Because diagnosing and treating glaucoma early in asymptomatic patients may prevent future vision loss and blindness, clinicians have begun to embrace the promise of glaucoma screening. Detecting disease, however, is only as effective as the treatment offered thereafter and patients' willingness to comply with it.
FOUR COMPONENTS OF SUCCESS
I believe that any screening effort must address four issues to be successful. First, it must identify the population at highest risk for glaucomatous disease in order to improve the screening examination's accuracy. Second, the examiners must have access to patients at high risk for glaucoma, and the screening examination must be capable of discriminating normal from diseased eyes. Third, patients diagnosed with glaucoma must be able to initiate and continue care, if necessary. Fourth, the treatment available must be a superior alternative to the natural history of the disease, and it should be efficacious and with as little risk as possible.
To my knowledge, a large-scale screening program such as I have described does not yet exist, but I believe that a comprehensive protocol addressing each of these issues is possible.
IDENTIFYING A HIGH-RISK POPULATION
Thanks to the results of large, population-based surveys, we have learned that glaucoma becomes more common with age and is more prevalent among certain racial groups. We also know that the positive predictive value of any examination increases when it tests populations with a higher prevalence of the disease at issue. For these reasons, screenings in shopping malls or businesses full of young and middle-aged people may be helpful from an educational standpoint, but these efforts are not likely to be productive for case detection. More appropriate locations for glaucoma screening efforts include senior centers, AARP conventions, and retirement communities.
GAINING ACCESS
William Sponsel, MD, of San Antonio, Texas, launched an excellent glaucoma screening project among veterans at VA hospitals and VFW conventions, while Harry Quigley, MD, has done notable work with the Hoffberger project in Baltimore community centers.1 In Philadelphia, my colleagues and I have performed free glaucoma screenings in senior centers and African American churches for more than 4 years. We specifically selected these locations because they are populated by persons at high risk for the disease and often have a social work network in place that can assist us with follow-up. We have newly diagnosed approximately 10% of the 1,500 patients we have examined as having glaucoma or being glaucoma suspects. Other locations where high-risk patients gather include advocacy organizations for the working poor, Parent Teacher Associations, and even the offices of general medical doctors.
IDENTIFYING DISEASE
As have other clinicians, we rely on clinical history, direct ophthalmoscopy, visual field testing, and tonometry to identify individuals with glaucoma or glaucoma suspects. Although the perfect screening test does not yet exist, I feel that any examination ought to evaluate the subject's optic nerve and visual field. The nerve examination provides the most information about the presence or absence of glaucomatous disease, whereas visual field testing helps to screen out individuals who do not have glaucoma but possess unusual optic nerves and also helps to indicate how the disease is affecting the overall vision of glaucoma patients.
The optic nerve examination is the most difficult component of the screening process, because it must be performed by a highly trained individual and involves the use of either an ophthalmoscope or nerve imaging. The advent of the Frequency Doubling Perimeter (Carl Zeiss Meditec, Dublin, CA) has simplified visual field testing. In my experience, however, the use of this device in an elderly population frequently generates a high number of false positives. Immediate repeat testing to confirm any visual field defects can markedly reduce these problems, but it usually requires the presence of multiple perimeters to be most efficient.
Obviously, the examination is only as accurate as the criteria for its interpretation. Glaucoma specialists are perhaps best qualified for this role, but their employment in this capacity may not be the most cost-efficient option for screening efforts. Another means of overcoming the problem is to develop standardized optic nerve evaluations, for instance, using the Disc Damage Likelihood Scale,2,3 and employing telemedicine examinations that are sent to centralized reading centers.
INITIATING CARE
Perhaps the biggest obstacle in achieving effective glaucoma screening is getting patients from the examination to a physician's office. In both the Hoffberger project and the one with which I am involved, follow-up was poor for patients who screened positive. The various reasons for this problem include the patient's forgetfulness, not recognizing the gravity of glaucoma, fear of the cost of treatment, lack of insurance, and lack of transportation.
In Philadelphia, my colleagues and I recently completed enrollment for a randomized trial of three different strategies to encourage follow-up. We randomized patients informed about their glaucoma or status as a glaucoma suspect, as well as of any other suspected eye disease, to receive (1) $10 transportation vouchers, (2) transportation vouchers and monthly telephone calls, or (3) transportation vouchers, monthly telephone calls, calls to social workers, and site visits for personal reminders if subjects could not be contacted by telephone.
Approximately two-thirds of the patients have completed the study. To date, the follow-up rate is poor, and we have found no significant difference in the follow-up rates between subject groups. The implication is that community screenings detect disease but are ultimately not very successful because they do not lead to treatment. One way to address this issue might be to conduct free screenings within the eye hospital and immediately provide appointments to glaucoma suspects and those diagnosed with glaucoma. Another option would be to enlist the help of these individuals' primary care physicians, who could remind patients of their need for follow-up.
PROVIDING EFFECTIVE TREATMENT
Effective treatment with an acceptable risk/benefit ratio must be available to patients who need it, or else glaucoma screening is valueless. Fortunately, recent clinical trials (ie, the Normal Tension Glaucoma Study, Advanced Glaucoma Intervention Study, Collaborative Initial Treatment of Glaucoma Study, Early Manifest Glaucoma Trial, and Ocular Hypertension Treatment Study) have provided evidence that justifies lowering IOP as a means of treating glaucoma. Newer glaucoma medications and surgical techniques offer additional therapeutic choices with fewer side effects than older options.
Unfortunately, because the cost of treatment is prohibitive and eye care is scarce in many parts of the world, cyclodestructive procedures may be the only practical option for patients in such areas of developing nations. Even within the developed world, the cost of therapy can limit patients' access to care. The full impact of glaucoma screening will remain unrealized without the development of a greater number of practical therapies.
CONCLUSION
Glaucoma is the leading cause of irreversible blindness in the world, and it will become a larger problem as the populations of various countries age. Glaucoma screening, however, is a difficult proposition. Formidable obstacles to its success range from designing appropriate screening tests to ensuring adequate follow-up and therapies. Screenings that only identify persons at risk without addressing the additional important issues outlined herein are of limited utility.
Although our understanding of glaucoma is incomplete, the disease is treatable. Researchers are actively pursuing better diagnostic tools and treatments. Integrating these options, when they are developed, into a comprehensive screening program that seeks, screens, and educates patients and introduces them into the medical system for treatment should more effectively combat glaucoma.
Jeffrey D. Henderer, MD, is a member of the Glaucoma staff and an assistant surgeon at the Wills Eye Hospital in Philadelphia, and he is Assistant Professor of Ophthalmology at Thomas Jefferson University School of Medicine in Philadelphia. He holds no financial interest in the product or company mentioned herein. Dr. Henderer may be reached at (215) 928-3272; henderer@willsglaucoma.org.
1. Quigley HA, Park CK, Tracey PA, Pollack IP. Community screening for eye disease by laypersons: The Hoffberger program. Am J Ophthalmol. 2002;133:386-392.
2. Bayer A, Harasymowycz P, Henderer JD, et al. Validity of a new disk grading scale for estimating glaucomatous damage: Correlation with visual field damage. Am J Ophthalmol. 2002;133:758-763.
3. Henderer JD, Liu C, Kesen M, et al. Reliability of the disk damage likelihood scale. Am J Ophthalmol. 2003;135:44-48.
