Methods in Cataract Epidemiology Studies Sasaki K, Hockwin O (eds): Distribution of Cataracts in the Population and Influencing Factors. Dei Ophthalmol. Basel, Karger, 1991, vol 21, pp 97-102
Cataract Classification Systems in Epidemiological Studies Kazuyuki Sasaki Department of Ophthalmology, Kanazawa Medical University, Uchinada, Ishikawa, Japan
Introduction
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Because longevity has been prolonged in advanced and developed countries, senile cataract as an ocular disease has occupied a more important place in the clinical field of ophthalmology. Even so, cataract epidemiology studies have still been few compared with other investigations into cataracts. However, recently the significance of this type of research has gradually been recognized worldwide. The author has become aware of this trend during the last three international cataract epidemiology meetings: first the Noto/Japan meeting (1986), second the Bonn meeting (1988), and third the Singapore meeting (1990). Both the national and international co-operative studies of cataract epidemiology have also increased recently. It is essential to apply a cataract classification system in any type of cataract epidemiological study. If a standardized classification system is used worldwide, it is then possible for researchers to compare their data with others. In the past few years, classification and grading systems have been proposed by several researchers, but at present a unified system has not been established. However, the author believes that it will not be long before it is. In this article, the cataract classification systems and gradings currently applied and problems which might be encountered at the time of their application are briefly discussed.
Sasaki
98
Cataract Classification Systems Currently Proposed
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Since the proposal of the CCRG cataract classification system by Chylack [ 1 ], several types of classification systems which are shown below have been proposed. (í) The Lens Opacities Classification System (LOCS): LOCS I was first proposed by Chylack et al. [2]. In this system, cataractous opacities were classified into nuclear, posterior subcapsular and cortical. The grading of cataractous states was in two steps. Grade I is the early stage and grade II shows prominent opacification. To assist in assessing the grade, standard photos have been prepared. LOCS II was developed based on the LOCS I [3]. The cataractous grading system and coloration were classified more precisely than in LOCS I. This system also adopts standard photographs as a guide for judgment. (íi) The Oxford system: The Oxford system is a very precise classification system for clinical cataract research. Cataract types are classified into nuclear, subcapsular and cortical opacities. Grading of opacification and coloration adopts a 6-step system including grade 0 [4]. This is considered in combination with photodocumentation. For application in epidemiological studies, some simplification may be necessary. (iíí) The Bonn system: This has been proposed by Hockwin et al. [5]. Each cataract type is classified as a Scheimpflug slit image. Types of opacification are not classified as cortical, subcapsular and nuclear, but classified by their opacification type and location: (1) nuclear cataracts; (2) opacities of the lens nucleus and the posterior subcapsular layer; (3) changes of the nucleus and the posterior as well as anterior subcapsular layers; (4) nuclear cataract and changes and the anterior cortex; (5a) waterclefts and spokes; (5b) wedge-shaped cataracts; (5c) coronary cataract; (5d) opacities of the deeper anterior cortex; (5e) combined anterior and posterior changes; (6) posterior subcapsular cataract; (7) opacities of the posterior and anterior subcapsular layer, and (8) mature cataracts. This classification system has been established on the basis of his many years' experience as a lens biochemist. This system would be useful for researchers who have an interest in the basic research of human cataracts. (ív) The Wilmer system: This system was proposed for nuclear cataract classification only. In this classification, consideration of visual acuity is combined with morphological changes [6]. Five-step grading (including grade 0) has been adopted. (v) The Japanese Cooperative Cataract Epidemiology Study Group (CCESG) system: This classification system has been established by the
Cataract Classification Systems
99
cataract study group in Japan [7]. Lens opacifications are classified into nuclear, subcapsular and cortical. A three-step grading system with standard photos has been adopted and a four-step grading is applied to lens coloration classification. A special recording chart was also provided.
Application of the Established Classification Systems and Problems Encountered Although there are still some differences between the above-mentioned systems, a common concept is noticed. Opacification types were divided into cortical and nuclear types or cortical, subcapsular and nuclear. Based on the author's experience, researchers who are familiar with using the Jap-CCESG system can apply the LOCS II without difficulty. Ideally, cataract epidemiological studies should adopt the same classification system in their studies. However, if the studies are performed applying a photodocumentation system, even if the classification system is different, the results obtained will be comparable with each other [8]. In several classification systems, recording charts have also been prepared. It is possible for each chart to have its own characteristic recording system depending on the purpose of the studies. Standard photos to assist in grading for diagnosis are useful. However, it is essential to prepare high quality standard pictures. A retroillumination image with less cross-shadows and slit images, taken with a Scheimpflug camera, would be preferable. At present, it is quite difficult to show the color gradings through standard pictures, especially a color grading system with a precise classification. In the Jap-CCESG system, we have not yet prepared standard lens color pictures.
Inter-Observer Agreement
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Usually, cataract examination performed for a survey is carried out by not only one examiner but by several or by a multicenter system. As described previously, the classification systems proposed today are not complicated. The inter-observer agreement ratio seems to be high. If the examinations in cataract epidemiology surveys are performed by ophthalmologists who have had sufficient experience with this type of study, they will have satisfactory results, but if the observer has not been trained before the
Sasaki
100
Table L Inter-observer agreement test (first trial) Type of cataract
κ value
% agreement
Cortical cataract Nuclear cataract Subcapsular cataract Lens coloration
0.58 0.22 0.58 0.32
68.8 37.5 83.3 56.3
Table 2. Inter-observer agreement test (second trial) Type of cataract
κ value
% agreement
Cortical cataract Nuclear cataract Subcapsular cataract Lens coloration
0.50 0.42 0.45 0.38
70.1 89.1 93.4 87.6
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survey, the results may be unsatisfactory. The most problematic area of assessment may be in an early stage nuclear cataract diagnosis, the grading of nuclear cataracts or that of nuclear coloration. Inter-observer agreement tests performed in the author's institution: a test was performed by two ophthalmologists who belong to the author's department. One was a highly trained specialist who has been involved in the development of our classification system. He can judge cataract grades without seeing standard photos. The other was a resident to whom we explained our classification system and had shown him standard pictures a few days before the examinations. Eighty subjects over 40 years old were used for the tests and the ophthalmological examination included visual acuity measurement, tonometry, crystalline lens observation with dilated pupils, fundus examination and photodocumentation of the crystalline lens, all of which were performed in 1 day. This meant that the assessment of the cataract type and its grading were performed within a short time. Compared with the inter-observer agreement for cortical and subcapsular cataracts, the agreement on nuclear cataracts was unsatisfactory (table 1). After the inexperienced ophthalmologist received training in
Cataract Classification Systems
101
utilizing photographed images, a second trial of the same test was performed by the same two ophthalmologists. The total number of subjects in the second test was 103. The results obtained showed an increase of % agreement and κ value (table 2). From this small trial the author considers that, in order to achieve reliable cataract epidemiology studies, several training sessions are necessary for the examiners before using an unfamiliar cataract classification system.
Necessity for Pupil Dilation in Cataract Examination In cataract epidemiology studies, it is not always possible to judge the type of cataract and its grading on a dilated pupil. However, no one will deny that data obtained from a slit examination with a dilated pupil and that obtained without pupil dilation are not comparable. In cases where the classification system includes the early stage of cataract in its grading, it is especially important that the examination should be performed on a dilated pupil. Information concerning the early stage of cataract obtained from epidemiological studies from the surveys in advanced countries is especially needed. A slitlamp used in the survey should function well. To judge lens coloration precisely, a slitlamp of high quality is essential.
Visual Acuity and Cataract Gradings
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Visual acuity is one of the important findings in the evaluation of cataract progression. However, for several reasons, it does not always reflect cataract progression. Because of this, the majority of cataract grading systems being proposed today do not consider deterioration of visual acuity in the assessment procedure of grading cataracts. However, the visual acuity measurement is still important for epidemiological surveys performed in developing countries. Regarding the correlation between visual acuity and cataract types, it can be said that visual acuity in the patients with cortical opacification located on the visual axis has a high correlation with deterioration of visual acuity. Clinically, deterioration of visual acuity is often experienced in cases with a small area of subcapsular opacity located in the pupillary zone. However, in
Sasaki
102
nuclear cataracts, ít should be remembered that the scattering of light intensity observed in the nuclear part is not always parallel to the deterioration of visual acuity in cases with mild to moderately advanced nuclear cataracts. According to the author's data, patients with a nuclear cataract of grade III (Jap-CCESG classification) or further advanced, often show a deterioration of visual acuity, but the range of visual acuity in grade I and grade II nuclear cataracts varies. Time is still needed before a standardized cataract classification system in cataract epidemiology studies can be introduced and, as has been described, there are no marked differences between the concepts in the systems proposed today: the simple classification of cataract type, a three-to-six step grading system, providing a standard photo to assist judgment and utilization of information from both slit and retroillumination findings. Within a few years, the differences between them will become less and less significant.
References 1 2
Chylack LT: Classification of human cataracts. Arch Ophthalmol 1978;96:888-892. Chylack LT, Leske MC, Sperduto R, et al: Lens opacities classification system. Arch Ophthalmol 1988;106:330-334. 3 Chylack LT, Leske MC, McCarthy D, et al: Lens opacities classification system II (LOCS II). Arch Ophthalmol 1989;107:991-997. 4 Sparrow JM, Bron AJ, Brown NAP, et al: The Oxford Clinical classification and grading system. Int Ophthalmol 1986;9:207-225. 5 Hockwin O, Eckerskorn U, Schmidtmann W, et al: Epidemiological study of the association between lens cataract and case history, blood composition and enzymes involved in lens carbohydrate metabolism. Lens Res 1984;2:23-42. 6 West SK, Rosenthal F, Newland HS, et al: Use of photographic techniques to grade nuclear cataracts. Invest Ophthalmol Sci 1988;29:73-77. 7 Sasaki K, Shibata T, Obazawa H, et al: Classification system for cataracts. Ophthalmic Res 1990;22(suppl):46-50. 8 Sasaki K, Karino K, Kojima M, et al: Cataract survey in the local area using photographic documentation. Dei Ophthalmol. Basel, Karger, 1987, 1/01 15, pp 28-36.
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
Kazuyuki Sasaki, Department of Ophthalmology, Kanazawa Medical University, Uchinada, Ishikawα 920-02 (Japan)
Cataract Classification Systems in Epidemiological Studies Kazuyuki Sasaki Department of Ophthalmology, Kanazawa Medical University, Uchinada, Ishikawa, Japan
Introduction
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
Because longevity has been prolonged in advanced and developed countries, senile cataract as an ocular disease has occupied a more important place in the clinical field of ophthalmology. Even so, cataract epidemiology studies have still been few compared with other investigations into cataracts. However, recently the significance of this type of research has gradually been recognized worldwide. The author has become aware of this trend during the last three international cataract epidemiology meetings: first the Noto/Japan meeting (1986), second the Bonn meeting (1988), and third the Singapore meeting (1990). Both the national and international co-operative studies of cataract epidemiology have also increased recently. It is essential to apply a cataract classification system in any type of cataract epidemiological study. If a standardized classification system is used worldwide, it is then possible for researchers to compare their data with others. In the past few years, classification and grading systems have been proposed by several researchers, but at present a unified system has not been established. However, the author believes that it will not be long before it is. In this article, the cataract classification systems and gradings currently applied and problems which might be encountered at the time of their application are briefly discussed.
Sasaki
98
Cataract Classification Systems Currently Proposed
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
Since the proposal of the CCRG cataract classification system by Chylack [ 1 ], several types of classification systems which are shown below have been proposed. (í) The Lens Opacities Classification System (LOCS): LOCS I was first proposed by Chylack et al. [2]. In this system, cataractous opacities were classified into nuclear, posterior subcapsular and cortical. The grading of cataractous states was in two steps. Grade I is the early stage and grade II shows prominent opacification. To assist in assessing the grade, standard photos have been prepared. LOCS II was developed based on the LOCS I [3]. The cataractous grading system and coloration were classified more precisely than in LOCS I. This system also adopts standard photographs as a guide for judgment. (íi) The Oxford system: The Oxford system is a very precise classification system for clinical cataract research. Cataract types are classified into nuclear, subcapsular and cortical opacities. Grading of opacification and coloration adopts a 6-step system including grade 0 [4]. This is considered in combination with photodocumentation. For application in epidemiological studies, some simplification may be necessary. (iíí) The Bonn system: This has been proposed by Hockwin et al. [5]. Each cataract type is classified as a Scheimpflug slit image. Types of opacification are not classified as cortical, subcapsular and nuclear, but classified by their opacification type and location: (1) nuclear cataracts; (2) opacities of the lens nucleus and the posterior subcapsular layer; (3) changes of the nucleus and the posterior as well as anterior subcapsular layers; (4) nuclear cataract and changes and the anterior cortex; (5a) waterclefts and spokes; (5b) wedge-shaped cataracts; (5c) coronary cataract; (5d) opacities of the deeper anterior cortex; (5e) combined anterior and posterior changes; (6) posterior subcapsular cataract; (7) opacities of the posterior and anterior subcapsular layer, and (8) mature cataracts. This classification system has been established on the basis of his many years' experience as a lens biochemist. This system would be useful for researchers who have an interest in the basic research of human cataracts. (ív) The Wilmer system: This system was proposed for nuclear cataract classification only. In this classification, consideration of visual acuity is combined with morphological changes [6]. Five-step grading (including grade 0) has been adopted. (v) The Japanese Cooperative Cataract Epidemiology Study Group (CCESG) system: This classification system has been established by the
Cataract Classification Systems
99
cataract study group in Japan [7]. Lens opacifications are classified into nuclear, subcapsular and cortical. A three-step grading system with standard photos has been adopted and a four-step grading is applied to lens coloration classification. A special recording chart was also provided.
Application of the Established Classification Systems and Problems Encountered Although there are still some differences between the above-mentioned systems, a common concept is noticed. Opacification types were divided into cortical and nuclear types or cortical, subcapsular and nuclear. Based on the author's experience, researchers who are familiar with using the Jap-CCESG system can apply the LOCS II without difficulty. Ideally, cataract epidemiological studies should adopt the same classification system in their studies. However, if the studies are performed applying a photodocumentation system, even if the classification system is different, the results obtained will be comparable with each other [8]. In several classification systems, recording charts have also been prepared. It is possible for each chart to have its own characteristic recording system depending on the purpose of the studies. Standard photos to assist in grading for diagnosis are useful. However, it is essential to prepare high quality standard pictures. A retroillumination image with less cross-shadows and slit images, taken with a Scheimpflug camera, would be preferable. At present, it is quite difficult to show the color gradings through standard pictures, especially a color grading system with a precise classification. In the Jap-CCESG system, we have not yet prepared standard lens color pictures.
Inter-Observer Agreement
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
Usually, cataract examination performed for a survey is carried out by not only one examiner but by several or by a multicenter system. As described previously, the classification systems proposed today are not complicated. The inter-observer agreement ratio seems to be high. If the examinations in cataract epidemiology surveys are performed by ophthalmologists who have had sufficient experience with this type of study, they will have satisfactory results, but if the observer has not been trained before the
Sasaki
100
Table L Inter-observer agreement test (first trial) Type of cataract
κ value
% agreement
Cortical cataract Nuclear cataract Subcapsular cataract Lens coloration
0.58 0.22 0.58 0.32
68.8 37.5 83.3 56.3
Table 2. Inter-observer agreement test (second trial) Type of cataract
κ value
% agreement
Cortical cataract Nuclear cataract Subcapsular cataract Lens coloration
0.50 0.42 0.45 0.38
70.1 89.1 93.4 87.6
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
survey, the results may be unsatisfactory. The most problematic area of assessment may be in an early stage nuclear cataract diagnosis, the grading of nuclear cataracts or that of nuclear coloration. Inter-observer agreement tests performed in the author's institution: a test was performed by two ophthalmologists who belong to the author's department. One was a highly trained specialist who has been involved in the development of our classification system. He can judge cataract grades without seeing standard photos. The other was a resident to whom we explained our classification system and had shown him standard pictures a few days before the examinations. Eighty subjects over 40 years old were used for the tests and the ophthalmological examination included visual acuity measurement, tonometry, crystalline lens observation with dilated pupils, fundus examination and photodocumentation of the crystalline lens, all of which were performed in 1 day. This meant that the assessment of the cataract type and its grading were performed within a short time. Compared with the inter-observer agreement for cortical and subcapsular cataracts, the agreement on nuclear cataracts was unsatisfactory (table 1). After the inexperienced ophthalmologist received training in
Cataract Classification Systems
101
utilizing photographed images, a second trial of the same test was performed by the same two ophthalmologists. The total number of subjects in the second test was 103. The results obtained showed an increase of % agreement and κ value (table 2). From this small trial the author considers that, in order to achieve reliable cataract epidemiology studies, several training sessions are necessary for the examiners before using an unfamiliar cataract classification system.
Necessity for Pupil Dilation in Cataract Examination In cataract epidemiology studies, it is not always possible to judge the type of cataract and its grading on a dilated pupil. However, no one will deny that data obtained from a slit examination with a dilated pupil and that obtained without pupil dilation are not comparable. In cases where the classification system includes the early stage of cataract in its grading, it is especially important that the examination should be performed on a dilated pupil. Information concerning the early stage of cataract obtained from epidemiological studies from the surveys in advanced countries is especially needed. A slitlamp used in the survey should function well. To judge lens coloration precisely, a slitlamp of high quality is essential.
Visual Acuity and Cataract Gradings
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
Visual acuity is one of the important findings in the evaluation of cataract progression. However, for several reasons, it does not always reflect cataract progression. Because of this, the majority of cataract grading systems being proposed today do not consider deterioration of visual acuity in the assessment procedure of grading cataracts. However, the visual acuity measurement is still important for epidemiological surveys performed in developing countries. Regarding the correlation between visual acuity and cataract types, it can be said that visual acuity in the patients with cortical opacification located on the visual axis has a high correlation with deterioration of visual acuity. Clinically, deterioration of visual acuity is often experienced in cases with a small area of subcapsular opacity located in the pupillary zone. However, in
Sasaki
102
nuclear cataracts, ít should be remembered that the scattering of light intensity observed in the nuclear part is not always parallel to the deterioration of visual acuity in cases with mild to moderately advanced nuclear cataracts. According to the author's data, patients with a nuclear cataract of grade III (Jap-CCESG classification) or further advanced, often show a deterioration of visual acuity, but the range of visual acuity in grade I and grade II nuclear cataracts varies. Time is still needed before a standardized cataract classification system in cataract epidemiology studies can be introduced and, as has been described, there are no marked differences between the concepts in the systems proposed today: the simple classification of cataract type, a three-to-six step grading system, providing a standard photo to assist judgment and utilization of information from both slit and retroillumination findings. Within a few years, the differences between them will become less and less significant.
References 1 2
Chylack LT: Classification of human cataracts. Arch Ophthalmol 1978;96:888-892. Chylack LT, Leske MC, Sperduto R, et al: Lens opacities classification system. Arch Ophthalmol 1988;106:330-334. 3 Chylack LT, Leske MC, McCarthy D, et al: Lens opacities classification system II (LOCS II). Arch Ophthalmol 1989;107:991-997. 4 Sparrow JM, Bron AJ, Brown NAP, et al: The Oxford Clinical classification and grading system. Int Ophthalmol 1986;9:207-225. 5 Hockwin O, Eckerskorn U, Schmidtmann W, et al: Epidemiological study of the association between lens cataract and case history, blood composition and enzymes involved in lens carbohydrate metabolism. Lens Res 1984;2:23-42. 6 West SK, Rosenthal F, Newland HS, et al: Use of photographic techniques to grade nuclear cataracts. Invest Ophthalmol Sci 1988;29:73-77. 7 Sasaki K, Shibata T, Obazawa H, et al: Classification system for cataracts. Ophthalmic Res 1990;22(suppl):46-50. 8 Sasaki K, Karino K, Kojima M, et al: Cataract survey in the local area using photographic documentation. Dei Ophthalmol. Basel, Karger, 1987, 1/01 15, pp 28-36.
Downloaded by: Université de Paris 193.51.85.197 - 1/6/2020 1:37:22 AM
Kazuyuki Sasaki, Department of Ophthalmology, Kanazawa Medical University, Uchinada, Ishikawα 920-02 (Japan)
