Distance visual acuity testing, ocular motility evaluation,
cycloplegic dilation, refraction, and a basic eye examination were
performed by one of two clinical teams from the Dr. Rajendra Prasad
Centre for Ophthalmic Sciences (R. P. Centre). An ophthalmologist
and two ophthalmic technicians were on each team. The two
ophthalmologists had 5 years of specialty experience, and the
ophthalmic technicians had completed the minimum of a 2-year diploma
course in optometry.
Visual acuity was measured at 4 m by an ophthalmic technician,
using a retroilluminated log minimum angle of resolution (MAR) chart
with five tumbling-E optotypes on each line (Precision Vision, La
Salle, IL) and was recorded as the smallest line read with one or no
errors. First, the right eye was tested and then the left eye, both
without (uncorrected visual acuity) and with (presenting visual acuity)
spectacles, if the child brought them. A lensometer was used in
measuring lens power. Ocular motility was evaluated at both 0.5 and
4.0 m by an ophthalmic technician. Tropias were categorized as
esotropia, exotropia, or vertical. The degree of tropia was measured
using the corneal light reflex. Examination of the anterior segment
(eyelid, conjunctiva, cornea, iris, and pupil) was performed by the
team ophthalmologist with a magnifying loupe. Pupils were dilated with
2 drops of 1% cyclopentolate, administered 5 minutes apart. After 20
minutes, if a pupillary light reflex was still present, a third drop
was administered. Light reflex and pupil dilation were evaluated after
an additional 15 minutes. Cycloplegia was considered complete if the
pupil dilated to 6 mm or greater and light reflex was absent. After
cycloplegia, vision was refracted by an ophthalmic technician,
regardless of visual acuity: first, using a streak retinoscope and then
a handheld autorefractor (Retinomax K-Plus; Nikon Corp., Tokyo, Japan).
The autorefractor was calibrated at the beginning of each working day.
Subjective refraction was performed on children with uncorrected visual
acuity of 20/40 or worse in either eye.
The eye examination was completed with slit lamp and direct
ophthalmoscopic examination of the lens, vitreous, and fundus. Eyes
with uncorrected visual acuity of 20/40 or worse were assigned a
principal cause of impairment by the examining ophthalmologist, using a
seven-item list (refractive error, amblyopia, corneal opacity due to
trachoma, other corneal opacity, cataract, retinal disorder, and other
causes). Refractive error was considered to be the cause of visual
impairment in all eyes improving to 20/32 or better with refractive
correction. Amblyopia was reported as the cause of impairment for eyes
with best corrected visual acuity of 20/40 or worse and no apparent
organic lesion, so long as one or more of the following criteria were
met: (1) esotropia, exotropia, or vertical tropia at 4 m fixation
or exotropia or vertical tropia at 0.5 m; (2) anisometropia of
2.00 spherical equivalent diopters or more; or (3) bilateral ametropia
of at least +6.00 spherical equivalent diopters. Further details
regarding examination methods are described in the original RESC
methods article.
5
Treatment of minor eye ailments and corrective spectacles were provided
at the examination site free of charge. For additional follow-up and
examination, children were referred to the R. P. Centre.
Survey fieldwork was preceded by 2 weeks of staff training, and a 5-day
field exercise was performed in an urban area similar to the study
area. A pilot study (full dress rehearsal) was performed in 2 nonstudy
clusters in the Trilokpuri area early in December of 2000. The pilot
study included evaluation of interobserver agreement among ophthalmic
technicians.
Human subject research approval for the study protocol was obtained
from the World Health Organization Secretariat Committee on Research
Involving Human Subjects and the Institutional Review Board of the All
India Institute of Medical Sciences. The research protocol adhered to
the provisions of the Declaration of Helsinki for research involving
human subjects.