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Optic Disc Cupping as Clinically Estimated from Photographs
Optic Disc Cupping as Clinically Estimated from Photographs BARBARA E. K. KLEIN, MD, MPH, SCOT E. MOSS, MA, YVONNE L. MAGLI, BS, RONALD KLEIN, MD, MPH, JUDYTH C. JOHNSON, BS, HARRY ROTH, MD
Abstract: Cup-to-disc ratios of 204 right eyes were evaluated by two clinicians and by a trained grader using a standardized grading scheme. Mean measure ments by the grader were greater than estimates made by either clinician. The measurement scheme used by the trained grader has a high degree of reliability and validity. The standard protocol provides an objective assessment of optic disc cupping and could be easily adapted for office use. [Key words: cupping, optic disc, quantitation of optic cup.] Ophthalmology 94:1481-1483, 1987
Cupping of the optic disc is one of the parameters that is evaluated frequently when following persons with glaucoma. Consistency in the quantitative estimation of the degree of cupping is important when the same ob server examines the same patient from one time to the next, and is also critical when more than one physician is examining and treating the same patient. In the course of clinical practice, estimates of cupping from photo graphs are usually based on the past experience of the clinician, without the use of auxiliary measuring de vices. We sought to determine whether a simple tech nique using a measuring device is a better method of estimating optic disc cupping.
MATERIALS AND METHODS Photographs of eyes of persons who had participated in a population-based study ofdiabetic retinopathy were evaluated for this investigation. 1 A sample of photo graphs of optic discs of 204 participants was selected. The mean age of subjects was ?3.6 years and the mean duration of diabetes was 17.2 years; 88 persons had dia betes diagnosed before 30 years of age and \Vere taking ' From the Department of Ophthalmology, University of Wisconsin-Madi son, Madison. Supported by National lnstill-ftes of Health grant EY03843 (BEKK). Reprint requests to Barbara E. K. Klein, MD, MPH, Department of Oph thalmology, University of Wisconsin-Madison, Madison, Wl53792.
insulin, 116 were diagnosed at older ages. Fifteen per sons reported that they had glaucoma or were taking medication for glaucoma. Photographs were taken with a Zeiss fundus camera (Carl Zeiss, Inc, Thornwood, NY) which takes a 30° field. An Allen Separator was used to photograph the stereoscopic pairs. The photographs were centered on the optic disc. Kodachrome ASA 25 film was used. Pho tographs were processed commercially and returned as 2 X 2-inch color slides. The two slides of a pair were placed side by side in plastic mounting sheets. These photographs were first graded by a trained grader ac cording to a specific protocol. The mounted stereo pairs were placed on a Logan slide sorter and examined using a Donaldson Stereoviewer. A plastic template with small circles ranging from 1/32 (0.031) to 1lf4 ( 1.250) inches in diameter in 1/64 (0.015)- to 1/32 (0.031)-inch incre ments was used (Pickett, small circles no. 1203) (Fig 1). The grader placed it under the right side of the pair of photographs. The circle whose diameter coincided with the margins of the structure being measured was found for the longest (usually vertical) and shortest (usually horizontal) disc and cup diameters. If the measurement fell between two circles, the smaller circle was used. The reliability of the grading scheme has appeared in another report. 2 In this scheme, if the view is obscured so that it is not possible to measure the diameter of the disc and/ or cup at any meridian, the.grade is "cannot grade." If it is possible to measure the disc and/or cup in any merid ian the grader does so. If any condition that may influ ence the grading is present, such as vitreous hemorrhage, papillary swelling, new vessels on the disc, optic disc 1481
OPHTHALMOLOGY
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NOVEMBER 1987
•
VOLUME 94
•
NUMBER 11
other and without knowledge of the grader's measure ments. Each was asked to estimate the cup-to-disc ratios without use of the measuring device. Each clinician, masked as to their previous grading, regraded a sample of 19 eyes about 2 months after the initial grading. Clini cian 1 had been involved in developing the grading scheme but performed gradings for this study as a clini cian. The Wisconsin Storage and Retrieval System and SAS were used for processing data files. 4 Analysis of variance was used to compute the significance of differences be tween classes.
RESULTS Fig 1. Template for measurement of optic disc and cup diameters.
drusen, the grader indicates this on the form. Data from these eyes are evaluated separately. There were no such eyes in the group reported on in this article. Photographs of both eyes were graded. Because there was no systematic difference between the eyes, gradings of the right eyes only are reported. Eleven eyes were aphakic; 20 eyes had evidence of either nuclear sclerotic or posterior subcapsular cataract diagnosed according to a standard protocol at the time of the clinical examina tion.3 However, these opacities did not obscure the view ofthe optic disc. In addition to the trained grader, 2 clinicians, both with subspecialty interests in glaucoma, graded the 204 stereoscopic fundus photographic pairs using a Donald son Stereoviewer (George Davco, Holbrook, MA). The clinicians graded the photographs independent of each Table 1. Mean Values of Cup-to-disc Ratios for 204 Right Eyes Observation
Mean Ratio
Clinician 1 Clinician 2 Grader-vertical diameter Grader-horizontal diameter
0.4 0.2 0.5 0.5
P*
<0.001
Range
0-0.9 0-0.7 0.1-0.9 0.1-0.8
* Based on two-way analysis of variance, F = 455.20 with 3 and
609 df.
Table 2. Pearson Correlation Coefficients Between Cup-to-disc Grading Observations
Clinician 2 Clinician 1 Clinician 2 Grader-vertical diameter
1482
0.65
Grader Vertical Diameter
Grader Horizontal Diameter
0.70 0.65
0.72 0.67 0.84
The clinicians assigned values of the cup-to-disc "overall"; that is, they did not specify whether their esti mate was based on a vertical or horizontal axis, whereas the trained grader did. Mean values are given in Table 1. Mean values were different among all three graders. Correlation coefficients for the cup-to-disc ratios be tween the observations are given in Table 2. Gradings for clinician 1 were more highly correlated with both values of the trained grader than were those of clinician 2. The intraobserver agreement between masked grad ings by the clinicians of 19 eyes was computed. For clinician 1, the estimate of cup-to-disc ratio in incre ments of 0.1 was identical in eight cases; in all 19 cases, second gradings were always within 0.1. For clinician 2, the estimates were identical in 11 cases, and in 18 of 19 cases the second grading was identical or within 0.1 of the original estimate.
DISCUSSION Kahn et al 5 have reviewed the interobserver reliability ofestimates ofoptic disc cupping. They found that when 10 expert examiners were asked to judge the optic cup to-disc ratios from pairs of stereoscopic fundus photo graphs, their estimates ranged from 0.2 to 0.8. 5 Palm berg asked 6 glaucoma specialists and fellows to estimate cup-to-disc ratios from stereoscopic photographs of 176 eyes (personal communication, 1983). They had been trained together in order to evaluate photographs in a similar fashion. He found exact agreement among ob servers to be within 0.2 in only 16% of eyes. In the current study, we, too, found significant variation be tween observers. It was of interest to note the relative consistency ofthe ratios for each clinician. When following their own pa tients, estimates may be reasonable for evaluating changes longitudinally; however, when more than one clinician is following patients, the variability in esti mates may result in changes in the therapeutic regimen that may be unwarranted. The measuring system used
KLEIN et al
•
OPTIC DISC CUPPING
by the trained grader, however, has been shown to have a high degree of reliability. 2 To estimate the validity of the system, a trained grader measured cupping in l 0 eyes with known glaucoma and in 20 eyes that were normal. The mean vertical ratio was 0.60 for eyes with glaucoma and 0.39 for the normal eyes; the mean hori zontal ratio was 0.55 for the eyes with glaucoma and 0.32 for the normal eyes. Thus, the system appears to have inherent validity. Computerized measurements of optic disc cupping are currently being developed. Some of these techniques will permit estimation of the volume of optic disc cup ping. There seems to be a definite advantage when fol lowing persons with glaucoma or glaucoma suspects to be able to follow this parameter. High-quality simulta neous stereoscopic photographs are preferred for these measurements. At this time, such systems are either not available or are too costly for routine office use. The data in this article support the notion that a simple stan dard measurement technique that is inexpensive and
can be easily adapted to office practice may be a practi cal way to evaluate optic disc cupping in a clinical set ting.
REFERENCES 1. Klein R, Klein BE, Syrjala SE, et al. Wisconsin Epidemiologic Study of Diabetic Retinopathy: I. Relationship of diabetic retinopathy to man agement of diabetes. Preliminary report. In: Friedman EA, L'Esper ance FA Jr eds. Diabetic Renal-Retinal Syndrome: New York, Grune & Stratton, 1982; 21-40. 2. Klein BEK, Magli YL, Richie KA, et al. Quantitation of optic disc cupping. Ophthalmology 1985; 92:1654-6. 3. Klein BEK, Klein R, Moss SE. Prevalence of cataracts in a popula tion-based study of persons with diabetes mellitus. Ophthalmology 1985; 92:1191-6. 4. Harberg J, Holladay D, Entine S, Gilberts B. WISAR: Wisconsin Stor age and Retrieval System. Madison: Wisconsin Clinical Cancer Center, 1979. 5. Kahn HA, Leibowitz H, Ganley JP, et al. Standardizing diagnostic procedures. Am J Ophthalmol1975; 79:768-75.
1483
Abstract: Cup-to-disc ratios of 204 right eyes were evaluated by two clinicians and by a trained grader using a standardized grading scheme. Mean measure ments by the grader were greater than estimates made by either clinician. The measurement scheme used by the trained grader has a high degree of reliability and validity. The standard protocol provides an objective assessment of optic disc cupping and could be easily adapted for office use. [Key words: cupping, optic disc, quantitation of optic cup.] Ophthalmology 94:1481-1483, 1987
Cupping of the optic disc is one of the parameters that is evaluated frequently when following persons with glaucoma. Consistency in the quantitative estimation of the degree of cupping is important when the same ob server examines the same patient from one time to the next, and is also critical when more than one physician is examining and treating the same patient. In the course of clinical practice, estimates of cupping from photo graphs are usually based on the past experience of the clinician, without the use of auxiliary measuring de vices. We sought to determine whether a simple tech nique using a measuring device is a better method of estimating optic disc cupping.
MATERIALS AND METHODS Photographs of eyes of persons who had participated in a population-based study ofdiabetic retinopathy were evaluated for this investigation. 1 A sample of photo graphs of optic discs of 204 participants was selected. The mean age of subjects was ?3.6 years and the mean duration of diabetes was 17.2 years; 88 persons had dia betes diagnosed before 30 years of age and \Vere taking ' From the Department of Ophthalmology, University of Wisconsin-Madi son, Madison. Supported by National lnstill-ftes of Health grant EY03843 (BEKK). Reprint requests to Barbara E. K. Klein, MD, MPH, Department of Oph thalmology, University of Wisconsin-Madison, Madison, Wl53792.
insulin, 116 were diagnosed at older ages. Fifteen per sons reported that they had glaucoma or were taking medication for glaucoma. Photographs were taken with a Zeiss fundus camera (Carl Zeiss, Inc, Thornwood, NY) which takes a 30° field. An Allen Separator was used to photograph the stereoscopic pairs. The photographs were centered on the optic disc. Kodachrome ASA 25 film was used. Pho tographs were processed commercially and returned as 2 X 2-inch color slides. The two slides of a pair were placed side by side in plastic mounting sheets. These photographs were first graded by a trained grader ac cording to a specific protocol. The mounted stereo pairs were placed on a Logan slide sorter and examined using a Donaldson Stereoviewer. A plastic template with small circles ranging from 1/32 (0.031) to 1lf4 ( 1.250) inches in diameter in 1/64 (0.015)- to 1/32 (0.031)-inch incre ments was used (Pickett, small circles no. 1203) (Fig 1). The grader placed it under the right side of the pair of photographs. The circle whose diameter coincided with the margins of the structure being measured was found for the longest (usually vertical) and shortest (usually horizontal) disc and cup diameters. If the measurement fell between two circles, the smaller circle was used. The reliability of the grading scheme has appeared in another report. 2 In this scheme, if the view is obscured so that it is not possible to measure the diameter of the disc and/ or cup at any meridian, the.grade is "cannot grade." If it is possible to measure the disc and/or cup in any merid ian the grader does so. If any condition that may influ ence the grading is present, such as vitreous hemorrhage, papillary swelling, new vessels on the disc, optic disc 1481
OPHTHALMOLOGY
•
NOVEMBER 1987
•
VOLUME 94
•
NUMBER 11
other and without knowledge of the grader's measure ments. Each was asked to estimate the cup-to-disc ratios without use of the measuring device. Each clinician, masked as to their previous grading, regraded a sample of 19 eyes about 2 months after the initial grading. Clini cian 1 had been involved in developing the grading scheme but performed gradings for this study as a clini cian. The Wisconsin Storage and Retrieval System and SAS were used for processing data files. 4 Analysis of variance was used to compute the significance of differences be tween classes.
RESULTS Fig 1. Template for measurement of optic disc and cup diameters.
drusen, the grader indicates this on the form. Data from these eyes are evaluated separately. There were no such eyes in the group reported on in this article. Photographs of both eyes were graded. Because there was no systematic difference between the eyes, gradings of the right eyes only are reported. Eleven eyes were aphakic; 20 eyes had evidence of either nuclear sclerotic or posterior subcapsular cataract diagnosed according to a standard protocol at the time of the clinical examina tion.3 However, these opacities did not obscure the view ofthe optic disc. In addition to the trained grader, 2 clinicians, both with subspecialty interests in glaucoma, graded the 204 stereoscopic fundus photographic pairs using a Donald son Stereoviewer (George Davco, Holbrook, MA). The clinicians graded the photographs independent of each Table 1. Mean Values of Cup-to-disc Ratios for 204 Right Eyes Observation
Mean Ratio
Clinician 1 Clinician 2 Grader-vertical diameter Grader-horizontal diameter
0.4 0.2 0.5 0.5
P*
<0.001
Range
0-0.9 0-0.7 0.1-0.9 0.1-0.8
* Based on two-way analysis of variance, F = 455.20 with 3 and
609 df.
Table 2. Pearson Correlation Coefficients Between Cup-to-disc Grading Observations
Clinician 2 Clinician 1 Clinician 2 Grader-vertical diameter
1482
0.65
Grader Vertical Diameter
Grader Horizontal Diameter
0.70 0.65
0.72 0.67 0.84
The clinicians assigned values of the cup-to-disc "overall"; that is, they did not specify whether their esti mate was based on a vertical or horizontal axis, whereas the trained grader did. Mean values are given in Table 1. Mean values were different among all three graders. Correlation coefficients for the cup-to-disc ratios be tween the observations are given in Table 2. Gradings for clinician 1 were more highly correlated with both values of the trained grader than were those of clinician 2. The intraobserver agreement between masked grad ings by the clinicians of 19 eyes was computed. For clinician 1, the estimate of cup-to-disc ratio in incre ments of 0.1 was identical in eight cases; in all 19 cases, second gradings were always within 0.1. For clinician 2, the estimates were identical in 11 cases, and in 18 of 19 cases the second grading was identical or within 0.1 of the original estimate.
DISCUSSION Kahn et al 5 have reviewed the interobserver reliability ofestimates ofoptic disc cupping. They found that when 10 expert examiners were asked to judge the optic cup to-disc ratios from pairs of stereoscopic fundus photo graphs, their estimates ranged from 0.2 to 0.8. 5 Palm berg asked 6 glaucoma specialists and fellows to estimate cup-to-disc ratios from stereoscopic photographs of 176 eyes (personal communication, 1983). They had been trained together in order to evaluate photographs in a similar fashion. He found exact agreement among ob servers to be within 0.2 in only 16% of eyes. In the current study, we, too, found significant variation be tween observers. It was of interest to note the relative consistency ofthe ratios for each clinician. When following their own pa tients, estimates may be reasonable for evaluating changes longitudinally; however, when more than one clinician is following patients, the variability in esti mates may result in changes in the therapeutic regimen that may be unwarranted. The measuring system used
KLEIN et al
•
OPTIC DISC CUPPING
by the trained grader, however, has been shown to have a high degree of reliability. 2 To estimate the validity of the system, a trained grader measured cupping in l 0 eyes with known glaucoma and in 20 eyes that were normal. The mean vertical ratio was 0.60 for eyes with glaucoma and 0.39 for the normal eyes; the mean hori zontal ratio was 0.55 for the eyes with glaucoma and 0.32 for the normal eyes. Thus, the system appears to have inherent validity. Computerized measurements of optic disc cupping are currently being developed. Some of these techniques will permit estimation of the volume of optic disc cup ping. There seems to be a definite advantage when fol lowing persons with glaucoma or glaucoma suspects to be able to follow this parameter. High-quality simulta neous stereoscopic photographs are preferred for these measurements. At this time, such systems are either not available or are too costly for routine office use. The data in this article support the notion that a simple stan dard measurement technique that is inexpensive and
can be easily adapted to office practice may be a practi cal way to evaluate optic disc cupping in a clinical set ting.
REFERENCES 1. Klein R, Klein BE, Syrjala SE, et al. Wisconsin Epidemiologic Study of Diabetic Retinopathy: I. Relationship of diabetic retinopathy to man agement of diabetes. Preliminary report. In: Friedman EA, L'Esper ance FA Jr eds. Diabetic Renal-Retinal Syndrome: New York, Grune & Stratton, 1982; 21-40. 2. Klein BEK, Magli YL, Richie KA, et al. Quantitation of optic disc cupping. Ophthalmology 1985; 92:1654-6. 3. Klein BEK, Klein R, Moss SE. Prevalence of cataracts in a popula tion-based study of persons with diabetes mellitus. Ophthalmology 1985; 92:1191-6. 4. Harberg J, Holladay D, Entine S, Gilberts B. WISAR: Wisconsin Stor age and Retrieval System. Madison: Wisconsin Clinical Cancer Center, 1979. 5. Kahn HA, Leibowitz H, Ganley JP, et al. Standardizing diagnostic procedures. Am J Ophthalmol1975; 79:768-75.
1483