|Year : 1966 | Volume
| Issue : 1 | Page : 1-5
Irvin P Pollack
From the Wilmer Institute, the Johns Hopkins University School of Medicine
|Date of Web Publication||12-Jan-2008|
Irvin P Pollack
From the Wilmer Institute, the Johns Hopkins University School of Medicine
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pollack IP. Glaucoma screening. Indian J Ophthalmol 1966;14:1-5
Mass screening in one form or another has come to be an expected service in many communities of the United States. Mobile units provide facilities for the detection of tuberculosis, diabetes mellitus, and cardiovascular disease; and do-it-yourself Papanicolaou smears can be sent by mail for diagnosis. During the past fifteen years the ophthalmologist, too, has been involved in mass screening. Large-scale testing of visual acuity has become common place, and screening for glaucoma is being utilized with increasing frequency.
Because glaucoma is the greatest cause of irreversible blindness in the United States today, detection of glaucoma is a service that, to the public, often exemplifies opthalmology at its best. Service organizations are impressed by the need for prevention of blindness and eagerly seek to associate themselves with such dramatic causes as glaucoma detection. Consequently, the popular demand for glaucoma screening is often strong, and the popular response to such projects, is enthusiastic.
Glaucoma screening can be conducted by: (A) testing a large number of unselected persons from a community; (B) testing an entire community or a selected cross section of that community; (or (C) special surveys of a small, but not necessarily representative, segment of the population chosen for more extensive testing or "longitudinal studies".
| A. Mass Screening of an Unselected Population|| |
The commonest type of glaucoma screening is based on offering glaucoma tests to anyone in a given community who is willing to participate. Whereas most earlier programs have tested only visual acuity and ocular tension, recent programs have also included ophthalmoscopy and, occasionally, visual fields.
The purpose of mass screening of this type is twofold: (1) to increase public awareness of glaucoma and of the need for periodic examinations by an ophthalmologist, and (2) to detect more cases of glaucoma than would be otherwise possible.
As a result of mass screening programs throughout the United States, the public is undoubtedly more aware than ever before of this important cause of blindness. Unfortunately, increased education about glaucoma sometimes produces an excessive fear of the disease. This is reflected in the greater number of patients who are coming to ophthalmologists with the primary intention of being examined for glaucoma. (As in the case of fears about cancer, however, public anxiety can have the benefit of leading to earlier diagnoses.) Another problem is the increasing number of persons who seek glaucoma tests from members of the ancillary professions, whose facilities and training do not permit an adequate examination for diagnosis of early glaucoma.
Regarding the second goal of mass screening-more effective detection-such programs have varied widely in their reports of glaucoma prevalence; from less than 1% to more than 60 per cent occurrence of glaucoma in the populations studied. These studies usually have included only patients over the age of forty. [Posner and Gilbert (1964), Graham and Hollows (1964)]
Those reports claiming an unusually high prevalence of glaucoma may result partly from statistical bias in the populations studied and partly from our inability to define the disease. Such studies frequently define glaucoma entirely on the basis of an ocular tension higher than 24, 26, and 30 mm Hg., without specific regard to the optic disc or visual fields. Subsequent examination often reveals no glaucoma pathology and, often, no confirmation of elevated ocular tensions. Consequently, the specific diagnotic benefits of such screening are few, and many false positives are included in the results. Unfortunately, many of these patients are thereby immediately frightened into seeking "emergency" treatment by their ophthalmologists and are left unsatisfied and suspicious when they are subsequently told that they do not, after all, have the disease. Also, the confidence of the ophthalmologic community in glaucoma screening itself may be undermined. Furthermore, if the test measures only the ocular pressure-and particularly if it is a single measurement-a significant number of cases will be missed. Still other persons, who may in the future develop glaucoma, may lack evidence of glaucoma at the time of screening. Thus, test methods that lack sensitivity can lead many people to the false conclusion that they are permanently free of danger from this disease.
Recognition of the seriousness of this situation has resulted in more complete testing programs for glaucoma screening. With the inclusion of ophthalmoscopy and tests of visual fields, in addition to visual acuity and tonometry a more reliable screening program can be carried out. Based on such studies, the prevalence of glaucoma in persons over the age of forty has been reported to be in the range from less than 1 per cent -Posner and Gilbert (1964) to as high as 3 per cent-Lasky, Zirnis and Sands (1959).
If one accepts the definition that glaucoma is a disease in which the intraocular pressure is sufficiently high to cause damage to the visual apparatus, one will base his diagnosis on the presence of glaucoinatous visual fields and/or glaucomatous cupping of the discs, in addition to elevated ocular tensions. The few studies that have adhered to this strict definition have actually revealed extremely small percentages of glaucoma in the population survey [Graham. and Hollows (1964), Hildreth and Becker (1957)]. This, then, clearly demonstrates the low yield and uncertain correlation of many current mass-screening programs for glaucoma detection.
Nevertheless, it is reasonable to expect that mass glaucoma screening that includes ophthalmoscopy and visual field testing can be a valuable service to the community. This is especially so if the program is planned well in advance, and if great care is taken not to mislead persons who might have false-negative test results into permanent apathy about the danger of glaucoma. Screening programs, while detecting extremely few new glaucoma suspects, do ignite an awareness of the disease in the population. Occasionally, persons who already have had reatment for glaucoma but were lost to follow-up appear at such clinics. They can then be redirected for proper care. Also, private and government sources may be indirectly inspired by the prospect of preventing blindness to make available the needed funds for further research in this field.
| B. Total Community Screening|| |
Screening programs have, on occasion, been designed to cover the entire population of a limited area. An area program requiring examination of every person (or everyone in a selected age range) is an ambitious undertaking. This requires that the equipment and personnel for testing be transported to the home of every person, or that means be arranged by which every person can he brought to the testing station. One such study in the United States was made for the purpose of determining the prevalence of diabetes mellitus in Oxford, Massachusetts-Wilkerson Krall (1947).
Only by complete screening of a population can one derive thorough comprehensive epidemiological information. Such a study for the detection of glaucoma was recently performed in Cardiff, Wales - where over 4,000 persons were screened by applanation as well as Schiotz tonometry, ophthalmoscopy, and measurement of visual acuity and visual fields-Graham and Hollows (1964). This investigation indicated that ophthalmoscopy was at least as important as tonometry in predicting the presence of glaucomatous field loss, and that several persons who had tensions of less than 21 mm Hg on the first examination had elevated tensions on the second examination some of whom also had glaucomatous disc and field changes. Such a study provides valuable information about the statistical distribution of various intraocular pressures, and the prevalence of glaucoma in the population studied. It may also offer an opportunity to study other aspects of eye disease and its treatment, but such studies furnish only limited information for predicting the likelihood that a given person will develop glaucoma in the future.
| C. Longitudinal Glaucoma Studies|| |
Although the various types of glaucoma screening already described may offer valuable statistical, epidemiological, and genetic information, only by longitudinal studies can one gain critical facts with regard to the life, history of this disease. The natural history of chronic open - angle glaucoma, and the basic factors responsible for the damage, remain largely unknown. The interrelating links between intraocular pressure, glaucomatous optic disc cupping, vascular nerve disease, glaucomatous field loss, and eventual blindness have yet to be defined. Whereas some eyes are resistant to the effect of increased intraocular pressure, others appear to be vulnerable; and although younger persons and some patients with systemic hypertension may safely tolerate elevated ocular tensions for long periods of time, older people and those with normal blood pressure cannot. The basic factors responsible for these differences and for the ocular damage in this disease remain unknown.
The extent to which patients with ocular hypertension are truly preglaucomatous can be demonstrated only by follow - up studies of these individuals over many years. Until this is done, all that can be said with certainty is that the eyes of these people are different in statistical terms of intraocular pressure and/or facility of aqueous outflow. Otherwise, however, the eyes of ocular hypertensives are not demonstrably different from the rest of the normal population -- unless they have already developed glaucomatous field loss or disc changes, and these can be distinguished only by tonometry or by tonography. Such studies can be designed to examine not only the relationship of ocular tension to glaucoma, but also to investigate patterns of inheritance and the ways in which medical therapy alters the course of this disease.
A carefully designed program of glaucoma studies is currently being undertaken, in which more than 3,000 persons are being surveyed by five clinics. The testing program includes determination of visual acuity and refractive errors, careful visual-field examination (Goldmann Perimetry and tangent screen), ophthalmoscopy, gonioscopy, water provocative tonography, and fundus photography. Most of the subjects are persons with a higher-than-normal risk, having been selected because of a family history of open-angle glaucoma or because of the presence of ocular hypertension.
Because of the method of selecting participants, the study contains many family units in which all of the siblings and offspring of persons with open-angle glaucoma are being followed. Consequently, useful genetic information will be gained in addition to the main goal of the study, which is to evaluate the relative validity of various test methods (for measuring ocular tension and aqueous flow) in predicting the development of open-angle glaucoma. In addition to the public service aspect inherent in any survey of his type, its rewards in terms of insight into the life history of glaucoma are incalculable.
| Comment|| |
The value of any glaucoma screening program is closely dependent on how that program has been designed to meet its objectives. Adequate epidemiological information on the prevalence of glaucoma cannot he obtained by the usual mass glaucoma-screening programs, as presently conducted in this country and abroad. Rather, carefully planned studies of total area populations, designed to eliminate factors that would prevent the securing of precise epidemiological information, must be developed. Similarly, beneficial genetic information can be acquired only by complete family studies. A basic problem of the entire program is our inability to adequately define glaucoma as a disease, or to predict its onset. Only carefully planned and closely followed longitudinal studies can be of benefit in this regard.
Mass glaucoma screenings of urn selected populations offer none of these advantages, but they do fulfil another need; they stimulate a public awareness of glaucoma. Such programs, however, do little more. Although they do detect previously unknown primary glaucoma, the diagnostic yield is extremely low if only intraocular pressure, ophthalmoscopy, and visual field tests are used; and the yield is still lower if only ocular tensions are tested. Even more disturbing is the fact that if ocular pressure is the only factor considered, as many patients with early open-angle glaucoma can be missed as are found. As a result, a significant number of persons who actually have glaucoma may be mistakenly informed that they do not have the disease, thus creating a false complacency. When these factors are considered, it would seem mandatory that such mass glaucomascreening programs include ophthalmoscopy and, if possible, visual field examination along with tonometry and visual acuity tests.
Although a glaucoma examination such as this cold be more satisfactorily carried out in the ophthalmologist's office, the shortage of specialized professionals precludes this possibility for mass screening. An alternative would be to teach general practitioners and internists how to perform routine tonometry and ophthalmoscopy and perhaps, to better train for and encourage similar screening by the paramedical professions. Certainly, the clinical use of tonometry should be taught as part of physical diagnosis in medical school, and measurement of ocular tensions should become part of the routine examination of all adults. In any case, mass screening of this type is destined to be practiced with even greater frequency in years to come.
| References|| |
Posner, A. and Gilbert, W. G. (1964) F. E. N. T. 43, 53.: Mass Screening for Glaucoma: A Critical Review of Methods Now in Use.
Graham, P. and Hollows, F. (1964) Trans. Ophth. Sec. U.K. 84, 597.: Sources of Variation in Tonometry.
Lasky, M. A., Zirnis, L. and Sands, A. (1959) Amer. J. Ophth. 48, 515. Glaucoma Detection in a General Hospital Clinic.
Ilildreth, H. R. and Becker, B. (1957) Amer. J. Ophth. 43, 21.: Routine Tonometry.
Wilkerson, H. L. and Krall, L. P. (1947) JAMA. 135, 209.: Diabetes in in a New England Town; A Study of 3, 516 Persons in Oxford, Massachusetts.