visual Sciece, July 995, Vol. 36, No. 8 Copyright Associatio for Research i Visio ad Ophthalmology Dowloaded From: o 08/6/08

2 Glaucoma Hemifield Test i Automated Perimetry 659 Hemifield Test for visual field classificatio, we have used data from a logitudial glaucoma study i which the protocol required automated visual field testig at yearly itervals. The advatages of this data set are that subjects without disease were erolled ad that subjects with glaucoma were classified as such o the basis of a reproducible visual field defect o separately performed detailed static ad kietic perimetry. Hece, the specificity ad the sesitivity of repeat automated field testig ca be examied agaist aother defied measure of visual field loss. The disadvatage of this data set is that the sesitivity ad specificity may be a uderestimate of what is attaiable by testig closer i time. I a subset of subjects, we also had obtaied testig at -moth itervals with automated perimetry. Hece, these data provide some ability to examie whether sesitivity ad specificity are reduced by icreasig the time betwee testig. Most repeated visual field data available i the literature have bee used to estimate the variability of threshold values at idividual locatios or areas of the field. " 8 Two ogoig cliical trials of glaucoma treatmet have reported their experieces with classificatio algorithms o repeat testig, oe for purposes of establishig eligibility for etry ito a trial, 3 ad the other for idetifyig whether patiets have demostrated progressio of visual field loss. ' 5 Neither study uses commercially available algorithms, ad they do ot have data o ormal subjects or those with ocular hypertesio who did ot meet eligibility criteria for etry ito the cliical trials. I this article, we examie the cosistecy of the Glaucoma Hemifield Test results i ormal subjects, subjects with ocular hypertesio, ad subjects with glaucoma ad estimate chages i sesitivity ad specificity associated with the use of two rather tha oe visual field i the diagosis of glaucoma or as etry criteria for cliical trials. METHODS The Glaucoma Screeig Study was a logitudial study of early idicators of glaucomatous damage that erolled ad followed subjects from 98 through ' 7 Detailed static ad kietic perimetry was performed by all subjects erolled i the study. The protocol for this perimetry has bee described elsewhere; it icluded testig with at least four test objects with two additioal isopters tested i the asal periphery, ad may static presetatios withi isopter boudaries. ' 6 " 8 O all observed occasios (miimum of two measuremets), ormal subjects were show to have itraocular pressures below mm Hg by applaatio toometry, ormal results of ophthalmic examiatio, ad o reproducible visual field loss o detailed maual perimetry. Subjects with ocular hypertesio had itraocular pressures above mm Hg o at least two occasios ad o reproducible visual field loss o detailed static ad kietic perimetry. Subjects with glaucoma had itraocular pressures above mm Hg o at least two occasios ad reproducible visual field loss o maual static ad kietic perimetry. For glaucoma to be diagosed, the same defect o maual perimetry had to be preset o two fields admiistered withi 3 moths of each other. Visual field loss o maual static ad kietic perimetry was defied as oe or more of the followig: a asal step at least 0 wide ad preset i at least two isopters; a paracetral scotoma at least 0. log uits deep ad 5 wide; cetral or temporal islads of remaiig visio. Subjects were erolled over several years ad uderwet aual examiatio, icludig maual perimetry. I 98, automated perimetry usig the C- 30- program of the Humphrey Field Aalyzer was itroduced ito the study. By 986, all subjects routiely uderwet automated testig aually, ad a subset i each diagostic group uderwet more frequet testig at -moth itervals. The protocol for automated testig has bee described elsewhere. 8 This icluded detailed moitorig of the test by techicias ad remappig of the blid spot if more tha oe fixatio loss occurred. The fial two automated visual fields of all subjects erolled i the Glaucoma Screeig Study were selected for iclusio i this aalysis. The protocol specified that all subjects be followed util the ed of the study. Although loss to follow-up did occur, oly 6.8% refused follow-up, ad oly a small proportio dropped out because of ocular or medical problems. Most dropouts were subjects who moved out of tow, ad some subjects died durig the course of the 0-year study. Forty-oe ormal subjects had two fields tested betwee ad years of each other. Of these, were tested every moths. Four hudred seve subjects with ocular hypertesio ad 95 subjects with glaucoma had at least two automated visual field tests spaced year apart, ad 5 of the subjects with ocular hypertesio ad of those with glaucoma were put o the more frequet testig schedule. Subjects who etered the study as subjects with ocular hypertesio ad were reclassified as havig glaucomatous field loss are icluded as subjects with glaucoma if they had two cosecutive automated fields after coversio to glaucoma. Hece, 68 (7%) of the subjects with glaucoma i this aalysis represet early but well-documeted visual field loss o maual perimetry. The left eye of each subject was selected for aalysis. The age of each subject was calculated at the time of the first of the two visits. The Glaucoma Hemifield Test was used to classify automated visual fields as ormal or abormal. 0 " The Glaucoma Hemifield Test classifies fields as "withi ormal limits," "borderlie," "outside ormal limits," "abormally high sesitivity," "geeral- Dowloaded From: o 08/6/08

3 660 Ivestigative Ophthalmology & Visual Sciece, July 995, Vol. 36, No. 8 ized reductio i sesitivity," ad "borderlie/geeralized reductio i sesitivity." Fields with abormally high sesitivity or borderlie fields were classified as ormal. Fields with geeralized reductio i sesitivity (icludig those with the borderlie desigatio) were classified as abormal. This was doe because the "borderlie" classificatio idicates a small upperlower hemifield differece, whereas the "geeralized reductio i sesitivity" idicates a diffuse loss of sesitivity across the etire field. We wated to iclude "geeralized reductio i sesitivity" i the abormal classificatio, regardless of whether there was a small upper-lower differetial. The percet with abormally high sesitivity raged betwee 0% ad 3%, depedig o whether it was the first or the secod test ad o the diagostic groupig. The percet with geeralized reductio i sesitivity was similar. The MD ad CPSD also were compared betwee the two tests. The MD provides a measure of diffuse field loss ad CPSD of more localized damage. 9 " Agreemet betwee fields was estimated usig the percet agreemet ad the kappa statistic, which adjusts the percet agreemet for chace cocordace. The teets of the Declaratio of Helsiki were followed with regard to study subjects. The study was approved by the Joit Committee o Cliical Ivestigatios of the Johs Hopkis Uiversity School of Medicie, ad iformed coset was obtaied from each subject before erollmet i the study. RESULTS The mea ages of ormal subjects, subjects with ocular hypertesio, ad subjects with glaucoma were 57.0 ± 3.6 years (rage, to 86 years), 59. ± 3.3 years (rage, to 9 years), ad 65. ±.9 years (rage, 3 to 86 years), respectively. The subjects with glaucoma were older tha the subjects with ocular hypertesio or ormal subjects, ad the differece was statistically sigificat (P < 0.05). Eighty-five percet of ormal subjects were give both tests spaced year apart. The remaiig subjects were give tests spaced years apart. All subjects had experiece with maual perimetry before automated testig. The mea umber of automated tests before those used here was 3.5, 3., ad 3.7 for ormal subjects, subjects with ocular hypertesio, ad subjects with glaucoma, respectively. The percet of subjects who had ot performed automated visual field testig previously was 7.3%, 7.3%, ad 3.% for ormal subjects, subjects with ocular hypertesio, ad subjects with glaucoma, respectively. The patiets with glaucoma represeted a rage of severity of visual field loss, although the majority had mild to moderate loss o the first test. The mea MD was -8.0 (: to -6.9), ad the mea CPSD was 6.83 (95% cofidece iterval: 6. to 7.5). Twety-five percet had MD below -3.5, ad 5% had a CPSD greater tha 9.. The mea MD for ormal subjects ad subjects with ocular hypertesio was 0.33 (95% cofidece iterval: -.07 to 0.0) ad -0.8 (95% cofidece iterval:.6 to 0.5), respectively. The mea CPSD for ormal subjects ad subjects with ocular hypertesio was.9 (:.35 to.53) ad.7 (:.98 to.36), respectively. The MD ad CPSD values for ormal subjects ad subjects with ocular hypertesio are well withi what are cosidered ormal values. Amog ormal subjects, the proportio with two abormal automated visual fields was.% (Table ). Based o the clusters of locatios used i the crossmeridioal method, 3 ' oe subject had a defect that was i the same locatio o both visual field tests. The proportio of subjects with glaucoma who had abormal results o two Glaucoma Hemifield Tests was 80.0%. Niety-six percet of these had at least oe defect i the same locatio o both tests. The proportio of subjects with glaucoma with two cosecutive ormal fields was 0.5%. Tests spaced year apart revealed that amog subjects with ocular hypertesio, 69.8% had two ormal automated fields ad 0.% had two abormal automated fields. I each of these subjects with ocular hypertesio, results of detailed maual testig was ormal. The percet agreemet was 8.9% for ormal subjects, 79.9% for subjects with ocular hypertesio, ad 90.5% for subjects with glaucoma. Each correspodig kappa statistic was lower tha the percet agreemet, with subjects with glaucoma havig the highest kappa of 0.63, deotig moderate agreemet betwee tests after adjustmet for chace agreemet. The average differece i MD betwee the first ad secod fields was 0.5 db (P = 0.8) for ormal subjects, -0.5 db (P < 0.00) for subjects with ocular hypertesio, ad.0 db (P < 0.0) for subjects with glaucoma. The differece i CPSD betwee first ad secod fields was 0. for ormal subjects, 0. for subjects with ocular hypertesio, ad 0. for subjects with glaucoma. Noe of the differeces i CPSD were statistically sigificat. The 5th percetile for a chage i MD amog ormal subjects was 3.68 db. Te percet of subjects with glaucoma ad 0% of subjects with ocular hypertesio had chages of this magitude or greater i a -year period. The 5th percetile for a chage i CPSD amog ormal subjects was 3.38 db. The percet of subjects with ocular hypertesio ad subjects with glaucoma with this magitude of chage was 5.% ad 5.%, respectively. This is what would be expected if there were o shift i the distributio of CPSD from oe test to aother. These data suggest that there was some worseig of Dowloaded From: o 08/6/08

4 Glaucoma Hemifield Test i Automated Perimetry 66 TABLE l. Agreemet Betwee Glaucoma Hemifield Test Results ad Global Idex Chages Betwee Two Cosecutive Visual Field Tests Normal ( = ) Ocular Hypertesio ( = 07) Glaucoma ( = 95) First Test Secod Test Normal* Normal Normal Abormal Abormal Normal Abormal Abormal Percet agreemet Kappa Chage i mea deviatio Chage i corrected patter stadard deviatio , , , 0.6 (80.5) (7.3) (9.8) (.) , , to 0.3 (69.8) (.) (9.) (0.) , , , 0.8 (0.5) (5.3) (.) (80.0) * Borderlie fields are classified as ormal. MD (either through a chage i the average MD or a shift i the distributio) but ot i CPSD over a - year period amog subjects with ocular hypertesio or glaucoma. I the subset of subjects who uderwet visual field testig at -moth itervals, there was o evidece to suggest that percet agreemet or kappas were larger for tests spaced moths apart compared to those spaced moths apart (Table ). A statistically sigificat declie i MD was observed for subjects with glaucoma over moths (.6 db declie, P = 0.05), but there was o such declie see with the tests spaced moths apart. No other statistically sigificat differeces betwee test results spaced ad moths apart were observed i this subset of subjects. For purposes of assessig the usefuless of a secod automated visual field test i the etry criteria for cliical trials, we have idetified two types of trials requirig differet eligibility criteria. Oe type of trial might eroll subjects with ocular hypertesio but without visual field defects at etry ito the study. I this case, the trial outcome is the icidece of field loss. I this trial, oly subjects with ocular hypertesio with ormal results of two successive visual field tests withi a specified time widow would be erolled. Aother type of trial might eroll subjects with glaucoma i whom oe of the defiig features of disease is established visual field loss. I such a study, oly those with two successive abormal visual fields would be eligible for erollmet. I this case, progressio of established visual field loss would be the outcome of iterest. Such strategies icrease the specificity of erollmet criteria relative to the use of oly oe test i the determiatio of eligibility. Table 3 gives the sesitivity ad specificity associated with the use of oe versus two tests as criteria for the ocular hypertesio ad glaucoma trials described above, usig cofirmed maual field loss as the "gold stadard." Our study had a total of 50 subjects with ocular hypertesio with ad without cofirmed visual field loss o maual perimetry (95 with field loss ad 07 without loss). If these subjects were potetially eligible for a ocular hypertesive trial, 3 would have had ormal results o the first test. Oly those with ormal results would be retested. Of these, 9 would have had ormal results o a secod test ad would have bee icluded i the trial. The sesitivity of this testig process would be 69.8% because 8 of the 07 subjects with ocular hypertesio without maual field loss would have bee icluded i the trial. The specificity would be 89.5% because 85 of 95 subjects with maual field loss would have bee excluded from the trial. Hece, usig the Glaucoma Hemifield Test, 0% of those with cofirmed field loss o maual perimetry would be erroeously icluded i the trial because they had two ormal automated visual fields. This strategy also would reject 30% of those without cofirmed field loss o maual perimetry because they did ot have two ormal Humphrey visual fields. For trials that eroll subjects with glaucomatous visual field loss o etry ito the trial, the sesitivity would have bee 80.0% ad the specificity 89.9% if two tests were used to determie eligibility. Hece, 0% of subjects without visual field loss o maual perimetry would have bee icluded i the trial because they had two abormal visual fields, ad 0% of subjects with cofirmed field loss o maual perimetry would have bee rejected from the trial because Dowloaded From: o 08/6/08

5 66 Ivestigative Ophthalmology & Visual Sciece, July 995, Vol. 36, No. 8 TABLE. Differeces i Agreemet Betwee Visual Fields ad Moths Apart Normal ( = ) Ocular Hypertesive ( = 5) Glaucoma ( = ) First Test Secod Test moths apart Normal Normal Normal Abormal Abormal Normal Abormal Abormal Percet agreemet Kappa Chage i mea deviatio Chage i corrected patter stadard deviatio moths apart Normal Normal Normal Abormal Abormal Normal Abormal Abormal Percet agreemet Kappa Chage i mea deviatio Chage i corrected patter stadard deviatio , , , 0.6 (78.6) (.3) (7.) (0.0) , , to 0.6 (68.5) (0.0) (7.) (.) , , ,. (.5) (.5) (9.) (8.8) , , , 0. (78.6) (7.) (7.) (7.) , , to 0.8 (6.8) (5.6) (.) (8.5) , , ,.6 (9.) (0.0) (9.) (8.8) they did ot have two cosecutive abormal visual fields. Sevetee percet of ormal subjects, 6% of subjects with ocular hypertesio, ad 8% of subjects with glaucoma had two ureliable fields (false-egative or false-positive rate ^ 33%, or fixatio loss rate s 0%). The sesitivity ad specificity usig oe or two tests was improved oly margially by excludig those with two ureliable test results. For example, the specificity for a glaucoma trial was 80.8% usig oe test ad 89.9% usig both tests. If those with two ureliable fields were excluded, the specificity was 8.9% usig oe test ad 90.7% usig both tests. DISCUSSION To determie that subjects do ot have visual field loss at the time of erollmet i a cliical trial, usig two visual fields for eligibility would improve specificity at the cost of reduced sesitivity. If both fields were used, 0% of subjects with glaucomatous field loss o maual perimetry would be icluded, compared with 6% if oly oe test were used. A similar patter would be see for erollmet of subjects with two abormal visual fields. I a glaucoma trial, 0% of those without cofirmed visual field loss o maual perimetry would be icluded i the trial because they had two cosecutive abormal Humphrey visual fields. It is importat to ote that these fidigs are based o a aalysis of data from patiets with mild to moderate visual field loss. This makes it most useful for examiig the use of the Glaucoma Hemifield Test i the detectio of icidet field loss. These fidigs may ot be true of trials i which patiets should have moderate to severe loss at etry ito the trial. These data also do ot address the questio of progressio of visual field loss amog patiets who already have visual field defects. Data from the Glaucoma Screeig Study have demostrated that visual field defects o automated perimetry preceded those o maual perimetry i subjects with ocular hypertesio. 5 Hece, two abormal automated fields i some of these subjects with ocular hypertesio may be a idicator of early glaucomatous field loss rather tha false-positive results, ad the 89.9% specificity is likely a uderestimate of the true specificity. I both types of trials, the empha- Dowloaded From: o 08/6/08

6 Glaucoma Hemifield Test i Automated Perimetry 663 TABLE 3. Sesitivity ad Specificity of Sigle ad Repeat Visual Field Testig Usig the Glaucoma Hemifield Test to Classify Visual Field Test Results Two Tests Oe Test OH Trial Glaucoma Trial Normal Abormal GFL OH GFL 0 5 OH GFL 76 OH OH Trial Glaucoma Trial Oe Test Tioo Tests Oe Test Two Tests Sesitivity Specificity GFL = patiets with glaucomatous field loss o maual kietic perimetry; OH = patiets with ocular hypertesio with o defects o maual kietic perimetry. sis should be placed o maximizig specificity over sesitivity, except whe sesitivity is so low that the majority of eligible persos would be rejected from etry ito the trial. Although visual field loss o automated perimetry has bee show to precede that detected o maual perimetry for a majority of patiets by at least year, 5 that study did fid that 5% of subjects with cofirmed defects o maual perimetry had a ormal Glaucoma Hemifield Test year before the idetificatio of the defect o maual testig. This is slightly higher tha the percet of patiets with glaucoma (those with cofirmed defects o maual perimetry) i the curret aalysis, who had oe or two abormal Glaucoma Hemifield Test results. Clearly, there are persos whose maual ad automated visual field test results are variable, ad cofirmatio of defects by repeat testig with maual perimetry does ot guaratee that the defect is real or that it will be idetified by automated testig. The agreemet betwee test results spaced ad moths apart was similar, although these data must be iterpreted with some cautio because of the small umbers of subjects with -moth fields i the ormal group ad the group with glaucoma. Whe all groups are combied (90 subjects), the percet agreemet was 89.0% at moths ad 85.6% at moths. Kappas were 0.77 (0.63, 0.90) at moths ad 0.70 (0.55, 0.85) at moths. Hece, the results for fields spaced moths apart are likely to be comparable with tests take closer i time, as is ofte the case whe determiig eligibility for cliical trials. There was o cosistet evidece of chage i the global idexes provided by the Humphrey Statpac over year, except for a statistically sigificat declie of db i MD amog those with glaucoma ad 0.5 db amog subjects with ocular hypertesio. A declie of.6 db i MD also was see over a -year period i subjects with glaucoma who had more frequet testig, but o declie was evidet whe tests were take moths apart i this group. Such diffuse chages may be caused by cataract i this older populatio (average age, 65 years) relative to subjects with ocular hypertesio ad ormal subjects whose average ages were 59 ad 57 years, respectively. These diffuse chages also may be caused by age-related loss of retial euros, but the relative cotributios of these factors caot be idetified usig these data. A larger proportio of subjects with ocular hypertesio tha those with glaucoma had a ormal result followed by a abormal result, though this differece was ot statistically sigificat. Threshold values at idividual locatios ad global idexes have bee foud to have high variability o repeat testig, eve with fields spaced relatively close i time. 6 The log-term fluctuatios of mea deviatio or mea threshold sesitivity amog ormal subjects raged from 0. db to.3 db depedig o the study populatio, type of field test, ad legth of time betwee fields. 36 ' 7 ' 7 " 9 Comparable fluctuatios were larger for subjects with glaucoma. 3 ' 7 The Advaced Glaucoma Itervetio Study foud a slight improvemet i visual fields spaced betwee ad 6 weeks apart based o a visual field score that combied reliability criteria with the extet of clusters of depressed locatios. 3 However, for purposes of classificatio ito ormal ad abormal, we foud a high proportio of fields were similarly classified o two tests spaced betwee ad years apart. I additio, for subjects with defects detected o both tests, the Dowloaded From: o 08/6/08

7 66 Ivestigative Ophthalmology & Visual Sciece, July 995, Vol. 36, No. 8 locatios of the defects were cosistet from the first to the secod test i the majority of subjects based o clusters of locatios defied by the cross-meridioal method of visual field classificatio. 3 ' Nevertheless, the disagreemets betwee fields did lead to improved specificity, suggestig a beefit to repeat testig i cliical trial settigs. KeyWards cliical trial, glaucoma, perimetry, sesitivity, specificity Refereces. Katz J, Sommer A. A logitudial study of the ageadjusted variability of automated visual fields. Arch Ophthalmol. 987; 05: Heijl A, Lidgre A, Lidgre G. Test-retest variability i glaucomatous visual fields. Am J Ophthalmol. 989; 08: Flammer J, Drace SM, Zulauf M. Differetial light threshold: Short- ad log-term fluctuatio i patiets with glaucoma, ormal cotrols ad patiets with suspected glaucoma. Arch Ophthalmol. 98; 0: Heijl A, Lidgre G, Olsso J. Normal variability of static perimetric threshold values across the cetral visual field. Arch Ophthalmol. 987; 05: Werer EB, Petrig B, Krupi T, Bishop KI. Variability of automated visualfieldsi cliically stable glaucoma patiets. Ivest Ophthalmol Vis Sci. 989;30: Bebie H, Fakhauser F, Spahr J. Static perimetry: Accuracy ad fluctuatios. Acta Ophthalmol. 976; 5: Breto RS, Argus WA. Fluctuatios o the Humphrey ad Octopus perimeters. Ivest Ophthalmol Vis Sci. 987; 8: Wilesky JT, Joodeph BC. Variatio i visual field measuremets with a automated perimeter. Am J Ophthalmol. 98; 97: Statpac User's Guide. Sa Leadro, CA: Allerga Humphrey; Asma P, Heijl A. Glaucoma Hemifield Test: Automated visual field evaluatio. Arch Ophthalmol. 99; 0: Asma P, Heijl A. Evaluatio of methods for automated hemifield aalysis i perimetry. Arch Ophthalmol. 99; 0: Katz J, Sommer A, Gaasterlad DE, Aderso DR. Compariso of aalytic algorithms for detectig glaucomatous visual field loss. Arch Ophthalmol. 99; 09: The Advaced Glaucoma Itervetio Study Ivestigators. Advaced Glaucoma Itervetio Study: II: Visual field test scorig ad reliability. Ophthalmology. 99; 0: Schulzer M, Aderso DR, Drace SM. Sesitivity ad specificity of a diagostic test determied by repeated observatios i the absece of a exteral stadard. / Cli Epidemiol. 99;: Schulzer M, The Normal-tesio Glaucoma Study Group. Error i the diagosis of visual field progressio i ormal-tesio glaucoma. Ophthalmology. 99; 0: Sommer A, Quigley HA, Robi AL, Miller NR, Katz J, Arkell S. Evaluatio of erve fiber layer assessmet. Arch Ophthalmol. 98; 0: Sommer A, Katz J, Quigley HA, et al. Cliically detectable erve fiber atrophy precedes the oset of glaucomatous field loss. Arch Ophthalmol. 99; 09: Katz J, Gilbert D, Quigley HA, Sommer A. The effect of test duratio o catch trial resposes i automated perimetry. / Glaucoma. 99; : Statpac User's Guide. Sa Leadro, CA: Allerga Humphrey; Heijl A, Lidgre G, Olsso J. A package for the statistical aalysis of visual fields. Doc Ophthalmol. 987; 9: Heijl A, Lidgre G, Olsso J, Asma P. Visual field iterpretatio with probability maps. Arch Ophthalmol. 988; 07: Fleiss JL. Statistical methods for rates ad proportios. d ed. New York: Joh Wiley; 98: Dugga C, Sommer A, Auer C, Burkhard K. Automated differetial threshold perimetry for detectig glaucomatous visual field loss. Am J Ophthalmol. 985; 00:0-3.. Sommer A, Eger C, Witt K. Screeig for glaucomatous field loss with automated threshold perimetry. Am] Ophthalmol 987; 03: Katz J, Tielsch JM, Quigley HA, Sommer A. Automated perimetry detects visual field loss prior to maual Goldma perimetry. Ophthalmology. 995; 0: Zulauf M, Caprioli J. Fluctuatios i the visual field i glaucoma. Ophthalmol Cli N Am. 99;:67l Heijl A. Computer test logics for automatic perimetry. Acta Ophthalmol. 977; 55: Lewis RA, Johso CA, Kelter JL, et al. Variability of quatitative automated perimetry i ormal observers. Ophthalmology. 986; 93: Youg WO, Stewart WC, Hut H, et al. Static threshold variability i the peripheral visual field i ormal subjects. Graefe's Arch Cli Exp Ophthalmol. 990; 8:5-57. Dowloaded From: o 08/6/08