The Tema Eye Survey (TES) & Glaucoma Prevalence In West Africa

There is a high prevalence of blindness and visual impairment among those aged ≥40 years in Tema, Ghana, West Africa. Refractive error is a major cause of blindness and visual impairment in this population, followed by cataract, glaucoma, and corneal disease.

Sub-Saharan Africa bears a disproportionate amount of theworld’s blindness, and the proportion of people blind inthis region is increasing at a faster rate than in other parts of the world. Ghana is a country of approximately 24 millionpeople located in West Africa.

It currently is in the middlestages of a demographic transition typical of many devel-oping countries in Africa, from a high birth rate and shortlife expectancy to a lower birth rate and increased longevity.

Part of this demographic transition is driven by a shiftfrom a primarily rural agrarian society (where high birthrates yield economic rewards) to an urban society (wherehigh birth rates have the opposite effect).

The percentage of Ghana’s population that lives in urban areas has more thandoubled in the past 50 years, from 23% in 1960 to 48% in 2009.

Chronic eye diseases such as cataract and glaucomamay represent a greater percentage of disease burden todaybecause of the reduced prevalence of infectious causes of blindness, such as trachoma and onchocerciasis, from im-provements in their prevention and treatment, as well as pop-ulation shifts away from endemic regions and increased lifeexpectancy in developing West African countries such as Ghana.

The Tema Eye Survey (TES), an international effort carried out by investigators from the United Kingdom, United States, and Ghana, was undertaken because of the recognized scarcity of comprehensive eye disease information from Africa as a whole and no data from West Africa.

Gathering such data can help Ghana’s Ministry of Health plan for future eye care needs in the country and the region to correctly appropriate resources.

Donald L. Budenz, MD, MPH, the Kittner Distinguished Professor and chairman of the Department of Ophthalmology at the University of North Carolina School of Medicine in Chapel Hill, and other investigators hypothesized that this region has the highest glaucoma prevalence in the world.

Glaucoma in Africans

In large population-based studies, such as the Baltimore Eye Survey and the Barbados and St Lucia studies, glaucoma has been shown to pose a triple threat compared with other ethnic groups to individuals of African heritage with an increased prevalence, younger age of onset, and more severe disease course.

Previous studies in East and South Africa have reported a lower prevalence of primary angle-closure glaucoma (POAG) compared with the North American studies.

Tema Eye Survey

The TES was randomly sampled, was population-based, and, importantly, did not rely on elevated IOP in its case definitions, Budenz said.

Before the TES, only one glaucoma survey had been performed in East Africa, in South Africa, and none in West Africa.

The primary goal of the TES was to determine the prevalence rates of blindness, visual disability, glaucoma, and other ocular diseases in adults in Tema, Ghana.

The survey included 5600 randomly sampled adults who were 40 years and older. The survey design required a random sampling of clusters of 400 to 600 individuals of voting age for a total of 30 to 40 clusters.

The investigators had to map the communities because of the absence of census data and used voting rolls to identify potential participants.

The clusters were randomly selected, and field examinations were performed on 5600 participants. Individuals who failed the field examinations then underwent clinic evaluations.

The criteria for a referral for a full dilated clinic examination were visual acuity below 20/40, two failures on frequency-doubling technology testing, IOP greater than 20 mm Hg, narrow chamber, and cup-to-disc ratio greater than 0.7.

Glaucoma was defined according to the standard definition developed by Foster and colleagues, Budenz said.

Another challenge was that the local staff required training in all instrumentation, including the SITA Fast Humphrey VF Analyzer, because these evaluations had never been performed in this location.

Findings

Budenz reported that a census was done of 6806 individuals, and field examinations were performed on 5607 individuals (response rate, 82.2%).

A total of 1869 failed the field examination, and 1538 underwent clinic examinations (response rate, 82.2%).

The prevalence rate of glaucoma in this population was 6.5%. When the data were adjusted for age and gender, the total POAG prevalence rate increased to 6.8%.

“The glaucoma types identified were primarily POAG in 94.5%, chronic narrow-angle glaucoma in 2.5%, traumatic glaucoma in 1.9%, and others that included uveitic, mixed-mechanism, steroid-induced, and unspecified glaucoma in 1.1%,” he said, noting the absence of pseudoexfoliation glaucoma.

A comparison of the total prevalence of POAG in this study population with the other studies showed that the prevalence was similar to rates reported from Barbados and St Lucia and almost double those found in East Africa, South Africa, and the US.

“We believe that the study population is very similar to the Caribbean populations in glaucoma prevalence, which is likely due to migration from West Africa to the Caribbean during the slave-trading years and lack of admixture,” Budenz said. “These populations are unique in the high prevalence of glaucoma.”

A noteworthy finding of the current study was that only approximately 3% of the patients identified with glaucoma were aware that they had the disease, which is in marked contrast with similar studies conducted in developed countries in which 50% of patients identified with glaucoma were aware they had the disease.

The prevalence of undiagnosed glaucoma in the TES study was 97%.

TES Phase 2

The extended study’s goal was to identify the incidence of glaucoma and the rates of progression among the original patients after 10 years.

Investigators examined 1200 individuals who had tested normal previously using the same methods, and they also tried to reexamine the original 362 individuals in the clinic who had received a diagnosis of glaucoma.

The incidence per 100 individuals of OAG was 4.7 per year. When results were compared with those of other studies with gender and age adjustment, the incidence rates of OAG in the TES survey and the Barbados Eye Study were “considerably higher.”

The population in Ghana is severely underserved by medical professionals, Budenz said. There are only 53 ophthalmologists to provide care for 27 million individuals; in contrast, there is one ophthalmologist for every 10,000 individuals in the US.

The Future

“The next steps in this population are to improve case detection of glaucoma through screening, train eye care providers in sub-Saharan Africa to diagnose and manage glaucoma, and find the best treatments for this population, which include selective laser trabeculoplasty, trabeculectomy with mitomycin C, glaucoma tube implants, and cyclophotocoagulation,” Budenz concluded.

“We are not sure how medications fit into this algorithm, in that they are expensive and not sustainable in this population.”