Assessment of visual status of the Aeta, a hunter-gatherer population of the Philippines
Cecilia Santiago-Turla, MD, Mary Katherine Rivera-Francia, MD, Bernardita Navarro, MD, Jose Joel Eclarinal, MD, Benjamin Dizon, MD, Paul Francia, MD, Sandra Stinnett, MD, R. Rand Allingham, MD
Assessment of visual status
of the Aeta, a hunter-gatherer
population of the Philippines
R. Rand Allingham, MD
2351 Erwin Road
Durham, NC 27710, USA
Fax : +1-919-6819801
E-mail : firstname.lastname@example.org
Cecilia Santiago-Turla, MD1
Mary Katherine Rivera-Francia, MD2
Bernardita Navarro, MD3
Jose Joel Eclarinal, MD4
Benjamin Dizon, MD4
Paul Francia, MD4
Sandra Stinnett, MD1
R. Rand Allingham, MD1
Department of Ophthalmology
Duke University Medical Center
Durham, North Carolina
Department of Ophthalmology
Iloilo Doctors College of Medicine
Department of Ophthalmology
Santo Tomas University Hospital
Department of Surgery
Iloilo Doctors College of Medicine
A study was performed to assess levels of visual impairment and blindness
among a representative sample of older members of the Aeta, an indigenous
hunter-gatherer population living on the island of Luzon in the Philippines.
Unrelated older Aeta couples from 4 villages were randomly invited to
participate in a visual-screening study. All participants had complete ophthalmic
examination and their ocular and medical history, height, and weight were
A total of 225 individuals were screened from 4 villages. The mean height
for the entire screened population was 54.6 inches (approximately 4.5 feet),
56.8 for men and 53.7 for women. Visual acuity, both uncorrected and pinholecorrected, was significantly worse among older vs. younger age groups for
women, men, and when combined (p < 0.001). Visual impairment, defined as
best-corrected VA > 20/40 and < 20/200, was present in 48% (100/208) of
uncorrected eyes and 43% (90/208) of pinhole-corrected eyes in the older
age group. Of all individuals screened, 6% (14/225) were bilaterally blind,
defined as best-corrected VA ≥ 20/200. The major causes of blindness were
readily treatable. The most common etiologies as a proportion of blind eyes
were cataract 66% (39/59), refractive error 20% (12/59), and trauma 7%
(4/59). No cases of primary open-angle (POAG), primary angle-closure
(PACG), or pseudoexfoliation-associated glaucoma were observed.
Visual impairment and blindness were common in the Aeta population.
Cataract was the most common cause of vision loss. Interestingly, POAG and
PACG, both major causes of blindness in most population-based studies, were
not observed in this population. The absence of these forms of glaucoma may
reflect random-sampling error. However, the Australian Aborigines, a related
indigenous population, also have a very low prevalence of these forms of
glaucoma. These data suggest that these populations may share genetic and/or
environmental factors that are protective against primary forms of glaucoma.
Keywords: Aeta, Visual-status assessment, Visual impairment, Blindness
IT IS ESSENTIAL to assess the medical status of a
population to determine the need for medical services.
This report describes a study to evaluate the types and
relative frequency of vision-related disorders among the
Aeta, an isolated population living in a remote region of
The Aeta (also Ayta or Agta), until recently a huntergatherer population, are indigenous to the main island
of Luzon in the Philippine archipelago.
They live in
isolated regions along the foothills of Mount Pinatubo in
the Zambales Range and in the province of Pampanga.
The massive eruption of Mount Pinatubo in 1991 forced
the relocation of thousands of members of this population
to less-affected areas. Many of these families moved to
settlement villages. The establishment of these settlements
has enabled a variety of social agencies to have greater
access to this population.
Recently, medical clinics have
been established adjacent to settlement villages to provide
basic medical care; however, vision services are not
currently available and there is little information available
for health agencies to utilize for planning vision-related
health-care interventions. To assess the need for vision
services among the Aetas, we determined the prevalence
and major causes of vision loss in older members of this
Participants were recruited from 4 villages (barangays)
within the Pampanga province on the island of Luzon.
Barangays selected for this study were exclusively occupied
by the Aeta population and comprised groups of smaller
family subunits. A census performed in 2001 was used to
coordinate selection of participants as evenly as possible
throughout the region.
The census data were very limited,
containing only population estimates for each barangay.
Age, sex, and other demographic data were not recorded
in this census. The National Commission on Indigenous
Peoples (NCIP) coordinator contacted the community
leaders (kapitans) of each barangay to assist the research
team in the conduct of the study according to customary
practices. The number of participants selected at each
location was determined from the available census data
with a target of 1% of the census total (estimated 175 to
The Aeta do not follow a calendar. To estimate age older
than 40 years, a historical reference, World War II (1941–
1945), an event well remembered by all older Aeta, was
employed as a substitute calendar. Using this as reference
date, Aeta who were alive or whose parents or
grandparents were alive during WW II were invited to
participate. Since generations are typically separated by
15 to 20 years we used this method to divide the screened
population into 3 age groups: the younger age group under age 40, the middle-aged group between 40 and 60,
and the older age group 60 years and above.
Facility and equipment
The St. James Parish Church, located in Betis, Guagua,
Pampanga was used as the venue for vision screening.
Electricity was available to power examination equipment.
Automated perimetry was not available and in cases where
perimetry was indicated a tangent screen was utilized.
Screening and examination process
Demographic data and general health information
were obtained, and height and weight were measured for
all subjects. Each individual was tested for visual acuity
(uncorrected and pinhole), intraocular pressure (IOP),
slitlamp, gonioscopy, and dilated-fundus examination.
Visual acuity was assessed using tumbling Es at a distance
of 20 feet. IOP was assessed in a sitting position using a
calibrated Tonopen (Mentor, Norwell, MA, USA). All
participants who had a vertical cup-to-disc ratio (VCDR)
≥ 0.6, asymmetry of VCDR ≥ 0.2, presence of focal
neuroretinal rim defects, disc hemorrhages, or IOP > 21
mm Hg in either eye had tangent-screen visual-field
testing. Tangent-screen visual-field testing was performed
at 1 meter for each eye with a standard 3 mm white target
for patients who met these criteria.
Definition of visual impairment and blindness
Visual impairment was categorized using criteria
commonly applied in most US studies that define low
vision as acuity worse than 20/40 and better than 20/200
and blindness as visual acuity of 20/200 or worse.
Descriptive statistics were computed for all variables in
all patients and separately for men and women. The
significance of the difference in medians among age
groups was assessed using the Kruskall-Wallis test. Pairwise comparisons of medians between age groups used
the Wilcoxon rank sum test. To assess the difference
between men and women with respect to age, the chisquare test was used.
The study was conducted in accordance with the
Declaration of Helsinki and the customary ways and
practices allowed by the Aeta community leaders and NCIP
regional office. Informed consent was obtained from all
Four towns were chosen based on accessibility and
willingness of the population to take part in the study.
They were Angeles, Floridablanca, Mabalacat, and Porac—all in the province of Pampanga. The census populations
of the barangays ranged from 1,800 to 7,219. The total
sampled population was 17,600. The percent of the
population screened from each barangay ranged from
0.85% in Floridablanca to 2.1% in Angeles. Approximately
1.3% of the total census populations of the selected
barangays was enrolled and screened.
Height and weight
The mean height for the entire screened population
was 54.6 inches (approximately 4.5 feet), 56.8 for men
and 53.7 for women. The mean height for women between
age groups was not significantly different. This varied from
the mean height in men, which was significantly greater
in both younger and middle-aged groups compared with
the older group (p < 0.001). The mean weight for all
participants was approximately 85 lbs; 84 lbs and 94 lbs
for women and men, respectively. The mean weight for
the combined group was significantly greater in the
younger and middle-aged groups compared with the older
group (p < 0.002). Weight increased from the older to
younger age groups for both women (p < 0.05) and men
(p < 0.001).
A total of 225 study participants were enrolled and
examined. The proportions of eyes with uncorrected and
pinhole-corrected visual acuity of 20/40 or better, low
vision (worse than 20/40 and better than 20/200), and
blind (20/200 or worse) were assesssed. As expected, the
vast majority of the younger age group had visual acuity
better than or equal to 20/40 in both uncorrected and
pinhole-corrected (90% and 96%, respectively) vision.
The one exception was an individual with refractive error
in one eye, correctable with pinhole to 20/50, and
amblyopia in the fellow eye (CF vision). In the middleaged and older groups, both uncorrected and corrected
visual acuity fell dramatically. Uncorrected visual acuity
≤20/40 dropped to 55% in the middle-aged group and
33% in the older group. Similarly, pinhole-corrected visual
acuity ≤20/40 decreased from 70% to 41%, respectively,
in the middle-aged and older groups.
The prevalence of low vision rose from 4% in the
younger group to 48% in the older group, while pinholecorrected visual acuity in both groups increased from 2%
to 43%, respectively. Blindness increased from 2 to 19%
in uncorrected eyes and 2 to 16% of pinhole-corrected
eyes in the younger and older age groups, respectively.
Interestingly, only 19 participants (11 female, 8 male)
specifically complained about blurred or reduced vision.
Of these, only 6 had uncorrected vision worse than 20/40
in at least 1 eye. The majority of participants, even those
who had significant visual impairment, did not report a functional complaint.
Visual acuity, after conversion to LogMAR units, was
analyzed for men, women, and combined by age group.
Overall visual acuity was significantly different between
age groups, with the younger group having better vision
than the older group. This pattern was consistent when
analyzed by sex and when data were combined (p < 0.001).
Mean IOP was 15.6 ± 3.1 for right eyes and 16.0 ± 4.6
for left eyes. Gonioscopy revealed 2 cases of narrow but
nonoccludable angles, 3 cases of heavily pigmented angles
(wi thout cor nea l endothel i a l pigment a t ion or iris
transillumination defects), 1 case of uveitis, and 5 cases of
peripheral anterior synechiae related to trauma or corneal
scarring. Ocular pathology found on anterior segment and
fundus examination, excluding cataracts, is summarized
in Table 1. There were also 2 cases of exotropia and a single
case each of entropion, blepharospasm, allergic conjunctivitis, panuveitis, and optic neuropathy. Pseudophakia and
aphakia were observed only in male participants. Subjects
with exotropia had normal vision in both eyes.
Blindness, excluding refractive error (pinhole-
corrected), was determined in 9% of right eyes and 11%
of left eyes. Bilateral blindness was determined in 6% of
participants, the incidence increasing dramatically by age
group. No individual was blind in both eyes in the younger
age group, although 1 subject had 20/200 uncorrected
visual acuity (phVA 20/50) and CF from amblyopia in the
fellow eye. There were 10 nonrefractive blind eyes in the
middle-aged group (5% of eyes) in which 2 individuals
were blind bilaterally (2%). In the older age group there
were 33 nonrefractive blind eyes (16% of eyes) of which
14 were bilaterally blind (6% of individuals). The causes of blindness in all cases are summarized in Table 2 and
presented as a percentage of total eyes per gender (female
= 308, male = 142), total eyes (n = 450), and total blind
eyes (n = 59). As expected, cataract, found in 15% of all
examined eyes, was the most common cause of blindness
(66% of blind eyes). This was followed in prevalence by
refractive error and trauma (20% and 7% of blind eyes,
respectively). Corneal scarring and amblyopia accounted
for 1 case each. Three cases of blindness were caused by
ocular trauma with associated glaucoma. These cases were
accompanied by opacified corneas and/or flat anterior
chambers. Highly elevated IOP measured by Tonopen or
tactile tension was present in these cases. A history of
penetrating trauma (e.g. arrow injury) preceded vision
loss in 2 cases. All cases were long-standing. There were
no cases of blindness from any cause that had occurred
No definite cases of primary open-angle glaucoma were
identified in any study subject. There were 6 cases classified
as open-angle glaucoma suspects based on optic-nerve
appearance alone. The VCDR was between 0.6 and 0.85
in all cases. In one case, the VCDR asymmetry was greater
than 0.2. Notching of the neuro-retinal rim, nerve-fiberlayer defects, and disc hemorrhages were not observed.
Tangent-screen assessment did not reveal visual-field loss
consistent with the diagnosis of glaucoma in any case. IOP
was normal in all glaucoma suspects.
Exfoliation syndrome was identified in 8 individuals. No
cases of exfoliation glaucoma were observed. One female
participant had unilateral exfoliation in the middle-aged
group. The remaining 7 cases were identified in the older
age group. Five cases of exfoliation syndrome were
bilateral (3 females, 2 male) and 2 were unilateral cases
(1 female, 1 male). There was one suspected case of exfoliation in a pseudophakic eye of a male subject. IOP was
elevated in 1 of 13 eyes with definite exfoliation syndrome
(26 mm Hg). Optic-nerve appearance and tangent screens
were normal in all eyes with exfoliation syndrome.
The primary intent of this study was to assess the status
of visual function in a population that has not been
systematically examined in the past, and as a result of their
isolation, has largely been outside the purview of
traditional medical care.
The Aeta are characterized by small stature and have a
distinctive Sub-Saharan African appearance with dark skin
and fine curly hair, in striking contrast to the majority
population of the Philippines. They have lived as huntergatherers in the mountainous interior of Luzon until
recent times. The social structure of hunter-gatherer
societies comprises collections of small family units that
are widely scattered. Family units migrate frequently as a
function of food gathering. In the case of the Aeta,
migrations often occur every 2 to 3 years when land used
to grow basic food crops is depleted of nutrients. The Aeta
system of slash-and-burn farming called kaingin has been
a practice for centuries. Although sustainable over long
periods of time, it can only support the low population
density of hunter-gatherer societies.
Due to their relative isolation and social structure,
traditional health-care delivery has been problematic for
the Aeta, and for the most part nonexistent. Recently, the
Aeta have started living in larger villages with higher
population densities, a process accelerated by the massive
eruption of Mt. Pinatubo in 1991. Mt. Pinatubo is revered
by the Aeta and occupies the center of the Aeta homeland
both geographically and figuratively. The eruption caused
two-thirds of the Aeta land to become uninhabitable from
the direct effect of pyroclastic flow or ash fall, forcing the
mass evacuation of a large number of the Aeta.
Recently, more consistent efforts have been made to
deliver medical care to the Aeta, primarily through
intermittent medical missions. There has been no
recorded ophthalmic mission for this population. For this
reason, it was felt appropriate that a vision survey would
be useful as a first step to gather information for future
use by government and other health-care agencies.
The primary focus of this project was to perform visual
screening of a representative sample of the Aeta with
emphasis on the older population. The goal was to gauge
the prevalence and major causes of visual compromise.
This was not a formal population-based study that would
require resources and personnel far beyond what was
available. Due to the remoteness of this population and
limitations of the census data, a large-scale study would
have been problematic, if not impossible. It is important
to note that we could only screen members of this
population who lived in resettlement centers. A large
percent of the Aeta live in areas inaccessible by motorized
vehicles. Therefore, the results of this study may not apply
to those living in more remote areas. We were able to
circumvent some of these challenges by working in close
association with personnel from the NCIP.
The available government census provided estimates
of Aeta village populations in the Pinatubo region.
census provided no data on sex, age, or village maps. We
arranged for the NCIP social workers to discuss the study
with kapitans months prior to our arrival. Kapitans were
given instruction by social workers on how to enroll
families and the need to select elder family couples
randomly and not based on perceived medical need. The
nature of the project, a vision screening rather than a
treatment study, was explained to the kapitans and study
We felt that it was feasible to screen 1% of this population, which had an estimated 17,500 individuals
living within the selected villages. We successfully recruited
and examined 225 individuals or 1.3% of the estimated
target population; between 0.85% and 2.1% of each
village. Female participants (67%) outnumbered the
males (33%). This was true for all age groups with the
lowest percent in the older age group (61%) and the
highest percent of female participants in the middle-aged
(75%) and younger (72%) groups. The precise method
that kapitans used to select older household members is
not known. We requested that older couples be invited to
participate in an effort to equalize gender representation
and reduce familial relatedness. We were unable to
determine what caused the differential representation by
females and males.
Since we were unable to monitor the activities of the
kapitans, it was not possible to assess to what degree
selection bias may have occurred during the recruitment
process. Furthermore, there was no method to record what
percent of those asked to participate were ultimately
screened—another potential source of bias. However,
considering the time and resources that were available
for a project of this type, we feel the results provide useful
information for future medical intervention or studies.
In our sample, the older Aeta averaged 4.5-feet tall and
weighed less than 80 lbs. We found that the middle-aged
and younger Aeta were significantly taller than the older
age group, an increase in height found almost exclusively
among men. Along with increased height was an increase
in weight among younger Aeta. Again, it was the male
group that accounted for most of the change in weight.
Presumably, this trend reflects changes in diet and/or
activity between older and younger Aeta which were also
suggested as contributing causes of reduced stature by
Clavano-Harding and colleagues.
Why the increases in
height and weight were primarily observed among the
male Aeta is unclear.
One of the primary goals of this study was to estimate
the prevalence of low vision in older members of the Aeta
population. The prevalence of low vision (VA > 20/40 and
< 20/200) and blindness (≥ 20/200) increased
dramatically with older age. Although the younger age
group was smaller in number, an intended consequence
of the study design, low vision from all causes was relatively
uncommon, present in 4% of eyes without correction. The
most frequent cause of low vision in the younger age group
was refractive error. Other than refractive error, there was
one case of amblyopia which accounted for the only blind
eye in younger age group. Low vision was present in 36%
of eyes without correction in the middle-aged group and
48% in the older age group. Blind eyes accounted for 9%
and 19% of uncorrected eyes in the middle-aged and older
groups, respectively. Since corrective glasses were not available to this population, uncorrected visual acuity most
accurately reflected the visual function for this population.
However, even if treatment for refractive error was
available, low vision and blindness in this study would have
been reduced by only 20%.
The prevalence of visual impairment and blindness in
the world varies greatly between populations. Resnikoff
and colleagues noted in a World Health Organization
report on global rates of visual impairment that the
prevalence of blindness (defined as visual acuity > 20/
400 in the better-seeing eye) varied between 0.4 and 9%
in populations aged 50 or more worldwide.
prevalence was in developed countries including Europe
and the US, while the highest was in several regions of
Africa. The prevalence of blindness was 6.3% in the
population over age 50 in the subregion that includes the
Philippines, Malaysia, Indonesia, and Thailand. In our
study, the prevalence of blindness was estimated to be 8%
in men and women. If blindness had been defined
similarly, the prevalence would have been lower. It is
challenging to compare studies that used different
methodologies and sample sizes. This study was not
powered to provide a precise estimate of blindness or
visual impairment; but designed to examine the common
causes of vision loss in a representative sample. It is
interesting, however, to find that the estimated prevalence
of blindness obtained in this sample was similar to that
observed in other studies in this region.
The leading cause of blindness in developing nations
is cataract; it was, therefore, not surprising to find that
cataract was also the largest single cause of visual
impairment and blindness in the Aeta population. A
number of the Aeta had obtained ophthalmic treatment,
mostly for cataracts. Seven, all of them men, had cataract
surgery; 6 were pseudophakic and 1 was aphakic. It is not
clear whether this represented a statistical aberration or
may be reflective of uneven access to the limited health
The major causes of blindness in this population were
similar to those reported in other populations from
It is important to note for the
purposes of continuing health care that the vast majority
of cases of low vision and blindness is readily treatable.
Other causes of treatable blindness, such as trachoma or
other infectious diseases, were uncommon. In this
population, less than 3% of the observed blindness would
be essentially untreatable.
Interestingly, glaucoma was conspicuously absent
among the causes of blindness. Worldwide glaucoma is
the second leading cause of blindness.
Only 3 cases of
blindness associated with glaucoma were observed in this
study and in each case a history of major ocular trauma
was present which was readily verified by examination.
There were no cases of blindness from primary forms of
open-angle or angle-closure glaucoma. Six cases were
classified as glaucoma suspects, all based on increased
vertical cup-to-disc ratio. One case had optic-cup asymmetry
greater than 0.2. None had other stigmata of glaucomatous optic neuropathy, such as focal neuroretinal-rim
thinning, disc hemorrhages, or nerve-fiber-layer defects.
Similarly, visual-field loss was not detected by tangentscreen assessment in these cases. No glaucoma suspect
had associated elevated IOP. Similarly, cases of chronic
angle-closure glaucoma were not observed in this study
population. Two individuals had narrow angles on
gonioscopy, but neither case was occludable. There were
no cases of appositional closure or posterior synechiae
related to narrow angles.
It is possible that the absence of observed open-angle
and angle-closure glaucoma among the Aeta was due to
the limited sample size. However, it is also possible that
the prevalence of these common forms of glaucoma is
very low in this population compared to others. Openangle glaucoma is a complex inherited disorder with three
known genes and many associated chromosomal loci.
Likewise, angle-closure glaucoma is likely to have a strong
underlying genetic component.
If the Aeta do have a very low prevalence of these
major forms of glaucoma, then one would anticipate that
closely related populations might have similarly low rates
of these inherited forms of glaucoma.
In an Australian
report, reference is made to one of the examiners (FCH),
“ who, in spite of a substantial background in the
epidemiology of glaucoma and in spite of examining more
Aborigines than any other examiner, did not find one
certain case of primary-open or closed-angle glaucoma in
In summary, we were able to perform vision screening
on a representative sample of older members of the Aeta, an isolated population of the Philippines. Visual impairment and blindness were relatively common among the
Aeta, particularly among the older age groups. The most
common causes of vision loss in this population were
cataract and refractive error, both of which are readily
amenable to treatment.
Although primary open- and closed-angle glaucomas
are major causes of visual impairment and blindness in
most populations, no cases were identified in this sample.
While this may be due to chance, it is possible, given the
data on Australian Aborigines, that this lack of glaucoma
cases may reflect differences in genetic susceptibility or
environmental factors that lower the risk for primary forms
of glaucoma in these populations. For these reasons,
further study of this and related populations is warranted.
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