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   Table of Contents      
ARTICLE
Year : 1966  |  Volume : 14  |  Issue : 1  |  Page : 1-5

Glaucoma screening


From the Wilmer Institute, the Johns Hopkins University School of Medicine

Date of Web Publication12-Jan-2008

Correspondence Address:
Irvin P Pollack
From the Wilmer Institute, the Johns Hopkins University School of Medicine

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Source of Support: None, Conflict of Interest: None


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How to cite this article:
Pollack IP. Glaucoma screening. Indian J Ophthalmol 1966;14:1-5

How to cite this URL:
Pollack IP. Glaucoma screening. Indian J Ophthalmol [serial online] 1966 [cited 2019 Sep 18];14:1-5. Available from: http://www.ijo.in/text.asp?1966/14/1/1/38556

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 Top


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 Top


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 Top


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 Top


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.[5]

 
  References Top

1.
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.  Back to cited text no. 1
    
2.
Graham, P. and Hollows, F. (1964) Trans. Ophth. Sec. U.K. 84, 597.: Sources of Variation in Tonometry.  Back to cited text no. 2
    
3.
Lasky, M. A., Zirnis, L. and Sands, A. (1959) Amer. J. Ophth. 48, 515. Glaucoma Detection in a General Hospital Clinic.  Back to cited text no. 3
    
4.
Ilildreth, H. R. and Becker, B. (1957) Amer. J. Ophth. 43, 21.: Routine Tonometry.  Back to cited text no. 4
    
5.
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.  Back to cited text no. 5
    




 

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