Presented at Hawaiian Eye Meeting, 2009
Brian Francis, MD, MS
Author's comments are in italics
Anne Coleman, MD, PhD, from the Jules Stein Eye Institute, UCLA School of Medicine, presented her thoughts on the risk of blindness from glaucoma. She began with data from a study by Chen et al in Ophthalmology, 2003, which followed 186 patients with glaucoma and found that the incidence of blindness in one eye was 15% and for both eyes was 6% at a follow up of 15 years. In a retrospective study of 295 patients in Olmsted County, Minnesota, the 20 year follow up discovered an incidence of glaucoma-related blindness of 27% in one eye and 9% in both eyes (Hattenhauer, Ophthalmology, 1998). Keep in mind that these are treated patients!
Risk factors evaluated for glaucoma progression include:
- Age
- Race or ethnicity
- Presentation at a late stage and greater severity of disease at the time of diagnosis
- Variability of IOP
- Noncompliance with the treatment regimen
- Living in developed versus developing countries
Some studies have found that the age at glaucoma diagnosis is significantly higher for those that go blind from the disease (69 years ± 12) than those that do not (65 years ± 14)(Oliver, AJO, 2002). However, others have found no association between age at diagnosis and blindness (Chen, Ophthalmology, 2003). It may simply be that greater age is associated with disease that is already further advanced. If one controls for disease severity with age, then there may not be an effect. In fact, one may find that those that develop the disease later in life may be less susceptible to optic nerve damage and therefore less likely to go blind.
In the United States, the rates of glaucoma related blindness in different racial/ethnic groups are: whites = 6.4%, blacks = 26.0%, and Hispanics = 28.6% (data from the Eye Diseases Prevalence Research Group, 2004). There are several possible explanations for this observed difference. Genetics may play a role either in the susceptibility of the optic nerve to damage, or the severity of intraocular pressure elevation by affecting aqueous humor dynamics, or in the response to medical, laser or surgical treatment. Another possibility is that there is a differential in the access to or quality of health care.
Variability of intraocular pressure (IOP) is another factor thought to impact glaucoma progression. In a case-control study by Oliver (AJO, 2002), variability of IOP was related to blindness, with a range of 9.9 ± 8.8 mmHg in those becoming blind, and 6.8 ± 6.8 mmHg in those without blindness. Studies have shown both diurnal IOP fluctuation and intervisit fluctuation to be possible risks for glaucoma progression. The hypothesis is that a wide fluctuation of IOP puts more mechanical stress on the retinal ganglion cells (possibly at the level of the lamina cribrosa) than a more stable IOP, and this may be as important as mean IOP.
There is good agreement among studies that presentation at a later stage of glaucoma has a higher risk of progression to blindness. Studies by Kwon (AJO, 2001) and Oliver (AJO, 2002) showed that late presentation is associated with eventual blindness in 29% to 41% of patients. Similarly, Chen(Ophthalmology, 2003) found that a greater disease severity at the time of diagnosis was also associated with glaucoma-related blindness, regardless of the treatment. Finally, progression to blindness was related to moderate or advanced visual field loss at the time of diagnosis (Oliver). This makes intuitive sense, as an individual that has already progressed to advanced disease has exhibited susceptibility for progression, and has a much narrower margin before the development of blindness.
Non-compliance with the treatment regimen was also found by Chen to be associated with the risk of blindness from glaucoma. The definition of noncompliance included: 1) failure to use drops correctly, 2) missing multiple office visits within 1 year, 3) having more than 8 months elapse between visits, or 4) refusing surgical treatment when recommended. We are all aware of the degree of non-compliance among glaucoma patients, and now have evidence that it can have severe consequences.
As we may expect, living in a developing country increases the risk of glaucoma blindness. One study by Rotchford (Ophthalmology, 2003) reported a prevalence of bilateral blindness from glaucoma in 33% of glaucoma patients in urban South Africa. In addition, the great majority (up to 87%) were unaware that they have glaucoma. Worldwide, the greatest risk factor for blindness is residence in a developing country.
Dr. Coleman concluded with some recommendations to prevent blindness from glaucoma:
The first is early diagnosis and treatment. This is the goal of visual field and optic nerve and nerve fiber layer imaging technology. Improvements in the sensitivity and specificity of these technologies, and also their incorporation into a quality screening program, are worthy goals. Current technology does not allow for adequate screening on a population scale, and the diagnosis of glaucoma still requires a detailed examination by an ophthalmologist.
The second is decreasing variability in IOP. More research is needed to firmly establish this as a risk factor, and to identify what levels of IOP fluctuation are clinically important. In order to accomplish this, we must first have a method to measure IOP at various times during the day and night. Clearly our current method of measuring IOP at one time point in the middle of the day 3 or 4 times a year is inadequate. A reliable home tonometry system would help patients to monitor their IOP much as patients can monitor their own blood glucose levels or blood pressure. However, this requires a level of compliance and commitment that many patients lack (see next point). There are currently many centers researching IOP monitors that will give us this valuable information. Currently there are two main areas of development: implantable IOP monitors and disposable external IOP monitors. The first devices can be inserted surgically, piggy-backed onto glaucoma drainage devices or intraocular lens, or as a stand alone device. The second category is harder to develop, and consists of an external platform worn like a contact lens that is able to measure IOP through the cornea, presumably via applanation. Both groups of devices must be powered through an external source, and also able to transmit information to a portable device. The data may also be transmitted wirelessly via the internet to the treating physician's office for immediate feedback, or linked to a valve system to release aqueous or a drug delivery system.
Increasing compliance with the treatment regimen is something that can be approached from many different angles.The first is through patient education about the disease, the importance of treatment and consequences of treatment failure. We need to develop medical therapies that are easier to use and better tolerated. We also need laser and surgical treatments that are more safe and effective.
Lastly, improving healthcare access and other socioeconomic issues in developing countries may reduce the disproportionate risk of glaucoma related blindness seen worldwide. I would also add that the same issues apply to our own country. In order to accomplish our goals of preventing blindness from glaucoma, patients need to be diagnosed and effectively treated, and this requires access to health care!
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